1 acpi= [HW,ACPI,X86,ARM64] 2 Advanced Configuration and Power Interface 3 Format: { force | on | off | strict | noirq | rsdt | 4 copy_dsdt } 5 force -- enable ACPI if default was off 6 on -- enable ACPI but allow fallback to DT [arm64] 7 off -- disable ACPI if default was on 8 noirq -- do not use ACPI for IRQ routing 9 strict -- Be less tolerant of platforms that are not 10 strictly ACPI specification compliant. 11 rsdt -- prefer RSDT over (default) XSDT 12 copy_dsdt -- copy DSDT to memory 13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force" 14 are available 15 16 See also Documentation/power/runtime_pm.rst, pci=noacpi 17 18 acpi_apic_instance= [ACPI, IOAPIC] 19 Format: <int> 20 2: use 2nd APIC table, if available 21 1,0: use 1st APIC table 22 default: 0 23 24 acpi_backlight= [HW,ACPI] 25 { vendor | video | native | none } 26 If set to vendor, prefer vendor-specific driver 27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 28 of the ACPI video.ko driver. 29 If set to video, use the ACPI video.ko driver. 30 If set to native, use the device's native backlight mode. 31 If set to none, disable the ACPI backlight interface. 32 33 acpi_force_32bit_fadt_addr 34 force FADT to use 32 bit addresses rather than the 35 64 bit X_* addresses. Some firmware have broken 64 36 bit addresses for force ACPI ignore these and use 37 the older legacy 32 bit addresses. 38 39 acpica_no_return_repair [HW, ACPI] 40 Disable AML predefined validation mechanism 41 This mechanism can repair the evaluation result to make 42 the return objects more ACPI specification compliant. 43 This option is useful for developers to identify the 44 root cause of an AML interpreter issue when the issue 45 has something to do with the repair mechanism. 46 47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 49 Format: <int> 50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 51 debug output. Bits in debug_layer correspond to a 52 _COMPONENT in an ACPI source file, e.g., 53 #define _COMPONENT ACPI_EVENTS 54 Bits in debug_level correspond to a level in 55 ACPI_DEBUG_PRINT statements, e.g., 56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 57 The debug_level mask defaults to "info". See 58 Documentation/firmware-guide/acpi/debug.rst for more information about 59 debug layers and levels. 60 61 Enable processor driver info messages: 62 acpi.debug_layer=0x20000000 63 Enable AML "Debug" output, i.e., stores to the Debug 64 object while interpreting AML: 65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 66 Enable all messages related to ACPI hardware: 67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 68 69 Some values produce so much output that the system is 70 unusable. The "log_buf_len" parameter may be useful 71 if you need to capture more output. 72 73 acpi_enforce_resources= [ACPI] 74 { strict | lax | no } 75 Check for resource conflicts between native drivers 76 and ACPI OperationRegions (SystemIO and SystemMemory 77 only). IO ports and memory declared in ACPI might be 78 used by the ACPI subsystem in arbitrary AML code and 79 can interfere with legacy drivers. 80 strict (default): access to resources claimed by ACPI 81 is denied; legacy drivers trying to access reserved 82 resources will fail to bind to device using them. 83 lax: access to resources claimed by ACPI is allowed; 84 legacy drivers trying to access reserved resources 85 will bind successfully but a warning message is logged. 86 no: ACPI OperationRegions are not marked as reserved, 87 no further checks are performed. 88 89 acpi_force_table_verification [HW,ACPI] 90 Enable table checksum verification during early stage. 91 By default, this is disabled due to x86 early mapping 92 size limitation. 93 94 acpi_irq_balance [HW,ACPI] 95 ACPI will balance active IRQs 96 default in APIC mode 97 98 acpi_irq_nobalance [HW,ACPI] 99 ACPI will not move active IRQs (default) 100 default in PIC mode 101 102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 103 Format: <irq>,<irq>... 104 105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 106 use by PCI 107 Format: <irq>,<irq>... 108 109 acpi_mask_gpe= [HW,ACPI] 110 Due to the existence of _Lxx/_Exx, some GPEs triggered 111 by unsupported hardware/firmware features can result in 112 GPE floodings that cannot be automatically disabled by 113 the GPE dispatcher. 114 This facility can be used to prevent such uncontrolled 115 GPE floodings. 116 Format: <byte> 117 118 acpi_no_auto_serialize [HW,ACPI] 119 Disable auto-serialization of AML methods 120 AML control methods that contain the opcodes to create 121 named objects will be marked as "Serialized" by the 122 auto-serialization feature. 123 This feature is enabled by default. 124 This option allows to turn off the feature. 125 126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 127 kernels. 128 129 acpi_no_static_ssdt [HW,ACPI] 130 Disable installation of static SSDTs at early boot time 131 By default, SSDTs contained in the RSDT/XSDT will be 132 installed automatically and they will appear under 133 /sys/firmware/acpi/tables. 134 This option turns off this feature. 135 Note that specifying this option does not affect 136 dynamic table installation which will install SSDT 137 tables to /sys/firmware/acpi/tables/dynamic. 138 139 acpi_no_watchdog [HW,ACPI,WDT] 140 Ignore the ACPI-based watchdog interface (WDAT) and let 141 a native driver control the watchdog device instead. 142 143 acpi_rsdp= [ACPI,EFI,KEXEC] 144 Pass the RSDP address to the kernel, mostly used 145 on machines running EFI runtime service to boot the 146 second kernel for kdump. 147 148 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 149 Format: To spoof as Windows 98: ="Microsoft Windows" 150 151 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 152 of 2 which is mandated by ACPI 6) as the supported ACPI 153 specification revision (when using this switch, it may 154 be necessary to carry out a cold reboot _twice_ in a 155 row to make it take effect on the platform firmware). 156 157 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 158 acpi_osi="string1" # add string1 159 acpi_osi="!string2" # remove string2 160 acpi_osi=!* # remove all strings 161 acpi_osi=! # disable all built-in OS vendor 162 strings 163 acpi_osi=!! # enable all built-in OS vendor 164 strings 165 acpi_osi= # disable all strings 166 167 'acpi_osi=!' can be used in combination with single or 168 multiple 'acpi_osi="string1"' to support specific OS 169 vendor string(s). Note that such command can only 170 affect the default state of the OS vendor strings, thus 171 it cannot affect the default state of the feature group 172 strings and the current state of the OS vendor strings, 173 specifying it multiple times through kernel command line 174 is meaningless. This command is useful when one do not 175 care about the state of the feature group strings which 176 should be controlled by the OSPM. 177 Examples: 178 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 179 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 180 can make '_OSI("Windows 2000")' TRUE. 181 182 'acpi_osi=' cannot be used in combination with other 183 'acpi_osi=' command lines, the _OSI method will not 184 exist in the ACPI namespace. NOTE that such command can 185 only affect the _OSI support state, thus specifying it 186 multiple times through kernel command line is also 187 meaningless. 188 Examples: 189 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 190 FALSE. 191 192 'acpi_osi=!*' can be used in combination with single or 193 multiple 'acpi_osi="string1"' to support specific 194 string(s). Note that such command can affect the 195 current state of both the OS vendor strings and the 196 feature group strings, thus specifying it multiple times 197 through kernel command line is meaningful. But it may 198 still not able to affect the final state of a string if 199 there are quirks related to this string. This command 200 is useful when one want to control the state of the 201 feature group strings to debug BIOS issues related to 202 the OSPM features. 203 Examples: 204 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 205 '_OSI("Module Device")' FALSE. 206 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 207 '_OSI("Module Device")' TRUE. 208 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 209 equivalent to 210 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 211 and 212 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 213 they all will make '_OSI("Windows 2000")' TRUE. 214 215 acpi_pm_good [X86] 216 Override the pmtimer bug detection: force the kernel 217 to assume that this machine's pmtimer latches its value 218 and always returns good values. 219 220 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 221 Format: { level | edge | high | low } 222 223 acpi_skip_timer_override [HW,ACPI] 224 Recognize and ignore IRQ0/pin2 Interrupt Override. 225 For broken nForce2 BIOS resulting in XT-PIC timer. 226 227 acpi_sleep= [HW,ACPI] Sleep options 228 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 229 old_ordering, nonvs, sci_force_enable, nobl } 230 See Documentation/power/video.rst for information on 231 s3_bios and s3_mode. 232 s3_beep is for debugging; it makes the PC's speaker beep 233 as soon as the kernel's real-mode entry point is called. 234 s4_nohwsig prevents ACPI hardware signature from being 235 used during resume from hibernation. 236 old_ordering causes the ACPI 1.0 ordering of the _PTS 237 control method, with respect to putting devices into 238 low power states, to be enforced (the ACPI 2.0 ordering 239 of _PTS is used by default). 240 nonvs prevents the kernel from saving/restoring the 241 ACPI NVS memory during suspend/hibernation and resume. 242 sci_force_enable causes the kernel to set SCI_EN directly 243 on resume from S1/S3 (which is against the ACPI spec, 244 but some broken systems don't work without it). 245 nobl causes the internal blacklist of systems known to 246 behave incorrectly in some ways with respect to system 247 suspend and resume to be ignored (use wisely). 248 249 acpi_use_timer_override [HW,ACPI] 250 Use timer override. For some broken Nvidia NF5 boards 251 that require a timer override, but don't have HPET 252 253 add_efi_memmap [EFI; X86] Include EFI memory map in 254 kernel's map of available physical RAM. 255 256 agp= [AGP] 257 { off | try_unsupported } 258 off: disable AGP support 259 try_unsupported: try to drive unsupported chipsets 260 (may crash computer or cause data corruption) 261 262 ALSA [HW,ALSA] 263 See Documentation/sound/alsa-configuration.rst 264 265 alignment= [KNL,ARM] 266 Allow the default userspace alignment fault handler 267 behaviour to be specified. Bit 0 enables warnings, 268 bit 1 enables fixups, and bit 2 sends a segfault. 269 270 align_va_addr= [X86-64] 271 Align virtual addresses by clearing slice [14:12] when 272 allocating a VMA at process creation time. This option 273 gives you up to 3% performance improvement on AMD F15h 274 machines (where it is enabled by default) for a 275 CPU-intensive style benchmark, and it can vary highly in 276 a microbenchmark depending on workload and compiler. 277 278 32: only for 32-bit processes 279 64: only for 64-bit processes 280 on: enable for both 32- and 64-bit processes 281 off: disable for both 32- and 64-bit processes 282 283 alloc_snapshot [FTRACE] 284 Allocate the ftrace snapshot buffer on boot up when the 285 main buffer is allocated. This is handy if debugging 286 and you need to use tracing_snapshot() on boot up, and 287 do not want to use tracing_snapshot_alloc() as it needs 288 to be done where GFP_KERNEL allocations are allowed. 289 290 amd_iommu= [HW,X86-64] 291 Pass parameters to the AMD IOMMU driver in the system. 292 Possible values are: 293 fullflush - enable flushing of IO/TLB entries when 294 they are unmapped. Otherwise they are 295 flushed before they will be reused, which 296 is a lot of faster 297 off - do not initialize any AMD IOMMU found in 298 the system 299 force_isolation - Force device isolation for all 300 devices. The IOMMU driver is not 301 allowed anymore to lift isolation 302 requirements as needed. This option 303 does not override iommu=pt 304 305 amd_iommu_dump= [HW,X86-64] 306 Enable AMD IOMMU driver option to dump the ACPI table 307 for AMD IOMMU. With this option enabled, AMD IOMMU 308 driver will print ACPI tables for AMD IOMMU during 309 IOMMU initialization. 310 311 amd_iommu_intr= [HW,X86-64] 312 Specifies one of the following AMD IOMMU interrupt 313 remapping modes: 314 legacy - Use legacy interrupt remapping mode. 315 vapic - Use virtual APIC mode, which allows IOMMU 316 to inject interrupts directly into guest. 317 This mode requires kvm-amd.avic=1. 318 (Default when IOMMU HW support is present.) 319 320 amijoy.map= [HW,JOY] Amiga joystick support 321 Map of devices attached to JOY0DAT and JOY1DAT 322 Format: <a>,<b> 323 See also Documentation/input/joydev/joystick.rst 324 325 analog.map= [HW,JOY] Analog joystick and gamepad support 326 Specifies type or capabilities of an analog joystick 327 connected to one of 16 gameports 328 Format: <type1>,<type2>,..<type16> 329 330 apc= [HW,SPARC] 331 Power management functions (SPARCstation-4/5 + deriv.) 332 Format: noidle 333 Disable APC CPU standby support. SPARCstation-Fox does 334 not play well with APC CPU idle - disable it if you have 335 APC and your system crashes randomly. 336 337 apic= [APIC,X86] Advanced Programmable Interrupt Controller 338 Change the output verbosity while booting 339 Format: { quiet (default) | verbose | debug } 340 Change the amount of debugging information output 341 when initialising the APIC and IO-APIC components. 342 For X86-32, this can also be used to specify an APIC 343 driver name. 344 Format: apic=driver_name 345 Examples: apic=bigsmp 346 347 apic_extnmi= [APIC,X86] External NMI delivery setting 348 Format: { bsp (default) | all | none } 349 bsp: External NMI is delivered only to CPU 0 350 all: External NMIs are broadcast to all CPUs as a 351 backup of CPU 0 352 none: External NMI is masked for all CPUs. This is 353 useful so that a dump capture kernel won't be 354 shot down by NMI 355 356 autoconf= [IPV6] 357 See Documentation/networking/ipv6.rst. 358 359 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 360 Limit apic dumping. The parameter defines the maximal 361 number of local apics being dumped. Also it is possible 362 to set it to "all" by meaning -- no limit here. 363 Format: { 1 (default) | 2 | ... | all }. 364 The parameter valid if only apic=debug or 365 apic=verbose is specified. 366 Example: apic=debug show_lapic=all 367 368 apm= [APM] Advanced Power Management 369 See header of arch/x86/kernel/apm_32.c. 370 371 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 372 Format: <io>,<irq>,<nodeID> 373 374 arm64.nobti [ARM64] Unconditionally disable Branch Target 375 Identification support 376 377 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 378 support 379 380 ataflop= [HW,M68k] 381 382 atarimouse= [HW,MOUSE] Atari Mouse 383 384 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 385 EzKey and similar keyboards 386 387 atkbd.reset= [HW] Reset keyboard during initialization 388 389 atkbd.set= [HW] Select keyboard code set 390 Format: <int> (2 = AT (default), 3 = PS/2) 391 392 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 393 keyboards 394 395 atkbd.softraw= [HW] Choose between synthetic and real raw mode 396 Format: <bool> (0 = real, 1 = synthetic (default)) 397 398 atkbd.softrepeat= [HW] 399 Use software keyboard repeat 400 401 audit= [KNL] Enable the audit sub-system 402 Format: { "0" | "1" | "off" | "on" } 403 0 | off - kernel audit is disabled and can not be 404 enabled until the next reboot 405 unset - kernel audit is initialized but disabled and 406 will be fully enabled by the userspace auditd. 407 1 | on - kernel audit is initialized and partially 408 enabled, storing at most audit_backlog_limit 409 messages in RAM until it is fully enabled by the 410 userspace auditd. 411 Default: unset 412 413 audit_backlog_limit= [KNL] Set the audit queue size limit. 414 Format: <int> (must be >=0) 415 Default: 64 416 417 bau= [X86_UV] Enable the BAU on SGI UV. The default 418 behavior is to disable the BAU (i.e. bau=0). 419 Format: { "0" | "1" } 420 0 - Disable the BAU. 421 1 - Enable the BAU. 422 unset - Disable the BAU. 423 424 baycom_epp= [HW,AX25] 425 Format: <io>,<mode> 426 427 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 428 Format: <io>,<mode> 429 See header of drivers/net/hamradio/baycom_par.c. 430 431 baycom_ser_fdx= [HW,AX25] 432 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 433 Format: <io>,<irq>,<mode>[,<baud>] 434 See header of drivers/net/hamradio/baycom_ser_fdx.c. 435 436 baycom_ser_hdx= [HW,AX25] 437 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 438 Format: <io>,<irq>,<mode> 439 See header of drivers/net/hamradio/baycom_ser_hdx.c. 440 441 blkdevparts= Manual partition parsing of block device(s) for 442 embedded devices based on command line input. 443 See Documentation/block/cmdline-partition.rst 444 445 boot_delay= Milliseconds to delay each printk during boot. 446 Values larger than 10 seconds (10000) are changed to 447 no delay (0). 448 Format: integer 449 450 bootconfig [KNL] 451 Extended command line options can be added to an initrd 452 and this will cause the kernel to look for it. 453 454 See Documentation/admin-guide/bootconfig.rst 455 456 bert_disable [ACPI] 457 Disable BERT OS support on buggy BIOSes. 458 459 bgrt_disable [ACPI][X86] 460 Disable BGRT to avoid flickering OEM logo. 461 462 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 463 bttv.radio= Most important insmod options are available as 464 kernel args too. 465 bttv.pll= See Documentation/admin-guide/media/bttv.rst 466 bttv.tuner= 467 468 bulk_remove=off [PPC] This parameter disables the use of the pSeries 469 firmware feature for flushing multiple hpte entries 470 at a time. 471 472 c101= [NET] Moxa C101 synchronous serial card 473 474 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 475 Sometimes CPU hardware bugs make them report the cache 476 size incorrectly. The kernel will attempt work arounds 477 to fix known problems, but for some CPUs it is not 478 possible to determine what the correct size should be. 479 This option provides an override for these situations. 480 481 carrier_timeout= 482 [NET] Specifies amount of time (in seconds) that 483 the kernel should wait for a network carrier. By default 484 it waits 120 seconds. 485 486 ca_keys= [KEYS] This parameter identifies a specific key(s) on 487 the system trusted keyring to be used for certificate 488 trust validation. 489 format: { id:<keyid> | builtin } 490 491 cca= [MIPS] Override the kernel pages' cache coherency 492 algorithm. Accepted values range from 0 to 7 493 inclusive. See arch/mips/include/asm/pgtable-bits.h 494 for platform specific values (SB1, Loongson3 and 495 others). 496 497 ccw_timeout_log [S390] 498 See Documentation/s390/common_io.rst for details. 499 500 cgroup_disable= [KNL] Disable a particular controller 501 Format: {name of the controller(s) to disable} 502 The effects of cgroup_disable=foo are: 503 - foo isn't auto-mounted if you mount all cgroups in 504 a single hierarchy 505 - foo isn't visible as an individually mountable 506 subsystem 507 {Currently only "memory" controller deal with this and 508 cut the overhead, others just disable the usage. So 509 only cgroup_disable=memory is actually worthy} 510 511 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 512 Format: { { controller | "all" | "named" } 513 [,{ controller | "all" | "named" }...] } 514 Like cgroup_disable, but only applies to cgroup v1; 515 the blacklisted controllers remain available in cgroup2. 516 "all" blacklists all controllers and "named" disables 517 named mounts. Specifying both "all" and "named" disables 518 all v1 hierarchies. 519 520 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 521 Format: <string> 522 nosocket -- Disable socket memory accounting. 523 nokmem -- Disable kernel memory accounting. 524 525 checkreqprot [SELINUX] Set initial checkreqprot flag value. 526 Format: { "0" | "1" } 527 See security/selinux/Kconfig help text. 528 0 -- check protection applied by kernel (includes 529 any implied execute protection). 530 1 -- check protection requested by application. 531 Default value is set via a kernel config option. 532 Value can be changed at runtime via 533 /sys/fs/selinux/checkreqprot. 534 Setting checkreqprot to 1 is deprecated. 535 536 cio_ignore= [S390] 537 See Documentation/s390/common_io.rst for details. 538 clk_ignore_unused 539 [CLK] 540 Prevents the clock framework from automatically gating 541 clocks that have not been explicitly enabled by a Linux 542 device driver but are enabled in hardware at reset or 543 by the bootloader/firmware. Note that this does not 544 force such clocks to be always-on nor does it reserve 545 those clocks in any way. This parameter is useful for 546 debug and development, but should not be needed on a 547 platform with proper driver support. For more 548 information, see Documentation/driver-api/clk.rst. 549 550 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 551 [Deprecated] 552 Forces specified clocksource (if available) to be used 553 when calculating gettimeofday(). If specified 554 clocksource is not available, it defaults to PIT. 555 Format: { pit | tsc | cyclone | pmtmr } 556 557 clocksource= Override the default clocksource 558 Format: <string> 559 Override the default clocksource and use the clocksource 560 with the name specified. 561 Some clocksource names to choose from, depending on 562 the platform: 563 [all] jiffies (this is the base, fallback clocksource) 564 [ACPI] acpi_pm 565 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 566 pxa_timer,timer3,32k_counter,timer0_1 567 [X86-32] pit,hpet,tsc; 568 scx200_hrt on Geode; cyclone on IBM x440 569 [MIPS] MIPS 570 [PARISC] cr16 571 [S390] tod 572 [SH] SuperH 573 [SPARC64] tick 574 [X86-64] hpet,tsc 575 576 clocksource.arm_arch_timer.evtstrm= 577 [ARM,ARM64] 578 Format: <bool> 579 Enable/disable the eventstream feature of the ARM 580 architected timer so that code using WFE-based polling 581 loops can be debugged more effectively on production 582 systems. 583 584 clearcpuid=BITNUM[,BITNUM...] [X86] 585 Disable CPUID feature X for the kernel. See 586 arch/x86/include/asm/cpufeatures.h for the valid bit 587 numbers. Note the Linux specific bits are not necessarily 588 stable over kernel options, but the vendor specific 589 ones should be. 590 Also note that user programs calling CPUID directly 591 or using the feature without checking anything 592 will still see it. This just prevents it from 593 being used by the kernel or shown in /proc/cpuinfo. 594 Also note the kernel might malfunction if you disable 595 some critical bits. 596 597 cma=nn[MG]@[start[MG][-end[MG]]] 598 [KNL,CMA] 599 Sets the size of kernel global memory area for 600 contiguous memory allocations and optionally the 601 placement constraint by the physical address range of 602 memory allocations. A value of 0 disables CMA 603 altogether. For more information, see 604 kernel/dma/contiguous.c 605 606 cma_pernuma=nn[MG] 607 [ARM64,KNL,CMA] 608 Sets the size of kernel per-numa memory area for 609 contiguous memory allocations. A value of 0 disables 610 per-numa CMA altogether. And If this option is not 611 specificed, the default value is 0. 612 With per-numa CMA enabled, DMA users on node nid will 613 first try to allocate buffer from the pernuma area 614 which is located in node nid, if the allocation fails, 615 they will fallback to the global default memory area. 616 617 cmo_free_hint= [PPC] Format: { yes | no } 618 Specify whether pages are marked as being inactive 619 when they are freed. This is used in CMO environments 620 to determine OS memory pressure for page stealing by 621 a hypervisor. 622 Default: yes 623 624 coherent_pool=nn[KMG] [ARM,KNL] 625 Sets the size of memory pool for coherent, atomic dma 626 allocations, by default set to 256K. 627 628 com20020= [HW,NET] ARCnet - COM20020 chipset 629 Format: 630 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 631 632 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 633 Format: <io>[,<irq>] 634 635 com90xx= [HW,NET] 636 ARCnet - COM90xx chipset (memory-mapped buffers) 637 Format: <io>[,<irq>[,<memstart>]] 638 639 condev= [HW,S390] console device 640 conmode= 641 642 console= [KNL] Output console device and options. 643 644 tty<n> Use the virtual console device <n>. 645 646 ttyS<n>[,options] 647 ttyUSB0[,options] 648 Use the specified serial port. The options are of 649 the form "bbbbpnf", where "bbbb" is the baud rate, 650 "p" is parity ("n", "o", or "e"), "n" is number of 651 bits, and "f" is flow control ("r" for RTS or 652 omit it). Default is "9600n8". 653 654 See Documentation/admin-guide/serial-console.rst for more 655 information. See 656 Documentation/networking/netconsole.rst for an 657 alternative. 658 659 uart[8250],io,<addr>[,options] 660 uart[8250],mmio,<addr>[,options] 661 uart[8250],mmio16,<addr>[,options] 662 uart[8250],mmio32,<addr>[,options] 663 uart[8250],0x<addr>[,options] 664 Start an early, polled-mode console on the 8250/16550 665 UART at the specified I/O port or MMIO address, 666 switching to the matching ttyS device later. 667 MMIO inter-register address stride is either 8-bit 668 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 669 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 670 to be equivalent to 'mmio'. 'options' are specified in 671 the same format described for ttyS above; if unspecified, 672 the h/w is not re-initialized. 673 674 hvc<n> Use the hypervisor console device <n>. This is for 675 both Xen and PowerPC hypervisors. 676 677 If the device connected to the port is not a TTY but a braille 678 device, prepend "brl," before the device type, for instance 679 console=brl,ttyS0 680 For now, only VisioBraille is supported. 681 682 console_msg_format= 683 [KNL] Change console messages format 684 default 685 By default we print messages on consoles in 686 "[time stamp] text\n" format (time stamp may not be 687 printed, depending on CONFIG_PRINTK_TIME or 688 `printk_time' param). 689 syslog 690 Switch to syslog format: "<%u>[time stamp] text\n" 691 IOW, each message will have a facility and loglevel 692 prefix. The format is similar to one used by syslog() 693 syscall, or to executing "dmesg -S --raw" or to reading 694 from /proc/kmsg. 695 696 consoleblank= [KNL] The console blank (screen saver) timeout in 697 seconds. A value of 0 disables the blank timer. 698 Defaults to 0. 699 700 coredump_filter= 701 [KNL] Change the default value for 702 /proc/<pid>/coredump_filter. 703 See also Documentation/filesystems/proc.rst. 704 705 coresight_cpu_debug.enable 706 [ARM,ARM64] 707 Format: <bool> 708 Enable/disable the CPU sampling based debugging. 709 0: default value, disable debugging 710 1: enable debugging at boot time 711 712 cpuidle.off=1 [CPU_IDLE] 713 disable the cpuidle sub-system 714 715 cpuidle.governor= 716 [CPU_IDLE] Name of the cpuidle governor to use. 717 718 cpufreq.off=1 [CPU_FREQ] 719 disable the cpufreq sub-system 720 721 cpufreq.default_governor= 722 [CPU_FREQ] Name of the default cpufreq governor or 723 policy to use. This governor must be registered in the 724 kernel before the cpufreq driver probes. 725 726 cpu_init_udelay=N 727 [X86] Delay for N microsec between assert and de-assert 728 of APIC INIT to start processors. This delay occurs 729 on every CPU online, such as boot, and resume from suspend. 730 Default: 10000 731 732 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 733 Format: 734 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 735 736 crashkernel=size[KMG][@offset[KMG]] 737 [KNL] Using kexec, Linux can switch to a 'crash kernel' 738 upon panic. This parameter reserves the physical 739 memory region [offset, offset + size] for that kernel 740 image. If '@offset' is omitted, then a suitable offset 741 is selected automatically. 742 [KNL, X86-64] Select a region under 4G first, and 743 fall back to reserve region above 4G when '@offset' 744 hasn't been specified. 745 See Documentation/admin-guide/kdump/kdump.rst for further details. 746 747 crashkernel=range1:size1[,range2:size2,...][@offset] 748 [KNL] Same as above, but depends on the memory 749 in the running system. The syntax of range is 750 start-[end] where start and end are both 751 a memory unit (amount[KMG]). See also 752 Documentation/admin-guide/kdump/kdump.rst for an example. 753 754 crashkernel=size[KMG],high 755 [KNL, X86-64] range could be above 4G. Allow kernel 756 to allocate physical memory region from top, so could 757 be above 4G if system have more than 4G ram installed. 758 Otherwise memory region will be allocated below 4G, if 759 available. 760 It will be ignored if crashkernel=X is specified. 761 crashkernel=size[KMG],low 762 [KNL, X86-64] range under 4G. When crashkernel=X,high 763 is passed, kernel could allocate physical memory region 764 above 4G, that cause second kernel crash on system 765 that require some amount of low memory, e.g. swiotlb 766 requires at least 64M+32K low memory, also enough extra 767 low memory is needed to make sure DMA buffers for 32-bit 768 devices won't run out. Kernel would try to allocate at 769 at least 256M below 4G automatically. 770 This one let user to specify own low range under 4G 771 for second kernel instead. 772 0: to disable low allocation. 773 It will be ignored when crashkernel=X,high is not used 774 or memory reserved is below 4G. 775 776 cryptomgr.notests 777 [KNL] Disable crypto self-tests 778 779 cs89x0_dma= [HW,NET] 780 Format: <dma> 781 782 cs89x0_media= [HW,NET] 783 Format: { rj45 | aui | bnc } 784 785 csdlock_debug= [KNL] Enable debug add-ons of cross-CPU function call 786 handling. When switched on, additional debug data is 787 printed to the console in case a hanging CPU is 788 detected, and that CPU is pinged again in order to try 789 to resolve the hang situation. 790 0: disable csdlock debugging (default) 791 1: enable basic csdlock debugging (minor impact) 792 ext: enable extended csdlock debugging (more impact, 793 but more data) 794 795 dasd= [HW,NET] 796 See header of drivers/s390/block/dasd_devmap.c. 797 798 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 799 (one device per port) 800 Format: <port#>,<type> 801 See also Documentation/input/devices/joystick-parport.rst 802 803 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 804 time. See 805 Documentation/admin-guide/dynamic-debug-howto.rst for 806 details. Deprecated, see dyndbg. 807 808 debug [KNL] Enable kernel debugging (events log level). 809 810 debug_boot_weak_hash 811 [KNL] Enable printing [hashed] pointers early in the 812 boot sequence. If enabled, we use a weak hash instead 813 of siphash to hash pointers. Use this option if you are 814 seeing instances of '(___ptrval___)') and need to see a 815 value (hashed pointer) instead. Cryptographically 816 insecure, please do not use on production kernels. 817 818 debug_locks_verbose= 819 [KNL] verbose locking self-tests 820 Format: <int> 821 Print debugging info while doing the locking API 822 self-tests. 823 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 824 (no extra messages), setting it to -1 (all bits set) 825 will print _a_lot_ more information - normally only 826 useful to lockdep developers. 827 828 debug_objects [KNL] Enable object debugging 829 830 no_debug_objects 831 [KNL] Disable object debugging 832 833 debug_guardpage_minorder= 834 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 835 parameter allows control of the order of pages that will 836 be intentionally kept free (and hence protected) by the 837 buddy allocator. Bigger value increase the probability 838 of catching random memory corruption, but reduce the 839 amount of memory for normal system use. The maximum 840 possible value is MAX_ORDER/2. Setting this parameter 841 to 1 or 2 should be enough to identify most random 842 memory corruption problems caused by bugs in kernel or 843 driver code when a CPU writes to (or reads from) a 844 random memory location. Note that there exists a class 845 of memory corruptions problems caused by buggy H/W or 846 F/W or by drivers badly programing DMA (basically when 847 memory is written at bus level and the CPU MMU is 848 bypassed) which are not detectable by 849 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 850 tracking down these problems. 851 852 debug_pagealloc= 853 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 854 enables the feature at boot time. By default, it is 855 disabled and the system will work mostly the same as a 856 kernel built without CONFIG_DEBUG_PAGEALLOC. 857 Note: to get most of debug_pagealloc error reports, it's 858 useful to also enable the page_owner functionality. 859 on: enable the feature 860 861 debugfs= [KNL] This parameter enables what is exposed to userspace 862 and debugfs internal clients. 863 Format: { on, no-mount, off } 864 on: All functions are enabled. 865 no-mount: 866 Filesystem is not registered but kernel clients can 867 access APIs and a crashkernel can be used to read 868 its content. There is nothing to mount. 869 off: Filesystem is not registered and clients 870 get a -EPERM as result when trying to register files 871 or directories within debugfs. 872 This is equivalent of the runtime functionality if 873 debugfs was not enabled in the kernel at all. 874 Default value is set in build-time with a kernel configuration. 875 876 debugpat [X86] Enable PAT debugging 877 878 decnet.addr= [HW,NET] 879 Format: <area>[,<node>] 880 See also Documentation/networking/decnet.rst. 881 882 default_hugepagesz= 883 [HW] The size of the default HugeTLB page. This is 884 the size represented by the legacy /proc/ hugepages 885 APIs. In addition, this is the default hugetlb size 886 used for shmget(), mmap() and mounting hugetlbfs 887 filesystems. If not specified, defaults to the 888 architecture's default huge page size. Huge page 889 sizes are architecture dependent. See also 890 Documentation/admin-guide/mm/hugetlbpage.rst. 891 Format: size[KMG] 892 893 deferred_probe_timeout= 894 [KNL] Debugging option to set a timeout in seconds for 895 deferred probe to give up waiting on dependencies to 896 probe. Only specific dependencies (subsystems or 897 drivers) that have opted in will be ignored. A timeout of 0 898 will timeout at the end of initcalls. This option will also 899 dump out devices still on the deferred probe list after 900 retrying. 901 902 dfltcc= [HW,S390] 903 Format: { on | off | def_only | inf_only | always } 904 on: s390 zlib hardware support for compression on 905 level 1 and decompression (default) 906 off: No s390 zlib hardware support 907 def_only: s390 zlib hardware support for deflate 908 only (compression on level 1) 909 inf_only: s390 zlib hardware support for inflate 910 only (decompression) 911 always: Same as 'on' but ignores the selected compression 912 level always using hardware support (used for debugging) 913 914 dhash_entries= [KNL] 915 Set number of hash buckets for dentry cache. 916 917 disable_1tb_segments [PPC] 918 Disables the use of 1TB hash page table segments. This 919 causes the kernel to fall back to 256MB segments which 920 can be useful when debugging issues that require an SLB 921 miss to occur. 922 923 stress_slb [PPC] 924 Limits the number of kernel SLB entries, and flushes 925 them frequently to increase the rate of SLB faults 926 on kernel addresses. 927 928 disable= [IPV6] 929 See Documentation/networking/ipv6.rst. 930 931 hardened_usercopy= 932 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 933 hardening is enabled for this boot. Hardened 934 usercopy checking is used to protect the kernel 935 from reading or writing beyond known memory 936 allocation boundaries as a proactive defense 937 against bounds-checking flaws in the kernel's 938 copy_to_user()/copy_from_user() interface. 939 on Perform hardened usercopy checks (default). 940 off Disable hardened usercopy checks. 941 942 disable_radix [PPC] 943 Disable RADIX MMU mode on POWER9 944 945 radix_hcall_invalidate=on [PPC/PSERIES] 946 Disable RADIX GTSE feature and use hcall for TLB 947 invalidate. 948 949 disable_tlbie [PPC] 950 Disable TLBIE instruction. Currently does not work 951 with KVM, with HASH MMU, or with coherent accelerators. 952 953 disable_cpu_apicid= [X86,APIC,SMP] 954 Format: <int> 955 The number of initial APIC ID for the 956 corresponding CPU to be disabled at boot, 957 mostly used for the kdump 2nd kernel to 958 disable BSP to wake up multiple CPUs without 959 causing system reset or hang due to sending 960 INIT from AP to BSP. 961 962 disable_ddw [PPC/PSERIES] 963 Disable Dynamic DMA Window support. Use this 964 to workaround buggy firmware. 965 966 disable_ipv6= [IPV6] 967 See Documentation/networking/ipv6.rst. 968 969 disable_mtrr_cleanup [X86] 970 The kernel tries to adjust MTRR layout from continuous 971 to discrete, to make X server driver able to add WB 972 entry later. This parameter disables that. 973 974 disable_mtrr_trim [X86, Intel and AMD only] 975 By default the kernel will trim any uncacheable 976 memory out of your available memory pool based on 977 MTRR settings. This parameter disables that behavior, 978 possibly causing your machine to run very slowly. 979 980 disable_timer_pin_1 [X86] 981 Disable PIN 1 of APIC timer 982 Can be useful to work around chipset bugs. 983 984 dis_ucode_ldr [X86] Disable the microcode loader. 985 986 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 987 this option disables the debugging code at boot. 988 989 dma_debug_entries=<number> 990 This option allows to tune the number of preallocated 991 entries for DMA-API debugging code. One entry is 992 required per DMA-API allocation. Use this if the 993 DMA-API debugging code disables itself because the 994 architectural default is too low. 995 996 dma_debug_driver=<driver_name> 997 With this option the DMA-API debugging driver 998 filter feature can be enabled at boot time. Just 999 pass the driver to filter for as the parameter. 1000 The filter can be disabled or changed to another 1001 driver later using sysfs. 1002 1003 driver_async_probe= [KNL] 1004 List of driver names to be probed asynchronously. 1005 Format: <driver_name1>,<driver_name2>... 1006 1007 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1008 Broken monitors, graphic adapters, KVMs and EDIDless 1009 panels may send no or incorrect EDID data sets. 1010 This parameter allows to specify an EDID data sets 1011 in the /lib/firmware directory that are used instead. 1012 Generic built-in EDID data sets are used, if one of 1013 edid/1024x768.bin, edid/1280x1024.bin, 1014 edid/1680x1050.bin, or edid/1920x1080.bin is given 1015 and no file with the same name exists. Details and 1016 instructions how to build your own EDID data are 1017 available in Documentation/admin-guide/edid.rst. An EDID 1018 data set will only be used for a particular connector, 1019 if its name and a colon are prepended to the EDID 1020 name. Each connector may use a unique EDID data 1021 set by separating the files with a comma. An EDID 1022 data set with no connector name will be used for 1023 any connectors not explicitly specified. 1024 1025 dscc4.setup= [NET] 1026 1027 dt_cpu_ftrs= [PPC] 1028 Format: {"off" | "known"} 1029 Control how the dt_cpu_ftrs device-tree binding is 1030 used for CPU feature discovery and setup (if it 1031 exists). 1032 off: Do not use it, fall back to legacy cpu table. 1033 known: Do not pass through unknown features to guests 1034 or userspace, only those that the kernel is aware of. 1035 1036 dump_apple_properties [X86] 1037 Dump name and content of EFI device properties on 1038 x86 Macs. Useful for driver authors to determine 1039 what data is available or for reverse-engineering. 1040 1041 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1042 <module>.dyndbg[="val"] 1043 Enable debug messages at boot time. See 1044 Documentation/admin-guide/dynamic-debug-howto.rst 1045 for details. 1046 1047 nopku [X86] Disable Memory Protection Keys CPU feature found 1048 in some Intel CPUs. 1049 1050 <module>.async_probe [KNL] 1051 Enable asynchronous probe on this module. 1052 1053 early_ioremap_debug [KNL] 1054 Enable debug messages in early_ioremap support. This 1055 is useful for tracking down temporary early mappings 1056 which are not unmapped. 1057 1058 earlycon= [KNL] Output early console device and options. 1059 1060 When used with no options, the early console is 1061 determined by stdout-path property in device tree's 1062 chosen node or the ACPI SPCR table if supported by 1063 the platform. 1064 1065 cdns,<addr>[,options] 1066 Start an early, polled-mode console on a Cadence 1067 (xuartps) serial port at the specified address. Only 1068 supported option is baud rate. If baud rate is not 1069 specified, the serial port must already be setup and 1070 configured. 1071 1072 uart[8250],io,<addr>[,options] 1073 uart[8250],mmio,<addr>[,options] 1074 uart[8250],mmio32,<addr>[,options] 1075 uart[8250],mmio32be,<addr>[,options] 1076 uart[8250],0x<addr>[,options] 1077 Start an early, polled-mode console on the 8250/16550 1078 UART at the specified I/O port or MMIO address. 1079 MMIO inter-register address stride is either 8-bit 1080 (mmio) or 32-bit (mmio32 or mmio32be). 1081 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1082 to be equivalent to 'mmio'. 'options' are specified 1083 in the same format described for "console=ttyS<n>"; if 1084 unspecified, the h/w is not initialized. 1085 1086 pl011,<addr> 1087 pl011,mmio32,<addr> 1088 Start an early, polled-mode console on a pl011 serial 1089 port at the specified address. The pl011 serial port 1090 must already be setup and configured. Options are not 1091 yet supported. If 'mmio32' is specified, then only 1092 the driver will use only 32-bit accessors to read/write 1093 the device registers. 1094 1095 meson,<addr> 1096 Start an early, polled-mode console on a meson serial 1097 port at the specified address. The serial port must 1098 already be setup and configured. Options are not yet 1099 supported. 1100 1101 msm_serial,<addr> 1102 Start an early, polled-mode console on an msm serial 1103 port at the specified address. The serial port 1104 must already be setup and configured. Options are not 1105 yet supported. 1106 1107 msm_serial_dm,<addr> 1108 Start an early, polled-mode console on an msm serial 1109 dm port at the specified address. The serial port 1110 must already be setup and configured. Options are not 1111 yet supported. 1112 1113 owl,<addr> 1114 Start an early, polled-mode console on a serial port 1115 of an Actions Semi SoC, such as S500 or S900, at the 1116 specified address. The serial port must already be 1117 setup and configured. Options are not yet supported. 1118 1119 rda,<addr> 1120 Start an early, polled-mode console on a serial port 1121 of an RDA Micro SoC, such as RDA8810PL, at the 1122 specified address. The serial port must already be 1123 setup and configured. Options are not yet supported. 1124 1125 sbi 1126 Use RISC-V SBI (Supervisor Binary Interface) for early 1127 console. 1128 1129 smh Use ARM semihosting calls for early console. 1130 1131 s3c2410,<addr> 1132 s3c2412,<addr> 1133 s3c2440,<addr> 1134 s3c6400,<addr> 1135 s5pv210,<addr> 1136 exynos4210,<addr> 1137 Use early console provided by serial driver available 1138 on Samsung SoCs, requires selecting proper type and 1139 a correct base address of the selected UART port. The 1140 serial port must already be setup and configured. 1141 Options are not yet supported. 1142 1143 lantiq,<addr> 1144 Start an early, polled-mode console on a lantiq serial 1145 (lqasc) port at the specified address. The serial port 1146 must already be setup and configured. Options are not 1147 yet supported. 1148 1149 lpuart,<addr> 1150 lpuart32,<addr> 1151 Use early console provided by Freescale LP UART driver 1152 found on Freescale Vybrid and QorIQ LS1021A processors. 1153 A valid base address must be provided, and the serial 1154 port must already be setup and configured. 1155 1156 ec_imx21,<addr> 1157 ec_imx6q,<addr> 1158 Start an early, polled-mode, output-only console on the 1159 Freescale i.MX UART at the specified address. The UART 1160 must already be setup and configured. 1161 1162 ar3700_uart,<addr> 1163 Start an early, polled-mode console on the 1164 Armada 3700 serial port at the specified 1165 address. The serial port must already be setup 1166 and configured. Options are not yet supported. 1167 1168 qcom_geni,<addr> 1169 Start an early, polled-mode console on a Qualcomm 1170 Generic Interface (GENI) based serial port at the 1171 specified address. The serial port must already be 1172 setup and configured. Options are not yet supported. 1173 1174 efifb,[options] 1175 Start an early, unaccelerated console on the EFI 1176 memory mapped framebuffer (if available). On cache 1177 coherent non-x86 systems that use system memory for 1178 the framebuffer, pass the 'ram' option so that it is 1179 mapped with the correct attributes. 1180 1181 linflex,<addr> 1182 Use early console provided by Freescale LINFlexD UART 1183 serial driver for NXP S32V234 SoCs. A valid base 1184 address must be provided, and the serial port must 1185 already be setup and configured. 1186 1187 earlyprintk= [X86,SH,ARM,M68k,S390] 1188 earlyprintk=vga 1189 earlyprintk=sclp 1190 earlyprintk=xen 1191 earlyprintk=serial[,ttySn[,baudrate]] 1192 earlyprintk=serial[,0x...[,baudrate]] 1193 earlyprintk=ttySn[,baudrate] 1194 earlyprintk=dbgp[debugController#] 1195 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1196 earlyprintk=xdbc[xhciController#] 1197 1198 earlyprintk is useful when the kernel crashes before 1199 the normal console is initialized. It is not enabled by 1200 default because it has some cosmetic problems. 1201 1202 Append ",keep" to not disable it when the real console 1203 takes over. 1204 1205 Only one of vga, efi, serial, or usb debug port can 1206 be used at a time. 1207 1208 Currently only ttyS0 and ttyS1 may be specified by 1209 name. Other I/O ports may be explicitly specified 1210 on some architectures (x86 and arm at least) by 1211 replacing ttySn with an I/O port address, like this: 1212 earlyprintk=serial,0x1008,115200 1213 You can find the port for a given device in 1214 /proc/tty/driver/serial: 1215 2: uart:ST16650V2 port:00001008 irq:18 ... 1216 1217 Interaction with the standard serial driver is not 1218 very good. 1219 1220 The VGA and EFI output is eventually overwritten by 1221 the real console. 1222 1223 The xen output can only be used by Xen PV guests. 1224 1225 The sclp output can only be used on s390. 1226 1227 The optional "force" to "pciserial" enables use of a 1228 PCI device even when its classcode is not of the 1229 UART class. 1230 1231 edac_report= [HW,EDAC] Control how to report EDAC event 1232 Format: {"on" | "off" | "force"} 1233 on: enable EDAC to report H/W event. May be overridden 1234 by other higher priority error reporting module. 1235 off: disable H/W event reporting through EDAC. 1236 force: enforce the use of EDAC to report H/W event. 1237 default: on. 1238 1239 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1240 ekgdboc=kbd 1241 1242 This is designed to be used in conjunction with 1243 the boot argument: earlyprintk=vga 1244 1245 This parameter works in place of the kgdboc parameter 1246 but can only be used if the backing tty is available 1247 very early in the boot process. For early debugging 1248 via a serial port see kgdboc_earlycon instead. 1249 1250 edd= [EDD] 1251 Format: {"off" | "on" | "skip[mbr]"} 1252 1253 efi= [EFI] 1254 Format: { "debug", "disable_early_pci_dma", 1255 "nochunk", "noruntime", "nosoftreserve", 1256 "novamap", "no_disable_early_pci_dma" } 1257 debug: enable misc debug output. 1258 disable_early_pci_dma: disable the busmaster bit on all 1259 PCI bridges while in the EFI boot stub. 1260 nochunk: disable reading files in "chunks" in the EFI 1261 boot stub, as chunking can cause problems with some 1262 firmware implementations. 1263 noruntime : disable EFI runtime services support 1264 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1265 attribute may cause the kernel to reserve the 1266 memory range for a memory mapping driver to 1267 claim. Specify efi=nosoftreserve to disable this 1268 reservation and treat the memory by its base type 1269 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1270 novamap: do not call SetVirtualAddressMap(). 1271 no_disable_early_pci_dma: Leave the busmaster bit set 1272 on all PCI bridges while in the EFI boot stub 1273 1274 efi_no_storage_paranoia [EFI; X86] 1275 Using this parameter you can use more than 50% of 1276 your efi variable storage. Use this parameter only if 1277 you are really sure that your UEFI does sane gc and 1278 fulfills the spec otherwise your board may brick. 1279 1280 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1281 Add arbitrary attribute to specific memory range by 1282 updating original EFI memory map. 1283 Region of memory which aa attribute is added to is 1284 from ss to ss+nn. 1285 1286 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1287 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1288 attribute is added to range 0x100000000-0x180000000 and 1289 0x10a0000000-0x1120000000. 1290 1291 If efi_fake_mem=8G@9G:0x40000 is specified, the 1292 EFI_MEMORY_SP(0x40000) attribute is added to 1293 range 0x240000000-0x43fffffff. 1294 1295 Using this parameter you can do debugging of EFI memmap 1296 related features. For example, you can do debugging of 1297 Address Range Mirroring feature even if your box 1298 doesn't support it, or mark specific memory as 1299 "soft reserved". 1300 1301 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1302 that is to be dynamically loaded by Linux. If there are 1303 multiple variables with the same name but with different 1304 vendor GUIDs, all of them will be loaded. See 1305 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1306 1307 1308 eisa_irq_edge= [PARISC,HW] 1309 See header of drivers/parisc/eisa.c. 1310 1311 elanfreq= [X86-32] 1312 See comment before function elanfreq_setup() in 1313 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1314 1315 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1316 Specifies physical address of start of kernel core 1317 image elf header and optionally the size. Generally 1318 kexec loader will pass this option to capture kernel. 1319 See Documentation/admin-guide/kdump/kdump.rst for details. 1320 1321 enable_mtrr_cleanup [X86] 1322 The kernel tries to adjust MTRR layout from continuous 1323 to discrete, to make X server driver able to add WB 1324 entry later. This parameter enables that. 1325 1326 enable_timer_pin_1 [X86] 1327 Enable PIN 1 of APIC timer 1328 Can be useful to work around chipset bugs 1329 (in particular on some ATI chipsets). 1330 The kernel tries to set a reasonable default. 1331 1332 enforcing [SELINUX] Set initial enforcing status. 1333 Format: {"0" | "1"} 1334 See security/selinux/Kconfig help text. 1335 0 -- permissive (log only, no denials). 1336 1 -- enforcing (deny and log). 1337 Default value is 0. 1338 Value can be changed at runtime via 1339 /sys/fs/selinux/enforce. 1340 1341 erst_disable [ACPI] 1342 Disable Error Record Serialization Table (ERST) 1343 support. 1344 1345 ether= [HW,NET] Ethernet cards parameters 1346 This option is obsoleted by the "netdev=" option, which 1347 has equivalent usage. See its documentation for details. 1348 1349 evm= [EVM] 1350 Format: { "fix" } 1351 Permit 'security.evm' to be updated regardless of 1352 current integrity status. 1353 1354 failslab= 1355 fail_usercopy= 1356 fail_page_alloc= 1357 fail_make_request=[KNL] 1358 General fault injection mechanism. 1359 Format: <interval>,<probability>,<space>,<times> 1360 See also Documentation/fault-injection/. 1361 1362 fb_tunnels= [NET] 1363 Format: { initns | none } 1364 See Documentation/admin-guide/sysctl/net.rst for 1365 fb_tunnels_only_for_init_ns 1366 1367 floppy= [HW] 1368 See Documentation/admin-guide/blockdev/floppy.rst. 1369 1370 force_pal_cache_flush 1371 [IA-64] Avoid check_sal_cache_flush which may hang on 1372 buggy SAL_CACHE_FLUSH implementations. Using this 1373 parameter will force ia64_sal_cache_flush to call 1374 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1375 1376 forcepae [X86-32] 1377 Forcefully enable Physical Address Extension (PAE). 1378 Many Pentium M systems disable PAE but may have a 1379 functionally usable PAE implementation. 1380 Warning: use of this parameter will taint the kernel 1381 and may cause unknown problems. 1382 1383 ftrace=[tracer] 1384 [FTRACE] will set and start the specified tracer 1385 as early as possible in order to facilitate early 1386 boot debugging. 1387 1388 ftrace_dump_on_oops[=orig_cpu] 1389 [FTRACE] will dump the trace buffers on oops. 1390 If no parameter is passed, ftrace will dump 1391 buffers of all CPUs, but if you pass orig_cpu, it will 1392 dump only the buffer of the CPU that triggered the 1393 oops. 1394 1395 ftrace_filter=[function-list] 1396 [FTRACE] Limit the functions traced by the function 1397 tracer at boot up. function-list is a comma-separated 1398 list of functions. This list can be changed at run 1399 time by the set_ftrace_filter file in the debugfs 1400 tracing directory. 1401 1402 ftrace_notrace=[function-list] 1403 [FTRACE] Do not trace the functions specified in 1404 function-list. This list can be changed at run time 1405 by the set_ftrace_notrace file in the debugfs 1406 tracing directory. 1407 1408 ftrace_graph_filter=[function-list] 1409 [FTRACE] Limit the top level callers functions traced 1410 by the function graph tracer at boot up. 1411 function-list is a comma-separated list of functions 1412 that can be changed at run time by the 1413 set_graph_function file in the debugfs tracing directory. 1414 1415 ftrace_graph_notrace=[function-list] 1416 [FTRACE] Do not trace from the functions specified in 1417 function-list. This list is a comma-separated list of 1418 functions that can be changed at run time by the 1419 set_graph_notrace file in the debugfs tracing directory. 1420 1421 ftrace_graph_max_depth=<uint> 1422 [FTRACE] Used with the function graph tracer. This is 1423 the max depth it will trace into a function. This value 1424 can be changed at run time by the max_graph_depth file 1425 in the tracefs tracing directory. default: 0 (no limit) 1426 1427 fw_devlink= [KNL] Create device links between consumer and supplier 1428 devices by scanning the firmware to infer the 1429 consumer/supplier relationships. This feature is 1430 especially useful when drivers are loaded as modules as 1431 it ensures proper ordering of tasks like device probing 1432 (suppliers first, then consumers), supplier boot state 1433 clean up (only after all consumers have probed), 1434 suspend/resume & runtime PM (consumers first, then 1435 suppliers). 1436 Format: { off | permissive | on | rpm } 1437 off -- Don't create device links from firmware info. 1438 permissive -- Create device links from firmware info 1439 but use it only for ordering boot state clean 1440 up (sync_state() calls). 1441 on -- Create device links from firmware info and use it 1442 to enforce probe and suspend/resume ordering. 1443 rpm -- Like "on", but also use to order runtime PM. 1444 1445 fw_devlink.strict=<bool> 1446 [KNL] Treat all inferred dependencies as mandatory 1447 dependencies. This only applies for fw_devlink=on|rpm. 1448 Format: <bool> 1449 1450 gamecon.map[2|3]= 1451 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1452 support via parallel port (up to 5 devices per port) 1453 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1454 See also Documentation/input/devices/joystick-parport.rst 1455 1456 gamma= [HW,DRM] 1457 1458 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART 1459 Format: off | on 1460 default: on 1461 1462 gcov_persist= [GCOV] When non-zero (default), profiling data for 1463 kernel modules is saved and remains accessible via 1464 debugfs, even when the module is unloaded/reloaded. 1465 When zero, profiling data is discarded and associated 1466 debugfs files are removed at module unload time. 1467 1468 goldfish [X86] Enable the goldfish android emulator platform. 1469 Don't use this when you are not running on the 1470 android emulator 1471 1472 gpio-mockup.gpio_mockup_ranges 1473 [HW] Sets the ranges of gpiochip of for this device. 1474 Format: <start1>,<end1>,<start2>,<end2>... 1475 gpio-mockup.gpio_mockup_named_lines 1476 [HW] Let the driver know GPIO lines should be named. 1477 1478 gpt [EFI] Forces disk with valid GPT signature but 1479 invalid Protective MBR to be treated as GPT. If the 1480 primary GPT is corrupted, it enables the backup/alternate 1481 GPT to be used instead. 1482 1483 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1484 the "Enable 0" bit of the configuration register. 1485 Format: 0 | 1 1486 Default: 0 1487 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1488 the "Enable 0" bit of the configuration register. 1489 Format: 0 | 1 1490 Default: 0 1491 grcan.select= [HW] Select which physical interface to use. 1492 Format: 0 | 1 1493 Default: 0 1494 grcan.txsize= [HW] Sets the size of the tx buffer. 1495 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1496 Default: 1024 1497 grcan.rxsize= [HW] Sets the size of the rx buffer. 1498 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1499 Default: 1024 1500 1501 hardlockup_all_cpu_backtrace= 1502 [KNL] Should the hard-lockup detector generate 1503 backtraces on all cpus. 1504 Format: 0 | 1 1505 1506 hashdist= [KNL,NUMA] Large hashes allocated during boot 1507 are distributed across NUMA nodes. Defaults on 1508 for 64-bit NUMA, off otherwise. 1509 Format: 0 | 1 (for off | on) 1510 1511 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1512 1513 hd= [EIDE] (E)IDE hard drive subsystem geometry 1514 Format: <cyl>,<head>,<sect> 1515 1516 hest_disable [ACPI] 1517 Disable Hardware Error Source Table (HEST) support; 1518 corresponding firmware-first mode error processing 1519 logic will be disabled. 1520 1521 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1522 size of <nn>. This works even on boxes that have no 1523 highmem otherwise. This also works to reduce highmem 1524 size on bigger boxes. 1525 1526 highres= [KNL] Enable/disable high resolution timer mode. 1527 Valid parameters: "on", "off" 1528 Default: "on" 1529 1530 hlt [BUGS=ARM,SH] 1531 1532 hpet= [X86-32,HPET] option to control HPET usage 1533 Format: { enable (default) | disable | force | 1534 verbose } 1535 disable: disable HPET and use PIT instead 1536 force: allow force enabled of undocumented chips (ICH4, 1537 VIA, nVidia) 1538 verbose: show contents of HPET registers during setup 1539 1540 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1541 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1542 1543 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation 1544 of gigantic hugepages. 1545 Format: nn[KMGTPE] 1546 1547 Reserve a CMA area of given size and allocate gigantic 1548 hugepages using the CMA allocator. If enabled, the 1549 boot-time allocation of gigantic hugepages is skipped. 1550 1551 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1552 If this follows hugepagesz (below), it specifies 1553 the number of pages of hugepagesz to be allocated. 1554 If this is the first HugeTLB parameter on the command 1555 line, it specifies the number of pages to allocate for 1556 the default huge page size. See also 1557 Documentation/admin-guide/mm/hugetlbpage.rst. 1558 Format: <integer> 1559 1560 hugepagesz= 1561 [HW] The size of the HugeTLB pages. This is used in 1562 conjunction with hugepages (above) to allocate huge 1563 pages of a specific size at boot. The pair 1564 hugepagesz=X hugepages=Y can be specified once for 1565 each supported huge page size. Huge page sizes are 1566 architecture dependent. See also 1567 Documentation/admin-guide/mm/hugetlbpage.rst. 1568 Format: size[KMG] 1569 1570 hung_task_panic= 1571 [KNL] Should the hung task detector generate panics. 1572 Format: 0 | 1 1573 1574 A value of 1 instructs the kernel to panic when a 1575 hung task is detected. The default value is controlled 1576 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1577 option. The value selected by this boot parameter can 1578 be changed later by the kernel.hung_task_panic sysctl. 1579 1580 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1581 terminal devices. Valid values: 0..8 1582 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1583 If specified, z/VM IUCV HVC accepts connections 1584 from listed z/VM user IDs only. 1585 1586 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1587 which allow the hypervisor to 'idle' the 1588 guest on lock contention. 1589 1590 keep_bootcon [KNL] 1591 Do not unregister boot console at start. This is only 1592 useful for debugging when something happens in the window 1593 between unregistering the boot console and initializing 1594 the real console. 1595 1596 i2c_bus= [HW] Override the default board specific I2C bus speed 1597 or register an additional I2C bus that is not 1598 registered from board initialization code. 1599 Format: 1600 <bus_id>,<clkrate> 1601 1602 i8042.debug [HW] Toggle i8042 debug mode 1603 i8042.unmask_kbd_data 1604 [HW] Enable printing of interrupt data from the KBD port 1605 (disabled by default, and as a pre-condition 1606 requires that i8042.debug=1 be enabled) 1607 i8042.direct [HW] Put keyboard port into non-translated mode 1608 i8042.dumbkbd [HW] Pretend that controller can only read data from 1609 keyboard and cannot control its state 1610 (Don't attempt to blink the leds) 1611 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1612 i8042.nokbd [HW] Don't check/create keyboard port 1613 i8042.noloop [HW] Disable the AUX Loopback command while probing 1614 for the AUX port 1615 i8042.nomux [HW] Don't check presence of an active multiplexing 1616 controller 1617 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1618 controllers 1619 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1620 i8042.reset [HW] Reset the controller during init, cleanup and 1621 suspend-to-ram transitions, only during s2r 1622 transitions, or never reset 1623 Format: { 1 | Y | y | 0 | N | n } 1624 1, Y, y: always reset controller 1625 0, N, n: don't ever reset controller 1626 Default: only on s2r transitions on x86; most other 1627 architectures force reset to be always executed 1628 i8042.unlock [HW] Unlock (ignore) the keylock 1629 i8042.kbdreset [HW] Reset device connected to KBD port 1630 1631 i810= [HW,DRM] 1632 1633 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1634 indicates that the driver is running on unsupported 1635 hardware. 1636 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1637 does not match list of supported models. 1638 i8k.power_status 1639 [HW] Report power status in /proc/i8k 1640 (disabled by default) 1641 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1642 capability is set. 1643 1644 i915.invert_brightness= 1645 [DRM] Invert the sense of the variable that is used to 1646 set the brightness of the panel backlight. Normally a 1647 brightness value of 0 indicates backlight switched off, 1648 and the maximum of the brightness value sets the backlight 1649 to maximum brightness. If this parameter is set to 0 1650 (default) and the machine requires it, or this parameter 1651 is set to 1, a brightness value of 0 sets the backlight 1652 to maximum brightness, and the maximum of the brightness 1653 value switches the backlight off. 1654 -1 -- never invert brightness 1655 0 -- machine default 1656 1 -- force brightness inversion 1657 1658 icn= [HW,ISDN] 1659 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1660 1661 ide-core.nodma= [HW] (E)IDE subsystem 1662 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1663 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1664 .cdrom .chs .ignore_cable are additional options 1665 See Documentation/ide/ide.rst. 1666 1667 ide-generic.probe-mask= [HW] (E)IDE subsystem 1668 Format: <int> 1669 Probe mask for legacy ISA IDE ports. Depending on 1670 platform up to 6 ports are supported, enabled by 1671 setting corresponding bits in the mask to 1. The 1672 default value is 0x0, which has a special meaning. 1673 On systems that have PCI, it triggers scanning the 1674 PCI bus for the first and the second port, which 1675 are then probed. On systems without PCI the value 1676 of 0x0 enables probing the two first ports as if it 1677 was 0x3. 1678 1679 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1680 Claim all unknown PCI IDE storage controllers. 1681 1682 idle= [X86] 1683 Format: idle=poll, idle=halt, idle=nomwait 1684 Poll forces a polling idle loop that can slightly 1685 improve the performance of waking up a idle CPU, but 1686 will use a lot of power and make the system run hot. 1687 Not recommended. 1688 idle=halt: Halt is forced to be used for CPU idle. 1689 In such case C2/C3 won't be used again. 1690 idle=nomwait: Disable mwait for CPU C-states 1691 1692 idxd.sva= [HW] 1693 Format: <bool> 1694 Allow force disabling of Shared Virtual Memory (SVA) 1695 support for the idxd driver. By default it is set to 1696 true (1). 1697 1698 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1699 Format: { strict | legacy | 2008 | relaxed } 1700 Default: strict 1701 1702 Choose which programs will be accepted for execution 1703 based on the IEEE 754 NaN encoding(s) supported by 1704 the FPU and the NaN encoding requested with the value 1705 of an ELF file header flag individually set by each 1706 binary. Hardware implementations are permitted to 1707 support either or both of the legacy and the 2008 NaN 1708 encoding mode. 1709 1710 Available settings are as follows: 1711 strict accept binaries that request a NaN encoding 1712 supported by the FPU 1713 legacy only accept legacy-NaN binaries, if supported 1714 by the FPU 1715 2008 only accept 2008-NaN binaries, if supported 1716 by the FPU 1717 relaxed accept any binaries regardless of whether 1718 supported by the FPU 1719 1720 The FPU emulator is always able to support both NaN 1721 encodings, so if no FPU hardware is present or it has 1722 been disabled with 'nofpu', then the settings of 1723 'legacy' and '2008' strap the emulator accordingly, 1724 'relaxed' straps the emulator for both legacy-NaN and 1725 2008-NaN, whereas 'strict' enables legacy-NaN only on 1726 legacy processors and both NaN encodings on MIPS32 or 1727 MIPS64 CPUs. 1728 1729 The setting for ABS.fmt/NEG.fmt instruction execution 1730 mode generally follows that for the NaN encoding, 1731 except where unsupported by hardware. 1732 1733 ignore_loglevel [KNL] 1734 Ignore loglevel setting - this will print /all/ 1735 kernel messages to the console. Useful for debugging. 1736 We also add it as printk module parameter, so users 1737 could change it dynamically, usually by 1738 /sys/module/printk/parameters/ignore_loglevel. 1739 1740 ignore_rlimit_data 1741 Ignore RLIMIT_DATA setting for data mappings, 1742 print warning at first misuse. Can be changed via 1743 /sys/module/kernel/parameters/ignore_rlimit_data. 1744 1745 ihash_entries= [KNL] 1746 Set number of hash buckets for inode cache. 1747 1748 ima_appraise= [IMA] appraise integrity measurements 1749 Format: { "off" | "enforce" | "fix" | "log" } 1750 default: "enforce" 1751 1752 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1753 The builtin appraise policy appraises all files 1754 owned by uid=0. 1755 1756 ima_canonical_fmt [IMA] 1757 Use the canonical format for the binary runtime 1758 measurements, instead of host native format. 1759 1760 ima_hash= [IMA] 1761 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1762 | sha512 | ... } 1763 default: "sha1" 1764 1765 The list of supported hash algorithms is defined 1766 in crypto/hash_info.h. 1767 1768 ima_policy= [IMA] 1769 The builtin policies to load during IMA setup. 1770 Format: "tcb | appraise_tcb | secure_boot | 1771 fail_securely | critical_data" 1772 1773 The "tcb" policy measures all programs exec'd, files 1774 mmap'd for exec, and all files opened with the read 1775 mode bit set by either the effective uid (euid=0) or 1776 uid=0. 1777 1778 The "appraise_tcb" policy appraises the integrity of 1779 all files owned by root. 1780 1781 The "secure_boot" policy appraises the integrity 1782 of files (eg. kexec kernel image, kernel modules, 1783 firmware, policy, etc) based on file signatures. 1784 1785 The "fail_securely" policy forces file signature 1786 verification failure also on privileged mounted 1787 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1788 flag. 1789 1790 The "critical_data" policy measures kernel integrity 1791 critical data. 1792 1793 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1794 Load a policy which meets the needs of the Trusted 1795 Computing Base. This means IMA will measure all 1796 programs exec'd, files mmap'd for exec, and all files 1797 opened for read by uid=0. 1798 1799 ima_template= [IMA] 1800 Select one of defined IMA measurements template formats. 1801 Formats: { "ima" | "ima-ng" | "ima-sig" } 1802 Default: "ima-ng" 1803 1804 ima_template_fmt= 1805 [IMA] Define a custom template format. 1806 Format: { "field1|...|fieldN" } 1807 1808 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1809 Format: <min_file_size> 1810 Set the minimal file size for using asynchronous hash. 1811 If left unspecified, ahash usage is disabled. 1812 1813 ahash performance varies for different data sizes on 1814 different crypto accelerators. This option can be used 1815 to achieve the best performance for a particular HW. 1816 1817 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1818 Format: <bufsize> 1819 Set hashing buffer size. Default: 4k. 1820 1821 ahash performance varies for different chunk sizes on 1822 different crypto accelerators. This option can be used 1823 to achieve best performance for particular HW. 1824 1825 init= [KNL] 1826 Format: <full_path> 1827 Run specified binary instead of /sbin/init as init 1828 process. 1829 1830 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1831 for working out where the kernel is dying during 1832 startup. 1833 1834 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1835 initcall functions. Useful for debugging built-in 1836 modules and initcalls. 1837 1838 initramfs_async= [KNL] 1839 Format: <bool> 1840 Default: 1 1841 This parameter controls whether the initramfs 1842 image is unpacked asynchronously, concurrently 1843 with devices being probed and 1844 initialized. This should normally just work, 1845 but as a debugging aid, one can get the 1846 historical behaviour of the initramfs 1847 unpacking being completed before device_ and 1848 late_ initcalls. 1849 1850 initrd= [BOOT] Specify the location of the initial ramdisk 1851 1852 initrdmem= [KNL] Specify a physical address and size from which to 1853 load the initrd. If an initrd is compiled in or 1854 specified in the bootparams, it takes priority over this 1855 setting. 1856 Format: ss[KMG],nn[KMG] 1857 Default is 0, 0 1858 1859 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1860 zeroes. 1861 Format: 0 | 1 1862 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1863 1864 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1865 Format: 0 | 1 1866 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1867 1868 init_pkru= [X86] Specify the default memory protection keys rights 1869 register contents for all processes. 0x55555554 by 1870 default (disallow access to all but pkey 0). Can 1871 override in debugfs after boot. 1872 1873 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1874 Format: <irq> 1875 1876 int_pln_enable [X86] Enable power limit notification interrupt 1877 1878 integrity_audit=[IMA] 1879 Format: { "0" | "1" } 1880 0 -- basic integrity auditing messages. (Default) 1881 1 -- additional integrity auditing messages. 1882 1883 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1884 on 1885 Enable intel iommu driver. 1886 off 1887 Disable intel iommu driver. 1888 igfx_off [Default Off] 1889 By default, gfx is mapped as normal device. If a gfx 1890 device has a dedicated DMAR unit, the DMAR unit is 1891 bypassed by not enabling DMAR with this option. In 1892 this case, gfx device will use physical address for 1893 DMA. 1894 strict [Default Off] 1895 With this option on every unmap_single operation will 1896 result in a hardware IOTLB flush operation as opposed 1897 to batching them for performance. 1898 sp_off [Default Off] 1899 By default, super page will be supported if Intel IOMMU 1900 has the capability. With this option, super page will 1901 not be supported. 1902 sm_on [Default Off] 1903 By default, scalable mode will be disabled even if the 1904 hardware advertises that it has support for the scalable 1905 mode translation. With this option set, scalable mode 1906 will be used on hardware which claims to support it. 1907 tboot_noforce [Default Off] 1908 Do not force the Intel IOMMU enabled under tboot. 1909 By default, tboot will force Intel IOMMU on, which 1910 could harm performance of some high-throughput 1911 devices like 40GBit network cards, even if identity 1912 mapping is enabled. 1913 Note that using this option lowers the security 1914 provided by tboot because it makes the system 1915 vulnerable to DMA attacks. 1916 1917 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1918 0 disables intel_idle and fall back on acpi_idle. 1919 1 to 9 specify maximum depth of C-state. 1920 1921 intel_pstate= [X86] 1922 disable 1923 Do not enable intel_pstate as the default 1924 scaling driver for the supported processors 1925 passive 1926 Use intel_pstate as a scaling driver, but configure it 1927 to work with generic cpufreq governors (instead of 1928 enabling its internal governor). This mode cannot be 1929 used along with the hardware-managed P-states (HWP) 1930 feature. 1931 force 1932 Enable intel_pstate on systems that prohibit it by default 1933 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1934 instead of acpi-cpufreq may disable platform features, such 1935 as thermal controls and power capping, that rely on ACPI 1936 P-States information being indicated to OSPM and therefore 1937 should be used with caution. This option does not work with 1938 processors that aren't supported by the intel_pstate driver 1939 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1940 no_hwp 1941 Do not enable hardware P state control (HWP) 1942 if available. 1943 hwp_only 1944 Only load intel_pstate on systems which support 1945 hardware P state control (HWP) if available. 1946 support_acpi_ppc 1947 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1948 Description Table, specifies preferred power management 1949 profile as "Enterprise Server" or "Performance Server", 1950 then this feature is turned on by default. 1951 per_cpu_perf_limits 1952 Allow per-logical-CPU P-State performance control limits using 1953 cpufreq sysfs interface 1954 1955 intremap= [X86-64, Intel-IOMMU] 1956 on enable Interrupt Remapping (default) 1957 off disable Interrupt Remapping 1958 nosid disable Source ID checking 1959 no_x2apic_optout 1960 BIOS x2APIC opt-out request will be ignored 1961 nopost disable Interrupt Posting 1962 1963 iomem= Disable strict checking of access to MMIO memory 1964 strict regions from userspace. 1965 relaxed 1966 1967 iommu= [X86] 1968 off 1969 force 1970 noforce 1971 biomerge 1972 panic 1973 nopanic 1974 merge 1975 nomerge 1976 soft 1977 pt [X86] 1978 nopt [X86] 1979 nobypass [PPC/POWERNV] 1980 Disable IOMMU bypass, using IOMMU for PCI devices. 1981 1982 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices. 1983 Format: { "0" | "1" } 1984 0 - Try to allocate a 32-bit DMA address first, before 1985 falling back to the full range if needed. 1986 1 - Allocate directly from the full usable range, 1987 forcing Dual Address Cycle for PCI cards supporting 1988 greater than 32-bit addressing. 1989 1990 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1991 Format: { "0" | "1" } 1992 0 - Lazy mode. 1993 Request that DMA unmap operations use deferred 1994 invalidation of hardware TLBs, for increased 1995 throughput at the cost of reduced device isolation. 1996 Will fall back to strict mode if not supported by 1997 the relevant IOMMU driver. 1998 1 - Strict mode (default). 1999 DMA unmap operations invalidate IOMMU hardware TLBs 2000 synchronously. 2001 2002 iommu.passthrough= 2003 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 2004 Format: { "0" | "1" } 2005 0 - Use IOMMU translation for DMA. 2006 1 - Bypass the IOMMU for DMA. 2007 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2008 2009 io7= [HW] IO7 for Marvel-based Alpha systems 2010 See comment before marvel_specify_io7 in 2011 arch/alpha/kernel/core_marvel.c. 2012 2013 io_delay= [X86] I/O delay method 2014 0x80 2015 Standard port 0x80 based delay 2016 0xed 2017 Alternate port 0xed based delay (needed on some systems) 2018 udelay 2019 Simple two microseconds delay 2020 none 2021 No delay 2022 2023 ip= [IP_PNP] 2024 See Documentation/admin-guide/nfs/nfsroot.rst. 2025 2026 ipcmni_extend [KNL] Extend the maximum number of unique System V 2027 IPC identifiers from 32,768 to 16,777,216. 2028 2029 irqaffinity= [SMP] Set the default irq affinity mask 2030 The argument is a cpu list, as described above. 2031 2032 irqchip.gicv2_force_probe= 2033 [ARM, ARM64] 2034 Format: <bool> 2035 Force the kernel to look for the second 4kB page 2036 of a GICv2 controller even if the memory range 2037 exposed by the device tree is too small. 2038 2039 irqchip.gicv3_nolpi= 2040 [ARM, ARM64] 2041 Force the kernel to ignore the availability of 2042 LPIs (and by consequence ITSs). Intended for system 2043 that use the kernel as a bootloader, and thus want 2044 to let secondary kernels in charge of setting up 2045 LPIs. 2046 2047 irqchip.gicv3_pseudo_nmi= [ARM64] 2048 Enables support for pseudo-NMIs in the kernel. This 2049 requires the kernel to be built with 2050 CONFIG_ARM64_PSEUDO_NMI. 2051 2052 irqfixup [HW] 2053 When an interrupt is not handled search all handlers 2054 for it. Intended to get systems with badly broken 2055 firmware running. 2056 2057 irqpoll [HW] 2058 When an interrupt is not handled search all handlers 2059 for it. Also check all handlers each timer 2060 interrupt. Intended to get systems with badly broken 2061 firmware running. 2062 2063 isapnp= [ISAPNP] 2064 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2065 2066 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2067 [Deprecated - use cpusets instead] 2068 Format: [flag-list,]<cpu-list> 2069 2070 Specify one or more CPUs to isolate from disturbances 2071 specified in the flag list (default: domain): 2072 2073 nohz 2074 Disable the tick when a single task runs. 2075 2076 A residual 1Hz tick is offloaded to workqueues, which you 2077 need to affine to housekeeping through the global 2078 workqueue's affinity configured via the 2079 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2080 by using the 'domain' flag described below. 2081 2082 NOTE: by default the global workqueue runs on all CPUs, 2083 so to protect individual CPUs the 'cpumask' file has to 2084 be configured manually after bootup. 2085 2086 domain 2087 Isolate from the general SMP balancing and scheduling 2088 algorithms. Note that performing domain isolation this way 2089 is irreversible: it's not possible to bring back a CPU to 2090 the domains once isolated through isolcpus. It's strongly 2091 advised to use cpusets instead to disable scheduler load 2092 balancing through the "cpuset.sched_load_balance" file. 2093 It offers a much more flexible interface where CPUs can 2094 move in and out of an isolated set anytime. 2095 2096 You can move a process onto or off an "isolated" CPU via 2097 the CPU affinity syscalls or cpuset. 2098 <cpu number> begins at 0 and the maximum value is 2099 "number of CPUs in system - 1". 2100 2101 managed_irq 2102 2103 Isolate from being targeted by managed interrupts 2104 which have an interrupt mask containing isolated 2105 CPUs. The affinity of managed interrupts is 2106 handled by the kernel and cannot be changed via 2107 the /proc/irq/* interfaces. 2108 2109 This isolation is best effort and only effective 2110 if the automatically assigned interrupt mask of a 2111 device queue contains isolated and housekeeping 2112 CPUs. If housekeeping CPUs are online then such 2113 interrupts are directed to the housekeeping CPU 2114 so that IO submitted on the housekeeping CPU 2115 cannot disturb the isolated CPU. 2116 2117 If a queue's affinity mask contains only isolated 2118 CPUs then this parameter has no effect on the 2119 interrupt routing decision, though interrupts are 2120 only delivered when tasks running on those 2121 isolated CPUs submit IO. IO submitted on 2122 housekeeping CPUs has no influence on those 2123 queues. 2124 2125 The format of <cpu-list> is described above. 2126 2127 iucv= [HW,NET] 2128 2129 ivrs_ioapic [HW,X86-64] 2130 Provide an override to the IOAPIC-ID<->DEVICE-ID 2131 mapping provided in the IVRS ACPI table. For 2132 example, to map IOAPIC-ID decimal 10 to 2133 PCI device 00:14.0 write the parameter as: 2134 ivrs_ioapic[10]=00:14.0 2135 2136 ivrs_hpet [HW,X86-64] 2137 Provide an override to the HPET-ID<->DEVICE-ID 2138 mapping provided in the IVRS ACPI table. For 2139 example, to map HPET-ID decimal 0 to 2140 PCI device 00:14.0 write the parameter as: 2141 ivrs_hpet[0]=00:14.0 2142 2143 ivrs_acpihid [HW,X86-64] 2144 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2145 mapping provided in the IVRS ACPI table. For 2146 example, to map UART-HID:UID AMD0020:0 to 2147 PCI device 00:14.5 write the parameter as: 2148 ivrs_acpihid[00:14.5]=AMD0020:0 2149 2150 js= [HW,JOY] Analog joystick 2151 See Documentation/input/joydev/joystick.rst. 2152 2153 nokaslr [KNL] 2154 When CONFIG_RANDOMIZE_BASE is set, this disables 2155 kernel and module base offset ASLR (Address Space 2156 Layout Randomization). 2157 2158 kasan_multi_shot 2159 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2160 report on every invalid memory access. Without this 2161 parameter KASAN will print report only for the first 2162 invalid access. 2163 2164 keepinitrd [HW,ARM] 2165 2166 kernelcore= [KNL,X86,IA-64,PPC] 2167 Format: nn[KMGTPE] | nn% | "mirror" 2168 This parameter specifies the amount of memory usable by 2169 the kernel for non-movable allocations. The requested 2170 amount is spread evenly throughout all nodes in the 2171 system as ZONE_NORMAL. The remaining memory is used for 2172 movable memory in its own zone, ZONE_MOVABLE. In the 2173 event, a node is too small to have both ZONE_NORMAL and 2174 ZONE_MOVABLE, kernelcore memory will take priority and 2175 other nodes will have a larger ZONE_MOVABLE. 2176 2177 ZONE_MOVABLE is used for the allocation of pages that 2178 may be reclaimed or moved by the page migration 2179 subsystem. Note that allocations like PTEs-from-HighMem 2180 still use the HighMem zone if it exists, and the Normal 2181 zone if it does not. 2182 2183 It is possible to specify the exact amount of memory in 2184 the form of "nn[KMGTPE]", a percentage of total system 2185 memory in the form of "nn%", or "mirror". If "mirror" 2186 option is specified, mirrored (reliable) memory is used 2187 for non-movable allocations and remaining memory is used 2188 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2189 are exclusive, so you cannot specify multiple forms. 2190 2191 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2192 Format: <Controller#>[,poll interval] 2193 The controller # is the number of the ehci usb debug 2194 port as it is probed via PCI. The poll interval is 2195 optional and is the number seconds in between 2196 each poll cycle to the debug port in case you need 2197 the functionality for interrupting the kernel with 2198 gdb or control-c on the dbgp connection. When 2199 not using this parameter you use sysrq-g to break into 2200 the kernel debugger. 2201 2202 kgdboc= [KGDB,HW] kgdb over consoles. 2203 Requires a tty driver that supports console polling, 2204 or a supported polling keyboard driver (non-usb). 2205 Serial only format: <serial_device>[,baud] 2206 keyboard only format: kbd 2207 keyboard and serial format: kbd,<serial_device>[,baud] 2208 Optional Kernel mode setting: 2209 kms, kbd format: kms,kbd 2210 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2211 2212 kgdboc_earlycon= [KGDB,HW] 2213 If the boot console provides the ability to read 2214 characters and can work in polling mode, you can use 2215 this parameter to tell kgdb to use it as a backend 2216 until the normal console is registered. Intended to 2217 be used together with the kgdboc parameter which 2218 specifies the normal console to transition to. 2219 2220 The name of the early console should be specified 2221 as the value of this parameter. Note that the name of 2222 the early console might be different than the tty 2223 name passed to kgdboc. It's OK to leave the value 2224 blank and the first boot console that implements 2225 read() will be picked. 2226 2227 kgdbwait [KGDB] Stop kernel execution and enter the 2228 kernel debugger at the earliest opportunity. 2229 2230 kmac= [MIPS] Korina ethernet MAC address. 2231 Configure the RouterBoard 532 series on-chip 2232 Ethernet adapter MAC address. 2233 2234 kmemleak= [KNL] Boot-time kmemleak enable/disable 2235 Valid arguments: on, off 2236 Default: on 2237 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2238 the default is off. 2239 2240 kprobe_event=[probe-list] 2241 [FTRACE] Add kprobe events and enable at boot time. 2242 The probe-list is a semicolon delimited list of probe 2243 definitions. Each definition is same as kprobe_events 2244 interface, but the parameters are comma delimited. 2245 For example, to add a kprobe event on vfs_read with 2246 arg1 and arg2, add to the command line; 2247 2248 kprobe_event=p,vfs_read,$arg1,$arg2 2249 2250 See also Documentation/trace/kprobetrace.rst "Kernel 2251 Boot Parameter" section. 2252 2253 kpti= [ARM64] Control page table isolation of user 2254 and kernel address spaces. 2255 Default: enabled on cores which need mitigation. 2256 0: force disabled 2257 1: force enabled 2258 2259 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2260 Default is 0 (don't ignore, but inject #GP) 2261 2262 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2263 Default is false (don't support). 2264 2265 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2266 KVM MMU at runtime. 2267 Default is 0 (off) 2268 2269 kvm.nx_huge_pages= 2270 [KVM] Controls the software workaround for the 2271 X86_BUG_ITLB_MULTIHIT bug. 2272 force : Always deploy workaround. 2273 off : Never deploy workaround. 2274 auto : Deploy workaround based on the presence of 2275 X86_BUG_ITLB_MULTIHIT. 2276 2277 Default is 'auto'. 2278 2279 If the software workaround is enabled for the host, 2280 guests do need not to enable it for nested guests. 2281 2282 kvm.nx_huge_pages_recovery_ratio= 2283 [KVM] Controls how many 4KiB pages are periodically zapped 2284 back to huge pages. 0 disables the recovery, otherwise if 2285 the value is N KVM will zap 1/Nth of the 4KiB pages every 2286 minute. The default is 60. 2287 2288 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2289 Default is 1 (enabled) 2290 2291 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2292 for all guests. 2293 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2294 2295 kvm-arm.mode= 2296 [KVM,ARM] Select one of KVM/arm64's modes of operation. 2297 2298 nvhe: Standard nVHE-based mode, without support for 2299 protected guests. 2300 2301 protected: nVHE-based mode with support for guests whose 2302 state is kept private from the host. 2303 Not valid if the kernel is running in EL2. 2304 2305 Defaults to VHE/nVHE based on hardware support. 2306 2307 kvm-arm.vgic_v3_group0_trap= 2308 [KVM,ARM] Trap guest accesses to GICv3 group-0 2309 system registers 2310 2311 kvm-arm.vgic_v3_group1_trap= 2312 [KVM,ARM] Trap guest accesses to GICv3 group-1 2313 system registers 2314 2315 kvm-arm.vgic_v3_common_trap= 2316 [KVM,ARM] Trap guest accesses to GICv3 common 2317 system registers 2318 2319 kvm-arm.vgic_v4_enable= 2320 [KVM,ARM] Allow use of GICv4 for direct injection of 2321 LPIs. 2322 2323 kvm_cma_resv_ratio=n [PPC] 2324 Reserves given percentage from system memory area for 2325 contiguous memory allocation for KVM hash pagetable 2326 allocation. 2327 By default it reserves 5% of total system memory. 2328 Format: <integer> 2329 Default: 5 2330 2331 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2332 (virtualized MMU) support on capable Intel chips. 2333 Default is 1 (enabled) 2334 2335 kvm-intel.emulate_invalid_guest_state= 2336 [KVM,Intel] Enable emulation of invalid guest states 2337 Default is 0 (disabled) 2338 2339 kvm-intel.flexpriority= 2340 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2341 Default is 1 (enabled) 2342 2343 kvm-intel.nested= 2344 [KVM,Intel] Enable VMX nesting (nVMX). 2345 Default is 0 (disabled) 2346 2347 kvm-intel.unrestricted_guest= 2348 [KVM,Intel] Disable unrestricted guest feature 2349 (virtualized real and unpaged mode) on capable 2350 Intel chips. Default is 1 (enabled) 2351 2352 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2353 CVE-2018-3620. 2354 2355 Valid arguments: never, cond, always 2356 2357 always: L1D cache flush on every VMENTER. 2358 cond: Flush L1D on VMENTER only when the code between 2359 VMEXIT and VMENTER can leak host memory. 2360 never: Disables the mitigation 2361 2362 Default is cond (do L1 cache flush in specific instances) 2363 2364 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2365 feature (tagged TLBs) on capable Intel chips. 2366 Default is 1 (enabled) 2367 2368 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2369 affected CPUs 2370 2371 The kernel PTE inversion protection is unconditionally 2372 enabled and cannot be disabled. 2373 2374 full 2375 Provides all available mitigations for the 2376 L1TF vulnerability. Disables SMT and 2377 enables all mitigations in the 2378 hypervisors, i.e. unconditional L1D flush. 2379 2380 SMT control and L1D flush control via the 2381 sysfs interface is still possible after 2382 boot. Hypervisors will issue a warning 2383 when the first VM is started in a 2384 potentially insecure configuration, 2385 i.e. SMT enabled or L1D flush disabled. 2386 2387 full,force 2388 Same as 'full', but disables SMT and L1D 2389 flush runtime control. Implies the 2390 'nosmt=force' command line option. 2391 (i.e. sysfs control of SMT is disabled.) 2392 2393 flush 2394 Leaves SMT enabled and enables the default 2395 hypervisor mitigation, i.e. conditional 2396 L1D flush. 2397 2398 SMT control and L1D flush control via the 2399 sysfs interface is still possible after 2400 boot. Hypervisors will issue a warning 2401 when the first VM is started in a 2402 potentially insecure configuration, 2403 i.e. SMT enabled or L1D flush disabled. 2404 2405 flush,nosmt 2406 2407 Disables SMT and enables the default 2408 hypervisor mitigation. 2409 2410 SMT control and L1D flush control via the 2411 sysfs interface is still possible after 2412 boot. Hypervisors will issue a warning 2413 when the first VM is started in a 2414 potentially insecure configuration, 2415 i.e. SMT enabled or L1D flush disabled. 2416 2417 flush,nowarn 2418 Same as 'flush', but hypervisors will not 2419 warn when a VM is started in a potentially 2420 insecure configuration. 2421 2422 off 2423 Disables hypervisor mitigations and doesn't 2424 emit any warnings. 2425 It also drops the swap size and available 2426 RAM limit restriction on both hypervisor and 2427 bare metal. 2428 2429 Default is 'flush'. 2430 2431 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2432 2433 l2cr= [PPC] 2434 2435 l3cr= [PPC] 2436 2437 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2438 disabled it. 2439 2440 lapic= [X86,APIC] Do not use TSC deadline 2441 value for LAPIC timer one-shot implementation. Default 2442 back to the programmable timer unit in the LAPIC. 2443 Format: notscdeadline 2444 2445 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2446 in C2 power state. 2447 2448 libata.dma= [LIBATA] DMA control 2449 libata.dma=0 Disable all PATA and SATA DMA 2450 libata.dma=1 PATA and SATA Disk DMA only 2451 libata.dma=2 ATAPI (CDROM) DMA only 2452 libata.dma=4 Compact Flash DMA only 2453 Combinations also work, so libata.dma=3 enables DMA 2454 for disks and CDROMs, but not CFs. 2455 2456 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2457 libata.ignore_hpa=0 keep BIOS limits (default) 2458 libata.ignore_hpa=1 ignore limits, using full disk 2459 2460 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2461 when set. 2462 Format: <int> 2463 2464 libata.force= [LIBATA] Force configurations. The format is comma- 2465 separated list of "[ID:]VAL" where ID is 2466 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2467 matching port, link or device. Basically, it matches 2468 the ATA ID string printed on console by libata. If 2469 the whole ID part is omitted, the last PORT and DEVICE 2470 values are used. If ID hasn't been specified yet, the 2471 configuration applies to all ports, links and devices. 2472 2473 If only DEVICE is omitted, the parameter applies to 2474 the port and all links and devices behind it. DEVICE 2475 number of 0 either selects the first device or the 2476 first fan-out link behind PMP device. It does not 2477 select the host link. DEVICE number of 15 selects the 2478 host link and device attached to it. 2479 2480 The VAL specifies the configuration to force. As long 2481 as there's no ambiguity shortcut notation is allowed. 2482 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2483 The following configurations can be forced. 2484 2485 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2486 Any ID with matching PORT is used. 2487 2488 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2489 2490 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2491 udma[/][16,25,33,44,66,100,133] notation is also 2492 allowed. 2493 2494 * [no]ncq: Turn on or off NCQ. 2495 2496 * [no]ncqtrim: Turn off queued DSM TRIM. 2497 2498 * nohrst, nosrst, norst: suppress hard, soft 2499 and both resets. 2500 2501 * rstonce: only attempt one reset during 2502 hot-unplug link recovery 2503 2504 * dump_id: dump IDENTIFY data. 2505 2506 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2507 2508 * disable: Disable this device. 2509 2510 If there are multiple matching configurations changing 2511 the same attribute, the last one is used. 2512 2513 memblock=debug [KNL] Enable memblock debug messages. 2514 2515 load_ramdisk= [RAM] [Deprecated] 2516 2517 lockd.nlm_grace_period=P [NFS] Assign grace period. 2518 Format: <integer> 2519 2520 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2521 Format: <integer> 2522 2523 lockd.nlm_timeout=T [NFS] Assign timeout value. 2524 Format: <integer> 2525 2526 lockd.nlm_udpport=M [NFS] Assign UDP port. 2527 Format: <integer> 2528 2529 lockdown= [SECURITY] 2530 { integrity | confidentiality } 2531 Enable the kernel lockdown feature. If set to 2532 integrity, kernel features that allow userland to 2533 modify the running kernel are disabled. If set to 2534 confidentiality, kernel features that allow userland 2535 to extract confidential information from the kernel 2536 are also disabled. 2537 2538 locktorture.nreaders_stress= [KNL] 2539 Set the number of locking read-acquisition kthreads. 2540 Defaults to being automatically set based on the 2541 number of online CPUs. 2542 2543 locktorture.nwriters_stress= [KNL] 2544 Set the number of locking write-acquisition kthreads. 2545 2546 locktorture.onoff_holdoff= [KNL] 2547 Set time (s) after boot for CPU-hotplug testing. 2548 2549 locktorture.onoff_interval= [KNL] 2550 Set time (s) between CPU-hotplug operations, or 2551 zero to disable CPU-hotplug testing. 2552 2553 locktorture.shuffle_interval= [KNL] 2554 Set task-shuffle interval (jiffies). Shuffling 2555 tasks allows some CPUs to go into dyntick-idle 2556 mode during the locktorture test. 2557 2558 locktorture.shutdown_secs= [KNL] 2559 Set time (s) after boot system shutdown. This 2560 is useful for hands-off automated testing. 2561 2562 locktorture.stat_interval= [KNL] 2563 Time (s) between statistics printk()s. 2564 2565 locktorture.stutter= [KNL] 2566 Time (s) to stutter testing, for example, 2567 specifying five seconds causes the test to run for 2568 five seconds, wait for five seconds, and so on. 2569 This tests the locking primitive's ability to 2570 transition abruptly to and from idle. 2571 2572 locktorture.torture_type= [KNL] 2573 Specify the locking implementation to test. 2574 2575 locktorture.verbose= [KNL] 2576 Enable additional printk() statements. 2577 2578 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2579 Format: <irq> 2580 2581 loglevel= All Kernel Messages with a loglevel smaller than the 2582 console loglevel will be printed to the console. It can 2583 also be changed with klogd or other programs. The 2584 loglevels are defined as follows: 2585 2586 0 (KERN_EMERG) system is unusable 2587 1 (KERN_ALERT) action must be taken immediately 2588 2 (KERN_CRIT) critical conditions 2589 3 (KERN_ERR) error conditions 2590 4 (KERN_WARNING) warning conditions 2591 5 (KERN_NOTICE) normal but significant condition 2592 6 (KERN_INFO) informational 2593 7 (KERN_DEBUG) debug-level messages 2594 2595 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2596 in bytes. n must be a power of two and greater 2597 than the minimal size. The minimal size is defined 2598 by LOG_BUF_SHIFT kernel config parameter. There is 2599 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2600 that allows to increase the default size depending on 2601 the number of CPUs. See init/Kconfig for more details. 2602 2603 logo.nologo [FB] Disables display of the built-in Linux logo. 2604 This may be used to provide more screen space for 2605 kernel log messages and is useful when debugging 2606 kernel boot problems. 2607 2608 lp=0 [LP] Specify parallel ports to use, e.g, 2609 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2610 lp=reset first parallel port). 'lp=0' disables the 2611 lp=auto printer driver. 'lp=reset' (which can be 2612 specified in addition to the ports) causes 2613 attached printers to be reset. Using 2614 lp=port1,port2,... specifies the parallel ports 2615 to associate lp devices with, starting with 2616 lp0. A port specification may be 'none' to skip 2617 that lp device, or a parport name such as 2618 'parport0'. Specifying 'lp=auto' instead of a 2619 port specification list means that device IDs 2620 from each port should be examined, to see if 2621 an IEEE 1284-compliant printer is attached; if 2622 so, the driver will manage that printer. 2623 See also header of drivers/char/lp.c. 2624 2625 lpj=n [KNL] 2626 Sets loops_per_jiffy to given constant, thus avoiding 2627 time-consuming boot-time autodetection (up to 250 ms per 2628 CPU). 0 enables autodetection (default). To determine 2629 the correct value for your kernel, boot with normal 2630 autodetection and see what value is printed. Note that 2631 on SMP systems the preset will be applied to all CPUs, 2632 which is likely to cause problems if your CPUs need 2633 significantly divergent settings. An incorrect value 2634 will cause delays in the kernel to be wrong, leading to 2635 unpredictable I/O errors and other breakage. Although 2636 unlikely, in the extreme case this might damage your 2637 hardware. 2638 2639 ltpc= [NET] 2640 Format: <io>,<irq>,<dma> 2641 2642 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2643 2644 lsm=lsm1,...,lsmN 2645 [SECURITY] Choose order of LSM initialization. This 2646 overrides CONFIG_LSM, and the "security=" parameter. 2647 2648 machvec= [IA-64] Force the use of a particular machine-vector 2649 (machvec) in a generic kernel. 2650 Example: machvec=hpzx1 2651 2652 machtype= [Loongson] Share the same kernel image file between 2653 different yeeloong laptops. 2654 Example: machtype=lemote-yeeloong-2f-7inch 2655 2656 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2657 than or equal to this physical address is ignored. 2658 2659 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2660 will bring up during bootup. maxcpus=n : n >= 0 limits 2661 the kernel to bring up 'n' processors. Surely after 2662 bootup you can bring up the other plugged cpu by executing 2663 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2664 only takes effect during system bootup. 2665 While n=0 is a special case, it is equivalent to "nosmp", 2666 which also disables the IO APIC. 2667 2668 max_loop= [LOOP] The number of loop block devices that get 2669 (loop.max_loop) unconditionally pre-created at init time. The default 2670 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2671 of statically allocating a predefined number, loop 2672 devices can be requested on-demand with the 2673 /dev/loop-control interface. 2674 2675 mce [X86-32] Machine Check Exception 2676 2677 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2678 2679 md= [HW] RAID subsystems devices and level 2680 See Documentation/admin-guide/md.rst. 2681 2682 mdacon= [MDA] 2683 Format: <first>,<last> 2684 Specifies range of consoles to be captured by the MDA. 2685 2686 mds= [X86,INTEL] 2687 Control mitigation for the Micro-architectural Data 2688 Sampling (MDS) vulnerability. 2689 2690 Certain CPUs are vulnerable to an exploit against CPU 2691 internal buffers which can forward information to a 2692 disclosure gadget under certain conditions. 2693 2694 In vulnerable processors, the speculatively 2695 forwarded data can be used in a cache side channel 2696 attack, to access data to which the attacker does 2697 not have direct access. 2698 2699 This parameter controls the MDS mitigation. The 2700 options are: 2701 2702 full - Enable MDS mitigation on vulnerable CPUs 2703 full,nosmt - Enable MDS mitigation and disable 2704 SMT on vulnerable CPUs 2705 off - Unconditionally disable MDS mitigation 2706 2707 On TAA-affected machines, mds=off can be prevented by 2708 an active TAA mitigation as both vulnerabilities are 2709 mitigated with the same mechanism so in order to disable 2710 this mitigation, you need to specify tsx_async_abort=off 2711 too. 2712 2713 Not specifying this option is equivalent to 2714 mds=full. 2715 2716 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2717 2718 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2719 Amount of memory to be used in cases as follows: 2720 2721 1 for test; 2722 2 when the kernel is not able to see the whole system memory; 2723 3 memory that lies after 'mem=' boundary is excluded from 2724 the hypervisor, then assigned to KVM guests. 2725 2726 [X86] Work as limiting max address. Use together 2727 with memmap= to avoid physical address space collisions. 2728 Without memmap= PCI devices could be placed at addresses 2729 belonging to unused RAM. 2730 2731 Note that this only takes effects during boot time since 2732 in above case 3, memory may need be hot added after boot 2733 if system memory of hypervisor is not sufficient. 2734 2735 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2736 memory. 2737 2738 memchunk=nn[KMG] 2739 [KNL,SH] Allow user to override the default size for 2740 per-device physically contiguous DMA buffers. 2741 2742 memhp_default_state=online/offline 2743 [KNL] Set the initial state for the memory hotplug 2744 onlining policy. If not specified, the default value is 2745 set according to the 2746 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2747 option. 2748 See Documentation/admin-guide/mm/memory-hotplug.rst. 2749 2750 memmap=exactmap [KNL,X86] Enable setting of an exact 2751 E820 memory map, as specified by the user. 2752 Such memmap=exactmap lines can be constructed based on 2753 BIOS output or other requirements. See the memmap=nn@ss 2754 option description. 2755 2756 memmap=nn[KMG]@ss[KMG] 2757 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory. 2758 Region of memory to be used is from ss to ss+nn. 2759 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2760 which limits max address to nn[KMG]. 2761 Multiple different regions can be specified, 2762 comma delimited. 2763 Example: 2764 memmap=100M@2G,100M#3G,1G!1024G 2765 2766 memmap=nn[KMG]#ss[KMG] 2767 [KNL,ACPI] Mark specific memory as ACPI data. 2768 Region of memory to be marked is from ss to ss+nn. 2769 2770 memmap=nn[KMG]$ss[KMG] 2771 [KNL,ACPI] Mark specific memory as reserved. 2772 Region of memory to be reserved is from ss to ss+nn. 2773 Example: Exclude memory from 0x18690000-0x1869ffff 2774 memmap=64K$0x18690000 2775 or 2776 memmap=0x10000$0x18690000 2777 Some bootloaders may need an escape character before '$', 2778 like Grub2, otherwise '$' and the following number 2779 will be eaten. 2780 2781 memmap=nn[KMG]!ss[KMG] 2782 [KNL,X86] Mark specific memory as protected. 2783 Region of memory to be used, from ss to ss+nn. 2784 The memory region may be marked as e820 type 12 (0xc) 2785 and is NVDIMM or ADR memory. 2786 2787 memmap=<size>%<offset>-<oldtype>+<newtype> 2788 [KNL,ACPI] Convert memory within the specified region 2789 from <oldtype> to <newtype>. If "-<oldtype>" is left 2790 out, the whole region will be marked as <newtype>, 2791 even if previously unavailable. If "+<newtype>" is left 2792 out, matching memory will be removed. Types are 2793 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2794 3 = ACPI, 12 = PRAM. 2795 2796 memory_corruption_check=0/1 [X86] 2797 Some BIOSes seem to corrupt the first 64k of 2798 memory when doing things like suspend/resume. 2799 Setting this option will scan the memory 2800 looking for corruption. Enabling this will 2801 both detect corruption and prevent the kernel 2802 from using the memory being corrupted. 2803 However, its intended as a diagnostic tool; if 2804 repeatable BIOS-originated corruption always 2805 affects the same memory, you can use memmap= 2806 to prevent the kernel from using that memory. 2807 2808 memory_corruption_check_size=size [X86] 2809 By default it checks for corruption in the low 2810 64k, making this memory unavailable for normal 2811 use. Use this parameter to scan for 2812 corruption in more or less memory. 2813 2814 memory_corruption_check_period=seconds [X86] 2815 By default it checks for corruption every 60 2816 seconds. Use this parameter to check at some 2817 other rate. 0 disables periodic checking. 2818 2819 memory_hotplug.memmap_on_memory 2820 [KNL,X86,ARM] Boolean flag to enable this feature. 2821 Format: {on | off (default)} 2822 When enabled, runtime hotplugged memory will 2823 allocate its internal metadata (struct pages) 2824 from the hotadded memory which will allow to 2825 hotadd a lot of memory without requiring 2826 additional memory to do so. 2827 This feature is disabled by default because it 2828 has some implication on large (e.g. GB) 2829 allocations in some configurations (e.g. small 2830 memory blocks). 2831 The state of the flag can be read in 2832 /sys/module/memory_hotplug/parameters/memmap_on_memory. 2833 Note that even when enabled, there are a few cases where 2834 the feature is not effective. 2835 2836 memtest= [KNL,X86,ARM,PPC,RISCV] Enable memtest 2837 Format: <integer> 2838 default : 0 <disable> 2839 Specifies the number of memtest passes to be 2840 performed. Each pass selects another test 2841 pattern from a given set of patterns. Memtest 2842 fills the memory with this pattern, validates 2843 memory contents and reserves bad memory 2844 regions that are detected. 2845 2846 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2847 Valid arguments: on, off 2848 Default (depends on kernel configuration option): 2849 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2850 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2851 mem_encrypt=on: Activate SME 2852 mem_encrypt=off: Do not activate SME 2853 2854 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2855 for details on when memory encryption can be activated. 2856 2857 mem_sleep_default= [SUSPEND] Default system suspend mode: 2858 s2idle - Suspend-To-Idle 2859 shallow - Power-On Suspend or equivalent (if supported) 2860 deep - Suspend-To-RAM or equivalent (if supported) 2861 See Documentation/admin-guide/pm/sleep-states.rst. 2862 2863 meye.*= [HW] Set MotionEye Camera parameters 2864 See Documentation/admin-guide/media/meye.rst. 2865 2866 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2867 Multi-Function General Purpose Timers on AMD Geode 2868 platforms. 2869 2870 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2871 the BIOS has incorrectly applied a workaround. TinyBIOS 2872 version 0.98 is known to be affected, 0.99 fixes the 2873 problem by letting the user disable the workaround. 2874 2875 mga= [HW,DRM] 2876 2877 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2878 physical address is ignored. 2879 2880 mini2440= [ARM,HW,KNL] 2881 Format:[0..2][b][c][t] 2882 Default: "0tb" 2883 MINI2440 configuration specification: 2884 0 - The attached screen is the 3.5" TFT 2885 1 - The attached screen is the 7" TFT 2886 2 - The VGA Shield is attached (1024x768) 2887 Leaving out the screen size parameter will not load 2888 the TFT driver, and the framebuffer will be left 2889 unconfigured. 2890 b - Enable backlight. The TFT backlight pin will be 2891 linked to the kernel VESA blanking code and a GPIO 2892 LED. This parameter is not necessary when using the 2893 VGA shield. 2894 c - Enable the s3c camera interface. 2895 t - Reserved for enabling touchscreen support. The 2896 touchscreen support is not enabled in the mainstream 2897 kernel as of 2.6.30, a preliminary port can be found 2898 in the "bleeding edge" mini2440 support kernel at 2899 https://repo.or.cz/w/linux-2.6/mini2440.git 2900 2901 mitigations= 2902 [X86,PPC,S390,ARM64] Control optional mitigations for 2903 CPU vulnerabilities. This is a set of curated, 2904 arch-independent options, each of which is an 2905 aggregation of existing arch-specific options. 2906 2907 off 2908 Disable all optional CPU mitigations. This 2909 improves system performance, but it may also 2910 expose users to several CPU vulnerabilities. 2911 Equivalent to: nopti [X86,PPC] 2912 kpti=0 [ARM64] 2913 nospectre_v1 [X86,PPC] 2914 nobp=0 [S390] 2915 nospectre_v2 [X86,PPC,S390,ARM64] 2916 spectre_v2_user=off [X86] 2917 spec_store_bypass_disable=off [X86,PPC] 2918 ssbd=force-off [ARM64] 2919 l1tf=off [X86] 2920 mds=off [X86] 2921 tsx_async_abort=off [X86] 2922 kvm.nx_huge_pages=off [X86] 2923 no_entry_flush [PPC] 2924 no_uaccess_flush [PPC] 2925 2926 Exceptions: 2927 This does not have any effect on 2928 kvm.nx_huge_pages when 2929 kvm.nx_huge_pages=force. 2930 2931 auto (default) 2932 Mitigate all CPU vulnerabilities, but leave SMT 2933 enabled, even if it's vulnerable. This is for 2934 users who don't want to be surprised by SMT 2935 getting disabled across kernel upgrades, or who 2936 have other ways of avoiding SMT-based attacks. 2937 Equivalent to: (default behavior) 2938 2939 auto,nosmt 2940 Mitigate all CPU vulnerabilities, disabling SMT 2941 if needed. This is for users who always want to 2942 be fully mitigated, even if it means losing SMT. 2943 Equivalent to: l1tf=flush,nosmt [X86] 2944 mds=full,nosmt [X86] 2945 tsx_async_abort=full,nosmt [X86] 2946 2947 mminit_loglevel= 2948 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2949 parameter allows control of the logging verbosity for 2950 the additional memory initialisation checks. A value 2951 of 0 disables mminit logging and a level of 4 will 2952 log everything. Information is printed at KERN_DEBUG 2953 so loglevel=8 may also need to be specified. 2954 2955 module.sig_enforce 2956 [KNL] When CONFIG_MODULE_SIG is set, this means that 2957 modules without (valid) signatures will fail to load. 2958 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2959 is always true, so this option does nothing. 2960 2961 module_blacklist= [KNL] Do not load a comma-separated list of 2962 modules. Useful for debugging problem modules. 2963 2964 mousedev.tap_time= 2965 [MOUSE] Maximum time between finger touching and 2966 leaving touchpad surface for touch to be considered 2967 a tap and be reported as a left button click (for 2968 touchpads working in absolute mode only). 2969 Format: <msecs> 2970 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2971 reporting absolute coordinates, such as tablets 2972 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2973 reporting absolute coordinates, such as tablets 2974 2975 movablecore= [KNL,X86,IA-64,PPC] 2976 Format: nn[KMGTPE] | nn% 2977 This parameter is the complement to kernelcore=, it 2978 specifies the amount of memory used for migratable 2979 allocations. If both kernelcore and movablecore is 2980 specified, then kernelcore will be at *least* the 2981 specified value but may be more. If movablecore on its 2982 own is specified, the administrator must be careful 2983 that the amount of memory usable for all allocations 2984 is not too small. 2985 2986 movable_node [KNL] Boot-time switch to make hotplugable memory 2987 NUMA nodes to be movable. This means that the memory 2988 of such nodes will be usable only for movable 2989 allocations which rules out almost all kernel 2990 allocations. Use with caution! 2991 2992 MTD_Partition= [MTD] 2993 Format: <name>,<region-number>,<size>,<offset> 2994 2995 MTD_Region= [MTD] Format: 2996 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2997 2998 mtdparts= [MTD] 2999 See drivers/mtd/parsers/cmdlinepart.c 3000 3001 multitce=off [PPC] This parameter disables the use of the pSeries 3002 firmware feature for updating multiple TCE entries 3003 at a time. 3004 3005 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 3006 3007 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 3008 3009 boundary - index of last SLC block on Flex-OneNAND. 3010 The remaining blocks are configured as MLC blocks. 3011 lock - Configure if Flex-OneNAND boundary should be locked. 3012 Once locked, the boundary cannot be changed. 3013 1 indicates lock status, 0 indicates unlock status. 3014 3015 mtdset= [ARM] 3016 ARM/S3C2412 JIVE boot control 3017 3018 See arch/arm/mach-s3c/mach-jive.c 3019 3020 mtouchusb.raw_coordinates= 3021 [HW] Make the MicroTouch USB driver use raw coordinates 3022 ('y', default) or cooked coordinates ('n') 3023 3024 mtrr_chunk_size=nn[KMG] [X86] 3025 used for mtrr cleanup. It is largest continuous chunk 3026 that could hold holes aka. UC entries. 3027 3028 mtrr_gran_size=nn[KMG] [X86] 3029 Used for mtrr cleanup. It is granularity of mtrr block. 3030 Default is 1. 3031 Large value could prevent small alignment from 3032 using up MTRRs. 3033 3034 mtrr_spare_reg_nr=n [X86] 3035 Format: <integer> 3036 Range: 0,7 : spare reg number 3037 Default : 1 3038 Used for mtrr cleanup. It is spare mtrr entries number. 3039 Set to 2 or more if your graphical card needs more. 3040 3041 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 3042 3043 netdev= [NET] Network devices parameters 3044 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 3045 Note that mem_start is often overloaded to mean 3046 something different and driver-specific. 3047 This usage is only documented in each driver source 3048 file if at all. 3049 3050 nf_conntrack.acct= 3051 [NETFILTER] Enable connection tracking flow accounting 3052 0 to disable accounting 3053 1 to enable accounting 3054 Default value is 0. 3055 3056 nfsaddrs= [NFS] Deprecated. Use ip= instead. 3057 See Documentation/admin-guide/nfs/nfsroot.rst. 3058 3059 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 3060 See Documentation/admin-guide/nfs/nfsroot.rst. 3061 3062 nfsrootdebug [NFS] enable nfsroot debugging messages. 3063 See Documentation/admin-guide/nfs/nfsroot.rst. 3064 3065 nfs.callback_nr_threads= 3066 [NFSv4] set the total number of threads that the 3067 NFS client will assign to service NFSv4 callback 3068 requests. 3069 3070 nfs.callback_tcpport= 3071 [NFS] set the TCP port on which the NFSv4 callback 3072 channel should listen. 3073 3074 nfs.cache_getent= 3075 [NFS] sets the pathname to the program which is used 3076 to update the NFS client cache entries. 3077 3078 nfs.cache_getent_timeout= 3079 [NFS] sets the timeout after which an attempt to 3080 update a cache entry is deemed to have failed. 3081 3082 nfs.idmap_cache_timeout= 3083 [NFS] set the maximum lifetime for idmapper cache 3084 entries. 3085 3086 nfs.enable_ino64= 3087 [NFS] enable 64-bit inode numbers. 3088 If zero, the NFS client will fake up a 32-bit inode 3089 number for the readdir() and stat() syscalls instead 3090 of returning the full 64-bit number. 3091 The default is to return 64-bit inode numbers. 3092 3093 nfs.max_session_cb_slots= 3094 [NFSv4.1] Sets the maximum number of session 3095 slots the client will assign to the callback 3096 channel. This determines the maximum number of 3097 callbacks the client will process in parallel for 3098 a particular server. 3099 3100 nfs.max_session_slots= 3101 [NFSv4.1] Sets the maximum number of session slots 3102 the client will attempt to negotiate with the server. 3103 This limits the number of simultaneous RPC requests 3104 that the client can send to the NFSv4.1 server. 3105 Note that there is little point in setting this 3106 value higher than the max_tcp_slot_table_limit. 3107 3108 nfs.nfs4_disable_idmapping= 3109 [NFSv4] When set to the default of '1', this option 3110 ensures that both the RPC level authentication 3111 scheme and the NFS level operations agree to use 3112 numeric uids/gids if the mount is using the 3113 'sec=sys' security flavour. In effect it is 3114 disabling idmapping, which can make migration from 3115 legacy NFSv2/v3 systems to NFSv4 easier. 3116 Servers that do not support this mode of operation 3117 will be autodetected by the client, and it will fall 3118 back to using the idmapper. 3119 To turn off this behaviour, set the value to '0'. 3120 nfs.nfs4_unique_id= 3121 [NFS4] Specify an additional fixed unique ident- 3122 ification string that NFSv4 clients can insert into 3123 their nfs_client_id4 string. This is typically a 3124 UUID that is generated at system install time. 3125 3126 nfs.send_implementation_id = 3127 [NFSv4.1] Send client implementation identification 3128 information in exchange_id requests. 3129 If zero, no implementation identification information 3130 will be sent. 3131 The default is to send the implementation identification 3132 information. 3133 3134 nfs.recover_lost_locks = 3135 [NFSv4] Attempt to recover locks that were lost due 3136 to a lease timeout on the server. Please note that 3137 doing this risks data corruption, since there are 3138 no guarantees that the file will remain unchanged 3139 after the locks are lost. 3140 If you want to enable the kernel legacy behaviour of 3141 attempting to recover these locks, then set this 3142 parameter to '1'. 3143 The default parameter value of '0' causes the kernel 3144 not to attempt recovery of lost locks. 3145 3146 nfs4.layoutstats_timer = 3147 [NFSv4.2] Change the rate at which the kernel sends 3148 layoutstats to the pNFS metadata server. 3149 3150 Setting this to value to 0 causes the kernel to use 3151 whatever value is the default set by the layout 3152 driver. A non-zero value sets the minimum interval 3153 in seconds between layoutstats transmissions. 3154 3155 nfsd.nfs4_disable_idmapping= 3156 [NFSv4] When set to the default of '1', the NFSv4 3157 server will return only numeric uids and gids to 3158 clients using auth_sys, and will accept numeric uids 3159 and gids from such clients. This is intended to ease 3160 migration from NFSv2/v3. 3161 3162 nmi_backtrace.backtrace_idle [KNL] 3163 Dump stacks even of idle CPUs in response to an 3164 NMI stack-backtrace request. 3165 3166 nmi_debug= [KNL,SH] Specify one or more actions to take 3167 when a NMI is triggered. 3168 Format: [state][,regs][,debounce][,die] 3169 3170 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3171 Format: [panic,][nopanic,][num] 3172 Valid num: 0 or 1 3173 0 - turn hardlockup detector in nmi_watchdog off 3174 1 - turn hardlockup detector in nmi_watchdog on 3175 When panic is specified, panic when an NMI watchdog 3176 timeout occurs (or 'nopanic' to not panic on an NMI 3177 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3178 To disable both hard and soft lockup detectors, 3179 please see 'nowatchdog'. 3180 This is useful when you use a panic=... timeout and 3181 need the box quickly up again. 3182 3183 These settings can be accessed at runtime via 3184 the nmi_watchdog and hardlockup_panic sysctls. 3185 3186 netpoll.carrier_timeout= 3187 [NET] Specifies amount of time (in seconds) that 3188 netpoll should wait for a carrier. By default netpoll 3189 waits 4 seconds. 3190 3191 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3192 emulation library even if a 387 maths coprocessor 3193 is present. 3194 3195 no5lvl [X86-64] Disable 5-level paging mode. Forces 3196 kernel to use 4-level paging instead. 3197 3198 nofsgsbase [X86] Disables FSGSBASE instructions. 3199 3200 no_console_suspend 3201 [HW] Never suspend the console 3202 Disable suspending of consoles during suspend and 3203 hibernate operations. Once disabled, debugging 3204 messages can reach various consoles while the rest 3205 of the system is being put to sleep (ie, while 3206 debugging driver suspend/resume hooks). This may 3207 not work reliably with all consoles, but is known 3208 to work with serial and VGA consoles. 3209 To facilitate more flexible debugging, we also add 3210 console_suspend, a printk module parameter to control 3211 it. Users could use console_suspend (usually 3212 /sys/module/printk/parameters/console_suspend) to 3213 turn on/off it dynamically. 3214 3215 novmcoredd [KNL,KDUMP] 3216 Disable device dump. Device dump allows drivers to 3217 append dump data to vmcore so you can collect driver 3218 specified debug info. Drivers can append the data 3219 without any limit and this data is stored in memory, 3220 so this may cause significant memory stress. Disabling 3221 device dump can help save memory but the driver debug 3222 data will be no longer available. This parameter 3223 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3224 is set. 3225 3226 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3227 caches in the slab allocator. Saves per-node memory, 3228 but will impact performance. 3229 3230 noalign [KNL,ARM] 3231 3232 noaltinstr [S390] Disables alternative instructions patching 3233 (CPU alternatives feature). 3234 3235 noapic [SMP,APIC] Tells the kernel to not make use of any 3236 IOAPICs that may be present in the system. 3237 3238 noautogroup Disable scheduler automatic task group creation. 3239 3240 nobats [PPC] Do not use BATs for mapping kernel lowmem 3241 on "Classic" PPC cores. 3242 3243 nocache [ARM] 3244 3245 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3246 3247 nodelayacct [KNL] Disable per-task delay accounting 3248 3249 nodsp [SH] Disable hardware DSP at boot time. 3250 3251 noefi Disable EFI runtime services support. 3252 3253 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. 3254 3255 noexec [IA-64] 3256 3257 noexec [X86] 3258 On X86-32 available only on PAE configured kernels. 3259 noexec=on: enable non-executable mappings (default) 3260 noexec=off: disable non-executable mappings 3261 3262 nosmap [X86,PPC] 3263 Disable SMAP (Supervisor Mode Access Prevention) 3264 even if it is supported by processor. 3265 3266 nosmep [X86,PPC] 3267 Disable SMEP (Supervisor Mode Execution Prevention) 3268 even if it is supported by processor. 3269 3270 noexec32 [X86-64] 3271 This affects only 32-bit executables. 3272 noexec32=on: enable non-executable mappings (default) 3273 read doesn't imply executable mappings 3274 noexec32=off: disable non-executable mappings 3275 read implies executable mappings 3276 3277 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3278 3279 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3280 register save and restore. The kernel will only save 3281 legacy floating-point registers on task switch. 3282 3283 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3284 3285 nohugevmalloc [PPC] Disable kernel huge vmalloc mappings. 3286 3287 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3288 Equivalent to smt=1. 3289 3290 [KNL,X86] Disable symmetric multithreading (SMT). 3291 nosmt=force: Force disable SMT, cannot be undone 3292 via the sysfs control file. 3293 3294 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3295 (bounds check bypass). With this option data leaks are 3296 possible in the system. 3297 3298 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3299 the Spectre variant 2 (indirect branch prediction) 3300 vulnerability. System may allow data leaks with this 3301 option. 3302 3303 nospec_store_bypass_disable 3304 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3305 3306 no_uaccess_flush 3307 [PPC] Don't flush the L1-D cache after accessing user data. 3308 3309 noxsave [BUGS=X86] Disables x86 extended register state save 3310 and restore using xsave. The kernel will fallback to 3311 enabling legacy floating-point and sse state. 3312 3313 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3314 register states. The kernel will fall back to use 3315 xsave to save the states. By using this parameter, 3316 performance of saving the states is degraded because 3317 xsave doesn't support modified optimization while 3318 xsaveopt supports it on xsaveopt enabled systems. 3319 3320 noxsaves [X86] Disables xsaves and xrstors used in saving and 3321 restoring x86 extended register state in compacted 3322 form of xsave area. The kernel will fall back to use 3323 xsaveopt and xrstor to save and restore the states 3324 in standard form of xsave area. By using this 3325 parameter, xsave area per process might occupy more 3326 memory on xsaves enabled systems. 3327 3328 nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait 3329 in do_idle() and not use the arch_cpu_idle() 3330 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 3331 to be effective. This is useful on platforms where the 3332 sleep(SH) or wfi(ARM,ARM64) instructions do not work 3333 correctly or when doing power measurements to evalute 3334 the impact of the sleep instructions. This is also 3335 useful when using JTAG debugger. 3336 3337 no_file_caps Tells the kernel not to honor file capabilities. The 3338 only way then for a file to be executed with privilege 3339 is to be setuid root or executed by root. 3340 3341 nohalt [IA-64] Tells the kernel not to use the power saving 3342 function PAL_HALT_LIGHT when idle. This increases 3343 power-consumption. On the positive side, it reduces 3344 interrupt wake-up latency, which may improve performance 3345 in certain environments such as networked servers or 3346 real-time systems. 3347 3348 no_hash_pointers 3349 Force pointers printed to the console or buffers to be 3350 unhashed. By default, when a pointer is printed via %p 3351 format string, that pointer is "hashed", i.e. obscured 3352 by hashing the pointer value. This is a security feature 3353 that hides actual kernel addresses from unprivileged 3354 users, but it also makes debugging the kernel more 3355 difficult since unequal pointers can no longer be 3356 compared. However, if this command-line option is 3357 specified, then all normal pointers will have their true 3358 value printed. Pointers printed via %pK may still be 3359 hashed. This option should only be specified when 3360 debugging the kernel. Please do not use on production 3361 kernels. 3362 3363 nohibernate [HIBERNATION] Disable hibernation and resume. 3364 3365 nohz= [KNL] Boottime enable/disable dynamic ticks 3366 Valid arguments: on, off 3367 Default: on 3368 3369 nohz_full= [KNL,BOOT,SMP,ISOL] 3370 The argument is a cpu list, as described above. 3371 In kernels built with CONFIG_NO_HZ_FULL=y, set 3372 the specified list of CPUs whose tick will be stopped 3373 whenever possible. The boot CPU will be forced outside 3374 the range to maintain the timekeeping. Any CPUs 3375 in this list will have their RCU callbacks offloaded, 3376 just as if they had also been called out in the 3377 rcu_nocbs= boot parameter. 3378 3379 noiotrap [SH] Disables trapped I/O port accesses. 3380 3381 noirqdebug [X86-32] Disables the code which attempts to detect and 3382 disable unhandled interrupt sources. 3383 3384 no_timer_check [X86,APIC] Disables the code which tests for 3385 broken timer IRQ sources. 3386 3387 noisapnp [ISAPNP] Disables ISA PnP code. 3388 3389 noinitrd [RAM] Tells the kernel not to load any configured 3390 initial RAM disk. 3391 3392 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3393 remapping. 3394 [Deprecated - use intremap=off] 3395 3396 nointroute [IA-64] 3397 3398 noinvpcid [X86] Disable the INVPCID cpu feature. 3399 3400 nojitter [IA-64] Disables jitter checking for ITC timers. 3401 3402 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3403 3404 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3405 fault handling. 3406 3407 no-vmw-sched-clock 3408 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3409 clock and use the default one. 3410 3411 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3412 accounting. steal time is computed, but won't 3413 influence scheduler behaviour 3414 3415 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3416 3417 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3418 3419 noltlbs [PPC] Do not use large page/tlb entries for kernel 3420 lowmem mapping on PPC40x and PPC8xx 3421 3422 nomca [IA-64] Disable machine check abort handling 3423 3424 nomce [X86-32] Disable Machine Check Exception 3425 3426 nomfgpt [X86-32] Disable Multi-Function General Purpose 3427 Timer usage (for AMD Geode machines). 3428 3429 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3430 shutdown the other cpus. Instead use the REBOOT_VECTOR 3431 irq. 3432 3433 nomodule Disable module load 3434 3435 nopat [X86] Disable PAT (page attribute table extension of 3436 pagetables) support. 3437 3438 nopcid [X86-64] Disable the PCID cpu feature. 3439 3440 norandmaps Don't use address space randomization. Equivalent to 3441 echo 0 > /proc/sys/kernel/randomize_va_space 3442 3443 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3444 with UP alternatives 3445 3446 nordrand [X86] Disable kernel use of the RDRAND and 3447 RDSEED instructions even if they are supported 3448 by the processor. RDRAND and RDSEED are still 3449 available to user space applications. 3450 3451 noresume [SWSUSP] Disables resume and restores original swap 3452 space. 3453 3454 no-scroll [VGA] Disables scrollback. 3455 This is required for the Braillex ib80-piezo Braille 3456 reader made by F.H. Papenmeier (Germany). 3457 3458 nosbagart [IA-64] 3459 3460 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3461 3462 nosgx [X86-64,SGX] Disables Intel SGX kernel support. 3463 3464 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3465 and disable the IO APIC. legacy for "maxcpus=0". 3466 3467 nosoftlockup [KNL] Disable the soft-lockup detector. 3468 3469 nosync [HW,M68K] Disables sync negotiation for all devices. 3470 3471 nowatchdog [KNL] Disable both lockup detectors, i.e. 3472 soft-lockup and NMI watchdog (hard-lockup). 3473 3474 nowb [ARM] 3475 3476 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3477 3478 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3479 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3480 Some features depend on CPU0. Known dependencies are: 3481 1. Resume from suspend/hibernate depends on CPU0. 3482 Suspend/hibernate will fail if CPU0 is offline and you 3483 need to online CPU0 before suspend/hibernate. 3484 2. PIC interrupts also depend on CPU0. CPU0 can't be 3485 removed if a PIC interrupt is detected. 3486 It's said poweroff/reboot may depend on CPU0 on some 3487 machines although I haven't seen such issues so far 3488 after CPU0 is offline on a few tested machines. 3489 If the dependencies are under your control, you can 3490 turn on cpu0_hotplug. 3491 3492 nps_mtm_hs_ctr= [KNL,ARC] 3493 This parameter sets the maximum duration, in 3494 cycles, each HW thread of the CTOP can run 3495 without interruptions, before HW switches it. 3496 The actual maximum duration is 16 times this 3497 parameter's value. 3498 Format: integer between 1 and 255 3499 Default: 255 3500 3501 nptcg= [IA-64] Override max number of concurrent global TLB 3502 purges which is reported from either PAL_VM_SUMMARY or 3503 SAL PALO. 3504 3505 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3506 could support. nr_cpus=n : n >= 1 limits the kernel to 3507 support 'n' processors. It could be larger than the 3508 number of already plugged CPU during bootup, later in 3509 runtime you can physically add extra cpu until it reaches 3510 n. So during boot up some boot time memory for per-cpu 3511 variables need be pre-allocated for later physical cpu 3512 hot plugging. 3513 3514 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3515 3516 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only 3517 set up a single NUMA node spanning all memory. 3518 3519 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 3520 NUMA balancing. 3521 Allowed values are enable and disable 3522 3523 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3524 'node', 'default' can be specified 3525 This can be set from sysctl after boot. 3526 See Documentation/admin-guide/sysctl/vm.rst for details. 3527 3528 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3529 See Documentation/core-api/debugging-via-ohci1394.rst for more 3530 info. 3531 3532 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3533 Rather than timing out after 20 ms if an EC 3534 command is not properly ACKed, override the length 3535 of the timeout. We have interrupts disabled while 3536 waiting for the ACK, so if this is set too high 3537 interrupts *may* be lost! 3538 3539 omap_mux= [OMAP] Override bootloader pin multiplexing. 3540 Format: <mux_mode0.mode_name=value>... 3541 For example, to override I2C bus2: 3542 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3543 3544 oops=panic Always panic on oopses. Default is to just kill the 3545 process, but there is a small probability of 3546 deadlocking the machine. 3547 This will also cause panics on machine check exceptions. 3548 Useful together with panic=30 to trigger a reboot. 3549 3550 page_alloc.shuffle= 3551 [KNL] Boolean flag to control whether the page allocator 3552 should randomize its free lists. The randomization may 3553 be automatically enabled if the kernel detects it is 3554 running on a platform with a direct-mapped memory-side 3555 cache, and this parameter can be used to 3556 override/disable that behavior. The state of the flag 3557 can be read from sysfs at: 3558 /sys/module/page_alloc/parameters/shuffle. 3559 3560 page_owner= [KNL] Boot-time page_owner enabling option. 3561 Storage of the information about who allocated 3562 each page is disabled in default. With this switch, 3563 we can turn it on. 3564 on: enable the feature 3565 3566 page_poison= [KNL] Boot-time parameter changing the state of 3567 poisoning on the buddy allocator, available with 3568 CONFIG_PAGE_POISONING=y. 3569 off: turn off poisoning (default) 3570 on: turn on poisoning 3571 3572 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3573 timeout > 0: seconds before rebooting 3574 timeout = 0: wait forever 3575 timeout < 0: reboot immediately 3576 Format: <timeout> 3577 3578 panic_print= Bitmask for printing system info when panic happens. 3579 User can chose combination of the following bits: 3580 bit 0: print all tasks info 3581 bit 1: print system memory info 3582 bit 2: print timer info 3583 bit 3: print locks info if CONFIG_LOCKDEP is on 3584 bit 4: print ftrace buffer 3585 bit 5: print all printk messages in buffer 3586 3587 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3588 Format: <hex>[,nousertaint] 3589 Hexadecimal bitmask representing the set of TAINT flags 3590 that will cause the kernel to panic when add_taint() is 3591 called with any of the flags in this set. 3592 The optional switch "nousertaint" can be utilized to 3593 prevent userspace forced crashes by writing to sysctl 3594 /proc/sys/kernel/tainted any flagset matching with the 3595 bitmask set on panic_on_taint. 3596 See Documentation/admin-guide/tainted-kernels.rst for 3597 extra details on the taint flags that users can pick 3598 to compose the bitmask to assign to panic_on_taint. 3599 3600 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3601 on a WARN(). 3602 3603 crash_kexec_post_notifiers 3604 Run kdump after running panic-notifiers and dumping 3605 kmsg. This only for the users who doubt kdump always 3606 succeeds in any situation. 3607 Note that this also increases risks of kdump failure, 3608 because some panic notifiers can make the crashed 3609 kernel more unstable. 3610 3611 parkbd.port= [HW] Parallel port number the keyboard adapter is 3612 connected to, default is 0. 3613 Format: <parport#> 3614 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3615 0 for XT, 1 for AT (default is AT). 3616 Format: <mode> 3617 3618 parport= [HW,PPT] Specify parallel ports. 0 disables. 3619 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3620 Use 'auto' to force the driver to use any 3621 IRQ/DMA settings detected (the default is to 3622 ignore detected IRQ/DMA settings because of 3623 possible conflicts). You can specify the base 3624 address, IRQ, and DMA settings; IRQ and DMA 3625 should be numbers, or 'auto' (for using detected 3626 settings on that particular port), or 'nofifo' 3627 (to avoid using a FIFO even if it is detected). 3628 Parallel ports are assigned in the order they 3629 are specified on the command line, starting 3630 with parport0. 3631 3632 parport_init_mode= [HW,PPT] 3633 Configure VIA parallel port to operate in 3634 a specific mode. This is necessary on Pegasos 3635 computer where firmware has no options for setting 3636 up parallel port mode and sets it to spp. 3637 Currently this function knows 686a and 8231 chips. 3638 Format: [spp|ps2|epp|ecp|ecpepp] 3639 3640 pata_legacy.all= [HW,LIBATA] 3641 Format: <int> 3642 Set to non-zero to probe primary and secondary ISA 3643 port ranges on PCI systems where no PCI PATA device 3644 has been found at either range. Disabled by default. 3645 3646 pata_legacy.autospeed= [HW,LIBATA] 3647 Format: <int> 3648 Set to non-zero if a chip is present that snoops speed 3649 changes. Disabled by default. 3650 3651 pata_legacy.ht6560a= [HW,LIBATA] 3652 Format: <int> 3653 Set to 1, 2, or 3 for HT 6560A on the primary channel, 3654 the secondary channel, or both channels respectively. 3655 Disabled by default. 3656 3657 pata_legacy.ht6560b= [HW,LIBATA] 3658 Format: <int> 3659 Set to 1, 2, or 3 for HT 6560B on the primary channel, 3660 the secondary channel, or both channels respectively. 3661 Disabled by default. 3662 3663 pata_legacy.iordy_mask= [HW,LIBATA] 3664 Format: <int> 3665 IORDY enable mask. Set individual bits to allow IORDY 3666 for the respective channel. Bit 0 is for the first 3667 legacy channel handled by this driver, bit 1 is for 3668 the second channel, and so on. The sequence will often 3669 correspond to the primary legacy channel, the secondary 3670 legacy channel, and so on, but the handling of a PCI 3671 bus and the use of other driver options may interfere 3672 with the sequence. By default IORDY is allowed across 3673 all channels. 3674 3675 pata_legacy.opti82c46x= [HW,LIBATA] 3676 Format: <int> 3677 Set to 1, 2, or 3 for Opti 82c611A on the primary 3678 channel, the secondary channel, or both channels 3679 respectively. Disabled by default. 3680 3681 pata_legacy.opti82c611a= [HW,LIBATA] 3682 Format: <int> 3683 Set to 1, 2, or 3 for Opti 82c465MV on the primary 3684 channel, the secondary channel, or both channels 3685 respectively. Disabled by default. 3686 3687 pata_legacy.pio_mask= [HW,LIBATA] 3688 Format: <int> 3689 PIO mode mask for autospeed devices. Set individual 3690 bits to allow the use of the respective PIO modes. 3691 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 3692 All modes allowed by default. 3693 3694 pata_legacy.probe_all= [HW,LIBATA] 3695 Format: <int> 3696 Set to non-zero to probe tertiary and further ISA 3697 port ranges on PCI systems. Disabled by default. 3698 3699 pata_legacy.probe_mask= [HW,LIBATA] 3700 Format: <int> 3701 Probe mask for legacy ISA PATA ports. Depending on 3702 platform configuration and the use of other driver 3703 options up to 6 legacy ports are supported: 0x1f0, 3704 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 3705 of individual ports can be disabled by setting the 3706 corresponding bits in the mask to 1. Bit 0 is for 3707 the first port in the list above (0x1f0), and so on. 3708 By default all supported ports are probed. 3709 3710 pata_legacy.qdi= [HW,LIBATA] 3711 Format: <int> 3712 Set to non-zero to probe QDI controllers. By default 3713 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 3714 3715 pata_legacy.winbond= [HW,LIBATA] 3716 Format: <int> 3717 Set to non-zero to probe Winbond controllers. Use 3718 the standard I/O port (0x130) if 1, otherwise the 3719 value given is the I/O port to use (typically 0x1b0). 3720 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 3721 0 otherwise. 3722 3723 pata_platform.pio_mask= [HW,LIBATA] 3724 Format: <int> 3725 Supported PIO mode mask. Set individual bits to allow 3726 the use of the respective PIO modes. Bit 0 is for 3727 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 3728 allowed by default. 3729 3730 pause_on_oops= 3731 Halt all CPUs after the first oops has been printed for 3732 the specified number of seconds. This is to be used if 3733 your oopses keep scrolling off the screen. 3734 3735 pcbit= [HW,ISDN] 3736 3737 pcd. [PARIDE] 3738 See header of drivers/block/paride/pcd.c. 3739 See also Documentation/admin-guide/blockdev/paride.rst. 3740 3741 pci=option[,option...] [PCI] various PCI subsystem options. 3742 3743 Some options herein operate on a specific device 3744 or a set of devices (<pci_dev>). These are 3745 specified in one of the following formats: 3746 3747 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3748 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3749 3750 Note: the first format specifies a PCI 3751 bus/device/function address which may change 3752 if new hardware is inserted, if motherboard 3753 firmware changes, or due to changes caused 3754 by other kernel parameters. If the 3755 domain is left unspecified, it is 3756 taken to be zero. Optionally, a path 3757 to a device through multiple device/function 3758 addresses can be specified after the base 3759 address (this is more robust against 3760 renumbering issues). The second format 3761 selects devices using IDs from the 3762 configuration space which may match multiple 3763 devices in the system. 3764 3765 earlydump dump PCI config space before the kernel 3766 changes anything 3767 off [X86] don't probe for the PCI bus 3768 bios [X86-32] force use of PCI BIOS, don't access 3769 the hardware directly. Use this if your machine 3770 has a non-standard PCI host bridge. 3771 nobios [X86-32] disallow use of PCI BIOS, only direct 3772 hardware access methods are allowed. Use this 3773 if you experience crashes upon bootup and you 3774 suspect they are caused by the BIOS. 3775 conf1 [X86] Force use of PCI Configuration Access 3776 Mechanism 1 (config address in IO port 0xCF8, 3777 data in IO port 0xCFC, both 32-bit). 3778 conf2 [X86] Force use of PCI Configuration Access 3779 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3780 the function, IO port 0xCFA, also 8-bit, sets 3781 bus number. The config space is then accessed 3782 through ports 0xC000-0xCFFF). 3783 See http://wiki.osdev.org/PCI for more info 3784 on the configuration access mechanisms. 3785 noaer [PCIE] If the PCIEAER kernel config parameter is 3786 enabled, this kernel boot option can be used to 3787 disable the use of PCIE advanced error reporting. 3788 nodomains [PCI] Disable support for multiple PCI 3789 root domains (aka PCI segments, in ACPI-speak). 3790 nommconf [X86] Disable use of MMCONFIG for PCI 3791 Configuration 3792 check_enable_amd_mmconf [X86] check for and enable 3793 properly configured MMIO access to PCI 3794 config space on AMD family 10h CPU 3795 nomsi [MSI] If the PCI_MSI kernel config parameter is 3796 enabled, this kernel boot option can be used to 3797 disable the use of MSI interrupts system-wide. 3798 noioapicquirk [APIC] Disable all boot interrupt quirks. 3799 Safety option to keep boot IRQs enabled. This 3800 should never be necessary. 3801 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3802 primary IO-APIC for bridges that cannot disable 3803 boot IRQs. This fixes a source of spurious IRQs 3804 when the system masks IRQs. 3805 noioapicreroute [APIC] Disable workaround that uses the 3806 boot IRQ equivalent of an IRQ that connects to 3807 a chipset where boot IRQs cannot be disabled. 3808 The opposite of ioapicreroute. 3809 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3810 routing table. These calls are known to be buggy 3811 on several machines and they hang the machine 3812 when used, but on other computers it's the only 3813 way to get the interrupt routing table. Try 3814 this option if the kernel is unable to allocate 3815 IRQs or discover secondary PCI buses on your 3816 motherboard. 3817 rom [X86] Assign address space to expansion ROMs. 3818 Use with caution as certain devices share 3819 address decoders between ROMs and other 3820 resources. 3821 norom [X86] Do not assign address space to 3822 expansion ROMs that do not already have 3823 BIOS assigned address ranges. 3824 nobar [X86] Do not assign address space to the 3825 BARs that weren't assigned by the BIOS. 3826 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3827 assigned automatically to PCI devices. You can 3828 make the kernel exclude IRQs of your ISA cards 3829 this way. 3830 pirqaddr=0xAAAAA [X86] Specify the physical address 3831 of the PIRQ table (normally generated 3832 by the BIOS) if it is outside the 3833 F0000h-100000h range. 3834 lastbus=N [X86] Scan all buses thru bus #N. Can be 3835 useful if the kernel is unable to find your 3836 secondary buses and you want to tell it 3837 explicitly which ones they are. 3838 assign-busses [X86] Always assign all PCI bus 3839 numbers ourselves, overriding 3840 whatever the firmware may have done. 3841 usepirqmask [X86] Honor the possible IRQ mask stored 3842 in the BIOS $PIR table. This is needed on 3843 some systems with broken BIOSes, notably 3844 some HP Pavilion N5400 and Omnibook XE3 3845 notebooks. This will have no effect if ACPI 3846 IRQ routing is enabled. 3847 noacpi [X86] Do not use ACPI for IRQ routing 3848 or for PCI scanning. 3849 use_crs [X86] Use PCI host bridge window information 3850 from ACPI. On BIOSes from 2008 or later, this 3851 is enabled by default. If you need to use this, 3852 please report a bug. 3853 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3854 If you need to use this, please report a bug. 3855 routeirq Do IRQ routing for all PCI devices. 3856 This is normally done in pci_enable_device(), 3857 so this option is a temporary workaround 3858 for broken drivers that don't call it. 3859 skip_isa_align [X86] do not align io start addr, so can 3860 handle more pci cards 3861 noearly [X86] Don't do any early type 1 scanning. 3862 This might help on some broken boards which 3863 machine check when some devices' config space 3864 is read. But various workarounds are disabled 3865 and some IOMMU drivers will not work. 3866 bfsort Sort PCI devices into breadth-first order. 3867 This sorting is done to get a device 3868 order compatible with older (<= 2.4) kernels. 3869 nobfsort Don't sort PCI devices into breadth-first order. 3870 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3871 tuning and use the BIOS-configured MPS defaults. 3872 pcie_bus_safe Set every device's MPS to the largest value 3873 supported by all devices below the root complex. 3874 pcie_bus_perf Set device MPS to the largest allowable MPS 3875 based on its parent bus. Also set MRRS (Max 3876 Read Request Size) to the largest supported 3877 value (no larger than the MPS that the device 3878 or bus can support) for best performance. 3879 pcie_bus_peer2peer Set every device's MPS to 128B, which 3880 every device is guaranteed to support. This 3881 configuration allows peer-to-peer DMA between 3882 any pair of devices, possibly at the cost of 3883 reduced performance. This also guarantees 3884 that hot-added devices will work. 3885 cbiosize=nn[KMG] The fixed amount of bus space which is 3886 reserved for the CardBus bridge's IO window. 3887 The default value is 256 bytes. 3888 cbmemsize=nn[KMG] The fixed amount of bus space which is 3889 reserved for the CardBus bridge's memory 3890 window. The default value is 64 megabytes. 3891 resource_alignment= 3892 Format: 3893 [<order of align>@]<pci_dev>[; ...] 3894 Specifies alignment and device to reassign 3895 aligned memory resources. How to 3896 specify the device is described above. 3897 If <order of align> is not specified, 3898 PAGE_SIZE is used as alignment. 3899 A PCI-PCI bridge can be specified if resource 3900 windows need to be expanded. 3901 To specify the alignment for several 3902 instances of a device, the PCI vendor, 3903 device, subvendor, and subdevice may be 3904 specified, e.g., 12@pci:8086:9c22:103c:198f 3905 for 4096-byte alignment. 3906 ecrc= Enable/disable PCIe ECRC (transaction layer 3907 end-to-end CRC checking). 3908 bios: Use BIOS/firmware settings. This is the 3909 the default. 3910 off: Turn ECRC off 3911 on: Turn ECRC on. 3912 hpiosize=nn[KMG] The fixed amount of bus space which is 3913 reserved for hotplug bridge's IO window. 3914 Default size is 256 bytes. 3915 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3916 reserved for hotplug bridge's MMIO window. 3917 Default size is 2 megabytes. 3918 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3919 reserved for hotplug bridge's MMIO_PREF window. 3920 Default size is 2 megabytes. 3921 hpmemsize=nn[KMG] The fixed amount of bus space which is 3922 reserved for hotplug bridge's MMIO and 3923 MMIO_PREF window. 3924 Default size is 2 megabytes. 3925 hpbussize=nn The minimum amount of additional bus numbers 3926 reserved for buses below a hotplug bridge. 3927 Default is 1. 3928 realloc= Enable/disable reallocating PCI bridge resources 3929 if allocations done by BIOS are too small to 3930 accommodate resources required by all child 3931 devices. 3932 off: Turn realloc off 3933 on: Turn realloc on 3934 realloc same as realloc=on 3935 noari do not use PCIe ARI. 3936 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3937 do not use PCIe ATS (and IOMMU device IOTLB). 3938 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3939 only look for one device below a PCIe downstream 3940 port. 3941 big_root_window Try to add a big 64bit memory window to the PCIe 3942 root complex on AMD CPUs. Some GFX hardware 3943 can resize a BAR to allow access to all VRAM. 3944 Adding the window is slightly risky (it may 3945 conflict with unreported devices), so this 3946 taints the kernel. 3947 disable_acs_redir=<pci_dev>[; ...] 3948 Specify one or more PCI devices (in the format 3949 specified above) separated by semicolons. 3950 Each device specified will have the PCI ACS 3951 redirect capabilities forced off which will 3952 allow P2P traffic between devices through 3953 bridges without forcing it upstream. Note: 3954 this removes isolation between devices and 3955 may put more devices in an IOMMU group. 3956 force_floating [S390] Force usage of floating interrupts. 3957 nomio [S390] Do not use MIO instructions. 3958 norid [S390] ignore the RID field and force use of 3959 one PCI domain per PCI function 3960 3961 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3962 Management. 3963 off Disable ASPM. 3964 force Enable ASPM even on devices that claim not to support it. 3965 WARNING: Forcing ASPM on may cause system lockups. 3966 3967 pcie_ports= [PCIE] PCIe port services handling: 3968 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3969 even if the platform doesn't give the OS permission to 3970 use them. This may cause conflicts if the platform 3971 also tries to use these services. 3972 dpc-native Use native PCIe service for DPC only. May 3973 cause conflicts if firmware uses AER or DPC. 3974 compat Disable native PCIe services (PME, AER, DPC, PCIe 3975 hotplug). 3976 3977 pcie_port_pm= [PCIE] PCIe port power management handling: 3978 off Disable power management of all PCIe ports 3979 force Forcibly enable power management of all PCIe ports 3980 3981 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3982 nomsi Do not use MSI for native PCIe PME signaling (this makes 3983 all PCIe root ports use INTx for all services). 3984 3985 pcmv= [HW,PCMCIA] BadgePAD 4 3986 3987 pd_ignore_unused 3988 [PM] 3989 Keep all power-domains already enabled by bootloader on, 3990 even if no driver has claimed them. This is useful 3991 for debug and development, but should not be 3992 needed on a platform with proper driver support. 3993 3994 pd. [PARIDE] 3995 See Documentation/admin-guide/blockdev/paride.rst. 3996 3997 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3998 boot time. 3999 Format: { 0 | 1 } 4000 See arch/parisc/kernel/pdc_chassis.c 4001 4002 percpu_alloc= Select which percpu first chunk allocator to use. 4003 Currently supported values are "embed" and "page". 4004 Archs may support subset or none of the selections. 4005 See comments in mm/percpu.c for details on each 4006 allocator. This parameter is primarily for debugging 4007 and performance comparison. 4008 4009 pf. [PARIDE] 4010 See Documentation/admin-guide/blockdev/paride.rst. 4011 4012 pg. [PARIDE] 4013 See Documentation/admin-guide/blockdev/paride.rst. 4014 4015 pirq= [SMP,APIC] Manual mp-table setup 4016 See Documentation/x86/i386/IO-APIC.rst. 4017 4018 plip= [PPT,NET] Parallel port network link 4019 Format: { parport<nr> | timid | 0 } 4020 See also Documentation/admin-guide/parport.rst. 4021 4022 pmtmr= [X86] Manual setup of pmtmr I/O Port. 4023 Override pmtimer IOPort with a hex value. 4024 e.g. pmtmr=0x508 4025 4026 pm_debug_messages [SUSPEND,KNL] 4027 Enable suspend/resume debug messages during boot up. 4028 4029 pnp.debug=1 [PNP] 4030 Enable PNP debug messages (depends on the 4031 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 4032 via /sys/module/pnp/parameters/debug. We always show 4033 current resource usage; turning this on also shows 4034 possible settings and some assignment information. 4035 4036 pnpacpi= [ACPI] 4037 { off } 4038 4039 pnpbios= [ISAPNP] 4040 { on | off | curr | res | no-curr | no-res } 4041 4042 pnp_reserve_irq= 4043 [ISAPNP] Exclude IRQs for the autoconfiguration 4044 4045 pnp_reserve_dma= 4046 [ISAPNP] Exclude DMAs for the autoconfiguration 4047 4048 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 4049 Ranges are in pairs (I/O port base and size). 4050 4051 pnp_reserve_mem= 4052 [ISAPNP] Exclude memory regions for the 4053 autoconfiguration. 4054 Ranges are in pairs (memory base and size). 4055 4056 ports= [IP_VS_FTP] IPVS ftp helper module 4057 Default is 21. 4058 Up to 8 (IP_VS_APP_MAX_PORTS) ports 4059 may be specified. 4060 Format: <port>,<port>.... 4061 4062 powersave=off [PPC] This option disables power saving features. 4063 It specifically disables cpuidle and sets the 4064 platform machine description specific power_save 4065 function to NULL. On Idle the CPU just reduces 4066 execution priority. 4067 4068 ppc_strict_facility_enable 4069 [PPC] This option catches any kernel floating point, 4070 Altivec, VSX and SPE outside of regions specifically 4071 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 4072 There is some performance impact when enabling this. 4073 4074 ppc_tm= [PPC] 4075 Format: {"off"} 4076 Disable Hardware Transactional Memory 4077 4078 preempt= [KNL] 4079 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 4080 none - Limited to cond_resched() calls 4081 voluntary - Limited to cond_resched() and might_sleep() calls 4082 full - Any section that isn't explicitly preempt disabled 4083 can be preempted anytime. 4084 4085 print-fatal-signals= 4086 [KNL] debug: print fatal signals 4087 4088 If enabled, warn about various signal handling 4089 related application anomalies: too many signals, 4090 too many POSIX.1 timers, fatal signals causing a 4091 coredump - etc. 4092 4093 If you hit the warning due to signal overflow, 4094 you might want to try "ulimit -i unlimited". 4095 4096 default: off. 4097 4098 printk.always_kmsg_dump= 4099 Trigger kmsg_dump for cases other than kernel oops or 4100 panics 4101 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4102 default: disabled 4103 4104 printk.devkmsg={on,off,ratelimit} 4105 Control writing to /dev/kmsg. 4106 on - unlimited logging to /dev/kmsg from userspace 4107 off - logging to /dev/kmsg disabled 4108 ratelimit - ratelimit the logging 4109 Default: ratelimit 4110 4111 printk.time= Show timing data prefixed to each printk message line 4112 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4113 4114 processor.max_cstate= [HW,ACPI] 4115 Limit processor to maximum C-state 4116 max_cstate=9 overrides any DMI blacklist limit. 4117 4118 processor.nocst [HW,ACPI] 4119 Ignore the _CST method to determine C-states, 4120 instead using the legacy FADT method 4121 4122 profile= [KNL] Enable kernel profiling via /proc/profile 4123 Format: [<profiletype>,]<number> 4124 Param: <profiletype>: "schedule", "sleep", or "kvm" 4125 [defaults to kernel profiling] 4126 Param: "schedule" - profile schedule points. 4127 Param: "sleep" - profile D-state sleeping (millisecs). 4128 Requires CONFIG_SCHEDSTATS 4129 Param: "kvm" - profile VM exits. 4130 Param: <number> - step/bucket size as a power of 2 for 4131 statistical time based profiling. 4132 4133 prompt_ramdisk= [RAM] [Deprecated] 4134 4135 prot_virt= [S390] enable hosting protected virtual machines 4136 isolated from the hypervisor (if hardware supports 4137 that). 4138 Format: <bool> 4139 4140 psi= [KNL] Enable or disable pressure stall information 4141 tracking. 4142 Format: <bool> 4143 4144 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 4145 probe for; one of (bare|imps|exps|lifebook|any). 4146 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 4147 per second. 4148 psmouse.resetafter= [HW,MOUSE] 4149 Try to reset the device after so many bad packets 4150 (0 = never). 4151 psmouse.resolution= 4152 [HW,MOUSE] Set desired mouse resolution, in dpi. 4153 psmouse.smartscroll= 4154 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 4155 0 = disabled, 1 = enabled (default). 4156 4157 pstore.backend= Specify the name of the pstore backend to use 4158 4159 pt. [PARIDE] 4160 See Documentation/admin-guide/blockdev/paride.rst. 4161 4162 pti= [X86-64] Control Page Table Isolation of user and 4163 kernel address spaces. Disabling this feature 4164 removes hardening, but improves performance of 4165 system calls and interrupts. 4166 4167 on - unconditionally enable 4168 off - unconditionally disable 4169 auto - kernel detects whether your CPU model is 4170 vulnerable to issues that PTI mitigates 4171 4172 Not specifying this option is equivalent to pti=auto. 4173 4174 nopti [X86-64] 4175 Equivalent to pti=off 4176 4177 pty.legacy_count= 4178 [KNL] Number of legacy pty's. Overwrites compiled-in 4179 default number. 4180 4181 quiet [KNL] Disable most log messages 4182 4183 r128= [HW,DRM] 4184 4185 raid= [HW,RAID] 4186 See Documentation/admin-guide/md.rst. 4187 4188 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 4189 See Documentation/admin-guide/blockdev/ramdisk.rst. 4190 4191 ramdisk_start= [RAM] RAM disk image start address 4192 4193 random.trust_cpu={on,off} 4194 [KNL] Enable or disable trusting the use of the 4195 CPU's random number generator (if available) to 4196 fully seed the kernel's CRNG. Default is controlled 4197 by CONFIG_RANDOM_TRUST_CPU. 4198 4199 randomize_kstack_offset= 4200 [KNL] Enable or disable kernel stack offset 4201 randomization, which provides roughly 5 bits of 4202 entropy, frustrating memory corruption attacks 4203 that depend on stack address determinism or 4204 cross-syscall address exposures. This is only 4205 available on architectures that have defined 4206 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 4207 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4208 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 4209 4210 ras=option[,option,...] [KNL] RAS-specific options 4211 4212 cec_disable [X86] 4213 Disable the Correctable Errors Collector, 4214 see CONFIG_RAS_CEC help text. 4215 4216 rcu_nocbs= [KNL] 4217 The argument is a cpu list, as described above. 4218 4219 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 4220 the specified list of CPUs to be no-callback CPUs. 4221 Invocation of these CPUs' RCU callbacks will be 4222 offloaded to "rcuox/N" kthreads created for that 4223 purpose, where "x" is "p" for RCU-preempt, and 4224 "s" for RCU-sched, and "N" is the CPU number. 4225 This reduces OS jitter on the offloaded CPUs, 4226 which can be useful for HPC and real-time 4227 workloads. It can also improve energy efficiency 4228 for asymmetric multiprocessors. 4229 4230 rcu_nocb_poll [KNL] 4231 Rather than requiring that offloaded CPUs 4232 (specified by rcu_nocbs= above) explicitly 4233 awaken the corresponding "rcuoN" kthreads, 4234 make these kthreads poll for callbacks. 4235 This improves the real-time response for the 4236 offloaded CPUs by relieving them of the need to 4237 wake up the corresponding kthread, but degrades 4238 energy efficiency by requiring that the kthreads 4239 periodically wake up to do the polling. 4240 4241 rcutree.blimit= [KNL] 4242 Set maximum number of finished RCU callbacks to 4243 process in one batch. 4244 4245 rcutree.dump_tree= [KNL] 4246 Dump the structure of the rcu_node combining tree 4247 out at early boot. This is used for diagnostic 4248 purposes, to verify correct tree setup. 4249 4250 rcutree.gp_cleanup_delay= [KNL] 4251 Set the number of jiffies to delay each step of 4252 RCU grace-period cleanup. 4253 4254 rcutree.gp_init_delay= [KNL] 4255 Set the number of jiffies to delay each step of 4256 RCU grace-period initialization. 4257 4258 rcutree.gp_preinit_delay= [KNL] 4259 Set the number of jiffies to delay each step of 4260 RCU grace-period pre-initialization, that is, 4261 the propagation of recent CPU-hotplug changes up 4262 the rcu_node combining tree. 4263 4264 rcutree.use_softirq= [KNL] 4265 If set to zero, move all RCU_SOFTIRQ processing to 4266 per-CPU rcuc kthreads. Defaults to a non-zero 4267 value, meaning that RCU_SOFTIRQ is used by default. 4268 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4269 4270 But note that CONFIG_PREEMPT_RT=y kernels disable 4271 this kernel boot parameter, forcibly setting it 4272 to zero. 4273 4274 rcutree.rcu_fanout_exact= [KNL] 4275 Disable autobalancing of the rcu_node combining 4276 tree. This is used by rcutorture, and might 4277 possibly be useful for architectures having high 4278 cache-to-cache transfer latencies. 4279 4280 rcutree.rcu_fanout_leaf= [KNL] 4281 Change the number of CPUs assigned to each 4282 leaf rcu_node structure. Useful for very 4283 large systems, which will choose the value 64, 4284 and for NUMA systems with large remote-access 4285 latencies, which will choose a value aligned 4286 with the appropriate hardware boundaries. 4287 4288 rcutree.rcu_min_cached_objs= [KNL] 4289 Minimum number of objects which are cached and 4290 maintained per one CPU. Object size is equal 4291 to PAGE_SIZE. The cache allows to reduce the 4292 pressure to page allocator, also it makes the 4293 whole algorithm to behave better in low memory 4294 condition. 4295 4296 rcutree.jiffies_till_first_fqs= [KNL] 4297 Set delay from grace-period initialization to 4298 first attempt to force quiescent states. 4299 Units are jiffies, minimum value is zero, 4300 and maximum value is HZ. 4301 4302 rcutree.jiffies_till_next_fqs= [KNL] 4303 Set delay between subsequent attempts to force 4304 quiescent states. Units are jiffies, minimum 4305 value is one, and maximum value is HZ. 4306 4307 rcutree.jiffies_till_sched_qs= [KNL] 4308 Set required age in jiffies for a 4309 given grace period before RCU starts 4310 soliciting quiescent-state help from 4311 rcu_note_context_switch() and cond_resched(). 4312 If not specified, the kernel will calculate 4313 a value based on the most recent settings 4314 of rcutree.jiffies_till_first_fqs 4315 and rcutree.jiffies_till_next_fqs. 4316 This calculated value may be viewed in 4317 rcutree.jiffies_to_sched_qs. Any attempt to set 4318 rcutree.jiffies_to_sched_qs will be cheerfully 4319 overwritten. 4320 4321 rcutree.kthread_prio= [KNL,BOOT] 4322 Set the SCHED_FIFO priority of the RCU per-CPU 4323 kthreads (rcuc/N). This value is also used for 4324 the priority of the RCU boost threads (rcub/N) 4325 and for the RCU grace-period kthreads (rcu_bh, 4326 rcu_preempt, and rcu_sched). If RCU_BOOST is 4327 set, valid values are 1-99 and the default is 1 4328 (the least-favored priority). Otherwise, when 4329 RCU_BOOST is not set, valid values are 0-99 and 4330 the default is zero (non-realtime operation). 4331 4332 rcutree.rcu_nocb_gp_stride= [KNL] 4333 Set the number of NOCB callback kthreads in 4334 each group, which defaults to the square root 4335 of the number of CPUs. Larger numbers reduce 4336 the wakeup overhead on the global grace-period 4337 kthread, but increases that same overhead on 4338 each group's NOCB grace-period kthread. 4339 4340 rcutree.qhimark= [KNL] 4341 Set threshold of queued RCU callbacks beyond which 4342 batch limiting is disabled. 4343 4344 rcutree.qlowmark= [KNL] 4345 Set threshold of queued RCU callbacks below which 4346 batch limiting is re-enabled. 4347 4348 rcutree.qovld= [KNL] 4349 Set threshold of queued RCU callbacks beyond which 4350 RCU's force-quiescent-state scan will aggressively 4351 enlist help from cond_resched() and sched IPIs to 4352 help CPUs more quickly reach quiescent states. 4353 Set to less than zero to make this be set based 4354 on rcutree.qhimark at boot time and to zero to 4355 disable more aggressive help enlistment. 4356 4357 rcutree.rcu_idle_gp_delay= [KNL] 4358 Set wakeup interval for idle CPUs that have 4359 RCU callbacks (RCU_FAST_NO_HZ=y). 4360 4361 rcutree.rcu_kick_kthreads= [KNL] 4362 Cause the grace-period kthread to get an extra 4363 wake_up() if it sleeps three times longer than 4364 it should at force-quiescent-state time. 4365 This wake_up() will be accompanied by a 4366 WARN_ONCE() splat and an ftrace_dump(). 4367 4368 rcutree.rcu_unlock_delay= [KNL] 4369 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 4370 this specifies an rcu_read_unlock()-time delay 4371 in microseconds. This defaults to zero. 4372 Larger delays increase the probability of 4373 catching RCU pointer leaks, that is, buggy use 4374 of RCU-protected pointers after the relevant 4375 rcu_read_unlock() has completed. 4376 4377 rcutree.sysrq_rcu= [KNL] 4378 Commandeer a sysrq key to dump out Tree RCU's 4379 rcu_node tree with an eye towards determining 4380 why a new grace period has not yet started. 4381 4382 rcuscale.gp_async= [KNL] 4383 Measure performance of asynchronous 4384 grace-period primitives such as call_rcu(). 4385 4386 rcuscale.gp_async_max= [KNL] 4387 Specify the maximum number of outstanding 4388 callbacks per writer thread. When a writer 4389 thread exceeds this limit, it invokes the 4390 corresponding flavor of rcu_barrier() to allow 4391 previously posted callbacks to drain. 4392 4393 rcuscale.gp_exp= [KNL] 4394 Measure performance of expedited synchronous 4395 grace-period primitives. 4396 4397 rcuscale.holdoff= [KNL] 4398 Set test-start holdoff period. The purpose of 4399 this parameter is to delay the start of the 4400 test until boot completes in order to avoid 4401 interference. 4402 4403 rcuscale.kfree_rcu_test= [KNL] 4404 Set to measure performance of kfree_rcu() flooding. 4405 4406 rcuscale.kfree_rcu_test_double= [KNL] 4407 Test the double-argument variant of kfree_rcu(). 4408 If this parameter has the same value as 4409 rcuscale.kfree_rcu_test_single, both the single- 4410 and double-argument variants are tested. 4411 4412 rcuscale.kfree_rcu_test_single= [KNL] 4413 Test the single-argument variant of kfree_rcu(). 4414 If this parameter has the same value as 4415 rcuscale.kfree_rcu_test_double, both the single- 4416 and double-argument variants are tested. 4417 4418 rcuscale.kfree_nthreads= [KNL] 4419 The number of threads running loops of kfree_rcu(). 4420 4421 rcuscale.kfree_alloc_num= [KNL] 4422 Number of allocations and frees done in an iteration. 4423 4424 rcuscale.kfree_loops= [KNL] 4425 Number of loops doing rcuscale.kfree_alloc_num number 4426 of allocations and frees. 4427 4428 rcuscale.nreaders= [KNL] 4429 Set number of RCU readers. The value -1 selects 4430 N, where N is the number of CPUs. A value 4431 "n" less than -1 selects N-n+1, where N is again 4432 the number of CPUs. For example, -2 selects N 4433 (the number of CPUs), -3 selects N+1, and so on. 4434 A value of "n" less than or equal to -N selects 4435 a single reader. 4436 4437 rcuscale.nwriters= [KNL] 4438 Set number of RCU writers. The values operate 4439 the same as for rcuscale.nreaders. 4440 N, where N is the number of CPUs 4441 4442 rcuscale.perf_type= [KNL] 4443 Specify the RCU implementation to test. 4444 4445 rcuscale.shutdown= [KNL] 4446 Shut the system down after performance tests 4447 complete. This is useful for hands-off automated 4448 testing. 4449 4450 rcuscale.verbose= [KNL] 4451 Enable additional printk() statements. 4452 4453 rcuscale.writer_holdoff= [KNL] 4454 Write-side holdoff between grace periods, 4455 in microseconds. The default of zero says 4456 no holdoff. 4457 4458 rcutorture.fqs_duration= [KNL] 4459 Set duration of force_quiescent_state bursts 4460 in microseconds. 4461 4462 rcutorture.fqs_holdoff= [KNL] 4463 Set holdoff time within force_quiescent_state bursts 4464 in microseconds. 4465 4466 rcutorture.fqs_stutter= [KNL] 4467 Set wait time between force_quiescent_state bursts 4468 in seconds. 4469 4470 rcutorture.fwd_progress= [KNL] 4471 Enable RCU grace-period forward-progress testing 4472 for the types of RCU supporting this notion. 4473 4474 rcutorture.fwd_progress_div= [KNL] 4475 Specify the fraction of a CPU-stall-warning 4476 period to do tight-loop forward-progress testing. 4477 4478 rcutorture.fwd_progress_holdoff= [KNL] 4479 Number of seconds to wait between successive 4480 forward-progress tests. 4481 4482 rcutorture.fwd_progress_need_resched= [KNL] 4483 Enclose cond_resched() calls within checks for 4484 need_resched() during tight-loop forward-progress 4485 testing. 4486 4487 rcutorture.gp_cond= [KNL] 4488 Use conditional/asynchronous update-side 4489 primitives, if available. 4490 4491 rcutorture.gp_exp= [KNL] 4492 Use expedited update-side primitives, if available. 4493 4494 rcutorture.gp_normal= [KNL] 4495 Use normal (non-expedited) asynchronous 4496 update-side primitives, if available. 4497 4498 rcutorture.gp_sync= [KNL] 4499 Use normal (non-expedited) synchronous 4500 update-side primitives, if available. If all 4501 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4502 rcutorture.gp_normal=, and rcutorture.gp_sync= 4503 are zero, rcutorture acts as if is interpreted 4504 they are all non-zero. 4505 4506 rcutorture.irqreader= [KNL] 4507 Run RCU readers from irq handlers, or, more 4508 accurately, from a timer handler. Not all RCU 4509 flavors take kindly to this sort of thing. 4510 4511 rcutorture.leakpointer= [KNL] 4512 Leak an RCU-protected pointer out of the reader. 4513 This can of course result in splats, and is 4514 intended to test the ability of things like 4515 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 4516 such leaks. 4517 4518 rcutorture.n_barrier_cbs= [KNL] 4519 Set callbacks/threads for rcu_barrier() testing. 4520 4521 rcutorture.nfakewriters= [KNL] 4522 Set number of concurrent RCU writers. These just 4523 stress RCU, they don't participate in the actual 4524 test, hence the "fake". 4525 4526 rcutorture.nocbs_nthreads= [KNL] 4527 Set number of RCU callback-offload togglers. 4528 Zero (the default) disables toggling. 4529 4530 rcutorture.nocbs_toggle= [KNL] 4531 Set the delay in milliseconds between successive 4532 callback-offload toggling attempts. 4533 4534 rcutorture.nreaders= [KNL] 4535 Set number of RCU readers. The value -1 selects 4536 N-1, where N is the number of CPUs. A value 4537 "n" less than -1 selects N-n-2, where N is again 4538 the number of CPUs. For example, -2 selects N 4539 (the number of CPUs), -3 selects N+1, and so on. 4540 4541 rcutorture.object_debug= [KNL] 4542 Enable debug-object double-call_rcu() testing. 4543 4544 rcutorture.onoff_holdoff= [KNL] 4545 Set time (s) after boot for CPU-hotplug testing. 4546 4547 rcutorture.onoff_interval= [KNL] 4548 Set time (jiffies) between CPU-hotplug operations, 4549 or zero to disable CPU-hotplug testing. 4550 4551 rcutorture.read_exit= [KNL] 4552 Set the number of read-then-exit kthreads used 4553 to test the interaction of RCU updaters and 4554 task-exit processing. 4555 4556 rcutorture.read_exit_burst= [KNL] 4557 The number of times in a given read-then-exit 4558 episode that a set of read-then-exit kthreads 4559 is spawned. 4560 4561 rcutorture.read_exit_delay= [KNL] 4562 The delay, in seconds, between successive 4563 read-then-exit testing episodes. 4564 4565 rcutorture.shuffle_interval= [KNL] 4566 Set task-shuffle interval (s). Shuffling tasks 4567 allows some CPUs to go into dyntick-idle mode 4568 during the rcutorture test. 4569 4570 rcutorture.shutdown_secs= [KNL] 4571 Set time (s) after boot system shutdown. This 4572 is useful for hands-off automated testing. 4573 4574 rcutorture.stall_cpu= [KNL] 4575 Duration of CPU stall (s) to test RCU CPU stall 4576 warnings, zero to disable. 4577 4578 rcutorture.stall_cpu_block= [KNL] 4579 Sleep while stalling if set. This will result 4580 in warnings from preemptible RCU in addition 4581 to any other stall-related activity. 4582 4583 rcutorture.stall_cpu_holdoff= [KNL] 4584 Time to wait (s) after boot before inducing stall. 4585 4586 rcutorture.stall_cpu_irqsoff= [KNL] 4587 Disable interrupts while stalling if set. 4588 4589 rcutorture.stall_gp_kthread= [KNL] 4590 Duration (s) of forced sleep within RCU 4591 grace-period kthread to test RCU CPU stall 4592 warnings, zero to disable. If both stall_cpu 4593 and stall_gp_kthread are specified, the 4594 kthread is starved first, then the CPU. 4595 4596 rcutorture.stat_interval= [KNL] 4597 Time (s) between statistics printk()s. 4598 4599 rcutorture.stutter= [KNL] 4600 Time (s) to stutter testing, for example, specifying 4601 five seconds causes the test to run for five seconds, 4602 wait for five seconds, and so on. This tests RCU's 4603 ability to transition abruptly to and from idle. 4604 4605 rcutorture.test_boost= [KNL] 4606 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4607 "Maybe" means test if the RCU implementation 4608 under test support RCU priority boosting. 4609 4610 rcutorture.test_boost_duration= [KNL] 4611 Duration (s) of each individual boost test. 4612 4613 rcutorture.test_boost_interval= [KNL] 4614 Interval (s) between each boost test. 4615 4616 rcutorture.test_no_idle_hz= [KNL] 4617 Test RCU's dyntick-idle handling. See also the 4618 rcutorture.shuffle_interval parameter. 4619 4620 rcutorture.torture_type= [KNL] 4621 Specify the RCU implementation to test. 4622 4623 rcutorture.verbose= [KNL] 4624 Enable additional printk() statements. 4625 4626 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4627 Dump ftrace buffer after reporting RCU CPU 4628 stall warning. 4629 4630 rcupdate.rcu_cpu_stall_suppress= [KNL] 4631 Suppress RCU CPU stall warning messages. 4632 4633 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4634 Suppress RCU CPU stall warning messages and 4635 rcutorture writer stall warnings that occur 4636 during early boot, that is, during the time 4637 before the init task is spawned. 4638 4639 rcupdate.rcu_cpu_stall_timeout= [KNL] 4640 Set timeout for RCU CPU stall warning messages. 4641 4642 rcupdate.rcu_expedited= [KNL] 4643 Use expedited grace-period primitives, for 4644 example, synchronize_rcu_expedited() instead 4645 of synchronize_rcu(). This reduces latency, 4646 but can increase CPU utilization, degrade 4647 real-time latency, and degrade energy efficiency. 4648 No effect on CONFIG_TINY_RCU kernels. 4649 4650 rcupdate.rcu_normal= [KNL] 4651 Use only normal grace-period primitives, 4652 for example, synchronize_rcu() instead of 4653 synchronize_rcu_expedited(). This improves 4654 real-time latency, CPU utilization, and 4655 energy efficiency, but can expose users to 4656 increased grace-period latency. This parameter 4657 overrides rcupdate.rcu_expedited. No effect on 4658 CONFIG_TINY_RCU kernels. 4659 4660 rcupdate.rcu_normal_after_boot= [KNL] 4661 Once boot has completed (that is, after 4662 rcu_end_inkernel_boot() has been invoked), use 4663 only normal grace-period primitives. No effect 4664 on CONFIG_TINY_RCU kernels. 4665 4666 But note that CONFIG_PREEMPT_RT=y kernels enables 4667 this kernel boot parameter, forcibly setting 4668 it to the value one, that is, converting any 4669 post-boot attempt at an expedited RCU grace 4670 period to instead use normal non-expedited 4671 grace-period processing. 4672 4673 rcupdate.rcu_task_ipi_delay= [KNL] 4674 Set time in jiffies during which RCU tasks will 4675 avoid sending IPIs, starting with the beginning 4676 of a given grace period. Setting a large 4677 number avoids disturbing real-time workloads, 4678 but lengthens grace periods. 4679 4680 rcupdate.rcu_task_stall_timeout= [KNL] 4681 Set timeout in jiffies for RCU task stall warning 4682 messages. Disable with a value less than or equal 4683 to zero. 4684 4685 rcupdate.rcu_self_test= [KNL] 4686 Run the RCU early boot self tests 4687 4688 rdinit= [KNL] 4689 Format: <full_path> 4690 Run specified binary instead of /init from the ramdisk, 4691 used for early userspace startup. See initrd. 4692 4693 rdrand= [X86] 4694 force - Override the decision by the kernel to hide the 4695 advertisement of RDRAND support (this affects 4696 certain AMD processors because of buggy BIOS 4697 support, specifically around the suspend/resume 4698 path). 4699 4700 rdt= [HW,X86,RDT] 4701 Turn on/off individual RDT features. List is: 4702 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4703 mba. 4704 E.g. to turn on cmt and turn off mba use: 4705 rdt=cmt,!mba 4706 4707 reboot= [KNL] 4708 Format (x86 or x86_64): 4709 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4710 [[,]s[mp]#### \ 4711 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4712 [[,]f[orce] 4713 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4714 (prefix with 'panic_' to set mode for panic 4715 reboot only), 4716 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4717 reboot_force is either force or not specified, 4718 reboot_cpu is s[mp]#### with #### being the processor 4719 to be used for rebooting. 4720 4721 refscale.holdoff= [KNL] 4722 Set test-start holdoff period. The purpose of 4723 this parameter is to delay the start of the 4724 test until boot completes in order to avoid 4725 interference. 4726 4727 refscale.loops= [KNL] 4728 Set the number of loops over the synchronization 4729 primitive under test. Increasing this number 4730 reduces noise due to loop start/end overhead, 4731 but the default has already reduced the per-pass 4732 noise to a handful of picoseconds on ca. 2020 4733 x86 laptops. 4734 4735 refscale.nreaders= [KNL] 4736 Set number of readers. The default value of -1 4737 selects N, where N is roughly 75% of the number 4738 of CPUs. A value of zero is an interesting choice. 4739 4740 refscale.nruns= [KNL] 4741 Set number of runs, each of which is dumped onto 4742 the console log. 4743 4744 refscale.readdelay= [KNL] 4745 Set the read-side critical-section duration, 4746 measured in microseconds. 4747 4748 refscale.scale_type= [KNL] 4749 Specify the read-protection implementation to test. 4750 4751 refscale.shutdown= [KNL] 4752 Shut down the system at the end of the performance 4753 test. This defaults to 1 (shut it down) when 4754 refscale is built into the kernel and to 0 (leave 4755 it running) when refscale is built as a module. 4756 4757 refscale.verbose= [KNL] 4758 Enable additional printk() statements. 4759 4760 refscale.verbose_batched= [KNL] 4761 Batch the additional printk() statements. If zero 4762 (the default) or negative, print everything. Otherwise, 4763 print every Nth verbose statement, where N is the value 4764 specified. 4765 4766 relax_domain_level= 4767 [KNL, SMP] Set scheduler's default relax_domain_level. 4768 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4769 4770 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4771 Format: <base1>,<size1>[,<base2>,<size2>,...] 4772 Reserve I/O ports or memory so the kernel won't use 4773 them. If <base> is less than 0x10000, the region 4774 is assumed to be I/O ports; otherwise it is memory. 4775 4776 reservetop= [X86-32] 4777 Format: nn[KMG] 4778 Reserves a hole at the top of the kernel virtual 4779 address space. 4780 4781 reservelow= [X86] 4782 Format: nn[K] 4783 Set the amount of memory to reserve for BIOS at 4784 the bottom of the address space. 4785 4786 reset_devices [KNL] Force drivers to reset the underlying device 4787 during initialization. 4788 4789 resume= [SWSUSP] 4790 Specify the partition device for software suspend 4791 Format: 4792 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4793 4794 resume_offset= [SWSUSP] 4795 Specify the offset from the beginning of the partition 4796 given by "resume=" at which the swap header is located, 4797 in <PAGE_SIZE> units (needed only for swap files). 4798 See Documentation/power/swsusp-and-swap-files.rst 4799 4800 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4801 read the resume files 4802 4803 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4804 Useful for devices that are detected asynchronously 4805 (e.g. USB and MMC devices). 4806 4807 hibernate= [HIBERNATION] 4808 noresume Don't check if there's a hibernation image 4809 present during boot. 4810 nocompress Don't compress/decompress hibernation images. 4811 no Disable hibernation and resume. 4812 protect_image Turn on image protection during restoration 4813 (that will set all pages holding image data 4814 during restoration read-only). 4815 4816 retain_initrd [RAM] Keep initrd memory after extraction 4817 4818 rfkill.default_state= 4819 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4820 etc. communication is blocked by default. 4821 1 Unblocked. 4822 4823 rfkill.master_switch_mode= 4824 0 The "airplane mode" button does nothing. 4825 1 The "airplane mode" button toggles between everything 4826 blocked and the previous configuration. 4827 2 The "airplane mode" button toggles between everything 4828 blocked and everything unblocked. 4829 4830 rhash_entries= [KNL,NET] 4831 Set number of hash buckets for route cache 4832 4833 ring3mwait=disable 4834 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4835 CPUs. 4836 4837 ro [KNL] Mount root device read-only on boot 4838 4839 rodata= [KNL] 4840 on Mark read-only kernel memory as read-only (default). 4841 off Leave read-only kernel memory writable for debugging. 4842 4843 rockchip.usb_uart 4844 Enable the uart passthrough on the designated usb port 4845 on Rockchip SoCs. When active, the signals of the 4846 debug-uart get routed to the D+ and D- pins of the usb 4847 port and the regular usb controller gets disabled. 4848 4849 root= [KNL] Root filesystem 4850 See name_to_dev_t comment in init/do_mounts.c. 4851 4852 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4853 mount the root filesystem 4854 4855 rootflags= [KNL] Set root filesystem mount option string 4856 4857 rootfstype= [KNL] Set root filesystem type 4858 4859 rootwait [KNL] Wait (indefinitely) for root device to show up. 4860 Useful for devices that are detected asynchronously 4861 (e.g. USB and MMC devices). 4862 4863 rproc_mem=nn[KMG][@address] 4864 [KNL,ARM,CMA] Remoteproc physical memory block. 4865 Memory area to be used by remote processor image, 4866 managed by CMA. 4867 4868 rw [KNL] Mount root device read-write on boot 4869 4870 S [KNL] Run init in single mode 4871 4872 s390_iommu= [HW,S390] 4873 Set s390 IOTLB flushing mode 4874 strict 4875 With strict flushing every unmap operation will result in 4876 an IOTLB flush. Default is lazy flushing before reuse, 4877 which is faster. 4878 4879 sa1100ir [NET] 4880 See drivers/net/irda/sa1100_ir.c. 4881 4882 sbni= [NET] Granch SBNI12 leased line adapter 4883 4884 sched_verbose [KNL] Enables verbose scheduler debug messages. 4885 4886 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4887 Allowed values are enable and disable. This feature 4888 incurs a small amount of overhead in the scheduler 4889 but is useful for debugging and performance tuning. 4890 4891 sched_thermal_decay_shift= 4892 [KNL, SMP] Set a decay shift for scheduler thermal 4893 pressure signal. Thermal pressure signal follows the 4894 default decay period of other scheduler pelt 4895 signals(usually 32 ms but configurable). Setting 4896 sched_thermal_decay_shift will left shift the decay 4897 period for the thermal pressure signal by the shift 4898 value. 4899 i.e. with the default pelt decay period of 32 ms 4900 sched_thermal_decay_shift thermal pressure decay pr 4901 1 64 ms 4902 2 128 ms 4903 and so on. 4904 Format: integer between 0 and 10 4905 Default is 0. 4906 4907 scftorture.holdoff= [KNL] 4908 Number of seconds to hold off before starting 4909 test. Defaults to zero for module insertion and 4910 to 10 seconds for built-in smp_call_function() 4911 tests. 4912 4913 scftorture.longwait= [KNL] 4914 Request ridiculously long waits randomly selected 4915 up to the chosen limit in seconds. Zero (the 4916 default) disables this feature. Please note 4917 that requesting even small non-zero numbers of 4918 seconds can result in RCU CPU stall warnings, 4919 softlockup complaints, and so on. 4920 4921 scftorture.nthreads= [KNL] 4922 Number of kthreads to spawn to invoke the 4923 smp_call_function() family of functions. 4924 The default of -1 specifies a number of kthreads 4925 equal to the number of CPUs. 4926 4927 scftorture.onoff_holdoff= [KNL] 4928 Number seconds to wait after the start of the 4929 test before initiating CPU-hotplug operations. 4930 4931 scftorture.onoff_interval= [KNL] 4932 Number seconds to wait between successive 4933 CPU-hotplug operations. Specifying zero (which 4934 is the default) disables CPU-hotplug operations. 4935 4936 scftorture.shutdown_secs= [KNL] 4937 The number of seconds following the start of the 4938 test after which to shut down the system. The 4939 default of zero avoids shutting down the system. 4940 Non-zero values are useful for automated tests. 4941 4942 scftorture.stat_interval= [KNL] 4943 The number of seconds between outputting the 4944 current test statistics to the console. A value 4945 of zero disables statistics output. 4946 4947 scftorture.stutter_cpus= [KNL] 4948 The number of jiffies to wait between each change 4949 to the set of CPUs under test. 4950 4951 scftorture.use_cpus_read_lock= [KNL] 4952 Use use_cpus_read_lock() instead of the default 4953 preempt_disable() to disable CPU hotplug 4954 while invoking one of the smp_call_function*() 4955 functions. 4956 4957 scftorture.verbose= [KNL] 4958 Enable additional printk() statements. 4959 4960 scftorture.weight_single= [KNL] 4961 The probability weighting to use for the 4962 smp_call_function_single() function with a zero 4963 "wait" parameter. A value of -1 selects the 4964 default if all other weights are -1. However, 4965 if at least one weight has some other value, a 4966 value of -1 will instead select a weight of zero. 4967 4968 scftorture.weight_single_wait= [KNL] 4969 The probability weighting to use for the 4970 smp_call_function_single() function with a 4971 non-zero "wait" parameter. See weight_single. 4972 4973 scftorture.weight_many= [KNL] 4974 The probability weighting to use for the 4975 smp_call_function_many() function with a zero 4976 "wait" parameter. See weight_single. 4977 Note well that setting a high probability for 4978 this weighting can place serious IPI load 4979 on the system. 4980 4981 scftorture.weight_many_wait= [KNL] 4982 The probability weighting to use for the 4983 smp_call_function_many() function with a 4984 non-zero "wait" parameter. See weight_single 4985 and weight_many. 4986 4987 scftorture.weight_all= [KNL] 4988 The probability weighting to use for the 4989 smp_call_function_all() function with a zero 4990 "wait" parameter. See weight_single and 4991 weight_many. 4992 4993 scftorture.weight_all_wait= [KNL] 4994 The probability weighting to use for the 4995 smp_call_function_all() function with a 4996 non-zero "wait" parameter. See weight_single 4997 and weight_many. 4998 4999 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 5000 xtime_lock contention on larger systems, and/or RCU lock 5001 contention on all systems with CONFIG_MAXSMP set. 5002 Format: { "0" | "1" } 5003 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 5004 1 -- enable. 5005 Note: increases power consumption, thus should only be 5006 enabled if running jitter sensitive (HPC/RT) workloads. 5007 5008 security= [SECURITY] Choose a legacy "major" security module to 5009 enable at boot. This has been deprecated by the 5010 "lsm=" parameter. 5011 5012 selinux= [SELINUX] Disable or enable SELinux at boot time. 5013 Format: { "0" | "1" } 5014 See security/selinux/Kconfig help text. 5015 0 -- disable. 5016 1 -- enable. 5017 Default value is 1. 5018 5019 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 5020 Format: { "0" | "1" } 5021 See security/apparmor/Kconfig help text 5022 0 -- disable. 5023 1 -- enable. 5024 Default value is set via kernel config option. 5025 5026 serialnumber [BUGS=X86-32] 5027 5028 shapers= [NET] 5029 Maximal number of shapers. 5030 5031 simeth= [IA-64] 5032 simscsi= 5033 5034 slram= [HW,MTD] 5035 5036 slab_merge [MM] 5037 Enable merging of slabs with similar size when the 5038 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 5039 5040 slab_nomerge [MM] 5041 Disable merging of slabs with similar size. May be 5042 necessary if there is some reason to distinguish 5043 allocs to different slabs, especially in hardened 5044 environments where the risk of heap overflows and 5045 layout control by attackers can usually be 5046 frustrated by disabling merging. This will reduce 5047 most of the exposure of a heap attack to a single 5048 cache (risks via metadata attacks are mostly 5049 unchanged). Debug options disable merging on their 5050 own. 5051 For more information see Documentation/vm/slub.rst. 5052 5053 slab_max_order= [MM, SLAB] 5054 Determines the maximum allowed order for slabs. 5055 A high setting may cause OOMs due to memory 5056 fragmentation. Defaults to 1 for systems with 5057 more than 32MB of RAM, 0 otherwise. 5058 5059 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 5060 Enabling slub_debug allows one to determine the 5061 culprit if slab objects become corrupted. Enabling 5062 slub_debug can create guard zones around objects and 5063 may poison objects when not in use. Also tracks the 5064 last alloc / free. For more information see 5065 Documentation/vm/slub.rst. 5066 5067 slub_max_order= [MM, SLUB] 5068 Determines the maximum allowed order for slabs. 5069 A high setting may cause OOMs due to memory 5070 fragmentation. For more information see 5071 Documentation/vm/slub.rst. 5072 5073 slub_min_objects= [MM, SLUB] 5074 The minimum number of objects per slab. SLUB will 5075 increase the slab order up to slub_max_order to 5076 generate a sufficiently large slab able to contain 5077 the number of objects indicated. The higher the number 5078 of objects the smaller the overhead of tracking slabs 5079 and the less frequently locks need to be acquired. 5080 For more information see Documentation/vm/slub.rst. 5081 5082 slub_min_order= [MM, SLUB] 5083 Determines the minimum page order for slabs. Must be 5084 lower than slub_max_order. 5085 For more information see Documentation/vm/slub.rst. 5086 5087 slub_merge [MM, SLUB] 5088 Same with slab_merge. 5089 5090 slub_nomerge [MM, SLUB] 5091 Same with slab_nomerge. This is supported for legacy. 5092 See slab_nomerge for more information. 5093 5094 smart2= [HW] 5095 Format: <io1>[,<io2>[,...,<io8>]] 5096 5097 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 5098 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 5099 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 5100 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 5101 smsc-ircc2.ircc_irq= [HW] IRQ line 5102 smsc-ircc2.ircc_dma= [HW] DMA channel 5103 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 5104 0: Toshiba Satellite 1800 (GP data pin select) 5105 1: Fast pin select (default) 5106 2: ATC IRMode 5107 5108 smt [KNL,S390] Set the maximum number of threads (logical 5109 CPUs) to use per physical CPU on systems capable of 5110 symmetric multithreading (SMT). Will be capped to the 5111 actual hardware limit. 5112 Format: <integer> 5113 Default: -1 (no limit) 5114 5115 softlockup_panic= 5116 [KNL] Should the soft-lockup detector generate panics. 5117 Format: 0 | 1 5118 5119 A value of 1 instructs the soft-lockup detector 5120 to panic the machine when a soft-lockup occurs. It is 5121 also controlled by the kernel.softlockup_panic sysctl 5122 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 5123 respective build-time switch to that functionality. 5124 5125 softlockup_all_cpu_backtrace= 5126 [KNL] Should the soft-lockup detector generate 5127 backtraces on all cpus. 5128 Format: 0 | 1 5129 5130 sonypi.*= [HW] Sony Programmable I/O Control Device driver 5131 See Documentation/admin-guide/laptops/sonypi.rst 5132 5133 spectre_v2= [X86] Control mitigation of Spectre variant 2 5134 (indirect branch speculation) vulnerability. 5135 The default operation protects the kernel from 5136 user space attacks. 5137 5138 on - unconditionally enable, implies 5139 spectre_v2_user=on 5140 off - unconditionally disable, implies 5141 spectre_v2_user=off 5142 auto - kernel detects whether your CPU model is 5143 vulnerable 5144 5145 Selecting 'on' will, and 'auto' may, choose a 5146 mitigation method at run time according to the 5147 CPU, the available microcode, the setting of the 5148 CONFIG_RETPOLINE configuration option, and the 5149 compiler with which the kernel was built. 5150 5151 Selecting 'on' will also enable the mitigation 5152 against user space to user space task attacks. 5153 5154 Selecting 'off' will disable both the kernel and 5155 the user space protections. 5156 5157 Specific mitigations can also be selected manually: 5158 5159 retpoline - replace indirect branches 5160 retpoline,generic - google's original retpoline 5161 retpoline,amd - AMD-specific minimal thunk 5162 5163 Not specifying this option is equivalent to 5164 spectre_v2=auto. 5165 5166 spectre_v2_user= 5167 [X86] Control mitigation of Spectre variant 2 5168 (indirect branch speculation) vulnerability between 5169 user space tasks 5170 5171 on - Unconditionally enable mitigations. Is 5172 enforced by spectre_v2=on 5173 5174 off - Unconditionally disable mitigations. Is 5175 enforced by spectre_v2=off 5176 5177 prctl - Indirect branch speculation is enabled, 5178 but mitigation can be enabled via prctl 5179 per thread. The mitigation control state 5180 is inherited on fork. 5181 5182 prctl,ibpb 5183 - Like "prctl" above, but only STIBP is 5184 controlled per thread. IBPB is issued 5185 always when switching between different user 5186 space processes. 5187 5188 seccomp 5189 - Same as "prctl" above, but all seccomp 5190 threads will enable the mitigation unless 5191 they explicitly opt out. 5192 5193 seccomp,ibpb 5194 - Like "seccomp" above, but only STIBP is 5195 controlled per thread. IBPB is issued 5196 always when switching between different 5197 user space processes. 5198 5199 auto - Kernel selects the mitigation depending on 5200 the available CPU features and vulnerability. 5201 5202 Default mitigation: 5203 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 5204 5205 Not specifying this option is equivalent to 5206 spectre_v2_user=auto. 5207 5208 spec_store_bypass_disable= 5209 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 5210 (Speculative Store Bypass vulnerability) 5211 5212 Certain CPUs are vulnerable to an exploit against a 5213 a common industry wide performance optimization known 5214 as "Speculative Store Bypass" in which recent stores 5215 to the same memory location may not be observed by 5216 later loads during speculative execution. The idea 5217 is that such stores are unlikely and that they can 5218 be detected prior to instruction retirement at the 5219 end of a particular speculation execution window. 5220 5221 In vulnerable processors, the speculatively forwarded 5222 store can be used in a cache side channel attack, for 5223 example to read memory to which the attacker does not 5224 directly have access (e.g. inside sandboxed code). 5225 5226 This parameter controls whether the Speculative Store 5227 Bypass optimization is used. 5228 5229 On x86 the options are: 5230 5231 on - Unconditionally disable Speculative Store Bypass 5232 off - Unconditionally enable Speculative Store Bypass 5233 auto - Kernel detects whether the CPU model contains an 5234 implementation of Speculative Store Bypass and 5235 picks the most appropriate mitigation. If the 5236 CPU is not vulnerable, "off" is selected. If the 5237 CPU is vulnerable the default mitigation is 5238 architecture and Kconfig dependent. See below. 5239 prctl - Control Speculative Store Bypass per thread 5240 via prctl. Speculative Store Bypass is enabled 5241 for a process by default. The state of the control 5242 is inherited on fork. 5243 seccomp - Same as "prctl" above, but all seccomp threads 5244 will disable SSB unless they explicitly opt out. 5245 5246 Default mitigations: 5247 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 5248 5249 On powerpc the options are: 5250 5251 on,auto - On Power8 and Power9 insert a store-forwarding 5252 barrier on kernel entry and exit. On Power7 5253 perform a software flush on kernel entry and 5254 exit. 5255 off - No action. 5256 5257 Not specifying this option is equivalent to 5258 spec_store_bypass_disable=auto. 5259 5260 spia_io_base= [HW,MTD] 5261 spia_fio_base= 5262 spia_pedr= 5263 spia_peddr= 5264 5265 split_lock_detect= 5266 [X86] Enable split lock detection or bus lock detection 5267 5268 When enabled (and if hardware support is present), atomic 5269 instructions that access data across cache line 5270 boundaries will result in an alignment check exception 5271 for split lock detection or a debug exception for 5272 bus lock detection. 5273 5274 off - not enabled 5275 5276 warn - the kernel will emit rate-limited warnings 5277 about applications triggering the #AC 5278 exception or the #DB exception. This mode is 5279 the default on CPUs that support split lock 5280 detection or bus lock detection. Default 5281 behavior is by #AC if both features are 5282 enabled in hardware. 5283 5284 fatal - the kernel will send SIGBUS to applications 5285 that trigger the #AC exception or the #DB 5286 exception. Default behavior is by #AC if 5287 both features are enabled in hardware. 5288 5289 If an #AC exception is hit in the kernel or in 5290 firmware (i.e. not while executing in user mode) 5291 the kernel will oops in either "warn" or "fatal" 5292 mode. 5293 5294 #DB exception for bus lock is triggered only when 5295 CPL > 0. 5296 5297 srbds= [X86,INTEL] 5298 Control the Special Register Buffer Data Sampling 5299 (SRBDS) mitigation. 5300 5301 Certain CPUs are vulnerable to an MDS-like 5302 exploit which can leak bits from the random 5303 number generator. 5304 5305 By default, this issue is mitigated by 5306 microcode. However, the microcode fix can cause 5307 the RDRAND and RDSEED instructions to become 5308 much slower. Among other effects, this will 5309 result in reduced throughput from /dev/urandom. 5310 5311 The microcode mitigation can be disabled with 5312 the following option: 5313 5314 off: Disable mitigation and remove 5315 performance impact to RDRAND and RDSEED 5316 5317 srcutree.counter_wrap_check [KNL] 5318 Specifies how frequently to check for 5319 grace-period sequence counter wrap for the 5320 srcu_data structure's ->srcu_gp_seq_needed field. 5321 The greater the number of bits set in this kernel 5322 parameter, the less frequently counter wrap will 5323 be checked for. Note that the bottom two bits 5324 are ignored. 5325 5326 srcutree.exp_holdoff [KNL] 5327 Specifies how many nanoseconds must elapse 5328 since the end of the last SRCU grace period for 5329 a given srcu_struct until the next normal SRCU 5330 grace period will be considered for automatic 5331 expediting. Set to zero to disable automatic 5332 expediting. 5333 5334 ssbd= [ARM64,HW] 5335 Speculative Store Bypass Disable control 5336 5337 On CPUs that are vulnerable to the Speculative 5338 Store Bypass vulnerability and offer a 5339 firmware based mitigation, this parameter 5340 indicates how the mitigation should be used: 5341 5342 force-on: Unconditionally enable mitigation for 5343 for both kernel and userspace 5344 force-off: Unconditionally disable mitigation for 5345 for both kernel and userspace 5346 kernel: Always enable mitigation in the 5347 kernel, and offer a prctl interface 5348 to allow userspace to register its 5349 interest in being mitigated too. 5350 5351 stack_guard_gap= [MM] 5352 override the default stack gap protection. The value 5353 is in page units and it defines how many pages prior 5354 to (for stacks growing down) resp. after (for stacks 5355 growing up) the main stack are reserved for no other 5356 mapping. Default value is 256 pages. 5357 5358 stack_depot_disable= [KNL] 5359 Setting this to true through kernel command line will 5360 disable the stack depot thereby saving the static memory 5361 consumed by the stack hash table. By default this is set 5362 to false. 5363 5364 stacktrace [FTRACE] 5365 Enabled the stack tracer on boot up. 5366 5367 stacktrace_filter=[function-list] 5368 [FTRACE] Limit the functions that the stack tracer 5369 will trace at boot up. function-list is a comma-separated 5370 list of functions. This list can be changed at run 5371 time by the stack_trace_filter file in the debugfs 5372 tracing directory. Note, this enables stack tracing 5373 and the stacktrace above is not needed. 5374 5375 sti= [PARISC,HW] 5376 Format: <num> 5377 Set the STI (builtin display/keyboard on the HP-PARISC 5378 machines) console (graphic card) which should be used 5379 as the initial boot-console. 5380 See also comment in drivers/video/console/sticore.c. 5381 5382 sti_font= [HW] 5383 See comment in drivers/video/console/sticore.c. 5384 5385 stifb= [HW] 5386 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5387 5388 sunrpc.min_resvport= 5389 sunrpc.max_resvport= 5390 [NFS,SUNRPC] 5391 SunRPC servers often require that client requests 5392 originate from a privileged port (i.e. a port in the 5393 range 0 < portnr < 1024). 5394 An administrator who wishes to reserve some of these 5395 ports for other uses may adjust the range that the 5396 kernel's sunrpc client considers to be privileged 5397 using these two parameters to set the minimum and 5398 maximum port values. 5399 5400 sunrpc.svc_rpc_per_connection_limit= 5401 [NFS,SUNRPC] 5402 Limit the number of requests that the server will 5403 process in parallel from a single connection. 5404 The default value is 0 (no limit). 5405 5406 sunrpc.pool_mode= 5407 [NFS] 5408 Control how the NFS server code allocates CPUs to 5409 service thread pools. Depending on how many NICs 5410 you have and where their interrupts are bound, this 5411 option will affect which CPUs will do NFS serving. 5412 Note: this parameter cannot be changed while the 5413 NFS server is running. 5414 5415 auto the server chooses an appropriate mode 5416 automatically using heuristics 5417 global a single global pool contains all CPUs 5418 percpu one pool for each CPU 5419 pernode one pool for each NUMA node (equivalent 5420 to global on non-NUMA machines) 5421 5422 sunrpc.tcp_slot_table_entries= 5423 sunrpc.udp_slot_table_entries= 5424 [NFS,SUNRPC] 5425 Sets the upper limit on the number of simultaneous 5426 RPC calls that can be sent from the client to a 5427 server. Increasing these values may allow you to 5428 improve throughput, but will also increase the 5429 amount of memory reserved for use by the client. 5430 5431 suspend.pm_test_delay= 5432 [SUSPEND] 5433 Sets the number of seconds to remain in a suspend test 5434 mode before resuming the system (see 5435 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5436 is set. Default value is 5. 5437 5438 svm= [PPC] 5439 Format: { on | off | y | n | 1 | 0 } 5440 This parameter controls use of the Protected 5441 Execution Facility on pSeries. 5442 5443 swapaccount=[0|1] 5444 [KNL] Enable accounting of swap in memory resource 5445 controller if no parameter or 1 is given or disable 5446 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5447 5448 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5449 Format: { <int> | force | noforce } 5450 <int> -- Number of I/O TLB slabs 5451 force -- force using of bounce buffers even if they 5452 wouldn't be automatically used by the kernel 5453 noforce -- Never use bounce buffers (for debugging) 5454 5455 switches= [HW,M68k] 5456 5457 sysctl.*= [KNL] 5458 Set a sysctl parameter, right before loading the init 5459 process, as if the value was written to the respective 5460 /proc/sys/... file. Both '.' and '/' are recognized as 5461 separators. Unrecognized parameters and invalid values 5462 are reported in the kernel log. Sysctls registered 5463 later by a loaded module cannot be set this way. 5464 Example: sysctl.vm.swappiness=40 5465 5466 sysfs.deprecated=0|1 [KNL] 5467 Enable/disable old style sysfs layout for old udev 5468 on older distributions. When this option is enabled 5469 very new udev will not work anymore. When this option 5470 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5471 in older udev will not work anymore. 5472 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5473 the kernel configuration. 5474 5475 sysrq_always_enabled 5476 [KNL] 5477 Ignore sysrq setting - this boot parameter will 5478 neutralize any effect of /proc/sys/kernel/sysrq. 5479 Useful for debugging. 5480 5481 tcpmhash_entries= [KNL,NET] 5482 Set the number of tcp_metrics_hash slots. 5483 Default value is 8192 or 16384 depending on total 5484 ram pages. This is used to specify the TCP metrics 5485 cache size. See Documentation/networking/ip-sysctl.rst 5486 "tcp_no_metrics_save" section for more details. 5487 5488 tdfx= [HW,DRM] 5489 5490 test_suspend= [SUSPEND][,N] 5491 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5492 standby suspend) or "freeze" (for suspend type freeze) 5493 as the system sleep state during system startup with 5494 the optional capability to repeat N number of times. 5495 The system is woken from this state using a 5496 wakeup-capable RTC alarm. 5497 5498 thash_entries= [KNL,NET] 5499 Set number of hash buckets for TCP connection 5500 5501 thermal.act= [HW,ACPI] 5502 -1: disable all active trip points in all thermal zones 5503 <degrees C>: override all lowest active trip points 5504 5505 thermal.crt= [HW,ACPI] 5506 -1: disable all critical trip points in all thermal zones 5507 <degrees C>: override all critical trip points 5508 5509 thermal.nocrt= [HW,ACPI] 5510 Set to disable actions on ACPI thermal zone 5511 critical and hot trip points. 5512 5513 thermal.off= [HW,ACPI] 5514 1: disable ACPI thermal control 5515 5516 thermal.psv= [HW,ACPI] 5517 -1: disable all passive trip points 5518 <degrees C>: override all passive trip points to this 5519 value 5520 5521 thermal.tzp= [HW,ACPI] 5522 Specify global default ACPI thermal zone polling rate 5523 <deci-seconds>: poll all this frequency 5524 0: no polling (default) 5525 5526 threadirqs [KNL] 5527 Force threading of all interrupt handlers except those 5528 marked explicitly IRQF_NO_THREAD. 5529 5530 topology= [S390] 5531 Format: {off | on} 5532 Specify if the kernel should make use of the cpu 5533 topology information if the hardware supports this. 5534 The scheduler will make use of this information and 5535 e.g. base its process migration decisions on it. 5536 Default is on. 5537 5538 topology_updates= [KNL, PPC, NUMA] 5539 Format: {off} 5540 Specify if the kernel should ignore (off) 5541 topology updates sent by the hypervisor to this 5542 LPAR. 5543 5544 torture.disable_onoff_at_boot= [KNL] 5545 Prevent the CPU-hotplug component of torturing 5546 until after init has spawned. 5547 5548 torture.ftrace_dump_at_shutdown= [KNL] 5549 Dump the ftrace buffer at torture-test shutdown, 5550 even if there were no errors. This can be a 5551 very costly operation when many torture tests 5552 are running concurrently, especially on systems 5553 with rotating-rust storage. 5554 5555 torture.verbose_sleep_frequency= [KNL] 5556 Specifies how many verbose printk()s should be 5557 emitted between each sleep. The default of zero 5558 disables verbose-printk() sleeping. 5559 5560 torture.verbose_sleep_duration= [KNL] 5561 Duration of each verbose-printk() sleep in jiffies. 5562 5563 tp720= [HW,PS2] 5564 5565 tpm_suspend_pcr=[HW,TPM] 5566 Format: integer pcr id 5567 Specify that at suspend time, the tpm driver 5568 should extend the specified pcr with zeros, 5569 as a workaround for some chips which fail to 5570 flush the last written pcr on TPM_SaveState. 5571 This will guarantee that all the other pcrs 5572 are saved. 5573 5574 trace_buf_size=nn[KMG] 5575 [FTRACE] will set tracing buffer size on each cpu. 5576 5577 trace_event=[event-list] 5578 [FTRACE] Set and start specified trace events in order 5579 to facilitate early boot debugging. The event-list is a 5580 comma-separated list of trace events to enable. See 5581 also Documentation/trace/events.rst 5582 5583 trace_options=[option-list] 5584 [FTRACE] Enable or disable tracer options at boot. 5585 The option-list is a comma delimited list of options 5586 that can be enabled or disabled just as if you were 5587 to echo the option name into 5588 5589 /sys/kernel/debug/tracing/trace_options 5590 5591 For example, to enable stacktrace option (to dump the 5592 stack trace of each event), add to the command line: 5593 5594 trace_options=stacktrace 5595 5596 See also Documentation/trace/ftrace.rst "trace options" 5597 section. 5598 5599 tp_printk[FTRACE] 5600 Have the tracepoints sent to printk as well as the 5601 tracing ring buffer. This is useful for early boot up 5602 where the system hangs or reboots and does not give the 5603 option for reading the tracing buffer or performing a 5604 ftrace_dump_on_oops. 5605 5606 To turn off having tracepoints sent to printk, 5607 echo 0 > /proc/sys/kernel/tracepoint_printk 5608 Note, echoing 1 into this file without the 5609 tracepoint_printk kernel cmdline option has no effect. 5610 5611 ** CAUTION ** 5612 5613 Having tracepoints sent to printk() and activating high 5614 frequency tracepoints such as irq or sched, can cause 5615 the system to live lock. 5616 5617 traceoff_on_warning 5618 [FTRACE] enable this option to disable tracing when a 5619 warning is hit. This turns off "tracing_on". Tracing can 5620 be enabled again by echoing '1' into the "tracing_on" 5621 file located in /sys/kernel/debug/tracing/ 5622 5623 This option is useful, as it disables the trace before 5624 the WARNING dump is called, which prevents the trace to 5625 be filled with content caused by the warning output. 5626 5627 This option can also be set at run time via the sysctl 5628 option: kernel/traceoff_on_warning 5629 5630 transparent_hugepage= 5631 [KNL] 5632 Format: [always|madvise|never] 5633 Can be used to control the default behavior of the system 5634 with respect to transparent hugepages. 5635 See Documentation/admin-guide/mm/transhuge.rst 5636 for more details. 5637 5638 trusted.source= [KEYS] 5639 Format: <string> 5640 This parameter identifies the trust source as a backend 5641 for trusted keys implementation. Supported trust 5642 sources: 5643 - "tpm" 5644 - "tee" 5645 If not specified then it defaults to iterating through 5646 the trust source list starting with TPM and assigns the 5647 first trust source as a backend which is initialized 5648 successfully during iteration. 5649 5650 tsc= Disable clocksource stability checks for TSC. 5651 Format: <string> 5652 [x86] reliable: mark tsc clocksource as reliable, this 5653 disables clocksource verification at runtime, as well 5654 as the stability checks done at bootup. Used to enable 5655 high-resolution timer mode on older hardware, and in 5656 virtualized environment. 5657 [x86] noirqtime: Do not use TSC to do irq accounting. 5658 Used to run time disable IRQ_TIME_ACCOUNTING on any 5659 platforms where RDTSC is slow and this accounting 5660 can add overhead. 5661 [x86] unstable: mark the TSC clocksource as unstable, this 5662 marks the TSC unconditionally unstable at bootup and 5663 avoids any further wobbles once the TSC watchdog notices. 5664 [x86] nowatchdog: disable clocksource watchdog. Used 5665 in situations with strict latency requirements (where 5666 interruptions from clocksource watchdog are not 5667 acceptable). 5668 5669 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5670 value instead. Useful when the early TSC frequency discovery 5671 procedure is not reliable, such as on overclocked systems 5672 with CPUID.16h support and partial CPUID.15h support. 5673 Format: <unsigned int> 5674 5675 tsx= [X86] Control Transactional Synchronization 5676 Extensions (TSX) feature in Intel processors that 5677 support TSX control. 5678 5679 This parameter controls the TSX feature. The options are: 5680 5681 on - Enable TSX on the system. Although there are 5682 mitigations for all known security vulnerabilities, 5683 TSX has been known to be an accelerator for 5684 several previous speculation-related CVEs, and 5685 so there may be unknown security risks associated 5686 with leaving it enabled. 5687 5688 off - Disable TSX on the system. (Note that this 5689 option takes effect only on newer CPUs which are 5690 not vulnerable to MDS, i.e., have 5691 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5692 the new IA32_TSX_CTRL MSR through a microcode 5693 update. This new MSR allows for the reliable 5694 deactivation of the TSX functionality.) 5695 5696 auto - Disable TSX if X86_BUG_TAA is present, 5697 otherwise enable TSX on the system. 5698 5699 Not specifying this option is equivalent to tsx=off. 5700 5701 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5702 for more details. 5703 5704 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5705 Abort (TAA) vulnerability. 5706 5707 Similar to Micro-architectural Data Sampling (MDS) 5708 certain CPUs that support Transactional 5709 Synchronization Extensions (TSX) are vulnerable to an 5710 exploit against CPU internal buffers which can forward 5711 information to a disclosure gadget under certain 5712 conditions. 5713 5714 In vulnerable processors, the speculatively forwarded 5715 data can be used in a cache side channel attack, to 5716 access data to which the attacker does not have direct 5717 access. 5718 5719 This parameter controls the TAA mitigation. The 5720 options are: 5721 5722 full - Enable TAA mitigation on vulnerable CPUs 5723 if TSX is enabled. 5724 5725 full,nosmt - Enable TAA mitigation and disable SMT on 5726 vulnerable CPUs. If TSX is disabled, SMT 5727 is not disabled because CPU is not 5728 vulnerable to cross-thread TAA attacks. 5729 off - Unconditionally disable TAA mitigation 5730 5731 On MDS-affected machines, tsx_async_abort=off can be 5732 prevented by an active MDS mitigation as both vulnerabilities 5733 are mitigated with the same mechanism so in order to disable 5734 this mitigation, you need to specify mds=off too. 5735 5736 Not specifying this option is equivalent to 5737 tsx_async_abort=full. On CPUs which are MDS affected 5738 and deploy MDS mitigation, TAA mitigation is not 5739 required and doesn't provide any additional 5740 mitigation. 5741 5742 For details see: 5743 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5744 5745 turbografx.map[2|3]= [HW,JOY] 5746 TurboGraFX parallel port interface 5747 Format: 5748 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5749 See also Documentation/input/devices/joystick-parport.rst 5750 5751 udbg-immortal [PPC] When debugging early kernel crashes that 5752 happen after console_init() and before a proper 5753 console driver takes over, this boot options might 5754 help "seeing" what's going on. 5755 5756 uhash_entries= [KNL,NET] 5757 Set number of hash buckets for UDP/UDP-Lite connections 5758 5759 uhci-hcd.ignore_oc= 5760 [USB] Ignore overcurrent events (default N). 5761 Some badly-designed motherboards generate lots of 5762 bogus events, for ports that aren't wired to 5763 anything. Set this parameter to avoid log spamming. 5764 Note that genuine overcurrent events won't be 5765 reported either. 5766 5767 unknown_nmi_panic 5768 [X86] Cause panic on unknown NMI. 5769 5770 usbcore.authorized_default= 5771 [USB] Default USB device authorization: 5772 (default -1 = authorized except for wireless USB, 5773 0 = not authorized, 1 = authorized, 2 = authorized 5774 if device connected to internal port) 5775 5776 usbcore.autosuspend= 5777 [USB] The autosuspend time delay (in seconds) used 5778 for newly-detected USB devices (default 2). This 5779 is the time required before an idle device will be 5780 autosuspended. Devices for which the delay is set 5781 to a negative value won't be autosuspended at all. 5782 5783 usbcore.usbfs_snoop= 5784 [USB] Set to log all usbfs traffic (default 0 = off). 5785 5786 usbcore.usbfs_snoop_max= 5787 [USB] Maximum number of bytes to snoop in each URB 5788 (default = 65536). 5789 5790 usbcore.blinkenlights= 5791 [USB] Set to cycle leds on hubs (default 0 = off). 5792 5793 usbcore.old_scheme_first= 5794 [USB] Start with the old device initialization 5795 scheme (default 0 = off). 5796 5797 usbcore.usbfs_memory_mb= 5798 [USB] Memory limit (in MB) for buffers allocated by 5799 usbfs (default = 16, 0 = max = 2047). 5800 5801 usbcore.use_both_schemes= 5802 [USB] Try the other device initialization scheme 5803 if the first one fails (default 1 = enabled). 5804 5805 usbcore.initial_descriptor_timeout= 5806 [USB] Specifies timeout for the initial 64-byte 5807 USB_REQ_GET_DESCRIPTOR request in milliseconds 5808 (default 5000 = 5.0 seconds). 5809 5810 usbcore.nousb [USB] Disable the USB subsystem 5811 5812 usbcore.quirks= 5813 [USB] A list of quirk entries to augment the built-in 5814 usb core quirk list. List entries are separated by 5815 commas. Each entry has the form 5816 VendorID:ProductID:Flags. The IDs are 4-digit hex 5817 numbers and Flags is a set of letters. Each letter 5818 will change the built-in quirk; setting it if it is 5819 clear and clearing it if it is set. The letters have 5820 the following meanings: 5821 a = USB_QUIRK_STRING_FETCH_255 (string 5822 descriptors must not be fetched using 5823 a 255-byte read); 5824 b = USB_QUIRK_RESET_RESUME (device can't resume 5825 correctly so reset it instead); 5826 c = USB_QUIRK_NO_SET_INTF (device can't handle 5827 Set-Interface requests); 5828 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5829 handle its Configuration or Interface 5830 strings); 5831 e = USB_QUIRK_RESET (device can't be reset 5832 (e.g morph devices), don't use reset); 5833 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5834 more interface descriptions than the 5835 bNumInterfaces count, and can't handle 5836 talking to these interfaces); 5837 g = USB_QUIRK_DELAY_INIT (device needs a pause 5838 during initialization, after we read 5839 the device descriptor); 5840 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5841 high speed and super speed interrupt 5842 endpoints, the USB 2.0 and USB 3.0 spec 5843 require the interval in microframes (1 5844 microframe = 125 microseconds) to be 5845 calculated as interval = 2 ^ 5846 (bInterval-1). 5847 Devices with this quirk report their 5848 bInterval as the result of this 5849 calculation instead of the exponent 5850 variable used in the calculation); 5851 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5852 handle device_qualifier descriptor 5853 requests); 5854 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5855 generates spurious wakeup, ignore 5856 remote wakeup capability); 5857 k = USB_QUIRK_NO_LPM (device can't handle Link 5858 Power Management); 5859 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5860 (Device reports its bInterval as linear 5861 frames instead of the USB 2.0 5862 calculation); 5863 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5864 to be disconnected before suspend to 5865 prevent spurious wakeup); 5866 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5867 pause after every control message); 5868 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5869 delay after resetting its port); 5870 Example: quirks=0781:5580:bk,0a5c:5834:gij 5871 5872 usbhid.mousepoll= 5873 [USBHID] The interval which mice are to be polled at. 5874 5875 usbhid.jspoll= 5876 [USBHID] The interval which joysticks are to be polled at. 5877 5878 usbhid.kbpoll= 5879 [USBHID] The interval which keyboards are to be polled at. 5880 5881 usb-storage.delay_use= 5882 [UMS] The delay in seconds before a new device is 5883 scanned for Logical Units (default 1). 5884 5885 usb-storage.quirks= 5886 [UMS] A list of quirks entries to supplement or 5887 override the built-in unusual_devs list. List 5888 entries are separated by commas. Each entry has 5889 the form VID:PID:Flags where VID and PID are Vendor 5890 and Product ID values (4-digit hex numbers) and 5891 Flags is a set of characters, each corresponding 5892 to a common usb-storage quirk flag as follows: 5893 a = SANE_SENSE (collect more than 18 bytes 5894 of sense data, not on uas); 5895 b = BAD_SENSE (don't collect more than 18 5896 bytes of sense data, not on uas); 5897 c = FIX_CAPACITY (decrease the reported 5898 device capacity by one sector); 5899 d = NO_READ_DISC_INFO (don't use 5900 READ_DISC_INFO command, not on uas); 5901 e = NO_READ_CAPACITY_16 (don't use 5902 READ_CAPACITY_16 command); 5903 f = NO_REPORT_OPCODES (don't use report opcodes 5904 command, uas only); 5905 g = MAX_SECTORS_240 (don't transfer more than 5906 240 sectors at a time, uas only); 5907 h = CAPACITY_HEURISTICS (decrease the 5908 reported device capacity by one 5909 sector if the number is odd); 5910 i = IGNORE_DEVICE (don't bind to this 5911 device); 5912 j = NO_REPORT_LUNS (don't use report luns 5913 command, uas only); 5914 k = NO_SAME (do not use WRITE_SAME, uas only) 5915 l = NOT_LOCKABLE (don't try to lock and 5916 unlock ejectable media, not on uas); 5917 m = MAX_SECTORS_64 (don't transfer more 5918 than 64 sectors = 32 KB at a time, 5919 not on uas); 5920 n = INITIAL_READ10 (force a retry of the 5921 initial READ(10) command, not on uas); 5922 o = CAPACITY_OK (accept the capacity 5923 reported by the device, not on uas); 5924 p = WRITE_CACHE (the device cache is ON 5925 by default, not on uas); 5926 r = IGNORE_RESIDUE (the device reports 5927 bogus residue values, not on uas); 5928 s = SINGLE_LUN (the device has only one 5929 Logical Unit); 5930 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5931 commands, uas only); 5932 u = IGNORE_UAS (don't bind to the uas driver); 5933 w = NO_WP_DETECT (don't test whether the 5934 medium is write-protected). 5935 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5936 even if the device claims no cache, 5937 not on uas) 5938 Example: quirks=0419:aaf5:rl,0421:0433:rc 5939 5940 user_debug= [KNL,ARM] 5941 Format: <int> 5942 See arch/arm/Kconfig.debug help text. 5943 1 - undefined instruction events 5944 2 - system calls 5945 4 - invalid data aborts 5946 8 - SIGSEGV faults 5947 16 - SIGBUS faults 5948 Example: user_debug=31 5949 5950 userpte= 5951 [X86] Flags controlling user PTE allocations. 5952 5953 nohigh = do not allocate PTE pages in 5954 HIGHMEM regardless of setting 5955 of CONFIG_HIGHPTE. 5956 5957 vdso= [X86,SH] 5958 On X86_32, this is an alias for vdso32=. Otherwise: 5959 5960 vdso=1: enable VDSO (the default) 5961 vdso=0: disable VDSO mapping 5962 5963 vdso32= [X86] Control the 32-bit vDSO 5964 vdso32=1: enable 32-bit VDSO 5965 vdso32=0 or vdso32=2: disable 32-bit VDSO 5966 5967 See the help text for CONFIG_COMPAT_VDSO for more 5968 details. If CONFIG_COMPAT_VDSO is set, the default is 5969 vdso32=0; otherwise, the default is vdso32=1. 5970 5971 For compatibility with older kernels, vdso32=2 is an 5972 alias for vdso32=0. 5973 5974 Try vdso32=0 if you encounter an error that says: 5975 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5976 5977 vector= [IA-64,SMP] 5978 vector=percpu: enable percpu vector domain 5979 5980 video= [FB] Frame buffer configuration 5981 See Documentation/fb/modedb.rst. 5982 5983 video.brightness_switch_enabled= [0,1] 5984 If set to 1, on receiving an ACPI notify event 5985 generated by hotkey, video driver will adjust brightness 5986 level and then send out the event to user space through 5987 the allocated input device; If set to 0, video driver 5988 will only send out the event without touching backlight 5989 brightness level. 5990 default: 1 5991 5992 virtio_mmio.device= 5993 [VMMIO] Memory mapped virtio (platform) device. 5994 5995 <size>@<baseaddr>:<irq>[:<id>] 5996 where: 5997 <size> := size (can use standard suffixes 5998 like K, M and G) 5999 <baseaddr> := physical base address 6000 <irq> := interrupt number (as passed to 6001 request_irq()) 6002 <id> := (optional) platform device id 6003 example: 6004 virtio_mmio.device=1K@0x100b0000:48:7 6005 6006 Can be used multiple times for multiple devices. 6007 6008 vga= [BOOT,X86-32] Select a particular video mode 6009 See Documentation/x86/boot.rst and 6010 Documentation/admin-guide/svga.rst. 6011 Use vga=ask for menu. 6012 This is actually a boot loader parameter; the value is 6013 passed to the kernel using a special protocol. 6014 6015 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 6016 May slow down system boot speed, especially when 6017 enabled on systems with a large amount of memory. 6018 All options are enabled by default, and this 6019 interface is meant to allow for selectively 6020 enabling or disabling specific virtual memory 6021 debugging features. 6022 6023 Available options are: 6024 P Enable page structure init time poisoning 6025 - Disable all of the above options 6026 6027 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 6028 size of <nn>. This can be used to increase the 6029 minimum size (128MB on x86). It can also be used to 6030 decrease the size and leave more room for directly 6031 mapped kernel RAM. 6032 6033 vmcp_cma=nn[MG] [KNL,S390] 6034 Sets the memory size reserved for contiguous memory 6035 allocations for the vmcp device driver. 6036 6037 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 6038 Format: <command> 6039 6040 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 6041 Format: <command> 6042 6043 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 6044 Format: <command> 6045 6046 vsyscall= [X86-64] 6047 Controls the behavior of vsyscalls (i.e. calls to 6048 fixed addresses of 0xffffffffff600x00 from legacy 6049 code). Most statically-linked binaries and older 6050 versions of glibc use these calls. Because these 6051 functions are at fixed addresses, they make nice 6052 targets for exploits that can control RIP. 6053 6054 emulate [default] Vsyscalls turn into traps and are 6055 emulated reasonably safely. The vsyscall 6056 page is readable. 6057 6058 xonly Vsyscalls turn into traps and are 6059 emulated reasonably safely. The vsyscall 6060 page is not readable. 6061 6062 none Vsyscalls don't work at all. This makes 6063 them quite hard to use for exploits but 6064 might break your system. 6065 6066 vt.color= [VT] Default text color. 6067 Format: 0xYX, X = foreground, Y = background. 6068 Default: 0x07 = light gray on black. 6069 6070 vt.cur_default= [VT] Default cursor shape. 6071 Format: 0xCCBBAA, where AA, BB, and CC are the same as 6072 the parameters of the <Esc>[?A;B;Cc escape sequence; 6073 see VGA-softcursor.txt. Default: 2 = underline. 6074 6075 vt.default_blu= [VT] 6076 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 6077 Change the default blue palette of the console. 6078 This is a 16-member array composed of values 6079 ranging from 0-255. 6080 6081 vt.default_grn= [VT] 6082 Format: <green0>,<green1>,<green2>,...,<green15> 6083 Change the default green palette of the console. 6084 This is a 16-member array composed of values 6085 ranging from 0-255. 6086 6087 vt.default_red= [VT] 6088 Format: <red0>,<red1>,<red2>,...,<red15> 6089 Change the default red palette of the console. 6090 This is a 16-member array composed of values 6091 ranging from 0-255. 6092 6093 vt.default_utf8= 6094 [VT] 6095 Format=<0|1> 6096 Set system-wide default UTF-8 mode for all tty's. 6097 Default is 1, i.e. UTF-8 mode is enabled for all 6098 newly opened terminals. 6099 6100 vt.global_cursor_default= 6101 [VT] 6102 Format=<-1|0|1> 6103 Set system-wide default for whether a cursor 6104 is shown on new VTs. Default is -1, 6105 i.e. cursors will be created by default unless 6106 overridden by individual drivers. 0 will hide 6107 cursors, 1 will display them. 6108 6109 vt.italic= [VT] Default color for italic text; 0-15. 6110 Default: 2 = green. 6111 6112 vt.underline= [VT] Default color for underlined text; 0-15. 6113 Default: 3 = cyan. 6114 6115 watchdog timers [HW,WDT] For information on watchdog timers, 6116 see Documentation/watchdog/watchdog-parameters.rst 6117 or other driver-specific files in the 6118 Documentation/watchdog/ directory. 6119 6120 watchdog_thresh= 6121 [KNL] 6122 Set the hard lockup detector stall duration 6123 threshold in seconds. The soft lockup detector 6124 threshold is set to twice the value. A value of 0 6125 disables both lockup detectors. Default is 10 6126 seconds. 6127 6128 workqueue.watchdog_thresh= 6129 If CONFIG_WQ_WATCHDOG is configured, workqueue can 6130 warn stall conditions and dump internal state to 6131 help debugging. 0 disables workqueue stall 6132 detection; otherwise, it's the stall threshold 6133 duration in seconds. The default value is 30 and 6134 it can be updated at runtime by writing to the 6135 corresponding sysfs file. 6136 6137 workqueue.disable_numa 6138 By default, all work items queued to unbound 6139 workqueues are affine to the NUMA nodes they're 6140 issued on, which results in better behavior in 6141 general. If NUMA affinity needs to be disabled for 6142 whatever reason, this option can be used. Note 6143 that this also can be controlled per-workqueue for 6144 workqueues visible under /sys/bus/workqueue/. 6145 6146 workqueue.power_efficient 6147 Per-cpu workqueues are generally preferred because 6148 they show better performance thanks to cache 6149 locality; unfortunately, per-cpu workqueues tend to 6150 be more power hungry than unbound workqueues. 6151 6152 Enabling this makes the per-cpu workqueues which 6153 were observed to contribute significantly to power 6154 consumption unbound, leading to measurably lower 6155 power usage at the cost of small performance 6156 overhead. 6157 6158 The default value of this parameter is determined by 6159 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 6160 6161 workqueue.debug_force_rr_cpu 6162 Workqueue used to implicitly guarantee that work 6163 items queued without explicit CPU specified are put 6164 on the local CPU. This guarantee is no longer true 6165 and while local CPU is still preferred work items 6166 may be put on foreign CPUs. This debug option 6167 forces round-robin CPU selection to flush out 6168 usages which depend on the now broken guarantee. 6169 When enabled, memory and cache locality will be 6170 impacted. 6171 6172 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 6173 default x2apic cluster mode on platforms 6174 supporting x2apic. 6175 6176 xen_512gb_limit [KNL,X86-64,XEN] 6177 Restricts the kernel running paravirtualized under Xen 6178 to use only up to 512 GB of RAM. The reason to do so is 6179 crash analysis tools and Xen tools for doing domain 6180 save/restore/migration must be enabled to handle larger 6181 domains. 6182 6183 xen_emul_unplug= [HW,X86,XEN] 6184 Unplug Xen emulated devices 6185 Format: [unplug0,][unplug1] 6186 ide-disks -- unplug primary master IDE devices 6187 aux-ide-disks -- unplug non-primary-master IDE devices 6188 nics -- unplug network devices 6189 all -- unplug all emulated devices (NICs and IDE disks) 6190 unnecessary -- unplugging emulated devices is 6191 unnecessary even if the host did not respond to 6192 the unplug protocol 6193 never -- do not unplug even if version check succeeds 6194 6195 xen_legacy_crash [X86,XEN] 6196 Crash from Xen panic notifier, without executing late 6197 panic() code such as dumping handler. 6198 6199 xen_nopvspin [X86,XEN] 6200 Disables the qspinlock slowpath using Xen PV optimizations. 6201 This parameter is obsoleted by "nopvspin" parameter, which 6202 has equivalent effect for XEN platform. 6203 6204 xen_nopv [X86] 6205 Disables the PV optimizations forcing the HVM guest to 6206 run as generic HVM guest with no PV drivers. 6207 This option is obsoleted by the "nopv" option, which 6208 has equivalent effect for XEN platform. 6209 6210 xen_no_vector_callback 6211 [KNL,X86,XEN] Disable the vector callback for Xen 6212 event channel interrupts. 6213 6214 xen_scrub_pages= [XEN] 6215 Boolean option to control scrubbing pages before giving them back 6216 to Xen, for use by other domains. Can be also changed at runtime 6217 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 6218 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 6219 6220 xen_timer_slop= [X86-64,XEN] 6221 Set the timer slop (in nanoseconds) for the virtual Xen 6222 timers (default is 100000). This adjusts the minimum 6223 delta of virtualized Xen timers, where lower values 6224 improve timer resolution at the expense of processing 6225 more timer interrupts. 6226 6227 xen.event_eoi_delay= [XEN] 6228 How long to delay EOI handling in case of event 6229 storms (jiffies). Default is 10. 6230 6231 xen.event_loop_timeout= [XEN] 6232 After which time (jiffies) the event handling loop 6233 should start to delay EOI handling. Default is 2. 6234 6235 xen.fifo_events= [XEN] 6236 Boolean parameter to disable using fifo event handling 6237 even if available. Normally fifo event handling is 6238 preferred over the 2-level event handling, as it is 6239 fairer and the number of possible event channels is 6240 much higher. Default is on (use fifo events). 6241 6242 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 6243 Disables the PV optimizations forcing the guest to run 6244 as generic guest with no PV drivers. Currently support 6245 XEN HVM, KVM, HYPER_V and VMWARE guest. 6246 6247 nopvspin [X86,XEN,KVM] 6248 Disables the qspinlock slow path using PV optimizations 6249 which allow the hypervisor to 'idle' the guest on lock 6250 contention. 6251 6252 xirc2ps_cs= [NET,PCMCIA] 6253 Format: 6254 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 6255 6256 xive= [PPC] 6257 By default on POWER9 and above, the kernel will 6258 natively use the XIVE interrupt controller. This option 6259 allows the fallback firmware mode to be used: 6260 6261 off Fallback to firmware control of XIVE interrupt 6262 controller on both pseries and powernv 6263 platforms. Only useful on POWER9 and above. 6264 6265 xhci-hcd.quirks [USB,KNL] 6266 A hex value specifying bitmask with supplemental xhci 6267 host controller quirks. Meaning of each bit can be 6268 consulted in header drivers/usb/host/xhci.h. 6269 6270 xmon [PPC] 6271 Format: { early | on | rw | ro | off } 6272 Controls if xmon debugger is enabled. Default is off. 6273 Passing only "xmon" is equivalent to "xmon=early". 6274 early Call xmon as early as possible on boot; xmon 6275 debugger is called from setup_arch(). 6276 on xmon debugger hooks will be installed so xmon 6277 is only called on a kernel crash. Default mode, 6278 i.e. either "ro" or "rw" mode, is controlled 6279 with CONFIG_XMON_DEFAULT_RO_MODE. 6280 rw xmon debugger hooks will be installed so xmon 6281 is called only on a kernel crash, mode is write, 6282 meaning SPR registers, memory and, other data 6283 can be written using xmon commands. 6284 ro same as "rw" option above but SPR registers, 6285 memory, and other data can't be written using 6286 xmon commands. 6287 off xmon is disabled. 6288