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.txt, 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 acpi_backlight=vendor 26 acpi_backlight=video 27 If set to vendor, prefer vendor specific driver 28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 29 of the ACPI video.ko driver. 30 31 acpi_force_32bit_fadt_addr 32 force FADT to use 32 bit addresses rather than the 33 64 bit X_* addresses. Some firmware have broken 64 34 bit addresses for force ACPI ignore these and use 35 the older legacy 32 bit addresses. 36 37 acpica_no_return_repair [HW, ACPI] 38 Disable AML predefined validation mechanism 39 This mechanism can repair the evaluation result to make 40 the return objects more ACPI specification compliant. 41 This option is useful for developers to identify the 42 root cause of an AML interpreter issue when the issue 43 has something to do with the repair mechanism. 44 45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 47 Format: <int> 48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 49 debug output. Bits in debug_layer correspond to a 50 _COMPONENT in an ACPI source file, e.g., 51 #define _COMPONENT ACPI_PCI_COMPONENT 52 Bits in debug_level correspond to a level in 53 ACPI_DEBUG_PRINT statements, e.g., 54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 55 The debug_level mask defaults to "info". See 56 Documentation/acpi/debug.txt for more information about 57 debug layers and levels. 58 59 Enable processor driver info messages: 60 acpi.debug_layer=0x20000000 61 Enable PCI/PCI interrupt routing info messages: 62 acpi.debug_layer=0x400000 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: <int> 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_rsdp= [ACPI,EFI,KEXEC] 140 Pass the RSDP address to the kernel, mostly used 141 on machines running EFI runtime service to boot the 142 second kernel for kdump. 143 144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 145 Format: To spoof as Windows 98: ="Microsoft Windows" 146 147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 148 of 2 which is mandated by ACPI 6) as the supported ACPI 149 specification revision (when using this switch, it may 150 be necessary to carry out a cold reboot _twice_ in a 151 row to make it take effect on the platform firmware). 152 153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 154 acpi_osi="string1" # add string1 155 acpi_osi="!string2" # remove string2 156 acpi_osi=!* # remove all strings 157 acpi_osi=! # disable all built-in OS vendor 158 strings 159 acpi_osi=!! # enable all built-in OS vendor 160 strings 161 acpi_osi= # disable all strings 162 163 'acpi_osi=!' can be used in combination with single or 164 multiple 'acpi_osi="string1"' to support specific OS 165 vendor string(s). Note that such command can only 166 affect the default state of the OS vendor strings, thus 167 it cannot affect the default state of the feature group 168 strings and the current state of the OS vendor strings, 169 specifying it multiple times through kernel command line 170 is meaningless. This command is useful when one do not 171 care about the state of the feature group strings which 172 should be controlled by the OSPM. 173 Examples: 174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 176 can make '_OSI("Windows 2000")' TRUE. 177 178 'acpi_osi=' cannot be used in combination with other 179 'acpi_osi=' command lines, the _OSI method will not 180 exist in the ACPI namespace. NOTE that such command can 181 only affect the _OSI support state, thus specifying it 182 multiple times through kernel command line is also 183 meaningless. 184 Examples: 185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 186 FALSE. 187 188 'acpi_osi=!*' can be used in combination with single or 189 multiple 'acpi_osi="string1"' to support specific 190 string(s). Note that such command can affect the 191 current state of both the OS vendor strings and the 192 feature group strings, thus specifying it multiple times 193 through kernel command line is meaningful. But it may 194 still not able to affect the final state of a string if 195 there are quirks related to this string. This command 196 is useful when one want to control the state of the 197 feature group strings to debug BIOS issues related to 198 the OSPM features. 199 Examples: 200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 201 '_OSI("Module Device")' FALSE. 202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 203 '_OSI("Module Device")' TRUE. 204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 205 equivalent to 206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 207 and 208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 209 they all will make '_OSI("Windows 2000")' TRUE. 210 211 acpi_pm_good [X86] 212 Override the pmtimer bug detection: force the kernel 213 to assume that this machine's pmtimer latches its value 214 and always returns good values. 215 216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 217 Format: { level | edge | high | low } 218 219 acpi_skip_timer_override [HW,ACPI] 220 Recognize and ignore IRQ0/pin2 Interrupt Override. 221 For broken nForce2 BIOS resulting in XT-PIC timer. 222 223 acpi_sleep= [HW,ACPI] Sleep options 224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 225 old_ordering, nonvs, sci_force_enable, nobl } 226 See Documentation/power/video.txt for information on 227 s3_bios and s3_mode. 228 s3_beep is for debugging; it makes the PC's speaker beep 229 as soon as the kernel's real-mode entry point is called. 230 s4_nohwsig prevents ACPI hardware signature from being 231 used during resume from hibernation. 232 old_ordering causes the ACPI 1.0 ordering of the _PTS 233 control method, with respect to putting devices into 234 low power states, to be enforced (the ACPI 2.0 ordering 235 of _PTS is used by default). 236 nonvs prevents the kernel from saving/restoring the 237 ACPI NVS memory during suspend/hibernation and resume. 238 sci_force_enable causes the kernel to set SCI_EN directly 239 on resume from S1/S3 (which is against the ACPI spec, 240 but some broken systems don't work without it). 241 nobl causes the internal blacklist of systems known to 242 behave incorrectly in some ways with respect to system 243 suspend and resume to be ignored (use wisely). 244 245 acpi_use_timer_override [HW,ACPI] 246 Use timer override. For some broken Nvidia NF5 boards 247 that require a timer override, but don't have HPET 248 249 add_efi_memmap [EFI; X86] Include EFI memory map in 250 kernel's map of available physical RAM. 251 252 agp= [AGP] 253 { off | try_unsupported } 254 off: disable AGP support 255 try_unsupported: try to drive unsupported chipsets 256 (may crash computer or cause data corruption) 257 258 ALSA [HW,ALSA] 259 See Documentation/sound/alsa-configuration.rst 260 261 alignment= [KNL,ARM] 262 Allow the default userspace alignment fault handler 263 behaviour to be specified. Bit 0 enables warnings, 264 bit 1 enables fixups, and bit 2 sends a segfault. 265 266 align_va_addr= [X86-64] 267 Align virtual addresses by clearing slice [14:12] when 268 allocating a VMA at process creation time. This option 269 gives you up to 3% performance improvement on AMD F15h 270 machines (where it is enabled by default) for a 271 CPU-intensive style benchmark, and it can vary highly in 272 a microbenchmark depending on workload and compiler. 273 274 32: only for 32-bit processes 275 64: only for 64-bit processes 276 on: enable for both 32- and 64-bit processes 277 off: disable for both 32- and 64-bit processes 278 279 alloc_snapshot [FTRACE] 280 Allocate the ftrace snapshot buffer on boot up when the 281 main buffer is allocated. This is handy if debugging 282 and you need to use tracing_snapshot() on boot up, and 283 do not want to use tracing_snapshot_alloc() as it needs 284 to be done where GFP_KERNEL allocations are allowed. 285 286 amd_iommu= [HW,X86-64] 287 Pass parameters to the AMD IOMMU driver in the system. 288 Possible values are: 289 fullflush - enable flushing of IO/TLB entries when 290 they are unmapped. Otherwise they are 291 flushed before they will be reused, which 292 is a lot of faster 293 off - do not initialize any AMD IOMMU found in 294 the system 295 force_isolation - Force device isolation for all 296 devices. The IOMMU driver is not 297 allowed anymore to lift isolation 298 requirements as needed. This option 299 does not override iommu=pt 300 301 amd_iommu_dump= [HW,X86-64] 302 Enable AMD IOMMU driver option to dump the ACPI table 303 for AMD IOMMU. With this option enabled, AMD IOMMU 304 driver will print ACPI tables for AMD IOMMU during 305 IOMMU initialization. 306 307 amd_iommu_intr= [HW,X86-64] 308 Specifies one of the following AMD IOMMU interrupt 309 remapping modes: 310 legacy - Use legacy interrupt remapping mode. 311 vapic - Use virtual APIC mode, which allows IOMMU 312 to inject interrupts directly into guest. 313 This mode requires kvm-amd.avic=1. 314 (Default when IOMMU HW support is present.) 315 316 amijoy.map= [HW,JOY] Amiga joystick support 317 Map of devices attached to JOY0DAT and JOY1DAT 318 Format: <a>,<b> 319 See also Documentation/input/joydev/joystick.rst 320 321 analog.map= [HW,JOY] Analog joystick and gamepad support 322 Specifies type or capabilities of an analog joystick 323 connected to one of 16 gameports 324 Format: <type1>,<type2>,..<type16> 325 326 apc= [HW,SPARC] 327 Power management functions (SPARCstation-4/5 + deriv.) 328 Format: noidle 329 Disable APC CPU standby support. SPARCstation-Fox does 330 not play well with APC CPU idle - disable it if you have 331 APC and your system crashes randomly. 332 333 apic= [APIC,X86] Advanced Programmable Interrupt Controller 334 Change the output verbosity while booting 335 Format: { quiet (default) | verbose | debug } 336 Change the amount of debugging information output 337 when initialising the APIC and IO-APIC components. 338 For X86-32, this can also be used to specify an APIC 339 driver name. 340 Format: apic=driver_name 341 Examples: apic=bigsmp 342 343 apic_extnmi= [APIC,X86] External NMI delivery setting 344 Format: { bsp (default) | all | none } 345 bsp: External NMI is delivered only to CPU 0 346 all: External NMIs are broadcast to all CPUs as a 347 backup of CPU 0 348 none: External NMI is masked for all CPUs. This is 349 useful so that a dump capture kernel won't be 350 shot down by NMI 351 352 autoconf= [IPV6] 353 See Documentation/networking/ipv6.txt. 354 355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 356 Limit apic dumping. The parameter defines the maximal 357 number of local apics being dumped. Also it is possible 358 to set it to "all" by meaning -- no limit here. 359 Format: { 1 (default) | 2 | ... | all }. 360 The parameter valid if only apic=debug or 361 apic=verbose is specified. 362 Example: apic=debug show_lapic=all 363 364 apm= [APM] Advanced Power Management 365 See header of arch/x86/kernel/apm_32.c. 366 367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 368 Format: <io>,<irq>,<nodeID> 369 370 ataflop= [HW,M68k] 371 372 atarimouse= [HW,MOUSE] Atari Mouse 373 374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 375 EzKey and similar keyboards 376 377 atkbd.reset= [HW] Reset keyboard during initialization 378 379 atkbd.set= [HW] Select keyboard code set 380 Format: <int> (2 = AT (default), 3 = PS/2) 381 382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 383 keyboards 384 385 atkbd.softraw= [HW] Choose between synthetic and real raw mode 386 Format: <bool> (0 = real, 1 = synthetic (default)) 387 388 atkbd.softrepeat= [HW] 389 Use software keyboard repeat 390 391 audit= [KNL] Enable the audit sub-system 392 Format: { "0" | "1" | "off" | "on" } 393 0 | off - kernel audit is disabled and can not be 394 enabled until the next reboot 395 unset - kernel audit is initialized but disabled and 396 will be fully enabled by the userspace auditd. 397 1 | on - kernel audit is initialized and partially 398 enabled, storing at most audit_backlog_limit 399 messages in RAM until it is fully enabled by the 400 userspace auditd. 401 Default: unset 402 403 audit_backlog_limit= [KNL] Set the audit queue size limit. 404 Format: <int> (must be >=0) 405 Default: 64 406 407 bau= [X86_UV] Enable the BAU on SGI UV. The default 408 behavior is to disable the BAU (i.e. bau=0). 409 Format: { "0" | "1" } 410 0 - Disable the BAU. 411 1 - Enable the BAU. 412 unset - Disable the BAU. 413 414 baycom_epp= [HW,AX25] 415 Format: <io>,<mode> 416 417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 418 Format: <io>,<mode> 419 See header of drivers/net/hamradio/baycom_par.c. 420 421 baycom_ser_fdx= [HW,AX25] 422 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 423 Format: <io>,<irq>,<mode>[,<baud>] 424 See header of drivers/net/hamradio/baycom_ser_fdx.c. 425 426 baycom_ser_hdx= [HW,AX25] 427 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 428 Format: <io>,<irq>,<mode> 429 See header of drivers/net/hamradio/baycom_ser_hdx.c. 430 431 blkdevparts= Manual partition parsing of block device(s) for 432 embedded devices based on command line input. 433 See Documentation/block/cmdline-partition.txt 434 435 boot_delay= Milliseconds to delay each printk during boot. 436 Values larger than 10 seconds (10000) are changed to 437 no delay (0). 438 Format: integer 439 440 bootmem_debug [KNL] Enable bootmem allocator debug messages. 441 442 bert_disable [ACPI] 443 Disable BERT OS support on buggy BIOSes. 444 445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 446 bttv.radio= Most important insmod options are available as 447 kernel args too. 448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst 449 bttv.tuner= 450 451 bulk_remove=off [PPC] This parameter disables the use of the pSeries 452 firmware feature for flushing multiple hpte entries 453 at a time. 454 455 c101= [NET] Moxa C101 synchronous serial card 456 457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 458 Sometimes CPU hardware bugs make them report the cache 459 size incorrectly. The kernel will attempt work arounds 460 to fix known problems, but for some CPUs it is not 461 possible to determine what the correct size should be. 462 This option provides an override for these situations. 463 464 carrier_timeout= 465 [NET] Specifies amount of time (in seconds) that 466 the kernel should wait for a network carrier. By default 467 it waits 120 seconds. 468 469 ca_keys= [KEYS] This parameter identifies a specific key(s) on 470 the system trusted keyring to be used for certificate 471 trust validation. 472 format: { id:<keyid> | builtin } 473 474 cca= [MIPS] Override the kernel pages' cache coherency 475 algorithm. Accepted values range from 0 to 7 476 inclusive. See arch/mips/include/asm/pgtable-bits.h 477 for platform specific values (SB1, Loongson3 and 478 others). 479 480 ccw_timeout_log [S390] 481 See Documentation/s390/CommonIO for details. 482 483 cgroup_disable= [KNL] Disable a particular controller 484 Format: {name of the controller(s) to disable} 485 The effects of cgroup_disable=foo are: 486 - foo isn't auto-mounted if you mount all cgroups in 487 a single hierarchy 488 - foo isn't visible as an individually mountable 489 subsystem 490 {Currently only "memory" controller deal with this and 491 cut the overhead, others just disable the usage. So 492 only cgroup_disable=memory is actually worthy} 493 494 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 495 Format: { { controller | "all" | "named" } 496 [,{ controller | "all" | "named" }...] } 497 Like cgroup_disable, but only applies to cgroup v1; 498 the blacklisted controllers remain available in cgroup2. 499 "all" blacklists all controllers and "named" disables 500 named mounts. Specifying both "all" and "named" disables 501 all v1 hierarchies. 502 503 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 504 Format: <string> 505 nosocket -- Disable socket memory accounting. 506 nokmem -- Disable kernel memory accounting. 507 508 checkreqprot [SELINUX] Set initial checkreqprot flag value. 509 Format: { "0" | "1" } 510 See security/selinux/Kconfig help text. 511 0 -- check protection applied by kernel (includes 512 any implied execute protection). 513 1 -- check protection requested by application. 514 Default value is set via a kernel config option. 515 Value can be changed at runtime via 516 /selinux/checkreqprot. 517 518 cio_ignore= [S390] 519 See Documentation/s390/CommonIO for details. 520 clk_ignore_unused 521 [CLK] 522 Prevents the clock framework from automatically gating 523 clocks that have not been explicitly enabled by a Linux 524 device driver but are enabled in hardware at reset or 525 by the bootloader/firmware. Note that this does not 526 force such clocks to be always-on nor does it reserve 527 those clocks in any way. This parameter is useful for 528 debug and development, but should not be needed on a 529 platform with proper driver support. For more 530 information, see Documentation/driver-api/clk.rst. 531 532 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 533 [Deprecated] 534 Forces specified clocksource (if available) to be used 535 when calculating gettimeofday(). If specified 536 clocksource is not available, it defaults to PIT. 537 Format: { pit | tsc | cyclone | pmtmr } 538 539 clocksource= Override the default clocksource 540 Format: <string> 541 Override the default clocksource and use the clocksource 542 with the name specified. 543 Some clocksource names to choose from, depending on 544 the platform: 545 [all] jiffies (this is the base, fallback clocksource) 546 [ACPI] acpi_pm 547 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 548 pxa_timer,timer3,32k_counter,timer0_1 549 [X86-32] pit,hpet,tsc; 550 scx200_hrt on Geode; cyclone on IBM x440 551 [MIPS] MIPS 552 [PARISC] cr16 553 [S390] tod 554 [SH] SuperH 555 [SPARC64] tick 556 [X86-64] hpet,tsc 557 558 clocksource.arm_arch_timer.evtstrm= 559 [ARM,ARM64] 560 Format: <bool> 561 Enable/disable the eventstream feature of the ARM 562 architected timer so that code using WFE-based polling 563 loops can be debugged more effectively on production 564 systems. 565 566 clearcpuid=BITNUM [X86] 567 Disable CPUID feature X for the kernel. See 568 arch/x86/include/asm/cpufeatures.h for the valid bit 569 numbers. Note the Linux specific bits are not necessarily 570 stable over kernel options, but the vendor specific 571 ones should be. 572 Also note that user programs calling CPUID directly 573 or using the feature without checking anything 574 will still see it. This just prevents it from 575 being used by the kernel or shown in /proc/cpuinfo. 576 Also note the kernel might malfunction if you disable 577 some critical bits. 578 579 cma=nn[MG]@[start[MG][-end[MG]]] 580 [ARM,X86,KNL] 581 Sets the size of kernel global memory area for 582 contiguous memory allocations and optionally the 583 placement constraint by the physical address range of 584 memory allocations. A value of 0 disables CMA 585 altogether. For more information, see 586 include/linux/dma-contiguous.h 587 588 cmo_free_hint= [PPC] Format: { yes | no } 589 Specify whether pages are marked as being inactive 590 when they are freed. This is used in CMO environments 591 to determine OS memory pressure for page stealing by 592 a hypervisor. 593 Default: yes 594 595 coherent_pool=nn[KMG] [ARM,KNL] 596 Sets the size of memory pool for coherent, atomic dma 597 allocations, by default set to 256K. 598 599 com20020= [HW,NET] ARCnet - COM20020 chipset 600 Format: 601 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 602 603 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 604 Format: <io>[,<irq>] 605 606 com90xx= [HW,NET] 607 ARCnet - COM90xx chipset (memory-mapped buffers) 608 Format: <io>[,<irq>[,<memstart>]] 609 610 condev= [HW,S390] console device 611 conmode= 612 613 console= [KNL] Output console device and options. 614 615 tty<n> Use the virtual console device <n>. 616 617 ttyS<n>[,options] 618 ttyUSB0[,options] 619 Use the specified serial port. The options are of 620 the form "bbbbpnf", where "bbbb" is the baud rate, 621 "p" is parity ("n", "o", or "e"), "n" is number of 622 bits, and "f" is flow control ("r" for RTS or 623 omit it). Default is "9600n8". 624 625 See Documentation/admin-guide/serial-console.rst for more 626 information. See 627 Documentation/networking/netconsole.txt for an 628 alternative. 629 630 uart[8250],io,<addr>[,options] 631 uart[8250],mmio,<addr>[,options] 632 uart[8250],mmio16,<addr>[,options] 633 uart[8250],mmio32,<addr>[,options] 634 uart[8250],0x<addr>[,options] 635 Start an early, polled-mode console on the 8250/16550 636 UART at the specified I/O port or MMIO address, 637 switching to the matching ttyS device later. 638 MMIO inter-register address stride is either 8-bit 639 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 640 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 641 to be equivalent to 'mmio'. 'options' are specified in 642 the same format described for ttyS above; if unspecified, 643 the h/w is not re-initialized. 644 645 hvc<n> Use the hypervisor console device <n>. This is for 646 both Xen and PowerPC hypervisors. 647 648 If the device connected to the port is not a TTY but a braille 649 device, prepend "brl," before the device type, for instance 650 console=brl,ttyS0 651 For now, only VisioBraille is supported. 652 653 console_msg_format= 654 [KNL] Change console messages format 655 default 656 By default we print messages on consoles in 657 "[time stamp] text\n" format (time stamp may not be 658 printed, depending on CONFIG_PRINTK_TIME or 659 `printk_time' param). 660 syslog 661 Switch to syslog format: "<%u>[time stamp] text\n" 662 IOW, each message will have a facility and loglevel 663 prefix. The format is similar to one used by syslog() 664 syscall, or to executing "dmesg -S --raw" or to reading 665 from /proc/kmsg. 666 667 consoleblank= [KNL] The console blank (screen saver) timeout in 668 seconds. A value of 0 disables the blank timer. 669 Defaults to 0. 670 671 coredump_filter= 672 [KNL] Change the default value for 673 /proc/<pid>/coredump_filter. 674 See also Documentation/filesystems/proc.txt. 675 676 coresight_cpu_debug.enable 677 [ARM,ARM64] 678 Format: <bool> 679 Enable/disable the CPU sampling based debugging. 680 0: default value, disable debugging 681 1: enable debugging at boot time 682 683 cpuidle.off=1 [CPU_IDLE] 684 disable the cpuidle sub-system 685 686 cpuidle.governor= 687 [CPU_IDLE] Name of the cpuidle governor to use. 688 689 cpufreq.off=1 [CPU_FREQ] 690 disable the cpufreq sub-system 691 692 cpu_init_udelay=N 693 [X86] Delay for N microsec between assert and de-assert 694 of APIC INIT to start processors. This delay occurs 695 on every CPU online, such as boot, and resume from suspend. 696 Default: 10000 697 698 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 699 Format: 700 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 701 702 crashkernel=size[KMG][@offset[KMG]] 703 [KNL] Using kexec, Linux can switch to a 'crash kernel' 704 upon panic. This parameter reserves the physical 705 memory region [offset, offset + size] for that kernel 706 image. If '@offset' is omitted, then a suitable offset 707 is selected automatically. 708 [KNL, x86_64] select a region under 4G first, and 709 fall back to reserve region above 4G when '@offset' 710 hasn't been specified. 711 See Documentation/kdump/kdump.txt for further details. 712 713 crashkernel=range1:size1[,range2:size2,...][@offset] 714 [KNL] Same as above, but depends on the memory 715 in the running system. The syntax of range is 716 start-[end] where start and end are both 717 a memory unit (amount[KMG]). See also 718 Documentation/kdump/kdump.txt for an example. 719 720 crashkernel=size[KMG],high 721 [KNL, x86_64] range could be above 4G. Allow kernel 722 to allocate physical memory region from top, so could 723 be above 4G if system have more than 4G ram installed. 724 Otherwise memory region will be allocated below 4G, if 725 available. 726 It will be ignored if crashkernel=X is specified. 727 crashkernel=size[KMG],low 728 [KNL, x86_64] range under 4G. When crashkernel=X,high 729 is passed, kernel could allocate physical memory region 730 above 4G, that cause second kernel crash on system 731 that require some amount of low memory, e.g. swiotlb 732 requires at least 64M+32K low memory, also enough extra 733 low memory is needed to make sure DMA buffers for 32-bit 734 devices won't run out. Kernel would try to allocate at 735 at least 256M below 4G automatically. 736 This one let user to specify own low range under 4G 737 for second kernel instead. 738 0: to disable low allocation. 739 It will be ignored when crashkernel=X,high is not used 740 or memory reserved is below 4G. 741 742 cryptomgr.notests 743 [KNL] Disable crypto self-tests 744 745 cs89x0_dma= [HW,NET] 746 Format: <dma> 747 748 cs89x0_media= [HW,NET] 749 Format: { rj45 | aui | bnc } 750 751 dasd= [HW,NET] 752 See header of drivers/s390/block/dasd_devmap.c. 753 754 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 755 (one device per port) 756 Format: <port#>,<type> 757 See also Documentation/input/devices/joystick-parport.rst 758 759 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 760 time. See 761 Documentation/admin-guide/dynamic-debug-howto.rst for 762 details. Deprecated, see dyndbg. 763 764 debug [KNL] Enable kernel debugging (events log level). 765 766 debug_boot_weak_hash 767 [KNL] Enable printing [hashed] pointers early in the 768 boot sequence. If enabled, we use a weak hash instead 769 of siphash to hash pointers. Use this option if you are 770 seeing instances of '(___ptrval___)') and need to see a 771 value (hashed pointer) instead. Cryptographically 772 insecure, please do not use on production kernels. 773 774 debug_locks_verbose= 775 [KNL] verbose self-tests 776 Format=<0|1> 777 Print debugging info while doing the locking API 778 self-tests. 779 We default to 0 (no extra messages), setting it to 780 1 will print _a lot_ more information - normally 781 only useful to kernel developers. 782 783 debug_objects [KNL] Enable object debugging 784 785 no_debug_objects 786 [KNL] Disable object debugging 787 788 debug_guardpage_minorder= 789 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 790 parameter allows control of the order of pages that will 791 be intentionally kept free (and hence protected) by the 792 buddy allocator. Bigger value increase the probability 793 of catching random memory corruption, but reduce the 794 amount of memory for normal system use. The maximum 795 possible value is MAX_ORDER/2. Setting this parameter 796 to 1 or 2 should be enough to identify most random 797 memory corruption problems caused by bugs in kernel or 798 driver code when a CPU writes to (or reads from) a 799 random memory location. Note that there exists a class 800 of memory corruptions problems caused by buggy H/W or 801 F/W or by drivers badly programing DMA (basically when 802 memory is written at bus level and the CPU MMU is 803 bypassed) which are not detectable by 804 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 805 tracking down these problems. 806 807 debug_pagealloc= 808 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 809 parameter enables the feature at boot time. In 810 default, it is disabled. We can avoid allocating huge 811 chunk of memory for debug pagealloc if we don't enable 812 it at boot time and the system will work mostly same 813 with the kernel built without CONFIG_DEBUG_PAGEALLOC. 814 on: enable the feature 815 816 debugpat [X86] Enable PAT debugging 817 818 decnet.addr= [HW,NET] 819 Format: <area>[,<node>] 820 See also Documentation/networking/decnet.txt. 821 822 default_hugepagesz= 823 [same as hugepagesz=] The size of the default 824 HugeTLB page size. This is the size represented by 825 the legacy /proc/ hugepages APIs, used for SHM, and 826 default size when mounting hugetlbfs filesystems. 827 Defaults to the default architecture's huge page size 828 if not specified. 829 830 deferred_probe_timeout= 831 [KNL] Debugging option to set a timeout in seconds for 832 deferred probe to give up waiting on dependencies to 833 probe. Only specific dependencies (subsystems or 834 drivers) that have opted in will be ignored. A timeout of 0 835 will timeout at the end of initcalls. This option will also 836 dump out devices still on the deferred probe list after 837 retrying. 838 839 dhash_entries= [KNL] 840 Set number of hash buckets for dentry cache. 841 842 disable_1tb_segments [PPC] 843 Disables the use of 1TB hash page table segments. This 844 causes the kernel to fall back to 256MB segments which 845 can be useful when debugging issues that require an SLB 846 miss to occur. 847 848 disable= [IPV6] 849 See Documentation/networking/ipv6.txt. 850 851 hardened_usercopy= 852 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 853 hardening is enabled for this boot. Hardened 854 usercopy checking is used to protect the kernel 855 from reading or writing beyond known memory 856 allocation boundaries as a proactive defense 857 against bounds-checking flaws in the kernel's 858 copy_to_user()/copy_from_user() interface. 859 on Perform hardened usercopy checks (default). 860 off Disable hardened usercopy checks. 861 862 disable_radix [PPC] 863 Disable RADIX MMU mode on POWER9 864 865 disable_cpu_apicid= [X86,APIC,SMP] 866 Format: <int> 867 The number of initial APIC ID for the 868 corresponding CPU to be disabled at boot, 869 mostly used for the kdump 2nd kernel to 870 disable BSP to wake up multiple CPUs without 871 causing system reset or hang due to sending 872 INIT from AP to BSP. 873 874 perf_v4_pmi= [X86,INTEL] 875 Format: <bool> 876 Disable Intel PMU counter freezing feature. 877 The feature only exists starting from 878 Arch Perfmon v4 (Skylake and newer). 879 880 disable_ddw [PPC/PSERIES] 881 Disable Dynamic DMA Window support. Use this if 882 to workaround buggy firmware. 883 884 disable_ipv6= [IPV6] 885 See Documentation/networking/ipv6.txt. 886 887 disable_mtrr_cleanup [X86] 888 The kernel tries to adjust MTRR layout from continuous 889 to discrete, to make X server driver able to add WB 890 entry later. This parameter disables that. 891 892 disable_mtrr_trim [X86, Intel and AMD only] 893 By default the kernel will trim any uncacheable 894 memory out of your available memory pool based on 895 MTRR settings. This parameter disables that behavior, 896 possibly causing your machine to run very slowly. 897 898 disable_timer_pin_1 [X86] 899 Disable PIN 1 of APIC timer 900 Can be useful to work around chipset bugs. 901 902 dis_ucode_ldr [X86] Disable the microcode loader. 903 904 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 905 this option disables the debugging code at boot. 906 907 dma_debug_entries=<number> 908 This option allows to tune the number of preallocated 909 entries for DMA-API debugging code. One entry is 910 required per DMA-API allocation. Use this if the 911 DMA-API debugging code disables itself because the 912 architectural default is too low. 913 914 dma_debug_driver=<driver_name> 915 With this option the DMA-API debugging driver 916 filter feature can be enabled at boot time. Just 917 pass the driver to filter for as the parameter. 918 The filter can be disabled or changed to another 919 driver later using sysfs. 920 921 driver_async_probe= [KNL] 922 List of driver names to be probed asynchronously. 923 Format: <driver_name1>,<driver_name2>... 924 925 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 926 Broken monitors, graphic adapters, KVMs and EDIDless 927 panels may send no or incorrect EDID data sets. 928 This parameter allows to specify an EDID data sets 929 in the /lib/firmware directory that are used instead. 930 Generic built-in EDID data sets are used, if one of 931 edid/1024x768.bin, edid/1280x1024.bin, 932 edid/1680x1050.bin, or edid/1920x1080.bin is given 933 and no file with the same name exists. Details and 934 instructions how to build your own EDID data are 935 available in Documentation/EDID/HOWTO.txt. An EDID 936 data set will only be used for a particular connector, 937 if its name and a colon are prepended to the EDID 938 name. Each connector may use a unique EDID data 939 set by separating the files with a comma. An EDID 940 data set with no connector name will be used for 941 any connectors not explicitly specified. 942 943 dscc4.setup= [NET] 944 945 dt_cpu_ftrs= [PPC] 946 Format: {"off" | "known"} 947 Control how the dt_cpu_ftrs device-tree binding is 948 used for CPU feature discovery and setup (if it 949 exists). 950 off: Do not use it, fall back to legacy cpu table. 951 known: Do not pass through unknown features to guests 952 or userspace, only those that the kernel is aware of. 953 954 dump_apple_properties [X86] 955 Dump name and content of EFI device properties on 956 x86 Macs. Useful for driver authors to determine 957 what data is available or for reverse-engineering. 958 959 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 960 module.dyndbg[="val"] 961 Enable debug messages at boot time. See 962 Documentation/admin-guide/dynamic-debug-howto.rst 963 for details. 964 965 nompx [X86] Disables Intel Memory Protection Extensions. 966 See Documentation/x86/intel_mpx.txt for more 967 information about the feature. 968 969 nopku [X86] Disable Memory Protection Keys CPU feature found 970 in some Intel CPUs. 971 972 module.async_probe [KNL] 973 Enable asynchronous probe on this module. 974 975 early_ioremap_debug [KNL] 976 Enable debug messages in early_ioremap support. This 977 is useful for tracking down temporary early mappings 978 which are not unmapped. 979 980 earlycon= [KNL] Output early console device and options. 981 982 [ARM64] The early console is determined by the 983 stdout-path property in device tree's chosen node, 984 or determined by the ACPI SPCR table. 985 986 [X86] When used with no options the early console is 987 determined by the ACPI SPCR table. 988 989 cdns,<addr>[,options] 990 Start an early, polled-mode console on a Cadence 991 (xuartps) serial port at the specified address. Only 992 supported option is baud rate. If baud rate is not 993 specified, the serial port must already be setup and 994 configured. 995 996 uart[8250],io,<addr>[,options] 997 uart[8250],mmio,<addr>[,options] 998 uart[8250],mmio32,<addr>[,options] 999 uart[8250],mmio32be,<addr>[,options] 1000 uart[8250],0x<addr>[,options] 1001 Start an early, polled-mode console on the 8250/16550 1002 UART at the specified I/O port or MMIO address. 1003 MMIO inter-register address stride is either 8-bit 1004 (mmio) or 32-bit (mmio32 or mmio32be). 1005 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1006 to be equivalent to 'mmio'. 'options' are specified 1007 in the same format described for "console=ttyS<n>"; if 1008 unspecified, the h/w is not initialized. 1009 1010 pl011,<addr> 1011 pl011,mmio32,<addr> 1012 Start an early, polled-mode console on a pl011 serial 1013 port at the specified address. The pl011 serial port 1014 must already be setup and configured. Options are not 1015 yet supported. If 'mmio32' is specified, then only 1016 the driver will use only 32-bit accessors to read/write 1017 the device registers. 1018 1019 meson,<addr> 1020 Start an early, polled-mode console on a meson serial 1021 port at the specified address. The serial port must 1022 already be setup and configured. Options are not yet 1023 supported. 1024 1025 msm_serial,<addr> 1026 Start an early, polled-mode console on an msm serial 1027 port at the specified address. The serial port 1028 must already be setup and configured. Options are not 1029 yet supported. 1030 1031 msm_serial_dm,<addr> 1032 Start an early, polled-mode console on an msm serial 1033 dm port at the specified address. The serial port 1034 must already be setup and configured. Options are not 1035 yet supported. 1036 1037 owl,<addr> 1038 Start an early, polled-mode console on a serial port 1039 of an Actions Semi SoC, such as S500 or S900, at the 1040 specified address. The serial port must already be 1041 setup and configured. Options are not yet supported. 1042 1043 rda,<addr> 1044 Start an early, polled-mode console on a serial port 1045 of an RDA Micro SoC, such as RDA8810PL, at the 1046 specified address. The serial port must already be 1047 setup and configured. Options are not yet supported. 1048 1049 smh Use ARM semihosting calls for early console. 1050 1051 s3c2410,<addr> 1052 s3c2412,<addr> 1053 s3c2440,<addr> 1054 s3c6400,<addr> 1055 s5pv210,<addr> 1056 exynos4210,<addr> 1057 Use early console provided by serial driver available 1058 on Samsung SoCs, requires selecting proper type and 1059 a correct base address of the selected UART port. The 1060 serial port must already be setup and configured. 1061 Options are not yet supported. 1062 1063 lantiq,<addr> 1064 Start an early, polled-mode console on a lantiq serial 1065 (lqasc) port at the specified address. The serial port 1066 must already be setup and configured. Options are not 1067 yet supported. 1068 1069 lpuart,<addr> 1070 lpuart32,<addr> 1071 Use early console provided by Freescale LP UART driver 1072 found on Freescale Vybrid and QorIQ LS1021A processors. 1073 A valid base address must be provided, and the serial 1074 port must already be setup and configured. 1075 1076 ar3700_uart,<addr> 1077 Start an early, polled-mode console on the 1078 Armada 3700 serial port at the specified 1079 address. The serial port must already be setup 1080 and configured. Options are not yet supported. 1081 1082 qcom_geni,<addr> 1083 Start an early, polled-mode console on a Qualcomm 1084 Generic Interface (GENI) based serial port at the 1085 specified address. The serial port must already be 1086 setup and configured. Options are not yet supported. 1087 1088 efifb,[options] 1089 Start an early, unaccelerated console on the EFI 1090 memory mapped framebuffer (if available). On cache 1091 coherent non-x86 systems that use system memory for 1092 the framebuffer, pass the 'ram' option so that it is 1093 mapped with the correct attributes. 1094 1095 earlyprintk= [X86,SH,ARM,M68k,S390] 1096 earlyprintk=vga 1097 earlyprintk=sclp 1098 earlyprintk=xen 1099 earlyprintk=serial[,ttySn[,baudrate]] 1100 earlyprintk=serial[,0x...[,baudrate]] 1101 earlyprintk=ttySn[,baudrate] 1102 earlyprintk=dbgp[debugController#] 1103 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1104 earlyprintk=xdbc[xhciController#] 1105 1106 earlyprintk is useful when the kernel crashes before 1107 the normal console is initialized. It is not enabled by 1108 default because it has some cosmetic problems. 1109 1110 Append ",keep" to not disable it when the real console 1111 takes over. 1112 1113 Only one of vga, efi, serial, or usb debug port can 1114 be used at a time. 1115 1116 Currently only ttyS0 and ttyS1 may be specified by 1117 name. Other I/O ports may be explicitly specified 1118 on some architectures (x86 and arm at least) by 1119 replacing ttySn with an I/O port address, like this: 1120 earlyprintk=serial,0x1008,115200 1121 You can find the port for a given device in 1122 /proc/tty/driver/serial: 1123 2: uart:ST16650V2 port:00001008 irq:18 ... 1124 1125 Interaction with the standard serial driver is not 1126 very good. 1127 1128 The VGA and EFI output is eventually overwritten by 1129 the real console. 1130 1131 The xen output can only be used by Xen PV guests. 1132 1133 The sclp output can only be used on s390. 1134 1135 The optional "force" to "pciserial" enables use of a 1136 PCI device even when its classcode is not of the 1137 UART class. 1138 1139 edac_report= [HW,EDAC] Control how to report EDAC event 1140 Format: {"on" | "off" | "force"} 1141 on: enable EDAC to report H/W event. May be overridden 1142 by other higher priority error reporting module. 1143 off: disable H/W event reporting through EDAC. 1144 force: enforce the use of EDAC to report H/W event. 1145 default: on. 1146 1147 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1148 ekgdboc=kbd 1149 1150 This is designed to be used in conjunction with 1151 the boot argument: earlyprintk=vga 1152 1153 edd= [EDD] 1154 Format: {"off" | "on" | "skip[mbr]"} 1155 1156 efi= [EFI] 1157 Format: { "old_map", "nochunk", "noruntime", "debug" } 1158 old_map [X86-64]: switch to the old ioremap-based EFI 1159 runtime services mapping. 32-bit still uses this one by 1160 default. 1161 nochunk: disable reading files in "chunks" in the EFI 1162 boot stub, as chunking can cause problems with some 1163 firmware implementations. 1164 noruntime : disable EFI runtime services support 1165 debug: enable misc debug output 1166 1167 efi_no_storage_paranoia [EFI; X86] 1168 Using this parameter you can use more than 50% of 1169 your efi variable storage. Use this parameter only if 1170 you are really sure that your UEFI does sane gc and 1171 fulfills the spec otherwise your board may brick. 1172 1173 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1174 Add arbitrary attribute to specific memory range by 1175 updating original EFI memory map. 1176 Region of memory which aa attribute is added to is 1177 from ss to ss+nn. 1178 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1179 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1180 attribute is added to range 0x100000000-0x180000000 and 1181 0x10a0000000-0x1120000000. 1182 1183 Using this parameter you can do debugging of EFI memmap 1184 related feature. For example, you can do debugging of 1185 Address Range Mirroring feature even if your box 1186 doesn't support it. 1187 1188 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1189 that is to be dynamically loaded by Linux. If there are 1190 multiple variables with the same name but with different 1191 vendor GUIDs, all of them will be loaded. See 1192 Documentation/acpi/ssdt-overlays.txt for details. 1193 1194 1195 eisa_irq_edge= [PARISC,HW] 1196 See header of drivers/parisc/eisa.c. 1197 1198 elanfreq= [X86-32] 1199 See comment before function elanfreq_setup() in 1200 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1201 1202 elevator= [IOSCHED] 1203 Format: { "mq-deadline" | "kyber" | "bfq" } 1204 See Documentation/block/deadline-iosched.txt, 1205 Documentation/block/kyber-iosched.txt and 1206 Documentation/block/bfq-iosched.txt for details. 1207 1208 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1209 Specifies physical address of start of kernel core 1210 image elf header and optionally the size. Generally 1211 kexec loader will pass this option to capture kernel. 1212 See Documentation/kdump/kdump.txt for details. 1213 1214 enable_mtrr_cleanup [X86] 1215 The kernel tries to adjust MTRR layout from continuous 1216 to discrete, to make X server driver able to add WB 1217 entry later. This parameter enables that. 1218 1219 enable_timer_pin_1 [X86] 1220 Enable PIN 1 of APIC timer 1221 Can be useful to work around chipset bugs 1222 (in particular on some ATI chipsets). 1223 The kernel tries to set a reasonable default. 1224 1225 enforcing [SELINUX] Set initial enforcing status. 1226 Format: {"0" | "1"} 1227 See security/selinux/Kconfig help text. 1228 0 -- permissive (log only, no denials). 1229 1 -- enforcing (deny and log). 1230 Default value is 0. 1231 Value can be changed at runtime via /selinux/enforce. 1232 1233 erst_disable [ACPI] 1234 Disable Error Record Serialization Table (ERST) 1235 support. 1236 1237 ether= [HW,NET] Ethernet cards parameters 1238 This option is obsoleted by the "netdev=" option, which 1239 has equivalent usage. See its documentation for details. 1240 1241 evm= [EVM] 1242 Format: { "fix" } 1243 Permit 'security.evm' to be updated regardless of 1244 current integrity status. 1245 1246 failslab= 1247 fail_page_alloc= 1248 fail_make_request=[KNL] 1249 General fault injection mechanism. 1250 Format: <interval>,<probability>,<space>,<times> 1251 See also Documentation/fault-injection/. 1252 1253 floppy= [HW] 1254 See Documentation/blockdev/floppy.txt. 1255 1256 force_pal_cache_flush 1257 [IA-64] Avoid check_sal_cache_flush which may hang on 1258 buggy SAL_CACHE_FLUSH implementations. Using this 1259 parameter will force ia64_sal_cache_flush to call 1260 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1261 1262 forcepae [X86-32] 1263 Forcefully enable Physical Address Extension (PAE). 1264 Many Pentium M systems disable PAE but may have a 1265 functionally usable PAE implementation. 1266 Warning: use of this parameter will taint the kernel 1267 and may cause unknown problems. 1268 1269 ftrace=[tracer] 1270 [FTRACE] will set and start the specified tracer 1271 as early as possible in order to facilitate early 1272 boot debugging. 1273 1274 ftrace_dump_on_oops[=orig_cpu] 1275 [FTRACE] will dump the trace buffers on oops. 1276 If no parameter is passed, ftrace will dump 1277 buffers of all CPUs, but if you pass orig_cpu, it will 1278 dump only the buffer of the CPU that triggered the 1279 oops. 1280 1281 ftrace_filter=[function-list] 1282 [FTRACE] Limit the functions traced by the function 1283 tracer at boot up. function-list is a comma separated 1284 list of functions. This list can be changed at run 1285 time by the set_ftrace_filter file in the debugfs 1286 tracing directory. 1287 1288 ftrace_notrace=[function-list] 1289 [FTRACE] Do not trace the functions specified in 1290 function-list. This list can be changed at run time 1291 by the set_ftrace_notrace file in the debugfs 1292 tracing directory. 1293 1294 ftrace_graph_filter=[function-list] 1295 [FTRACE] Limit the top level callers functions traced 1296 by the function graph tracer at boot up. 1297 function-list is a comma separated list of functions 1298 that can be changed at run time by the 1299 set_graph_function file in the debugfs tracing directory. 1300 1301 ftrace_graph_notrace=[function-list] 1302 [FTRACE] Do not trace from the functions specified in 1303 function-list. This list is a comma separated list of 1304 functions that can be changed at run time by the 1305 set_graph_notrace file in the debugfs tracing directory. 1306 1307 ftrace_graph_max_depth=<uint> 1308 [FTRACE] Used with the function graph tracer. This is 1309 the max depth it will trace into a function. This value 1310 can be changed at run time by the max_graph_depth file 1311 in the tracefs tracing directory. default: 0 (no limit) 1312 1313 gamecon.map[2|3]= 1314 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1315 support via parallel port (up to 5 devices per port) 1316 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1317 See also Documentation/input/devices/joystick-parport.rst 1318 1319 gamma= [HW,DRM] 1320 1321 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1322 Format: off | on 1323 default: on 1324 1325 gcov_persist= [GCOV] When non-zero (default), profiling data for 1326 kernel modules is saved and remains accessible via 1327 debugfs, even when the module is unloaded/reloaded. 1328 When zero, profiling data is discarded and associated 1329 debugfs files are removed at module unload time. 1330 1331 goldfish [X86] Enable the goldfish android emulator platform. 1332 Don't use this when you are not running on the 1333 android emulator 1334 1335 gpt [EFI] Forces disk with valid GPT signature but 1336 invalid Protective MBR to be treated as GPT. If the 1337 primary GPT is corrupted, it enables the backup/alternate 1338 GPT to be used instead. 1339 1340 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1341 the "Enable 0" bit of the configuration register. 1342 Format: 0 | 1 1343 Default: 0 1344 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1345 the "Enable 0" bit of the configuration register. 1346 Format: 0 | 1 1347 Default: 0 1348 grcan.select= [HW] Select which physical interface to use. 1349 Format: 0 | 1 1350 Default: 0 1351 grcan.txsize= [HW] Sets the size of the tx buffer. 1352 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1353 Default: 1024 1354 grcan.rxsize= [HW] Sets the size of the rx buffer. 1355 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1356 Default: 1024 1357 1358 gpio-mockup.gpio_mockup_ranges 1359 [HW] Sets the ranges of gpiochip of for this device. 1360 Format: <start1>,<end1>,<start2>,<end2>... 1361 1362 hardlockup_all_cpu_backtrace= 1363 [KNL] Should the hard-lockup detector generate 1364 backtraces on all cpus. 1365 Format: <integer> 1366 1367 hashdist= [KNL,NUMA] Large hashes allocated during boot 1368 are distributed across NUMA nodes. Defaults on 1369 for 64-bit NUMA, off otherwise. 1370 Format: 0 | 1 (for off | on) 1371 1372 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1373 1374 hd= [EIDE] (E)IDE hard drive subsystem geometry 1375 Format: <cyl>,<head>,<sect> 1376 1377 hest_disable [ACPI] 1378 Disable Hardware Error Source Table (HEST) support; 1379 corresponding firmware-first mode error processing 1380 logic will be disabled. 1381 1382 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1383 size of <nn>. This works even on boxes that have no 1384 highmem otherwise. This also works to reduce highmem 1385 size on bigger boxes. 1386 1387 highres= [KNL] Enable/disable high resolution timer mode. 1388 Valid parameters: "on", "off" 1389 Default: "on" 1390 1391 hisax= [HW,ISDN] 1392 See Documentation/isdn/README.HiSax. 1393 1394 hlt [BUGS=ARM,SH] 1395 1396 hpet= [X86-32,HPET] option to control HPET usage 1397 Format: { enable (default) | disable | force | 1398 verbose } 1399 disable: disable HPET and use PIT instead 1400 force: allow force enabled of undocumented chips (ICH4, 1401 VIA, nVidia) 1402 verbose: show contents of HPET registers during setup 1403 1404 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1405 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1406 1407 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1408 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1409 On x86-64 and powerpc, this option can be specified 1410 multiple times interleaved with hugepages= to reserve 1411 huge pages of different sizes. Valid pages sizes on 1412 x86-64 are 2M (when the CPU supports "pse") and 1G 1413 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1414 1415 hung_task_panic= 1416 [KNL] Should the hung task detector generate panics. 1417 Format: <integer> 1418 1419 A nonzero value instructs the kernel to panic when a 1420 hung task is detected. The default value is controlled 1421 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1422 option. The value selected by this boot parameter can 1423 be changed later by the kernel.hung_task_panic sysctl. 1424 1425 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1426 terminal devices. Valid values: 0..8 1427 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1428 If specified, z/VM IUCV HVC accepts connections 1429 from listed z/VM user IDs only. 1430 1431 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1432 which allow the hypervisor to 'idle' the 1433 guest on lock contention. 1434 1435 keep_bootcon [KNL] 1436 Do not unregister boot console at start. This is only 1437 useful for debugging when something happens in the window 1438 between unregistering the boot console and initializing 1439 the real console. 1440 1441 i2c_bus= [HW] Override the default board specific I2C bus speed 1442 or register an additional I2C bus that is not 1443 registered from board initialization code. 1444 Format: 1445 <bus_id>,<clkrate> 1446 1447 i8042.debug [HW] Toggle i8042 debug mode 1448 i8042.unmask_kbd_data 1449 [HW] Enable printing of interrupt data from the KBD port 1450 (disabled by default, and as a pre-condition 1451 requires that i8042.debug=1 be enabled) 1452 i8042.direct [HW] Put keyboard port into non-translated mode 1453 i8042.dumbkbd [HW] Pretend that controller can only read data from 1454 keyboard and cannot control its state 1455 (Don't attempt to blink the leds) 1456 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1457 i8042.nokbd [HW] Don't check/create keyboard port 1458 i8042.noloop [HW] Disable the AUX Loopback command while probing 1459 for the AUX port 1460 i8042.nomux [HW] Don't check presence of an active multiplexing 1461 controller 1462 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1463 controllers 1464 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1465 i8042.reset [HW] Reset the controller during init, cleanup and 1466 suspend-to-ram transitions, only during s2r 1467 transitions, or never reset 1468 Format: { 1 | Y | y | 0 | N | n } 1469 1, Y, y: always reset controller 1470 0, N, n: don't ever reset controller 1471 Default: only on s2r transitions on x86; most other 1472 architectures force reset to be always executed 1473 i8042.unlock [HW] Unlock (ignore) the keylock 1474 i8042.kbdreset [HW] Reset device connected to KBD port 1475 1476 i810= [HW,DRM] 1477 1478 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1479 indicates that the driver is running on unsupported 1480 hardware. 1481 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1482 does not match list of supported models. 1483 i8k.power_status 1484 [HW] Report power status in /proc/i8k 1485 (disabled by default) 1486 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1487 capability is set. 1488 1489 i915.invert_brightness= 1490 [DRM] Invert the sense of the variable that is used to 1491 set the brightness of the panel backlight. Normally a 1492 brightness value of 0 indicates backlight switched off, 1493 and the maximum of the brightness value sets the backlight 1494 to maximum brightness. If this parameter is set to 0 1495 (default) and the machine requires it, or this parameter 1496 is set to 1, a brightness value of 0 sets the backlight 1497 to maximum brightness, and the maximum of the brightness 1498 value switches the backlight off. 1499 -1 -- never invert brightness 1500 0 -- machine default 1501 1 -- force brightness inversion 1502 1503 icn= [HW,ISDN] 1504 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1505 1506 ide-core.nodma= [HW] (E)IDE subsystem 1507 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1508 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1509 .cdrom .chs .ignore_cable are additional options 1510 See Documentation/ide/ide.txt. 1511 1512 ide-generic.probe-mask= [HW] (E)IDE subsystem 1513 Format: <int> 1514 Probe mask for legacy ISA IDE ports. Depending on 1515 platform up to 6 ports are supported, enabled by 1516 setting corresponding bits in the mask to 1. The 1517 default value is 0x0, which has a special meaning. 1518 On systems that have PCI, it triggers scanning the 1519 PCI bus for the first and the second port, which 1520 are then probed. On systems without PCI the value 1521 of 0x0 enables probing the two first ports as if it 1522 was 0x3. 1523 1524 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1525 Claim all unknown PCI IDE storage controllers. 1526 1527 idle= [X86] 1528 Format: idle=poll, idle=halt, idle=nomwait 1529 Poll forces a polling idle loop that can slightly 1530 improve the performance of waking up a idle CPU, but 1531 will use a lot of power and make the system run hot. 1532 Not recommended. 1533 idle=halt: Halt is forced to be used for CPU idle. 1534 In such case C2/C3 won't be used again. 1535 idle=nomwait: Disable mwait for CPU C-states 1536 1537 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1538 Format: { strict | legacy | 2008 | relaxed } 1539 Default: strict 1540 1541 Choose which programs will be accepted for execution 1542 based on the IEEE 754 NaN encoding(s) supported by 1543 the FPU and the NaN encoding requested with the value 1544 of an ELF file header flag individually set by each 1545 binary. Hardware implementations are permitted to 1546 support either or both of the legacy and the 2008 NaN 1547 encoding mode. 1548 1549 Available settings are as follows: 1550 strict accept binaries that request a NaN encoding 1551 supported by the FPU 1552 legacy only accept legacy-NaN binaries, if supported 1553 by the FPU 1554 2008 only accept 2008-NaN binaries, if supported 1555 by the FPU 1556 relaxed accept any binaries regardless of whether 1557 supported by the FPU 1558 1559 The FPU emulator is always able to support both NaN 1560 encodings, so if no FPU hardware is present or it has 1561 been disabled with 'nofpu', then the settings of 1562 'legacy' and '2008' strap the emulator accordingly, 1563 'relaxed' straps the emulator for both legacy-NaN and 1564 2008-NaN, whereas 'strict' enables legacy-NaN only on 1565 legacy processors and both NaN encodings on MIPS32 or 1566 MIPS64 CPUs. 1567 1568 The setting for ABS.fmt/NEG.fmt instruction execution 1569 mode generally follows that for the NaN encoding, 1570 except where unsupported by hardware. 1571 1572 ignore_loglevel [KNL] 1573 Ignore loglevel setting - this will print /all/ 1574 kernel messages to the console. Useful for debugging. 1575 We also add it as printk module parameter, so users 1576 could change it dynamically, usually by 1577 /sys/module/printk/parameters/ignore_loglevel. 1578 1579 ignore_rlimit_data 1580 Ignore RLIMIT_DATA setting for data mappings, 1581 print warning at first misuse. Can be changed via 1582 /sys/module/kernel/parameters/ignore_rlimit_data. 1583 1584 ihash_entries= [KNL] 1585 Set number of hash buckets for inode cache. 1586 1587 ima_appraise= [IMA] appraise integrity measurements 1588 Format: { "off" | "enforce" | "fix" | "log" } 1589 default: "enforce" 1590 1591 ima_appraise_tcb [IMA] 1592 The builtin appraise policy appraises all files 1593 owned by uid=0. 1594 1595 ima_canonical_fmt [IMA] 1596 Use the canonical format for the binary runtime 1597 measurements, instead of host native format. 1598 1599 ima_hash= [IMA] 1600 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1601 | sha512 | ... } 1602 default: "sha1" 1603 1604 The list of supported hash algorithms is defined 1605 in crypto/hash_info.h. 1606 1607 ima_policy= [IMA] 1608 The builtin policies to load during IMA setup. 1609 Format: "tcb | appraise_tcb | secure_boot | 1610 fail_securely" 1611 1612 The "tcb" policy measures all programs exec'd, files 1613 mmap'd for exec, and all files opened with the read 1614 mode bit set by either the effective uid (euid=0) or 1615 uid=0. 1616 1617 The "appraise_tcb" policy appraises the integrity of 1618 all files owned by root. (This is the equivalent 1619 of ima_appraise_tcb.) 1620 1621 The "secure_boot" policy appraises the integrity 1622 of files (eg. kexec kernel image, kernel modules, 1623 firmware, policy, etc) based on file signatures. 1624 1625 The "fail_securely" policy forces file signature 1626 verification failure also on privileged mounted 1627 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1628 flag. 1629 1630 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1631 Load a policy which meets the needs of the Trusted 1632 Computing Base. This means IMA will measure all 1633 programs exec'd, files mmap'd for exec, and all files 1634 opened for read by uid=0. 1635 1636 ima_template= [IMA] 1637 Select one of defined IMA measurements template formats. 1638 Formats: { "ima" | "ima-ng" | "ima-sig" } 1639 Default: "ima-ng" 1640 1641 ima_template_fmt= 1642 [IMA] Define a custom template format. 1643 Format: { "field1|...|fieldN" } 1644 1645 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1646 Format: <min_file_size> 1647 Set the minimal file size for using asynchronous hash. 1648 If left unspecified, ahash usage is disabled. 1649 1650 ahash performance varies for different data sizes on 1651 different crypto accelerators. This option can be used 1652 to achieve the best performance for a particular HW. 1653 1654 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1655 Format: <bufsize> 1656 Set hashing buffer size. Default: 4k. 1657 1658 ahash performance varies for different chunk sizes on 1659 different crypto accelerators. This option can be used 1660 to achieve best performance for particular HW. 1661 1662 init= [KNL] 1663 Format: <full_path> 1664 Run specified binary instead of /sbin/init as init 1665 process. 1666 1667 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1668 for working out where the kernel is dying during 1669 startup. 1670 1671 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1672 initcall functions. Useful for debugging built-in 1673 modules and initcalls. 1674 1675 initrd= [BOOT] Specify the location of the initial ramdisk 1676 1677 init_pkru= [x86] Specify the default memory protection keys rights 1678 register contents for all processes. 0x55555554 by 1679 default (disallow access to all but pkey 0). Can 1680 override in debugfs after boot. 1681 1682 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1683 Format: <irq> 1684 1685 int_pln_enable [x86] Enable power limit notification interrupt 1686 1687 integrity_audit=[IMA] 1688 Format: { "0" | "1" } 1689 0 -- basic integrity auditing messages. (Default) 1690 1 -- additional integrity auditing messages. 1691 1692 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1693 on 1694 Enable intel iommu driver. 1695 off 1696 Disable intel iommu driver. 1697 igfx_off [Default Off] 1698 By default, gfx is mapped as normal device. If a gfx 1699 device has a dedicated DMAR unit, the DMAR unit is 1700 bypassed by not enabling DMAR with this option. In 1701 this case, gfx device will use physical address for 1702 DMA. 1703 forcedac [x86_64] 1704 With this option iommu will not optimize to look 1705 for io virtual address below 32-bit forcing dual 1706 address cycle on pci bus for cards supporting greater 1707 than 32-bit addressing. The default is to look 1708 for translation below 32-bit and if not available 1709 then look in the higher range. 1710 strict [Default Off] 1711 With this option on every unmap_single operation will 1712 result in a hardware IOTLB flush operation as opposed 1713 to batching them for performance. 1714 sp_off [Default Off] 1715 By default, super page will be supported if Intel IOMMU 1716 has the capability. With this option, super page will 1717 not be supported. 1718 sm_on [Default Off] 1719 By default, scalable mode will be disabled even if the 1720 hardware advertises that it has support for the scalable 1721 mode translation. With this option set, scalable mode 1722 will be used on hardware which claims to support it. 1723 tboot_noforce [Default Off] 1724 Do not force the Intel IOMMU enabled under tboot. 1725 By default, tboot will force Intel IOMMU on, which 1726 could harm performance of some high-throughput 1727 devices like 40GBit network cards, even if identity 1728 mapping is enabled. 1729 Note that using this option lowers the security 1730 provided by tboot because it makes the system 1731 vulnerable to DMA attacks. 1732 1733 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1734 0 disables intel_idle and fall back on acpi_idle. 1735 1 to 9 specify maximum depth of C-state. 1736 1737 intel_pstate= [X86] 1738 disable 1739 Do not enable intel_pstate as the default 1740 scaling driver for the supported processors 1741 passive 1742 Use intel_pstate as a scaling driver, but configure it 1743 to work with generic cpufreq governors (instead of 1744 enabling its internal governor). This mode cannot be 1745 used along with the hardware-managed P-states (HWP) 1746 feature. 1747 force 1748 Enable intel_pstate on systems that prohibit it by default 1749 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1750 instead of acpi-cpufreq may disable platform features, such 1751 as thermal controls and power capping, that rely on ACPI 1752 P-States information being indicated to OSPM and therefore 1753 should be used with caution. This option does not work with 1754 processors that aren't supported by the intel_pstate driver 1755 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1756 no_hwp 1757 Do not enable hardware P state control (HWP) 1758 if available. 1759 hwp_only 1760 Only load intel_pstate on systems which support 1761 hardware P state control (HWP) if available. 1762 support_acpi_ppc 1763 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1764 Description Table, specifies preferred power management 1765 profile as "Enterprise Server" or "Performance Server", 1766 then this feature is turned on by default. 1767 per_cpu_perf_limits 1768 Allow per-logical-CPU P-State performance control limits using 1769 cpufreq sysfs interface 1770 1771 intremap= [X86-64, Intel-IOMMU] 1772 on enable Interrupt Remapping (default) 1773 off disable Interrupt Remapping 1774 nosid disable Source ID checking 1775 no_x2apic_optout 1776 BIOS x2APIC opt-out request will be ignored 1777 nopost disable Interrupt Posting 1778 1779 iomem= Disable strict checking of access to MMIO memory 1780 strict regions from userspace. 1781 relaxed 1782 1783 iommu= [x86] 1784 off 1785 force 1786 noforce 1787 biomerge 1788 panic 1789 nopanic 1790 merge 1791 nomerge 1792 soft 1793 pt [x86] 1794 nopt [x86] 1795 nobypass [PPC/POWERNV] 1796 Disable IOMMU bypass, using IOMMU for PCI devices. 1797 1798 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1799 Format: { "0" | "1" } 1800 0 - Lazy mode. 1801 Request that DMA unmap operations use deferred 1802 invalidation of hardware TLBs, for increased 1803 throughput at the cost of reduced device isolation. 1804 Will fall back to strict mode if not supported by 1805 the relevant IOMMU driver. 1806 1 - Strict mode (default). 1807 DMA unmap operations invalidate IOMMU hardware TLBs 1808 synchronously. 1809 1810 iommu.passthrough= 1811 [ARM64] Configure DMA to bypass the IOMMU by default. 1812 Format: { "0" | "1" } 1813 0 - Use IOMMU translation for DMA. 1814 1 - Bypass the IOMMU for DMA. 1815 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1816 1817 io7= [HW] IO7 for Marvel based alpha systems 1818 See comment before marvel_specify_io7 in 1819 arch/alpha/kernel/core_marvel.c. 1820 1821 io_delay= [X86] I/O delay method 1822 0x80 1823 Standard port 0x80 based delay 1824 0xed 1825 Alternate port 0xed based delay (needed on some systems) 1826 udelay 1827 Simple two microseconds delay 1828 none 1829 No delay 1830 1831 ip= [IP_PNP] 1832 See Documentation/filesystems/nfs/nfsroot.txt. 1833 1834 irqaffinity= [SMP] Set the default irq affinity mask 1835 The argument is a cpu list, as described above. 1836 1837 irqchip.gicv2_force_probe= 1838 [ARM, ARM64] 1839 Format: <bool> 1840 Force the kernel to look for the second 4kB page 1841 of a GICv2 controller even if the memory range 1842 exposed by the device tree is too small. 1843 1844 irqchip.gicv3_nolpi= 1845 [ARM, ARM64] 1846 Force the kernel to ignore the availability of 1847 LPIs (and by consequence ITSs). Intended for system 1848 that use the kernel as a bootloader, and thus want 1849 to let secondary kernels in charge of setting up 1850 LPIs. 1851 1852 irqchip.gicv3_pseudo_nmi= [ARM64] 1853 Enables support for pseudo-NMIs in the kernel. This 1854 requires the kernel to be built with 1855 CONFIG_ARM64_PSEUDO_NMI. 1856 1857 irqfixup [HW] 1858 When an interrupt is not handled search all handlers 1859 for it. Intended to get systems with badly broken 1860 firmware running. 1861 1862 irqpoll [HW] 1863 When an interrupt is not handled search all handlers 1864 for it. Also check all handlers each timer 1865 interrupt. Intended to get systems with badly broken 1866 firmware running. 1867 1868 isapnp= [ISAPNP] 1869 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1870 1871 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 1872 [Deprecated - use cpusets instead] 1873 Format: [flag-list,]<cpu-list> 1874 1875 Specify one or more CPUs to isolate from disturbances 1876 specified in the flag list (default: domain): 1877 1878 nohz 1879 Disable the tick when a single task runs. 1880 1881 A residual 1Hz tick is offloaded to workqueues, which you 1882 need to affine to housekeeping through the global 1883 workqueue's affinity configured via the 1884 /sys/devices/virtual/workqueue/cpumask sysfs file, or 1885 by using the 'domain' flag described below. 1886 1887 NOTE: by default the global workqueue runs on all CPUs, 1888 so to protect individual CPUs the 'cpumask' file has to 1889 be configured manually after bootup. 1890 1891 domain 1892 Isolate from the general SMP balancing and scheduling 1893 algorithms. Note that performing domain isolation this way 1894 is irreversible: it's not possible to bring back a CPU to 1895 the domains once isolated through isolcpus. It's strongly 1896 advised to use cpusets instead to disable scheduler load 1897 balancing through the "cpuset.sched_load_balance" file. 1898 It offers a much more flexible interface where CPUs can 1899 move in and out of an isolated set anytime. 1900 1901 You can move a process onto or off an "isolated" CPU via 1902 the CPU affinity syscalls or cpuset. 1903 <cpu number> begins at 0 and the maximum value is 1904 "number of CPUs in system - 1". 1905 1906 The format of <cpu-list> is described above. 1907 1908 1909 1910 iucv= [HW,NET] 1911 1912 ivrs_ioapic [HW,X86_64] 1913 Provide an override to the IOAPIC-ID<->DEVICE-ID 1914 mapping provided in the IVRS ACPI table. For 1915 example, to map IOAPIC-ID decimal 10 to 1916 PCI device 00:14.0 write the parameter as: 1917 ivrs_ioapic[10]=00:14.0 1918 1919 ivrs_hpet [HW,X86_64] 1920 Provide an override to the HPET-ID<->DEVICE-ID 1921 mapping provided in the IVRS ACPI table. For 1922 example, to map HPET-ID decimal 0 to 1923 PCI device 00:14.0 write the parameter as: 1924 ivrs_hpet[0]=00:14.0 1925 1926 ivrs_acpihid [HW,X86_64] 1927 Provide an override to the ACPI-HID:UID<->DEVICE-ID 1928 mapping provided in the IVRS ACPI table. For 1929 example, to map UART-HID:UID AMD0020:0 to 1930 PCI device 00:14.5 write the parameter as: 1931 ivrs_acpihid[00:14.5]=AMD0020:0 1932 1933 js= [HW,JOY] Analog joystick 1934 See Documentation/input/joydev/joystick.rst. 1935 1936 nokaslr [KNL] 1937 When CONFIG_RANDOMIZE_BASE is set, this disables 1938 kernel and module base offset ASLR (Address Space 1939 Layout Randomization). 1940 1941 kasan_multi_shot 1942 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 1943 report on every invalid memory access. Without this 1944 parameter KASAN will print report only for the first 1945 invalid access. 1946 1947 keepinitrd [HW,ARM] 1948 1949 kernelcore= [KNL,X86,IA-64,PPC] 1950 Format: nn[KMGTPE] | nn% | "mirror" 1951 This parameter specifies the amount of memory usable by 1952 the kernel for non-movable allocations. The requested 1953 amount is spread evenly throughout all nodes in the 1954 system as ZONE_NORMAL. The remaining memory is used for 1955 movable memory in its own zone, ZONE_MOVABLE. In the 1956 event, a node is too small to have both ZONE_NORMAL and 1957 ZONE_MOVABLE, kernelcore memory will take priority and 1958 other nodes will have a larger ZONE_MOVABLE. 1959 1960 ZONE_MOVABLE is used for the allocation of pages that 1961 may be reclaimed or moved by the page migration 1962 subsystem. Note that allocations like PTEs-from-HighMem 1963 still use the HighMem zone if it exists, and the Normal 1964 zone if it does not. 1965 1966 It is possible to specify the exact amount of memory in 1967 the form of "nn[KMGTPE]", a percentage of total system 1968 memory in the form of "nn%", or "mirror". If "mirror" 1969 option is specified, mirrored (reliable) memory is used 1970 for non-movable allocations and remaining memory is used 1971 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 1972 are exclusive, so you cannot specify multiple forms. 1973 1974 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1975 Format: <Controller#>[,poll interval] 1976 The controller # is the number of the ehci usb debug 1977 port as it is probed via PCI. The poll interval is 1978 optional and is the number seconds in between 1979 each poll cycle to the debug port in case you need 1980 the functionality for interrupting the kernel with 1981 gdb or control-c on the dbgp connection. When 1982 not using this parameter you use sysrq-g to break into 1983 the kernel debugger. 1984 1985 kgdboc= [KGDB,HW] kgdb over consoles. 1986 Requires a tty driver that supports console polling, 1987 or a supported polling keyboard driver (non-usb). 1988 Serial only format: <serial_device>[,baud] 1989 keyboard only format: kbd 1990 keyboard and serial format: kbd,<serial_device>[,baud] 1991 Optional Kernel mode setting: 1992 kms, kbd format: kms,kbd 1993 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 1994 1995 kgdbwait [KGDB] Stop kernel execution and enter the 1996 kernel debugger at the earliest opportunity. 1997 1998 kmac= [MIPS] korina ethernet MAC address. 1999 Configure the RouterBoard 532 series on-chip 2000 Ethernet adapter MAC address. 2001 2002 kmemleak= [KNL] Boot-time kmemleak enable/disable 2003 Valid arguments: on, off 2004 Default: on 2005 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2006 the default is off. 2007 2008 kpti= [ARM64] Control page table isolation of user 2009 and kernel address spaces. 2010 Default: enabled on cores which need mitigation. 2011 0: force disabled 2012 1: force enabled 2013 2014 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2015 Default is 0 (don't ignore, but inject #GP) 2016 2017 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2018 Default is false (don't support). 2019 2020 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2021 KVM MMU at runtime. 2022 Default is 0 (off) 2023 2024 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2025 Default is 1 (enabled) 2026 2027 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2028 for all guests. 2029 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2030 2031 kvm-arm.vgic_v3_group0_trap= 2032 [KVM,ARM] Trap guest accesses to GICv3 group-0 2033 system registers 2034 2035 kvm-arm.vgic_v3_group1_trap= 2036 [KVM,ARM] Trap guest accesses to GICv3 group-1 2037 system registers 2038 2039 kvm-arm.vgic_v3_common_trap= 2040 [KVM,ARM] Trap guest accesses to GICv3 common 2041 system registers 2042 2043 kvm-arm.vgic_v4_enable= 2044 [KVM,ARM] Allow use of GICv4 for direct injection of 2045 LPIs. 2046 2047 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2048 (virtualized MMU) support on capable Intel chips. 2049 Default is 1 (enabled) 2050 2051 kvm-intel.emulate_invalid_guest_state= 2052 [KVM,Intel] Enable emulation of invalid guest states 2053 Default is 0 (disabled) 2054 2055 kvm-intel.flexpriority= 2056 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2057 Default is 1 (enabled) 2058 2059 kvm-intel.nested= 2060 [KVM,Intel] Enable VMX nesting (nVMX). 2061 Default is 0 (disabled) 2062 2063 kvm-intel.unrestricted_guest= 2064 [KVM,Intel] Disable unrestricted guest feature 2065 (virtualized real and unpaged mode) on capable 2066 Intel chips. Default is 1 (enabled) 2067 2068 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2069 CVE-2018-3620. 2070 2071 Valid arguments: never, cond, always 2072 2073 always: L1D cache flush on every VMENTER. 2074 cond: Flush L1D on VMENTER only when the code between 2075 VMEXIT and VMENTER can leak host memory. 2076 never: Disables the mitigation 2077 2078 Default is cond (do L1 cache flush in specific instances) 2079 2080 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2081 feature (tagged TLBs) on capable Intel chips. 2082 Default is 1 (enabled) 2083 2084 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2085 affected CPUs 2086 2087 The kernel PTE inversion protection is unconditionally 2088 enabled and cannot be disabled. 2089 2090 full 2091 Provides all available mitigations for the 2092 L1TF vulnerability. Disables SMT and 2093 enables all mitigations in the 2094 hypervisors, i.e. unconditional L1D flush. 2095 2096 SMT control and L1D flush control via the 2097 sysfs interface is still possible after 2098 boot. Hypervisors will issue a warning 2099 when the first VM is started in a 2100 potentially insecure configuration, 2101 i.e. SMT enabled or L1D flush disabled. 2102 2103 full,force 2104 Same as 'full', but disables SMT and L1D 2105 flush runtime control. Implies the 2106 'nosmt=force' command line option. 2107 (i.e. sysfs control of SMT is disabled.) 2108 2109 flush 2110 Leaves SMT enabled and enables the default 2111 hypervisor mitigation, i.e. conditional 2112 L1D flush. 2113 2114 SMT control and L1D flush control via the 2115 sysfs interface is still possible after 2116 boot. Hypervisors will issue a warning 2117 when the first VM is started in a 2118 potentially insecure configuration, 2119 i.e. SMT enabled or L1D flush disabled. 2120 2121 flush,nosmt 2122 2123 Disables SMT and enables the default 2124 hypervisor mitigation. 2125 2126 SMT control and L1D flush control via the 2127 sysfs interface is still possible after 2128 boot. Hypervisors will issue a warning 2129 when the first VM is started in a 2130 potentially insecure configuration, 2131 i.e. SMT enabled or L1D flush disabled. 2132 2133 flush,nowarn 2134 Same as 'flush', but hypervisors will not 2135 warn when a VM is started in a potentially 2136 insecure configuration. 2137 2138 off 2139 Disables hypervisor mitigations and doesn't 2140 emit any warnings. 2141 It also drops the swap size and available 2142 RAM limit restriction on both hypervisor and 2143 bare metal. 2144 2145 Default is 'flush'. 2146 2147 For details see: Documentation/admin-guide/l1tf.rst 2148 2149 l2cr= [PPC] 2150 2151 l3cr= [PPC] 2152 2153 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2154 disabled it. 2155 2156 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2157 value for LAPIC timer one-shot implementation. Default 2158 back to the programmable timer unit in the LAPIC. 2159 2160 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2161 in C2 power state. 2162 2163 libata.dma= [LIBATA] DMA control 2164 libata.dma=0 Disable all PATA and SATA DMA 2165 libata.dma=1 PATA and SATA Disk DMA only 2166 libata.dma=2 ATAPI (CDROM) DMA only 2167 libata.dma=4 Compact Flash DMA only 2168 Combinations also work, so libata.dma=3 enables DMA 2169 for disks and CDROMs, but not CFs. 2170 2171 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2172 libata.ignore_hpa=0 keep BIOS limits (default) 2173 libata.ignore_hpa=1 ignore limits, using full disk 2174 2175 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2176 when set. 2177 Format: <int> 2178 2179 libata.force= [LIBATA] Force configurations. The format is comma 2180 separated list of "[ID:]VAL" where ID is 2181 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2182 matching port, link or device. Basically, it matches 2183 the ATA ID string printed on console by libata. If 2184 the whole ID part is omitted, the last PORT and DEVICE 2185 values are used. If ID hasn't been specified yet, the 2186 configuration applies to all ports, links and devices. 2187 2188 If only DEVICE is omitted, the parameter applies to 2189 the port and all links and devices behind it. DEVICE 2190 number of 0 either selects the first device or the 2191 first fan-out link behind PMP device. It does not 2192 select the host link. DEVICE number of 15 selects the 2193 host link and device attached to it. 2194 2195 The VAL specifies the configuration to force. As long 2196 as there's no ambiguity shortcut notation is allowed. 2197 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2198 The following configurations can be forced. 2199 2200 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2201 Any ID with matching PORT is used. 2202 2203 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2204 2205 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2206 udma[/][16,25,33,44,66,100,133] notation is also 2207 allowed. 2208 2209 * [no]ncq: Turn on or off NCQ. 2210 2211 * [no]ncqtrim: Turn off queued DSM TRIM. 2212 2213 * nohrst, nosrst, norst: suppress hard, soft 2214 and both resets. 2215 2216 * rstonce: only attempt one reset during 2217 hot-unplug link recovery 2218 2219 * dump_id: dump IDENTIFY data. 2220 2221 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2222 2223 * disable: Disable this device. 2224 2225 If there are multiple matching configurations changing 2226 the same attribute, the last one is used. 2227 2228 memblock=debug [KNL] Enable memblock debug messages. 2229 2230 load_ramdisk= [RAM] List of ramdisks to load from floppy 2231 See Documentation/blockdev/ramdisk.txt. 2232 2233 lockd.nlm_grace_period=P [NFS] Assign grace period. 2234 Format: <integer> 2235 2236 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2237 Format: <integer> 2238 2239 lockd.nlm_timeout=T [NFS] Assign timeout value. 2240 Format: <integer> 2241 2242 lockd.nlm_udpport=M [NFS] Assign UDP port. 2243 Format: <integer> 2244 2245 locktorture.nreaders_stress= [KNL] 2246 Set the number of locking read-acquisition kthreads. 2247 Defaults to being automatically set based on the 2248 number of online CPUs. 2249 2250 locktorture.nwriters_stress= [KNL] 2251 Set the number of locking write-acquisition kthreads. 2252 2253 locktorture.onoff_holdoff= [KNL] 2254 Set time (s) after boot for CPU-hotplug testing. 2255 2256 locktorture.onoff_interval= [KNL] 2257 Set time (s) between CPU-hotplug operations, or 2258 zero to disable CPU-hotplug testing. 2259 2260 locktorture.shuffle_interval= [KNL] 2261 Set task-shuffle interval (jiffies). Shuffling 2262 tasks allows some CPUs to go into dyntick-idle 2263 mode during the locktorture test. 2264 2265 locktorture.shutdown_secs= [KNL] 2266 Set time (s) after boot system shutdown. This 2267 is useful for hands-off automated testing. 2268 2269 locktorture.stat_interval= [KNL] 2270 Time (s) between statistics printk()s. 2271 2272 locktorture.stutter= [KNL] 2273 Time (s) to stutter testing, for example, 2274 specifying five seconds causes the test to run for 2275 five seconds, wait for five seconds, and so on. 2276 This tests the locking primitive's ability to 2277 transition abruptly to and from idle. 2278 2279 locktorture.torture_type= [KNL] 2280 Specify the locking implementation to test. 2281 2282 locktorture.verbose= [KNL] 2283 Enable additional printk() statements. 2284 2285 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2286 Format: <irq> 2287 2288 loglevel= All Kernel Messages with a loglevel smaller than the 2289 console loglevel will be printed to the console. It can 2290 also be changed with klogd or other programs. The 2291 loglevels are defined as follows: 2292 2293 0 (KERN_EMERG) system is unusable 2294 1 (KERN_ALERT) action must be taken immediately 2295 2 (KERN_CRIT) critical conditions 2296 3 (KERN_ERR) error conditions 2297 4 (KERN_WARNING) warning conditions 2298 5 (KERN_NOTICE) normal but significant condition 2299 6 (KERN_INFO) informational 2300 7 (KERN_DEBUG) debug-level messages 2301 2302 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2303 in bytes. n must be a power of two and greater 2304 than the minimal size. The minimal size is defined 2305 by LOG_BUF_SHIFT kernel config parameter. There is 2306 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2307 that allows to increase the default size depending on 2308 the number of CPUs. See init/Kconfig for more details. 2309 2310 logo.nologo [FB] Disables display of the built-in Linux logo. 2311 This may be used to provide more screen space for 2312 kernel log messages and is useful when debugging 2313 kernel boot problems. 2314 2315 lp=0 [LP] Specify parallel ports to use, e.g, 2316 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2317 lp=reset first parallel port). 'lp=0' disables the 2318 lp=auto printer driver. 'lp=reset' (which can be 2319 specified in addition to the ports) causes 2320 attached printers to be reset. Using 2321 lp=port1,port2,... specifies the parallel ports 2322 to associate lp devices with, starting with 2323 lp0. A port specification may be 'none' to skip 2324 that lp device, or a parport name such as 2325 'parport0'. Specifying 'lp=auto' instead of a 2326 port specification list means that device IDs 2327 from each port should be examined, to see if 2328 an IEEE 1284-compliant printer is attached; if 2329 so, the driver will manage that printer. 2330 See also header of drivers/char/lp.c. 2331 2332 lpj=n [KNL] 2333 Sets loops_per_jiffy to given constant, thus avoiding 2334 time-consuming boot-time autodetection (up to 250 ms per 2335 CPU). 0 enables autodetection (default). To determine 2336 the correct value for your kernel, boot with normal 2337 autodetection and see what value is printed. Note that 2338 on SMP systems the preset will be applied to all CPUs, 2339 which is likely to cause problems if your CPUs need 2340 significantly divergent settings. An incorrect value 2341 will cause delays in the kernel to be wrong, leading to 2342 unpredictable I/O errors and other breakage. Although 2343 unlikely, in the extreme case this might damage your 2344 hardware. 2345 2346 ltpc= [NET] 2347 Format: <io>,<irq>,<dma> 2348 2349 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2350 2351 lsm=lsm1,...,lsmN 2352 [SECURITY] Choose order of LSM initialization. This 2353 overrides CONFIG_LSM, and the "security=" parameter. 2354 2355 machvec= [IA-64] Force the use of a particular machine-vector 2356 (machvec) in a generic kernel. 2357 Example: machvec=hpzx1_swiotlb 2358 2359 machtype= [Loongson] Share the same kernel image file between different 2360 yeeloong laptop. 2361 Example: machtype=lemote-yeeloong-2f-7inch 2362 2363 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2364 than or equal to this physical address is ignored. 2365 2366 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2367 will bring up during bootup. maxcpus=n : n >= 0 limits 2368 the kernel to bring up 'n' processors. Surely after 2369 bootup you can bring up the other plugged cpu by executing 2370 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2371 only takes effect during system bootup. 2372 While n=0 is a special case, it is equivalent to "nosmp", 2373 which also disables the IO APIC. 2374 2375 max_loop= [LOOP] The number of loop block devices that get 2376 (loop.max_loop) unconditionally pre-created at init time. The default 2377 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2378 of statically allocating a predefined number, loop 2379 devices can be requested on-demand with the 2380 /dev/loop-control interface. 2381 2382 mce [X86-32] Machine Check Exception 2383 2384 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt 2385 2386 md= [HW] RAID subsystems devices and level 2387 See Documentation/admin-guide/md.rst. 2388 2389 mdacon= [MDA] 2390 Format: <first>,<last> 2391 Specifies range of consoles to be captured by the MDA. 2392 2393 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2394 Amount of memory to be used when the kernel is not able 2395 to see the whole system memory or for test. 2396 [X86] Work as limiting max address. Use together 2397 with memmap= to avoid physical address space collisions. 2398 Without memmap= PCI devices could be placed at addresses 2399 belonging to unused RAM. 2400 2401 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2402 memory. 2403 2404 memchunk=nn[KMG] 2405 [KNL,SH] Allow user to override the default size for 2406 per-device physically contiguous DMA buffers. 2407 2408 memhp_default_state=online/offline 2409 [KNL] Set the initial state for the memory hotplug 2410 onlining policy. If not specified, the default value is 2411 set according to the 2412 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2413 option. 2414 See Documentation/memory-hotplug.txt. 2415 2416 memmap=exactmap [KNL,X86] Enable setting of an exact 2417 E820 memory map, as specified by the user. 2418 Such memmap=exactmap lines can be constructed based on 2419 BIOS output or other requirements. See the memmap=nn@ss 2420 option description. 2421 2422 memmap=nn[KMG]@ss[KMG] 2423 [KNL] Force usage of a specific region of memory. 2424 Region of memory to be used is from ss to ss+nn. 2425 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2426 which limits max address to nn[KMG]. 2427 Multiple different regions can be specified, 2428 comma delimited. 2429 Example: 2430 memmap=100M@2G,100M#3G,1G!1024G 2431 2432 memmap=nn[KMG]#ss[KMG] 2433 [KNL,ACPI] Mark specific memory as ACPI data. 2434 Region of memory to be marked is from ss to ss+nn. 2435 2436 memmap=nn[KMG]$ss[KMG] 2437 [KNL,ACPI] Mark specific memory as reserved. 2438 Region of memory to be reserved is from ss to ss+nn. 2439 Example: Exclude memory from 0x18690000-0x1869ffff 2440 memmap=64K$0x18690000 2441 or 2442 memmap=0x10000$0x18690000 2443 Some bootloaders may need an escape character before '$', 2444 like Grub2, otherwise '$' and the following number 2445 will be eaten. 2446 2447 memmap=nn[KMG]!ss[KMG] 2448 [KNL,X86] Mark specific memory as protected. 2449 Region of memory to be used, from ss to ss+nn. 2450 The memory region may be marked as e820 type 12 (0xc) 2451 and is NVDIMM or ADR memory. 2452 2453 memmap=<size>%<offset>-<oldtype>+<newtype> 2454 [KNL,ACPI] Convert memory within the specified region 2455 from <oldtype> to <newtype>. If "-<oldtype>" is left 2456 out, the whole region will be marked as <newtype>, 2457 even if previously unavailable. If "+<newtype>" is left 2458 out, matching memory will be removed. Types are 2459 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2460 3 = ACPI, 12 = PRAM. 2461 2462 memory_corruption_check=0/1 [X86] 2463 Some BIOSes seem to corrupt the first 64k of 2464 memory when doing things like suspend/resume. 2465 Setting this option will scan the memory 2466 looking for corruption. Enabling this will 2467 both detect corruption and prevent the kernel 2468 from using the memory being corrupted. 2469 However, its intended as a diagnostic tool; if 2470 repeatable BIOS-originated corruption always 2471 affects the same memory, you can use memmap= 2472 to prevent the kernel from using that memory. 2473 2474 memory_corruption_check_size=size [X86] 2475 By default it checks for corruption in the low 2476 64k, making this memory unavailable for normal 2477 use. Use this parameter to scan for 2478 corruption in more or less memory. 2479 2480 memory_corruption_check_period=seconds [X86] 2481 By default it checks for corruption every 60 2482 seconds. Use this parameter to check at some 2483 other rate. 0 disables periodic checking. 2484 2485 memtest= [KNL,X86,ARM,PPC] Enable memtest 2486 Format: <integer> 2487 default : 0 <disable> 2488 Specifies the number of memtest passes to be 2489 performed. Each pass selects another test 2490 pattern from a given set of patterns. Memtest 2491 fills the memory with this pattern, validates 2492 memory contents and reserves bad memory 2493 regions that are detected. 2494 2495 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2496 Valid arguments: on, off 2497 Default (depends on kernel configuration option): 2498 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2499 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2500 mem_encrypt=on: Activate SME 2501 mem_encrypt=off: Do not activate SME 2502 2503 Refer to Documentation/x86/amd-memory-encryption.txt 2504 for details on when memory encryption can be activated. 2505 2506 mem_sleep_default= [SUSPEND] Default system suspend mode: 2507 s2idle - Suspend-To-Idle 2508 shallow - Power-On Suspend or equivalent (if supported) 2509 deep - Suspend-To-RAM or equivalent (if supported) 2510 See Documentation/admin-guide/pm/sleep-states.rst. 2511 2512 meye.*= [HW] Set MotionEye Camera parameters 2513 See Documentation/media/v4l-drivers/meye.rst. 2514 2515 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2516 Multi-Function General Purpose Timers on AMD Geode 2517 platforms. 2518 2519 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2520 the BIOS has incorrectly applied a workaround. TinyBIOS 2521 version 0.98 is known to be affected, 0.99 fixes the 2522 problem by letting the user disable the workaround. 2523 2524 mga= [HW,DRM] 2525 2526 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2527 physical address is ignored. 2528 2529 mini2440= [ARM,HW,KNL] 2530 Format:[0..2][b][c][t] 2531 Default: "0tb" 2532 MINI2440 configuration specification: 2533 0 - The attached screen is the 3.5" TFT 2534 1 - The attached screen is the 7" TFT 2535 2 - The VGA Shield is attached (1024x768) 2536 Leaving out the screen size parameter will not load 2537 the TFT driver, and the framebuffer will be left 2538 unconfigured. 2539 b - Enable backlight. The TFT backlight pin will be 2540 linked to the kernel VESA blanking code and a GPIO 2541 LED. This parameter is not necessary when using the 2542 VGA shield. 2543 c - Enable the s3c camera interface. 2544 t - Reserved for enabling touchscreen support. The 2545 touchscreen support is not enabled in the mainstream 2546 kernel as of 2.6.30, a preliminary port can be found 2547 in the "bleeding edge" mini2440 support kernel at 2548 http://repo.or.cz/w/linux-2.6/mini2440.git 2549 2550 mitigations= 2551 [X86,PPC,S390,ARM64] Control optional mitigations for 2552 CPU vulnerabilities. This is a set of curated, 2553 arch-independent options, each of which is an 2554 aggregation of existing arch-specific options. 2555 2556 off 2557 Disable all optional CPU mitigations. This 2558 improves system performance, but it may also 2559 expose users to several CPU vulnerabilities. 2560 Equivalent to: nopti [X86,PPC] 2561 kpti=0 [ARM64] 2562 nospectre_v1 [PPC] 2563 nobp=0 [S390] 2564 nospectre_v2 [X86,PPC,S390,ARM64] 2565 spectre_v2_user=off [X86] 2566 spec_store_bypass_disable=off [X86,PPC] 2567 ssbd=force-off [ARM64] 2568 l1tf=off [X86] 2569 2570 auto (default) 2571 Mitigate all CPU vulnerabilities, but leave SMT 2572 enabled, even if it's vulnerable. This is for 2573 users who don't want to be surprised by SMT 2574 getting disabled across kernel upgrades, or who 2575 have other ways of avoiding SMT-based attacks. 2576 Equivalent to: (default behavior) 2577 2578 auto,nosmt 2579 Mitigate all CPU vulnerabilities, disabling SMT 2580 if needed. This is for users who always want to 2581 be fully mitigated, even if it means losing SMT. 2582 Equivalent to: l1tf=flush,nosmt [X86] 2583 2584 mminit_loglevel= 2585 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2586 parameter allows control of the logging verbosity for 2587 the additional memory initialisation checks. A value 2588 of 0 disables mminit logging and a level of 4 will 2589 log everything. Information is printed at KERN_DEBUG 2590 so loglevel=8 may also need to be specified. 2591 2592 module.sig_enforce 2593 [KNL] When CONFIG_MODULE_SIG is set, this means that 2594 modules without (valid) signatures will fail to load. 2595 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2596 is always true, so this option does nothing. 2597 2598 module_blacklist= [KNL] Do not load a comma-separated list of 2599 modules. Useful for debugging problem modules. 2600 2601 mousedev.tap_time= 2602 [MOUSE] Maximum time between finger touching and 2603 leaving touchpad surface for touch to be considered 2604 a tap and be reported as a left button click (for 2605 touchpads working in absolute mode only). 2606 Format: <msecs> 2607 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2608 reporting absolute coordinates, such as tablets 2609 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2610 reporting absolute coordinates, such as tablets 2611 2612 movablecore= [KNL,X86,IA-64,PPC] 2613 Format: nn[KMGTPE] | nn% 2614 This parameter is the complement to kernelcore=, it 2615 specifies the amount of memory used for migratable 2616 allocations. If both kernelcore and movablecore is 2617 specified, then kernelcore will be at *least* the 2618 specified value but may be more. If movablecore on its 2619 own is specified, the administrator must be careful 2620 that the amount of memory usable for all allocations 2621 is not too small. 2622 2623 movable_node [KNL] Boot-time switch to make hotplugable memory 2624 NUMA nodes to be movable. This means that the memory 2625 of such nodes will be usable only for movable 2626 allocations which rules out almost all kernel 2627 allocations. Use with caution! 2628 2629 MTD_Partition= [MTD] 2630 Format: <name>,<region-number>,<size>,<offset> 2631 2632 MTD_Region= [MTD] Format: 2633 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2634 2635 mtdparts= [MTD] 2636 See drivers/mtd/cmdlinepart.c. 2637 2638 multitce=off [PPC] This parameter disables the use of the pSeries 2639 firmware feature for updating multiple TCE entries 2640 at a time. 2641 2642 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2643 2644 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2645 2646 boundary - index of last SLC block on Flex-OneNAND. 2647 The remaining blocks are configured as MLC blocks. 2648 lock - Configure if Flex-OneNAND boundary should be locked. 2649 Once locked, the boundary cannot be changed. 2650 1 indicates lock status, 0 indicates unlock status. 2651 2652 mtdset= [ARM] 2653 ARM/S3C2412 JIVE boot control 2654 2655 See arch/arm/mach-s3c2412/mach-jive.c 2656 2657 mtouchusb.raw_coordinates= 2658 [HW] Make the MicroTouch USB driver use raw coordinates 2659 ('y', default) or cooked coordinates ('n') 2660 2661 mtrr_chunk_size=nn[KMG] [X86] 2662 used for mtrr cleanup. It is largest continuous chunk 2663 that could hold holes aka. UC entries. 2664 2665 mtrr_gran_size=nn[KMG] [X86] 2666 Used for mtrr cleanup. It is granularity of mtrr block. 2667 Default is 1. 2668 Large value could prevent small alignment from 2669 using up MTRRs. 2670 2671 mtrr_spare_reg_nr=n [X86] 2672 Format: <integer> 2673 Range: 0,7 : spare reg number 2674 Default : 1 2675 Used for mtrr cleanup. It is spare mtrr entries number. 2676 Set to 2 or more if your graphical card needs more. 2677 2678 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2679 2680 netdev= [NET] Network devices parameters 2681 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2682 Note that mem_start is often overloaded to mean 2683 something different and driver-specific. 2684 This usage is only documented in each driver source 2685 file if at all. 2686 2687 nf_conntrack.acct= 2688 [NETFILTER] Enable connection tracking flow accounting 2689 0 to disable accounting 2690 1 to enable accounting 2691 Default value is 0. 2692 2693 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2694 See Documentation/filesystems/nfs/nfsroot.txt. 2695 2696 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2697 See Documentation/filesystems/nfs/nfsroot.txt. 2698 2699 nfsrootdebug [NFS] enable nfsroot debugging messages. 2700 See Documentation/filesystems/nfs/nfsroot.txt. 2701 2702 nfs.callback_nr_threads= 2703 [NFSv4] set the total number of threads that the 2704 NFS client will assign to service NFSv4 callback 2705 requests. 2706 2707 nfs.callback_tcpport= 2708 [NFS] set the TCP port on which the NFSv4 callback 2709 channel should listen. 2710 2711 nfs.cache_getent= 2712 [NFS] sets the pathname to the program which is used 2713 to update the NFS client cache entries. 2714 2715 nfs.cache_getent_timeout= 2716 [NFS] sets the timeout after which an attempt to 2717 update a cache entry is deemed to have failed. 2718 2719 nfs.idmap_cache_timeout= 2720 [NFS] set the maximum lifetime for idmapper cache 2721 entries. 2722 2723 nfs.enable_ino64= 2724 [NFS] enable 64-bit inode numbers. 2725 If zero, the NFS client will fake up a 32-bit inode 2726 number for the readdir() and stat() syscalls instead 2727 of returning the full 64-bit number. 2728 The default is to return 64-bit inode numbers. 2729 2730 nfs.max_session_cb_slots= 2731 [NFSv4.1] Sets the maximum number of session 2732 slots the client will assign to the callback 2733 channel. This determines the maximum number of 2734 callbacks the client will process in parallel for 2735 a particular server. 2736 2737 nfs.max_session_slots= 2738 [NFSv4.1] Sets the maximum number of session slots 2739 the client will attempt to negotiate with the server. 2740 This limits the number of simultaneous RPC requests 2741 that the client can send to the NFSv4.1 server. 2742 Note that there is little point in setting this 2743 value higher than the max_tcp_slot_table_limit. 2744 2745 nfs.nfs4_disable_idmapping= 2746 [NFSv4] When set to the default of '1', this option 2747 ensures that both the RPC level authentication 2748 scheme and the NFS level operations agree to use 2749 numeric uids/gids if the mount is using the 2750 'sec=sys' security flavour. In effect it is 2751 disabling idmapping, which can make migration from 2752 legacy NFSv2/v3 systems to NFSv4 easier. 2753 Servers that do not support this mode of operation 2754 will be autodetected by the client, and it will fall 2755 back to using the idmapper. 2756 To turn off this behaviour, set the value to '0'. 2757 nfs.nfs4_unique_id= 2758 [NFS4] Specify an additional fixed unique ident- 2759 ification string that NFSv4 clients can insert into 2760 their nfs_client_id4 string. This is typically a 2761 UUID that is generated at system install time. 2762 2763 nfs.send_implementation_id = 2764 [NFSv4.1] Send client implementation identification 2765 information in exchange_id requests. 2766 If zero, no implementation identification information 2767 will be sent. 2768 The default is to send the implementation identification 2769 information. 2770 2771 nfs.recover_lost_locks = 2772 [NFSv4] Attempt to recover locks that were lost due 2773 to a lease timeout on the server. Please note that 2774 doing this risks data corruption, since there are 2775 no guarantees that the file will remain unchanged 2776 after the locks are lost. 2777 If you want to enable the kernel legacy behaviour of 2778 attempting to recover these locks, then set this 2779 parameter to '1'. 2780 The default parameter value of '0' causes the kernel 2781 not to attempt recovery of lost locks. 2782 2783 nfs4.layoutstats_timer = 2784 [NFSv4.2] Change the rate at which the kernel sends 2785 layoutstats to the pNFS metadata server. 2786 2787 Setting this to value to 0 causes the kernel to use 2788 whatever value is the default set by the layout 2789 driver. A non-zero value sets the minimum interval 2790 in seconds between layoutstats transmissions. 2791 2792 nfsd.nfs4_disable_idmapping= 2793 [NFSv4] When set to the default of '1', the NFSv4 2794 server will return only numeric uids and gids to 2795 clients using auth_sys, and will accept numeric uids 2796 and gids from such clients. This is intended to ease 2797 migration from NFSv2/v3. 2798 2799 nmi_debug= [KNL,SH] Specify one or more actions to take 2800 when a NMI is triggered. 2801 Format: [state][,regs][,debounce][,die] 2802 2803 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2804 Format: [panic,][nopanic,][num] 2805 Valid num: 0 or 1 2806 0 - turn hardlockup detector in nmi_watchdog off 2807 1 - turn hardlockup detector in nmi_watchdog on 2808 When panic is specified, panic when an NMI watchdog 2809 timeout occurs (or 'nopanic' to override the opposite 2810 default). To disable both hard and soft lockup detectors, 2811 please see 'nowatchdog'. 2812 This is useful when you use a panic=... timeout and 2813 need the box quickly up again. 2814 2815 These settings can be accessed at runtime via 2816 the nmi_watchdog and hardlockup_panic sysctls. 2817 2818 netpoll.carrier_timeout= 2819 [NET] Specifies amount of time (in seconds) that 2820 netpoll should wait for a carrier. By default netpoll 2821 waits 4 seconds. 2822 2823 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2824 emulation library even if a 387 maths coprocessor 2825 is present. 2826 2827 no5lvl [X86-64] Disable 5-level paging mode. Forces 2828 kernel to use 4-level paging instead. 2829 2830 no_console_suspend 2831 [HW] Never suspend the console 2832 Disable suspending of consoles during suspend and 2833 hibernate operations. Once disabled, debugging 2834 messages can reach various consoles while the rest 2835 of the system is being put to sleep (ie, while 2836 debugging driver suspend/resume hooks). This may 2837 not work reliably with all consoles, but is known 2838 to work with serial and VGA consoles. 2839 To facilitate more flexible debugging, we also add 2840 console_suspend, a printk module parameter to control 2841 it. Users could use console_suspend (usually 2842 /sys/module/printk/parameters/console_suspend) to 2843 turn on/off it dynamically. 2844 2845 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2846 caches in the slab allocator. Saves per-node memory, 2847 but will impact performance. 2848 2849 noalign [KNL,ARM] 2850 2851 noaltinstr [S390] Disables alternative instructions patching 2852 (CPU alternatives feature). 2853 2854 noapic [SMP,APIC] Tells the kernel to not make use of any 2855 IOAPICs that may be present in the system. 2856 2857 noautogroup Disable scheduler automatic task group creation. 2858 2859 nobats [PPC] Do not use BATs for mapping kernel lowmem 2860 on "Classic" PPC cores. 2861 2862 nocache [ARM] 2863 2864 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2865 2866 nodelayacct [KNL] Disable per-task delay accounting 2867 2868 nodsp [SH] Disable hardware DSP at boot time. 2869 2870 noefi Disable EFI runtime services support. 2871 2872 noexec [IA-64] 2873 2874 noexec [X86] 2875 On X86-32 available only on PAE configured kernels. 2876 noexec=on: enable non-executable mappings (default) 2877 noexec=off: disable non-executable mappings 2878 2879 nosmap [X86] 2880 Disable SMAP (Supervisor Mode Access Prevention) 2881 even if it is supported by processor. 2882 2883 nosmep [X86] 2884 Disable SMEP (Supervisor Mode Execution Prevention) 2885 even if it is supported by processor. 2886 2887 noexec32 [X86-64] 2888 This affects only 32-bit executables. 2889 noexec32=on: enable non-executable mappings (default) 2890 read doesn't imply executable mappings 2891 noexec32=off: disable non-executable mappings 2892 read implies executable mappings 2893 2894 nofpu [MIPS,SH] Disable hardware FPU at boot time. 2895 2896 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2897 register save and restore. The kernel will only save 2898 legacy floating-point registers on task switch. 2899 2900 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings. 2901 2902 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 2903 Equivalent to smt=1. 2904 2905 [KNL,x86] Disable symmetric multithreading (SMT). 2906 nosmt=force: Force disable SMT, cannot be undone 2907 via the sysfs control file. 2908 2909 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds 2910 check bypass). With this option data leaks are possible 2911 in the system. 2912 2913 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 2914 the Spectre variant 2 (indirect branch prediction) 2915 vulnerability. System may allow data leaks with this 2916 option. 2917 2918 nospec_store_bypass_disable 2919 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 2920 2921 noxsave [BUGS=X86] Disables x86 extended register state save 2922 and restore using xsave. The kernel will fallback to 2923 enabling legacy floating-point and sse state. 2924 2925 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 2926 register states. The kernel will fall back to use 2927 xsave to save the states. By using this parameter, 2928 performance of saving the states is degraded because 2929 xsave doesn't support modified optimization while 2930 xsaveopt supports it on xsaveopt enabled systems. 2931 2932 noxsaves [X86] Disables xsaves and xrstors used in saving and 2933 restoring x86 extended register state in compacted 2934 form of xsave area. The kernel will fall back to use 2935 xsaveopt and xrstor to save and restore the states 2936 in standard form of xsave area. By using this 2937 parameter, xsave area per process might occupy more 2938 memory on xsaves enabled systems. 2939 2940 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 2941 wfi(ARM) instruction doesn't work correctly and not to 2942 use it. This is also useful when using JTAG debugger. 2943 2944 no_file_caps Tells the kernel not to honor file capabilities. The 2945 only way then for a file to be executed with privilege 2946 is to be setuid root or executed by root. 2947 2948 nohalt [IA-64] Tells the kernel not to use the power saving 2949 function PAL_HALT_LIGHT when idle. This increases 2950 power-consumption. On the positive side, it reduces 2951 interrupt wake-up latency, which may improve performance 2952 in certain environments such as networked servers or 2953 real-time systems. 2954 2955 nohibernate [HIBERNATION] Disable hibernation and resume. 2956 2957 nohz= [KNL] Boottime enable/disable dynamic ticks 2958 Valid arguments: on, off 2959 Default: on 2960 2961 nohz_full= [KNL,BOOT,SMP,ISOL] 2962 The argument is a cpu list, as described above. 2963 In kernels built with CONFIG_NO_HZ_FULL=y, set 2964 the specified list of CPUs whose tick will be stopped 2965 whenever possible. The boot CPU will be forced outside 2966 the range to maintain the timekeeping. Any CPUs 2967 in this list will have their RCU callbacks offloaded, 2968 just as if they had also been called out in the 2969 rcu_nocbs= boot parameter. 2970 2971 noiotrap [SH] Disables trapped I/O port accesses. 2972 2973 noirqdebug [X86-32] Disables the code which attempts to detect and 2974 disable unhandled interrupt sources. 2975 2976 no_timer_check [X86,APIC] Disables the code which tests for 2977 broken timer IRQ sources. 2978 2979 noisapnp [ISAPNP] Disables ISA PnP code. 2980 2981 noinitrd [RAM] Tells the kernel not to load any configured 2982 initial RAM disk. 2983 2984 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 2985 remapping. 2986 [Deprecated - use intremap=off] 2987 2988 nointroute [IA-64] 2989 2990 noinvpcid [X86] Disable the INVPCID cpu feature. 2991 2992 nojitter [IA-64] Disables jitter checking for ITC timers. 2993 2994 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 2995 2996 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 2997 fault handling. 2998 2999 no-vmw-sched-clock 3000 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3001 clock and use the default one. 3002 3003 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 3004 steal time is computed, but won't influence scheduler 3005 behaviour 3006 3007 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3008 3009 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3010 3011 noltlbs [PPC] Do not use large page/tlb entries for kernel 3012 lowmem mapping on PPC40x and PPC8xx 3013 3014 nomca [IA-64] Disable machine check abort handling 3015 3016 nomce [X86-32] Disable Machine Check Exception 3017 3018 nomfgpt [X86-32] Disable Multi-Function General Purpose 3019 Timer usage (for AMD Geode machines). 3020 3021 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3022 shutdown the other cpus. Instead use the REBOOT_VECTOR 3023 irq. 3024 3025 nomodule Disable module load 3026 3027 nopat [X86] Disable PAT (page attribute table extension of 3028 pagetables) support. 3029 3030 nopcid [X86-64] Disable the PCID cpu feature. 3031 3032 norandmaps Don't use address space randomization. Equivalent to 3033 echo 0 > /proc/sys/kernel/randomize_va_space 3034 3035 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3036 with UP alternatives 3037 3038 nordrand [X86] Disable kernel use of the RDRAND and 3039 RDSEED instructions even if they are supported 3040 by the processor. RDRAND and RDSEED are still 3041 available to user space applications. 3042 3043 noresume [SWSUSP] Disables resume and restores original swap 3044 space. 3045 3046 no-scroll [VGA] Disables scrollback. 3047 This is required for the Braillex ib80-piezo Braille 3048 reader made by F.H. Papenmeier (Germany). 3049 3050 nosbagart [IA-64] 3051 3052 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3053 3054 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3055 and disable the IO APIC. legacy for "maxcpus=0". 3056 3057 nosoftlockup [KNL] Disable the soft-lockup detector. 3058 3059 nosync [HW,M68K] Disables sync negotiation for all devices. 3060 3061 nowatchdog [KNL] Disable both lockup detectors, i.e. 3062 soft-lockup and NMI watchdog (hard-lockup). 3063 3064 nowb [ARM] 3065 3066 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3067 3068 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3069 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3070 Some features depend on CPU0. Known dependencies are: 3071 1. Resume from suspend/hibernate depends on CPU0. 3072 Suspend/hibernate will fail if CPU0 is offline and you 3073 need to online CPU0 before suspend/hibernate. 3074 2. PIC interrupts also depend on CPU0. CPU0 can't be 3075 removed if a PIC interrupt is detected. 3076 It's said poweroff/reboot may depend on CPU0 on some 3077 machines although I haven't seen such issues so far 3078 after CPU0 is offline on a few tested machines. 3079 If the dependencies are under your control, you can 3080 turn on cpu0_hotplug. 3081 3082 nps_mtm_hs_ctr= [KNL,ARC] 3083 This parameter sets the maximum duration, in 3084 cycles, each HW thread of the CTOP can run 3085 without interruptions, before HW switches it. 3086 The actual maximum duration is 16 times this 3087 parameter's value. 3088 Format: integer between 1 and 255 3089 Default: 255 3090 3091 nptcg= [IA-64] Override max number of concurrent global TLB 3092 purges which is reported from either PAL_VM_SUMMARY or 3093 SAL PALO. 3094 3095 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3096 could support. nr_cpus=n : n >= 1 limits the kernel to 3097 support 'n' processors. It could be larger than the 3098 number of already plugged CPU during bootup, later in 3099 runtime you can physically add extra cpu until it reaches 3100 n. So during boot up some boot time memory for per-cpu 3101 variables need be pre-allocated for later physical cpu 3102 hot plugging. 3103 3104 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3105 3106 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3107 Allowed values are enable and disable 3108 3109 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3110 'node', 'default' can be specified 3111 This can be set from sysctl after boot. 3112 See Documentation/sysctl/vm.txt for details. 3113 3114 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3115 See Documentation/debugging-via-ohci1394.txt for more 3116 info. 3117 3118 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3119 Rather than timing out after 20 ms if an EC 3120 command is not properly ACKed, override the length 3121 of the timeout. We have interrupts disabled while 3122 waiting for the ACK, so if this is set too high 3123 interrupts *may* be lost! 3124 3125 omap_mux= [OMAP] Override bootloader pin multiplexing. 3126 Format: <mux_mode0.mode_name=value>... 3127 For example, to override I2C bus2: 3128 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3129 3130 oprofile.timer= [HW] 3131 Use timer interrupt instead of performance counters 3132 3133 oprofile.cpu_type= Force an oprofile cpu type 3134 This might be useful if you have an older oprofile 3135 userland or if you want common events. 3136 Format: { arch_perfmon } 3137 arch_perfmon: [X86] Force use of architectural 3138 perfmon on Intel CPUs instead of the 3139 CPU specific event set. 3140 timer: [X86] Force use of architectural NMI 3141 timer mode (see also oprofile.timer 3142 for generic hr timer mode) 3143 3144 oops=panic Always panic on oopses. Default is to just kill the 3145 process, but there is a small probability of 3146 deadlocking the machine. 3147 This will also cause panics on machine check exceptions. 3148 Useful together with panic=30 to trigger a reboot. 3149 3150 page_owner= [KNL] Boot-time page_owner enabling option. 3151 Storage of the information about who allocated 3152 each page is disabled in default. With this switch, 3153 we can turn it on. 3154 on: enable the feature 3155 3156 page_poison= [KNL] Boot-time parameter changing the state of 3157 poisoning on the buddy allocator, available with 3158 CONFIG_PAGE_POISONING=y. 3159 off: turn off poisoning (default) 3160 on: turn on poisoning 3161 3162 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3163 timeout > 0: seconds before rebooting 3164 timeout = 0: wait forever 3165 timeout < 0: reboot immediately 3166 Format: <timeout> 3167 3168 panic_print= Bitmask for printing system info when panic happens. 3169 User can chose combination of the following bits: 3170 bit 0: print all tasks info 3171 bit 1: print system memory info 3172 bit 2: print timer info 3173 bit 3: print locks info if CONFIG_LOCKDEP is on 3174 bit 4: print ftrace buffer 3175 3176 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3177 on a WARN(). 3178 3179 crash_kexec_post_notifiers 3180 Run kdump after running panic-notifiers and dumping 3181 kmsg. This only for the users who doubt kdump always 3182 succeeds in any situation. 3183 Note that this also increases risks of kdump failure, 3184 because some panic notifiers can make the crashed 3185 kernel more unstable. 3186 3187 parkbd.port= [HW] Parallel port number the keyboard adapter is 3188 connected to, default is 0. 3189 Format: <parport#> 3190 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3191 0 for XT, 1 for AT (default is AT). 3192 Format: <mode> 3193 3194 parport= [HW,PPT] Specify parallel ports. 0 disables. 3195 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3196 Use 'auto' to force the driver to use any 3197 IRQ/DMA settings detected (the default is to 3198 ignore detected IRQ/DMA settings because of 3199 possible conflicts). You can specify the base 3200 address, IRQ, and DMA settings; IRQ and DMA 3201 should be numbers, or 'auto' (for using detected 3202 settings on that particular port), or 'nofifo' 3203 (to avoid using a FIFO even if it is detected). 3204 Parallel ports are assigned in the order they 3205 are specified on the command line, starting 3206 with parport0. 3207 3208 parport_init_mode= [HW,PPT] 3209 Configure VIA parallel port to operate in 3210 a specific mode. This is necessary on Pegasos 3211 computer where firmware has no options for setting 3212 up parallel port mode and sets it to spp. 3213 Currently this function knows 686a and 8231 chips. 3214 Format: [spp|ps2|epp|ecp|ecpepp] 3215 3216 pause_on_oops= 3217 Halt all CPUs after the first oops has been printed for 3218 the specified number of seconds. This is to be used if 3219 your oopses keep scrolling off the screen. 3220 3221 pcbit= [HW,ISDN] 3222 3223 pcd. [PARIDE] 3224 See header of drivers/block/paride/pcd.c. 3225 See also Documentation/blockdev/paride.txt. 3226 3227 pci=option[,option...] [PCI] various PCI subsystem options. 3228 3229 Some options herein operate on a specific device 3230 or a set of devices (<pci_dev>). These are 3231 specified in one of the following formats: 3232 3233 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3234 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3235 3236 Note: the first format specifies a PCI 3237 bus/device/function address which may change 3238 if new hardware is inserted, if motherboard 3239 firmware changes, or due to changes caused 3240 by other kernel parameters. If the 3241 domain is left unspecified, it is 3242 taken to be zero. Optionally, a path 3243 to a device through multiple device/function 3244 addresses can be specified after the base 3245 address (this is more robust against 3246 renumbering issues). The second format 3247 selects devices using IDs from the 3248 configuration space which may match multiple 3249 devices in the system. 3250 3251 earlydump dump PCI config space before the kernel 3252 changes anything 3253 off [X86] don't probe for the PCI bus 3254 bios [X86-32] force use of PCI BIOS, don't access 3255 the hardware directly. Use this if your machine 3256 has a non-standard PCI host bridge. 3257 nobios [X86-32] disallow use of PCI BIOS, only direct 3258 hardware access methods are allowed. Use this 3259 if you experience crashes upon bootup and you 3260 suspect they are caused by the BIOS. 3261 conf1 [X86] Force use of PCI Configuration Access 3262 Mechanism 1 (config address in IO port 0xCF8, 3263 data in IO port 0xCFC, both 32-bit). 3264 conf2 [X86] Force use of PCI Configuration Access 3265 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3266 the function, IO port 0xCFA, also 8-bit, sets 3267 bus number. The config space is then accessed 3268 through ports 0xC000-0xCFFF). 3269 See http://wiki.osdev.org/PCI for more info 3270 on the configuration access mechanisms. 3271 noaer [PCIE] If the PCIEAER kernel config parameter is 3272 enabled, this kernel boot option can be used to 3273 disable the use of PCIE advanced error reporting. 3274 nodomains [PCI] Disable support for multiple PCI 3275 root domains (aka PCI segments, in ACPI-speak). 3276 nommconf [X86] Disable use of MMCONFIG for PCI 3277 Configuration 3278 check_enable_amd_mmconf [X86] check for and enable 3279 properly configured MMIO access to PCI 3280 config space on AMD family 10h CPU 3281 nomsi [MSI] If the PCI_MSI kernel config parameter is 3282 enabled, this kernel boot option can be used to 3283 disable the use of MSI interrupts system-wide. 3284 noioapicquirk [APIC] Disable all boot interrupt quirks. 3285 Safety option to keep boot IRQs enabled. This 3286 should never be necessary. 3287 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3288 primary IO-APIC for bridges that cannot disable 3289 boot IRQs. This fixes a source of spurious IRQs 3290 when the system masks IRQs. 3291 noioapicreroute [APIC] Disable workaround that uses the 3292 boot IRQ equivalent of an IRQ that connects to 3293 a chipset where boot IRQs cannot be disabled. 3294 The opposite of ioapicreroute. 3295 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3296 routing table. These calls are known to be buggy 3297 on several machines and they hang the machine 3298 when used, but on other computers it's the only 3299 way to get the interrupt routing table. Try 3300 this option if the kernel is unable to allocate 3301 IRQs or discover secondary PCI buses on your 3302 motherboard. 3303 rom [X86] Assign address space to expansion ROMs. 3304 Use with caution as certain devices share 3305 address decoders between ROMs and other 3306 resources. 3307 norom [X86] Do not assign address space to 3308 expansion ROMs that do not already have 3309 BIOS assigned address ranges. 3310 nobar [X86] Do not assign address space to the 3311 BARs that weren't assigned by the BIOS. 3312 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3313 assigned automatically to PCI devices. You can 3314 make the kernel exclude IRQs of your ISA cards 3315 this way. 3316 pirqaddr=0xAAAAA [X86] Specify the physical address 3317 of the PIRQ table (normally generated 3318 by the BIOS) if it is outside the 3319 F0000h-100000h range. 3320 lastbus=N [X86] Scan all buses thru bus #N. Can be 3321 useful if the kernel is unable to find your 3322 secondary buses and you want to tell it 3323 explicitly which ones they are. 3324 assign-busses [X86] Always assign all PCI bus 3325 numbers ourselves, overriding 3326 whatever the firmware may have done. 3327 usepirqmask [X86] Honor the possible IRQ mask stored 3328 in the BIOS $PIR table. This is needed on 3329 some systems with broken BIOSes, notably 3330 some HP Pavilion N5400 and Omnibook XE3 3331 notebooks. This will have no effect if ACPI 3332 IRQ routing is enabled. 3333 noacpi [X86] Do not use ACPI for IRQ routing 3334 or for PCI scanning. 3335 use_crs [X86] Use PCI host bridge window information 3336 from ACPI. On BIOSes from 2008 or later, this 3337 is enabled by default. If you need to use this, 3338 please report a bug. 3339 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3340 If you need to use this, please report a bug. 3341 routeirq Do IRQ routing for all PCI devices. 3342 This is normally done in pci_enable_device(), 3343 so this option is a temporary workaround 3344 for broken drivers that don't call it. 3345 skip_isa_align [X86] do not align io start addr, so can 3346 handle more pci cards 3347 noearly [X86] Don't do any early type 1 scanning. 3348 This might help on some broken boards which 3349 machine check when some devices' config space 3350 is read. But various workarounds are disabled 3351 and some IOMMU drivers will not work. 3352 bfsort Sort PCI devices into breadth-first order. 3353 This sorting is done to get a device 3354 order compatible with older (<= 2.4) kernels. 3355 nobfsort Don't sort PCI devices into breadth-first order. 3356 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3357 tuning and use the BIOS-configured MPS defaults. 3358 pcie_bus_safe Set every device's MPS to the largest value 3359 supported by all devices below the root complex. 3360 pcie_bus_perf Set device MPS to the largest allowable MPS 3361 based on its parent bus. Also set MRRS (Max 3362 Read Request Size) to the largest supported 3363 value (no larger than the MPS that the device 3364 or bus can support) for best performance. 3365 pcie_bus_peer2peer Set every device's MPS to 128B, which 3366 every device is guaranteed to support. This 3367 configuration allows peer-to-peer DMA between 3368 any pair of devices, possibly at the cost of 3369 reduced performance. This also guarantees 3370 that hot-added devices will work. 3371 cbiosize=nn[KMG] The fixed amount of bus space which is 3372 reserved for the CardBus bridge's IO window. 3373 The default value is 256 bytes. 3374 cbmemsize=nn[KMG] The fixed amount of bus space which is 3375 reserved for the CardBus bridge's memory 3376 window. The default value is 64 megabytes. 3377 resource_alignment= 3378 Format: 3379 [<order of align>@]<pci_dev>[; ...] 3380 Specifies alignment and device to reassign 3381 aligned memory resources. How to 3382 specify the device is described above. 3383 If <order of align> is not specified, 3384 PAGE_SIZE is used as alignment. 3385 PCI-PCI bridge can be specified, if resource 3386 windows need to be expanded. 3387 To specify the alignment for several 3388 instances of a device, the PCI vendor, 3389 device, subvendor, and subdevice may be 3390 specified, e.g., 4096@pci:8086:9c22:103c:198f 3391 ecrc= Enable/disable PCIe ECRC (transaction layer 3392 end-to-end CRC checking). 3393 bios: Use BIOS/firmware settings. This is the 3394 the default. 3395 off: Turn ECRC off 3396 on: Turn ECRC on. 3397 hpiosize=nn[KMG] The fixed amount of bus space which is 3398 reserved for hotplug bridge's IO window. 3399 Default size is 256 bytes. 3400 hpmemsize=nn[KMG] The fixed amount of bus space which is 3401 reserved for hotplug bridge's memory window. 3402 Default size is 2 megabytes. 3403 hpbussize=nn The minimum amount of additional bus numbers 3404 reserved for buses below a hotplug bridge. 3405 Default is 1. 3406 realloc= Enable/disable reallocating PCI bridge resources 3407 if allocations done by BIOS are too small to 3408 accommodate resources required by all child 3409 devices. 3410 off: Turn realloc off 3411 on: Turn realloc on 3412 realloc same as realloc=on 3413 noari do not use PCIe ARI. 3414 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3415 do not use PCIe ATS (and IOMMU device IOTLB). 3416 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3417 only look for one device below a PCIe downstream 3418 port. 3419 big_root_window Try to add a big 64bit memory window to the PCIe 3420 root complex on AMD CPUs. Some GFX hardware 3421 can resize a BAR to allow access to all VRAM. 3422 Adding the window is slightly risky (it may 3423 conflict with unreported devices), so this 3424 taints the kernel. 3425 disable_acs_redir=<pci_dev>[; ...] 3426 Specify one or more PCI devices (in the format 3427 specified above) separated by semicolons. 3428 Each device specified will have the PCI ACS 3429 redirect capabilities forced off which will 3430 allow P2P traffic between devices through 3431 bridges without forcing it upstream. Note: 3432 this removes isolation between devices and 3433 may put more devices in an IOMMU group. 3434 force_floating [S390] Force usage of floating interrupts. 3435 nomio [S390] Do not use MIO instructions. 3436 3437 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3438 Management. 3439 off Disable ASPM. 3440 force Enable ASPM even on devices that claim not to support it. 3441 WARNING: Forcing ASPM on may cause system lockups. 3442 3443 pcie_ports= [PCIE] PCIe port services handling: 3444 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3445 even if the platform doesn't give the OS permission to 3446 use them. This may cause conflicts if the platform 3447 also tries to use these services. 3448 compat Disable native PCIe services (PME, AER, DPC, PCIe 3449 hotplug). 3450 3451 pcie_port_pm= [PCIE] PCIe port power management handling: 3452 off Disable power management of all PCIe ports 3453 force Forcibly enable power management of all PCIe ports 3454 3455 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3456 nomsi Do not use MSI for native PCIe PME signaling (this makes 3457 all PCIe root ports use INTx for all services). 3458 3459 pcmv= [HW,PCMCIA] BadgePAD 4 3460 3461 pd_ignore_unused 3462 [PM] 3463 Keep all power-domains already enabled by bootloader on, 3464 even if no driver has claimed them. This is useful 3465 for debug and development, but should not be 3466 needed on a platform with proper driver support. 3467 3468 pd. [PARIDE] 3469 See Documentation/blockdev/paride.txt. 3470 3471 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3472 boot time. 3473 Format: { 0 | 1 } 3474 See arch/parisc/kernel/pdc_chassis.c 3475 3476 percpu_alloc= Select which percpu first chunk allocator to use. 3477 Currently supported values are "embed" and "page". 3478 Archs may support subset or none of the selections. 3479 See comments in mm/percpu.c for details on each 3480 allocator. This parameter is primarily for debugging 3481 and performance comparison. 3482 3483 pf. [PARIDE] 3484 See Documentation/blockdev/paride.txt. 3485 3486 pg. [PARIDE] 3487 See Documentation/blockdev/paride.txt. 3488 3489 pirq= [SMP,APIC] Manual mp-table setup 3490 See Documentation/x86/i386/IO-APIC.txt. 3491 3492 plip= [PPT,NET] Parallel port network link 3493 Format: { parport<nr> | timid | 0 } 3494 See also Documentation/admin-guide/parport.rst. 3495 3496 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3497 Override pmtimer IOPort with a hex value. 3498 e.g. pmtmr=0x508 3499 3500 pnp.debug=1 [PNP] 3501 Enable PNP debug messages (depends on the 3502 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3503 via /sys/module/pnp/parameters/debug. We always show 3504 current resource usage; turning this on also shows 3505 possible settings and some assignment information. 3506 3507 pnpacpi= [ACPI] 3508 { off } 3509 3510 pnpbios= [ISAPNP] 3511 { on | off | curr | res | no-curr | no-res } 3512 3513 pnp_reserve_irq= 3514 [ISAPNP] Exclude IRQs for the autoconfiguration 3515 3516 pnp_reserve_dma= 3517 [ISAPNP] Exclude DMAs for the autoconfiguration 3518 3519 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3520 Ranges are in pairs (I/O port base and size). 3521 3522 pnp_reserve_mem= 3523 [ISAPNP] Exclude memory regions for the 3524 autoconfiguration. 3525 Ranges are in pairs (memory base and size). 3526 3527 ports= [IP_VS_FTP] IPVS ftp helper module 3528 Default is 21. 3529 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3530 may be specified. 3531 Format: <port>,<port>.... 3532 3533 powersave=off [PPC] This option disables power saving features. 3534 It specifically disables cpuidle and sets the 3535 platform machine description specific power_save 3536 function to NULL. On Idle the CPU just reduces 3537 execution priority. 3538 3539 ppc_strict_facility_enable 3540 [PPC] This option catches any kernel floating point, 3541 Altivec, VSX and SPE outside of regions specifically 3542 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3543 There is some performance impact when enabling this. 3544 3545 ppc_tm= [PPC] 3546 Format: {"off"} 3547 Disable Hardware Transactional Memory 3548 3549 print-fatal-signals= 3550 [KNL] debug: print fatal signals 3551 3552 If enabled, warn about various signal handling 3553 related application anomalies: too many signals, 3554 too many POSIX.1 timers, fatal signals causing a 3555 coredump - etc. 3556 3557 If you hit the warning due to signal overflow, 3558 you might want to try "ulimit -i unlimited". 3559 3560 default: off. 3561 3562 printk.always_kmsg_dump= 3563 Trigger kmsg_dump for cases other than kernel oops or 3564 panics 3565 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3566 default: disabled 3567 3568 printk.devkmsg={on,off,ratelimit} 3569 Control writing to /dev/kmsg. 3570 on - unlimited logging to /dev/kmsg from userspace 3571 off - logging to /dev/kmsg disabled 3572 ratelimit - ratelimit the logging 3573 Default: ratelimit 3574 3575 printk.time= Show timing data prefixed to each printk message line 3576 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3577 3578 processor.max_cstate= [HW,ACPI] 3579 Limit processor to maximum C-state 3580 max_cstate=9 overrides any DMI blacklist limit. 3581 3582 processor.nocst [HW,ACPI] 3583 Ignore the _CST method to determine C-states, 3584 instead using the legacy FADT method 3585 3586 profile= [KNL] Enable kernel profiling via /proc/profile 3587 Format: [<profiletype>,]<number> 3588 Param: <profiletype>: "schedule", "sleep", or "kvm" 3589 [defaults to kernel profiling] 3590 Param: "schedule" - profile schedule points. 3591 Param: "sleep" - profile D-state sleeping (millisecs). 3592 Requires CONFIG_SCHEDSTATS 3593 Param: "kvm" - profile VM exits. 3594 Param: <number> - step/bucket size as a power of 2 for 3595 statistical time based profiling. 3596 3597 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3598 before loading. 3599 See Documentation/blockdev/ramdisk.txt. 3600 3601 psi= [KNL] Enable or disable pressure stall information 3602 tracking. 3603 Format: <bool> 3604 3605 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3606 probe for; one of (bare|imps|exps|lifebook|any). 3607 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3608 per second. 3609 psmouse.resetafter= [HW,MOUSE] 3610 Try to reset the device after so many bad packets 3611 (0 = never). 3612 psmouse.resolution= 3613 [HW,MOUSE] Set desired mouse resolution, in dpi. 3614 psmouse.smartscroll= 3615 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3616 0 = disabled, 1 = enabled (default). 3617 3618 pstore.backend= Specify the name of the pstore backend to use 3619 3620 pt. [PARIDE] 3621 See Documentation/blockdev/paride.txt. 3622 3623 pti= [X86_64] Control Page Table Isolation of user and 3624 kernel address spaces. Disabling this feature 3625 removes hardening, but improves performance of 3626 system calls and interrupts. 3627 3628 on - unconditionally enable 3629 off - unconditionally disable 3630 auto - kernel detects whether your CPU model is 3631 vulnerable to issues that PTI mitigates 3632 3633 Not specifying this option is equivalent to pti=auto. 3634 3635 nopti [X86_64] 3636 Equivalent to pti=off 3637 3638 pty.legacy_count= 3639 [KNL] Number of legacy pty's. Overwrites compiled-in 3640 default number. 3641 3642 quiet [KNL] Disable most log messages 3643 3644 r128= [HW,DRM] 3645 3646 raid= [HW,RAID] 3647 See Documentation/admin-guide/md.rst. 3648 3649 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3650 See Documentation/blockdev/ramdisk.txt. 3651 3652 random.trust_cpu={on,off} 3653 [KNL] Enable or disable trusting the use of the 3654 CPU's random number generator (if available) to 3655 fully seed the kernel's CRNG. Default is controlled 3656 by CONFIG_RANDOM_TRUST_CPU. 3657 3658 ras=option[,option,...] [KNL] RAS-specific options 3659 3660 cec_disable [X86] 3661 Disable the Correctable Errors Collector, 3662 see CONFIG_RAS_CEC help text. 3663 3664 rcu_nocbs= [KNL] 3665 The argument is a cpu list, as described above, 3666 except that the string "all" can be used to 3667 specify every CPU on the system. 3668 3669 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3670 the specified list of CPUs to be no-callback CPUs. 3671 Invocation of these CPUs' RCU callbacks will be 3672 offloaded to "rcuox/N" kthreads created for that 3673 purpose, where "x" is "p" for RCU-preempt, and 3674 "s" for RCU-sched, and "N" is the CPU number. 3675 This reduces OS jitter on the offloaded CPUs, 3676 which can be useful for HPC and real-time 3677 workloads. It can also improve energy efficiency 3678 for asymmetric multiprocessors. 3679 3680 rcu_nocb_poll [KNL] 3681 Rather than requiring that offloaded CPUs 3682 (specified by rcu_nocbs= above) explicitly 3683 awaken the corresponding "rcuoN" kthreads, 3684 make these kthreads poll for callbacks. 3685 This improves the real-time response for the 3686 offloaded CPUs by relieving them of the need to 3687 wake up the corresponding kthread, but degrades 3688 energy efficiency by requiring that the kthreads 3689 periodically wake up to do the polling. 3690 3691 rcutree.blimit= [KNL] 3692 Set maximum number of finished RCU callbacks to 3693 process in one batch. 3694 3695 rcutree.dump_tree= [KNL] 3696 Dump the structure of the rcu_node combining tree 3697 out at early boot. This is used for diagnostic 3698 purposes, to verify correct tree setup. 3699 3700 rcutree.gp_cleanup_delay= [KNL] 3701 Set the number of jiffies to delay each step of 3702 RCU grace-period cleanup. 3703 3704 rcutree.gp_init_delay= [KNL] 3705 Set the number of jiffies to delay each step of 3706 RCU grace-period initialization. 3707 3708 rcutree.gp_preinit_delay= [KNL] 3709 Set the number of jiffies to delay each step of 3710 RCU grace-period pre-initialization, that is, 3711 the propagation of recent CPU-hotplug changes up 3712 the rcu_node combining tree. 3713 3714 rcutree.rcu_fanout_exact= [KNL] 3715 Disable autobalancing of the rcu_node combining 3716 tree. This is used by rcutorture, and might 3717 possibly be useful for architectures having high 3718 cache-to-cache transfer latencies. 3719 3720 rcutree.rcu_fanout_leaf= [KNL] 3721 Change the number of CPUs assigned to each 3722 leaf rcu_node structure. Useful for very 3723 large systems, which will choose the value 64, 3724 and for NUMA systems with large remote-access 3725 latencies, which will choose a value aligned 3726 with the appropriate hardware boundaries. 3727 3728 rcutree.jiffies_till_first_fqs= [KNL] 3729 Set delay from grace-period initialization to 3730 first attempt to force quiescent states. 3731 Units are jiffies, minimum value is zero, 3732 and maximum value is HZ. 3733 3734 rcutree.jiffies_till_next_fqs= [KNL] 3735 Set delay between subsequent attempts to force 3736 quiescent states. Units are jiffies, minimum 3737 value is one, and maximum value is HZ. 3738 3739 rcutree.jiffies_till_sched_qs= [KNL] 3740 Set required age in jiffies for a 3741 given grace period before RCU starts 3742 soliciting quiescent-state help from 3743 rcu_note_context_switch() and cond_resched(). 3744 If not specified, the kernel will calculate 3745 a value based on the most recent settings 3746 of rcutree.jiffies_till_first_fqs 3747 and rcutree.jiffies_till_next_fqs. 3748 This calculated value may be viewed in 3749 rcutree.jiffies_to_sched_qs. Any attempt to set 3750 rcutree.jiffies_to_sched_qs will be cheerfully 3751 overwritten. 3752 3753 rcutree.kthread_prio= [KNL,BOOT] 3754 Set the SCHED_FIFO priority of the RCU per-CPU 3755 kthreads (rcuc/N). This value is also used for 3756 the priority of the RCU boost threads (rcub/N) 3757 and for the RCU grace-period kthreads (rcu_bh, 3758 rcu_preempt, and rcu_sched). If RCU_BOOST is 3759 set, valid values are 1-99 and the default is 1 3760 (the least-favored priority). Otherwise, when 3761 RCU_BOOST is not set, valid values are 0-99 and 3762 the default is zero (non-realtime operation). 3763 3764 rcutree.rcu_nocb_leader_stride= [KNL] 3765 Set the number of NOCB kthread groups, which 3766 defaults to the square root of the number of 3767 CPUs. Larger numbers reduces the wakeup overhead 3768 on the per-CPU grace-period kthreads, but increases 3769 that same overhead on each group's leader. 3770 3771 rcutree.qhimark= [KNL] 3772 Set threshold of queued RCU callbacks beyond which 3773 batch limiting is disabled. 3774 3775 rcutree.qlowmark= [KNL] 3776 Set threshold of queued RCU callbacks below which 3777 batch limiting is re-enabled. 3778 3779 rcutree.rcu_idle_gp_delay= [KNL] 3780 Set wakeup interval for idle CPUs that have 3781 RCU callbacks (RCU_FAST_NO_HZ=y). 3782 3783 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3784 Set wakeup interval for idle CPUs that have 3785 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3786 Lazy RCU callbacks are those which RCU can 3787 prove do nothing more than free memory. 3788 3789 rcutree.rcu_kick_kthreads= [KNL] 3790 Cause the grace-period kthread to get an extra 3791 wake_up() if it sleeps three times longer than 3792 it should at force-quiescent-state time. 3793 This wake_up() will be accompanied by a 3794 WARN_ONCE() splat and an ftrace_dump(). 3795 3796 rcutree.sysrq_rcu= [KNL] 3797 Commandeer a sysrq key to dump out Tree RCU's 3798 rcu_node tree with an eye towards determining 3799 why a new grace period has not yet started. 3800 3801 rcuperf.gp_async= [KNL] 3802 Measure performance of asynchronous 3803 grace-period primitives such as call_rcu(). 3804 3805 rcuperf.gp_async_max= [KNL] 3806 Specify the maximum number of outstanding 3807 callbacks per writer thread. When a writer 3808 thread exceeds this limit, it invokes the 3809 corresponding flavor of rcu_barrier() to allow 3810 previously posted callbacks to drain. 3811 3812 rcuperf.gp_exp= [KNL] 3813 Measure performance of expedited synchronous 3814 grace-period primitives. 3815 3816 rcuperf.holdoff= [KNL] 3817 Set test-start holdoff period. The purpose of 3818 this parameter is to delay the start of the 3819 test until boot completes in order to avoid 3820 interference. 3821 3822 rcuperf.nreaders= [KNL] 3823 Set number of RCU readers. The value -1 selects 3824 N, where N is the number of CPUs. A value 3825 "n" less than -1 selects N-n+1, where N is again 3826 the number of CPUs. For example, -2 selects N 3827 (the number of CPUs), -3 selects N+1, and so on. 3828 A value of "n" less than or equal to -N selects 3829 a single reader. 3830 3831 rcuperf.nwriters= [KNL] 3832 Set number of RCU writers. The values operate 3833 the same as for rcuperf.nreaders. 3834 N, where N is the number of CPUs 3835 3836 rcuperf.perf_type= [KNL] 3837 Specify the RCU implementation to test. 3838 3839 rcuperf.shutdown= [KNL] 3840 Shut the system down after performance tests 3841 complete. This is useful for hands-off automated 3842 testing. 3843 3844 rcuperf.verbose= [KNL] 3845 Enable additional printk() statements. 3846 3847 rcuperf.writer_holdoff= [KNL] 3848 Write-side holdoff between grace periods, 3849 in microseconds. The default of zero says 3850 no holdoff. 3851 3852 rcutorture.fqs_duration= [KNL] 3853 Set duration of force_quiescent_state bursts 3854 in microseconds. 3855 3856 rcutorture.fqs_holdoff= [KNL] 3857 Set holdoff time within force_quiescent_state bursts 3858 in microseconds. 3859 3860 rcutorture.fqs_stutter= [KNL] 3861 Set wait time between force_quiescent_state bursts 3862 in seconds. 3863 3864 rcutorture.fwd_progress= [KNL] 3865 Enable RCU grace-period forward-progress testing 3866 for the types of RCU supporting this notion. 3867 3868 rcutorture.fwd_progress_div= [KNL] 3869 Specify the fraction of a CPU-stall-warning 3870 period to do tight-loop forward-progress testing. 3871 3872 rcutorture.fwd_progress_holdoff= [KNL] 3873 Number of seconds to wait between successive 3874 forward-progress tests. 3875 3876 rcutorture.fwd_progress_need_resched= [KNL] 3877 Enclose cond_resched() calls within checks for 3878 need_resched() during tight-loop forward-progress 3879 testing. 3880 3881 rcutorture.gp_cond= [KNL] 3882 Use conditional/asynchronous update-side 3883 primitives, if available. 3884 3885 rcutorture.gp_exp= [KNL] 3886 Use expedited update-side primitives, if available. 3887 3888 rcutorture.gp_normal= [KNL] 3889 Use normal (non-expedited) asynchronous 3890 update-side primitives, if available. 3891 3892 rcutorture.gp_sync= [KNL] 3893 Use normal (non-expedited) synchronous 3894 update-side primitives, if available. If all 3895 of rcutorture.gp_cond=, rcutorture.gp_exp=, 3896 rcutorture.gp_normal=, and rcutorture.gp_sync= 3897 are zero, rcutorture acts as if is interpreted 3898 they are all non-zero. 3899 3900 rcutorture.n_barrier_cbs= [KNL] 3901 Set callbacks/threads for rcu_barrier() testing. 3902 3903 rcutorture.nfakewriters= [KNL] 3904 Set number of concurrent RCU writers. These just 3905 stress RCU, they don't participate in the actual 3906 test, hence the "fake". 3907 3908 rcutorture.nreaders= [KNL] 3909 Set number of RCU readers. The value -1 selects 3910 N-1, where N is the number of CPUs. A value 3911 "n" less than -1 selects N-n-2, where N is again 3912 the number of CPUs. For example, -2 selects N 3913 (the number of CPUs), -3 selects N+1, and so on. 3914 3915 rcutorture.object_debug= [KNL] 3916 Enable debug-object double-call_rcu() testing. 3917 3918 rcutorture.onoff_holdoff= [KNL] 3919 Set time (s) after boot for CPU-hotplug testing. 3920 3921 rcutorture.onoff_interval= [KNL] 3922 Set time (jiffies) between CPU-hotplug operations, 3923 or zero to disable CPU-hotplug testing. 3924 3925 rcutorture.shuffle_interval= [KNL] 3926 Set task-shuffle interval (s). Shuffling tasks 3927 allows some CPUs to go into dyntick-idle mode 3928 during the rcutorture test. 3929 3930 rcutorture.shutdown_secs= [KNL] 3931 Set time (s) after boot system shutdown. This 3932 is useful for hands-off automated testing. 3933 3934 rcutorture.stall_cpu= [KNL] 3935 Duration of CPU stall (s) to test RCU CPU stall 3936 warnings, zero to disable. 3937 3938 rcutorture.stall_cpu_holdoff= [KNL] 3939 Time to wait (s) after boot before inducing stall. 3940 3941 rcutorture.stall_cpu_irqsoff= [KNL] 3942 Disable interrupts while stalling if set. 3943 3944 rcutorture.stat_interval= [KNL] 3945 Time (s) between statistics printk()s. 3946 3947 rcutorture.stutter= [KNL] 3948 Time (s) to stutter testing, for example, specifying 3949 five seconds causes the test to run for five seconds, 3950 wait for five seconds, and so on. This tests RCU's 3951 ability to transition abruptly to and from idle. 3952 3953 rcutorture.test_boost= [KNL] 3954 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 3955 "Maybe" means test if the RCU implementation 3956 under test support RCU priority boosting. 3957 3958 rcutorture.test_boost_duration= [KNL] 3959 Duration (s) of each individual boost test. 3960 3961 rcutorture.test_boost_interval= [KNL] 3962 Interval (s) between each boost test. 3963 3964 rcutorture.test_no_idle_hz= [KNL] 3965 Test RCU's dyntick-idle handling. See also the 3966 rcutorture.shuffle_interval parameter. 3967 3968 rcutorture.torture_type= [KNL] 3969 Specify the RCU implementation to test. 3970 3971 rcutorture.verbose= [KNL] 3972 Enable additional printk() statements. 3973 3974 rcupdate.rcu_cpu_stall_suppress= [KNL] 3975 Suppress RCU CPU stall warning messages. 3976 3977 rcupdate.rcu_cpu_stall_timeout= [KNL] 3978 Set timeout for RCU CPU stall warning messages. 3979 3980 rcupdate.rcu_expedited= [KNL] 3981 Use expedited grace-period primitives, for 3982 example, synchronize_rcu_expedited() instead 3983 of synchronize_rcu(). This reduces latency, 3984 but can increase CPU utilization, degrade 3985 real-time latency, and degrade energy efficiency. 3986 No effect on CONFIG_TINY_RCU kernels. 3987 3988 rcupdate.rcu_normal= [KNL] 3989 Use only normal grace-period primitives, 3990 for example, synchronize_rcu() instead of 3991 synchronize_rcu_expedited(). This improves 3992 real-time latency, CPU utilization, and 3993 energy efficiency, but can expose users to 3994 increased grace-period latency. This parameter 3995 overrides rcupdate.rcu_expedited. No effect on 3996 CONFIG_TINY_RCU kernels. 3997 3998 rcupdate.rcu_normal_after_boot= [KNL] 3999 Once boot has completed (that is, after 4000 rcu_end_inkernel_boot() has been invoked), use 4001 only normal grace-period primitives. No effect 4002 on CONFIG_TINY_RCU kernels. 4003 4004 rcupdate.rcu_task_stall_timeout= [KNL] 4005 Set timeout in jiffies for RCU task stall warning 4006 messages. Disable with a value less than or equal 4007 to zero. 4008 4009 rcupdate.rcu_self_test= [KNL] 4010 Run the RCU early boot self tests 4011 4012 rdinit= [KNL] 4013 Format: <full_path> 4014 Run specified binary instead of /init from the ramdisk, 4015 used for early userspace startup. See initrd. 4016 4017 rdt= [HW,X86,RDT] 4018 Turn on/off individual RDT features. List is: 4019 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4020 mba. 4021 E.g. to turn on cmt and turn off mba use: 4022 rdt=cmt,!mba 4023 4024 reboot= [KNL] 4025 Format (x86 or x86_64): 4026 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4027 [[,]s[mp]#### \ 4028 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4029 [[,]f[orce] 4030 Where reboot_mode is one of warm (soft) or cold (hard) or gpio, 4031 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4032 reboot_force is either force or not specified, 4033 reboot_cpu is s[mp]#### with #### being the processor 4034 to be used for rebooting. 4035 4036 relax_domain_level= 4037 [KNL, SMP] Set scheduler's default relax_domain_level. 4038 See Documentation/cgroup-v1/cpusets.txt. 4039 4040 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4041 Format: <base1>,<size1>[,<base2>,<size2>,...] 4042 Reserve I/O ports or memory so the kernel won't use 4043 them. If <base> is less than 0x10000, the region 4044 is assumed to be I/O ports; otherwise it is memory. 4045 4046 reservetop= [X86-32] 4047 Format: nn[KMG] 4048 Reserves a hole at the top of the kernel virtual 4049 address space. 4050 4051 reservelow= [X86] 4052 Format: nn[K] 4053 Set the amount of memory to reserve for BIOS at 4054 the bottom of the address space. 4055 4056 reset_devices [KNL] Force drivers to reset the underlying device 4057 during initialization. 4058 4059 resume= [SWSUSP] 4060 Specify the partition device for software suspend 4061 Format: 4062 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4063 4064 resume_offset= [SWSUSP] 4065 Specify the offset from the beginning of the partition 4066 given by "resume=" at which the swap header is located, 4067 in <PAGE_SIZE> units (needed only for swap files). 4068 See Documentation/power/swsusp-and-swap-files.txt 4069 4070 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4071 read the resume files 4072 4073 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4074 Useful for devices that are detected asynchronously 4075 (e.g. USB and MMC devices). 4076 4077 hibernate= [HIBERNATION] 4078 noresume Don't check if there's a hibernation image 4079 present during boot. 4080 nocompress Don't compress/decompress hibernation images. 4081 no Disable hibernation and resume. 4082 protect_image Turn on image protection during restoration 4083 (that will set all pages holding image data 4084 during restoration read-only). 4085 4086 retain_initrd [RAM] Keep initrd memory after extraction 4087 4088 rfkill.default_state= 4089 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4090 etc. communication is blocked by default. 4091 1 Unblocked. 4092 4093 rfkill.master_switch_mode= 4094 0 The "airplane mode" button does nothing. 4095 1 The "airplane mode" button toggles between everything 4096 blocked and the previous configuration. 4097 2 The "airplane mode" button toggles between everything 4098 blocked and everything unblocked. 4099 4100 rhash_entries= [KNL,NET] 4101 Set number of hash buckets for route cache 4102 4103 ring3mwait=disable 4104 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4105 CPUs. 4106 4107 ro [KNL] Mount root device read-only on boot 4108 4109 rodata= [KNL] 4110 on Mark read-only kernel memory as read-only (default). 4111 off Leave read-only kernel memory writable for debugging. 4112 4113 rockchip.usb_uart 4114 Enable the uart passthrough on the designated usb port 4115 on Rockchip SoCs. When active, the signals of the 4116 debug-uart get routed to the D+ and D- pins of the usb 4117 port and the regular usb controller gets disabled. 4118 4119 root= [KNL] Root filesystem 4120 See name_to_dev_t comment in init/do_mounts.c. 4121 4122 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4123 mount the root filesystem 4124 4125 rootflags= [KNL] Set root filesystem mount option string 4126 4127 rootfstype= [KNL] Set root filesystem type 4128 4129 rootwait [KNL] Wait (indefinitely) for root device to show up. 4130 Useful for devices that are detected asynchronously 4131 (e.g. USB and MMC devices). 4132 4133 rproc_mem=nn[KMG][@address] 4134 [KNL,ARM,CMA] Remoteproc physical memory block. 4135 Memory area to be used by remote processor image, 4136 managed by CMA. 4137 4138 rw [KNL] Mount root device read-write on boot 4139 4140 S [KNL] Run init in single mode 4141 4142 s390_iommu= [HW,S390] 4143 Set s390 IOTLB flushing mode 4144 strict 4145 With strict flushing every unmap operation will result in 4146 an IOTLB flush. Default is lazy flushing before reuse, 4147 which is faster. 4148 4149 sa1100ir [NET] 4150 See drivers/net/irda/sa1100_ir.c. 4151 4152 sbni= [NET] Granch SBNI12 leased line adapter 4153 4154 sched_debug [KNL] Enables verbose scheduler debug messages. 4155 4156 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4157 Allowed values are enable and disable. This feature 4158 incurs a small amount of overhead in the scheduler 4159 but is useful for debugging and performance tuning. 4160 4161 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4162 xtime_lock contention on larger systems, and/or RCU lock 4163 contention on all systems with CONFIG_MAXSMP set. 4164 Format: { "0" | "1" } 4165 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4166 1 -- enable. 4167 Note: increases power consumption, thus should only be 4168 enabled if running jitter sensitive (HPC/RT) workloads. 4169 4170 security= [SECURITY] Choose a legacy "major" security module to 4171 enable at boot. This has been deprecated by the 4172 "lsm=" parameter. 4173 4174 selinux= [SELINUX] Disable or enable SELinux at boot time. 4175 Format: { "0" | "1" } 4176 See security/selinux/Kconfig help text. 4177 0 -- disable. 4178 1 -- enable. 4179 Default value is set via kernel config option. 4180 If enabled at boot time, /selinux/disable can be used 4181 later to disable prior to initial policy load. 4182 4183 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4184 Format: { "0" | "1" } 4185 See security/apparmor/Kconfig help text 4186 0 -- disable. 4187 1 -- enable. 4188 Default value is set via kernel config option. 4189 4190 serialnumber [BUGS=X86-32] 4191 4192 shapers= [NET] 4193 Maximal number of shapers. 4194 4195 simeth= [IA-64] 4196 simscsi= 4197 4198 slram= [HW,MTD] 4199 4200 slab_nomerge [MM] 4201 Disable merging of slabs with similar size. May be 4202 necessary if there is some reason to distinguish 4203 allocs to different slabs, especially in hardened 4204 environments where the risk of heap overflows and 4205 layout control by attackers can usually be 4206 frustrated by disabling merging. This will reduce 4207 most of the exposure of a heap attack to a single 4208 cache (risks via metadata attacks are mostly 4209 unchanged). Debug options disable merging on their 4210 own. 4211 For more information see Documentation/vm/slub.rst. 4212 4213 slab_max_order= [MM, SLAB] 4214 Determines the maximum allowed order for slabs. 4215 A high setting may cause OOMs due to memory 4216 fragmentation. Defaults to 1 for systems with 4217 more than 32MB of RAM, 0 otherwise. 4218 4219 slub_debug[=options[,slabs]] [MM, SLUB] 4220 Enabling slub_debug allows one to determine the 4221 culprit if slab objects become corrupted. Enabling 4222 slub_debug can create guard zones around objects and 4223 may poison objects when not in use. Also tracks the 4224 last alloc / free. For more information see 4225 Documentation/vm/slub.rst. 4226 4227 slub_memcg_sysfs= [MM, SLUB] 4228 Determines whether to enable sysfs directories for 4229 memory cgroup sub-caches. 1 to enable, 0 to disable. 4230 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4231 Enabling this can lead to a very high number of debug 4232 directories and files being created under 4233 /sys/kernel/slub. 4234 4235 slub_max_order= [MM, SLUB] 4236 Determines the maximum allowed order for slabs. 4237 A high setting may cause OOMs due to memory 4238 fragmentation. For more information see 4239 Documentation/vm/slub.rst. 4240 4241 slub_min_objects= [MM, SLUB] 4242 The minimum number of objects per slab. SLUB will 4243 increase the slab order up to slub_max_order to 4244 generate a sufficiently large slab able to contain 4245 the number of objects indicated. The higher the number 4246 of objects the smaller the overhead of tracking slabs 4247 and the less frequently locks need to be acquired. 4248 For more information see Documentation/vm/slub.rst. 4249 4250 slub_min_order= [MM, SLUB] 4251 Determines the minimum page order for slabs. Must be 4252 lower than slub_max_order. 4253 For more information see Documentation/vm/slub.rst. 4254 4255 slub_nomerge [MM, SLUB] 4256 Same with slab_nomerge. This is supported for legacy. 4257 See slab_nomerge for more information. 4258 4259 smart2= [HW] 4260 Format: <io1>[,<io2>[,...,<io8>]] 4261 4262 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4263 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4264 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4265 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4266 smsc-ircc2.ircc_irq= [HW] IRQ line 4267 smsc-ircc2.ircc_dma= [HW] DMA channel 4268 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4269 0: Toshiba Satellite 1800 (GP data pin select) 4270 1: Fast pin select (default) 4271 2: ATC IRMode 4272 4273 smt [KNL,S390] Set the maximum number of threads (logical 4274 CPUs) to use per physical CPU on systems capable of 4275 symmetric multithreading (SMT). Will be capped to the 4276 actual hardware limit. 4277 Format: <integer> 4278 Default: -1 (no limit) 4279 4280 softlockup_panic= 4281 [KNL] Should the soft-lockup detector generate panics. 4282 Format: <integer> 4283 4284 A nonzero value instructs the soft-lockup detector 4285 to panic the machine when a soft-lockup occurs. This 4286 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC 4287 which is the respective build-time switch to that 4288 functionality. 4289 4290 softlockup_all_cpu_backtrace= 4291 [KNL] Should the soft-lockup detector generate 4292 backtraces on all cpus. 4293 Format: <integer> 4294 4295 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4296 See Documentation/laptops/sonypi.txt 4297 4298 spectre_v2= [X86] Control mitigation of Spectre variant 2 4299 (indirect branch speculation) vulnerability. 4300 The default operation protects the kernel from 4301 user space attacks. 4302 4303 on - unconditionally enable, implies 4304 spectre_v2_user=on 4305 off - unconditionally disable, implies 4306 spectre_v2_user=off 4307 auto - kernel detects whether your CPU model is 4308 vulnerable 4309 4310 Selecting 'on' will, and 'auto' may, choose a 4311 mitigation method at run time according to the 4312 CPU, the available microcode, the setting of the 4313 CONFIG_RETPOLINE configuration option, and the 4314 compiler with which the kernel was built. 4315 4316 Selecting 'on' will also enable the mitigation 4317 against user space to user space task attacks. 4318 4319 Selecting 'off' will disable both the kernel and 4320 the user space protections. 4321 4322 Specific mitigations can also be selected manually: 4323 4324 retpoline - replace indirect branches 4325 retpoline,generic - google's original retpoline 4326 retpoline,amd - AMD-specific minimal thunk 4327 4328 Not specifying this option is equivalent to 4329 spectre_v2=auto. 4330 4331 spectre_v2_user= 4332 [X86] Control mitigation of Spectre variant 2 4333 (indirect branch speculation) vulnerability between 4334 user space tasks 4335 4336 on - Unconditionally enable mitigations. Is 4337 enforced by spectre_v2=on 4338 4339 off - Unconditionally disable mitigations. Is 4340 enforced by spectre_v2=off 4341 4342 prctl - Indirect branch speculation is enabled, 4343 but mitigation can be enabled via prctl 4344 per thread. The mitigation control state 4345 is inherited on fork. 4346 4347 prctl,ibpb 4348 - Like "prctl" above, but only STIBP is 4349 controlled per thread. IBPB is issued 4350 always when switching between different user 4351 space processes. 4352 4353 seccomp 4354 - Same as "prctl" above, but all seccomp 4355 threads will enable the mitigation unless 4356 they explicitly opt out. 4357 4358 seccomp,ibpb 4359 - Like "seccomp" above, but only STIBP is 4360 controlled per thread. IBPB is issued 4361 always when switching between different 4362 user space processes. 4363 4364 auto - Kernel selects the mitigation depending on 4365 the available CPU features and vulnerability. 4366 4367 Default mitigation: 4368 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4369 4370 Not specifying this option is equivalent to 4371 spectre_v2_user=auto. 4372 4373 spec_store_bypass_disable= 4374 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4375 (Speculative Store Bypass vulnerability) 4376 4377 Certain CPUs are vulnerable to an exploit against a 4378 a common industry wide performance optimization known 4379 as "Speculative Store Bypass" in which recent stores 4380 to the same memory location may not be observed by 4381 later loads during speculative execution. The idea 4382 is that such stores are unlikely and that they can 4383 be detected prior to instruction retirement at the 4384 end of a particular speculation execution window. 4385 4386 In vulnerable processors, the speculatively forwarded 4387 store can be used in a cache side channel attack, for 4388 example to read memory to which the attacker does not 4389 directly have access (e.g. inside sandboxed code). 4390 4391 This parameter controls whether the Speculative Store 4392 Bypass optimization is used. 4393 4394 On x86 the options are: 4395 4396 on - Unconditionally disable Speculative Store Bypass 4397 off - Unconditionally enable Speculative Store Bypass 4398 auto - Kernel detects whether the CPU model contains an 4399 implementation of Speculative Store Bypass and 4400 picks the most appropriate mitigation. If the 4401 CPU is not vulnerable, "off" is selected. If the 4402 CPU is vulnerable the default mitigation is 4403 architecture and Kconfig dependent. See below. 4404 prctl - Control Speculative Store Bypass per thread 4405 via prctl. Speculative Store Bypass is enabled 4406 for a process by default. The state of the control 4407 is inherited on fork. 4408 seccomp - Same as "prctl" above, but all seccomp threads 4409 will disable SSB unless they explicitly opt out. 4410 4411 Default mitigations: 4412 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4413 4414 On powerpc the options are: 4415 4416 on,auto - On Power8 and Power9 insert a store-forwarding 4417 barrier on kernel entry and exit. On Power7 4418 perform a software flush on kernel entry and 4419 exit. 4420 off - No action. 4421 4422 Not specifying this option is equivalent to 4423 spec_store_bypass_disable=auto. 4424 4425 spia_io_base= [HW,MTD] 4426 spia_fio_base= 4427 spia_pedr= 4428 spia_peddr= 4429 4430 srcutree.counter_wrap_check [KNL] 4431 Specifies how frequently to check for 4432 grace-period sequence counter wrap for the 4433 srcu_data structure's ->srcu_gp_seq_needed field. 4434 The greater the number of bits set in this kernel 4435 parameter, the less frequently counter wrap will 4436 be checked for. Note that the bottom two bits 4437 are ignored. 4438 4439 srcutree.exp_holdoff [KNL] 4440 Specifies how many nanoseconds must elapse 4441 since the end of the last SRCU grace period for 4442 a given srcu_struct until the next normal SRCU 4443 grace period will be considered for automatic 4444 expediting. Set to zero to disable automatic 4445 expediting. 4446 4447 ssbd= [ARM64,HW] 4448 Speculative Store Bypass Disable control 4449 4450 On CPUs that are vulnerable to the Speculative 4451 Store Bypass vulnerability and offer a 4452 firmware based mitigation, this parameter 4453 indicates how the mitigation should be used: 4454 4455 force-on: Unconditionally enable mitigation for 4456 for both kernel and userspace 4457 force-off: Unconditionally disable mitigation for 4458 for both kernel and userspace 4459 kernel: Always enable mitigation in the 4460 kernel, and offer a prctl interface 4461 to allow userspace to register its 4462 interest in being mitigated too. 4463 4464 stack_guard_gap= [MM] 4465 override the default stack gap protection. The value 4466 is in page units and it defines how many pages prior 4467 to (for stacks growing down) resp. after (for stacks 4468 growing up) the main stack are reserved for no other 4469 mapping. Default value is 256 pages. 4470 4471 stacktrace [FTRACE] 4472 Enabled the stack tracer on boot up. 4473 4474 stacktrace_filter=[function-list] 4475 [FTRACE] Limit the functions that the stack tracer 4476 will trace at boot up. function-list is a comma separated 4477 list of functions. This list can be changed at run 4478 time by the stack_trace_filter file in the debugfs 4479 tracing directory. Note, this enables stack tracing 4480 and the stacktrace above is not needed. 4481 4482 sti= [PARISC,HW] 4483 Format: <num> 4484 Set the STI (builtin display/keyboard on the HP-PARISC 4485 machines) console (graphic card) which should be used 4486 as the initial boot-console. 4487 See also comment in drivers/video/console/sticore.c. 4488 4489 sti_font= [HW] 4490 See comment in drivers/video/console/sticore.c. 4491 4492 stifb= [HW] 4493 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4494 4495 sunrpc.min_resvport= 4496 sunrpc.max_resvport= 4497 [NFS,SUNRPC] 4498 SunRPC servers often require that client requests 4499 originate from a privileged port (i.e. a port in the 4500 range 0 < portnr < 1024). 4501 An administrator who wishes to reserve some of these 4502 ports for other uses may adjust the range that the 4503 kernel's sunrpc client considers to be privileged 4504 using these two parameters to set the minimum and 4505 maximum port values. 4506 4507 sunrpc.svc_rpc_per_connection_limit= 4508 [NFS,SUNRPC] 4509 Limit the number of requests that the server will 4510 process in parallel from a single connection. 4511 The default value is 0 (no limit). 4512 4513 sunrpc.pool_mode= 4514 [NFS] 4515 Control how the NFS server code allocates CPUs to 4516 service thread pools. Depending on how many NICs 4517 you have and where their interrupts are bound, this 4518 option will affect which CPUs will do NFS serving. 4519 Note: this parameter cannot be changed while the 4520 NFS server is running. 4521 4522 auto the server chooses an appropriate mode 4523 automatically using heuristics 4524 global a single global pool contains all CPUs 4525 percpu one pool for each CPU 4526 pernode one pool for each NUMA node (equivalent 4527 to global on non-NUMA machines) 4528 4529 sunrpc.tcp_slot_table_entries= 4530 sunrpc.udp_slot_table_entries= 4531 [NFS,SUNRPC] 4532 Sets the upper limit on the number of simultaneous 4533 RPC calls that can be sent from the client to a 4534 server. Increasing these values may allow you to 4535 improve throughput, but will also increase the 4536 amount of memory reserved for use by the client. 4537 4538 suspend.pm_test_delay= 4539 [SUSPEND] 4540 Sets the number of seconds to remain in a suspend test 4541 mode before resuming the system (see 4542 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4543 is set. Default value is 5. 4544 4545 swapaccount=[0|1] 4546 [KNL] Enable accounting of swap in memory resource 4547 controller if no parameter or 1 is given or disable 4548 it if 0 is given (See Documentation/cgroup-v1/memory.txt) 4549 4550 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4551 Format: { <int> | force | noforce } 4552 <int> -- Number of I/O TLB slabs 4553 force -- force using of bounce buffers even if they 4554 wouldn't be automatically used by the kernel 4555 noforce -- Never use bounce buffers (for debugging) 4556 4557 switches= [HW,M68k] 4558 4559 sysfs.deprecated=0|1 [KNL] 4560 Enable/disable old style sysfs layout for old udev 4561 on older distributions. When this option is enabled 4562 very new udev will not work anymore. When this option 4563 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4564 in older udev will not work anymore. 4565 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4566 the kernel configuration. 4567 4568 sysrq_always_enabled 4569 [KNL] 4570 Ignore sysrq setting - this boot parameter will 4571 neutralize any effect of /proc/sys/kernel/sysrq. 4572 Useful for debugging. 4573 4574 tcpmhash_entries= [KNL,NET] 4575 Set the number of tcp_metrics_hash slots. 4576 Default value is 8192 or 16384 depending on total 4577 ram pages. This is used to specify the TCP metrics 4578 cache size. See Documentation/networking/ip-sysctl.txt 4579 "tcp_no_metrics_save" section for more details. 4580 4581 tdfx= [HW,DRM] 4582 4583 test_suspend= [SUSPEND][,N] 4584 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4585 standby suspend) or "freeze" (for suspend type freeze) 4586 as the system sleep state during system startup with 4587 the optional capability to repeat N number of times. 4588 The system is woken from this state using a 4589 wakeup-capable RTC alarm. 4590 4591 thash_entries= [KNL,NET] 4592 Set number of hash buckets for TCP connection 4593 4594 thermal.act= [HW,ACPI] 4595 -1: disable all active trip points in all thermal zones 4596 <degrees C>: override all lowest active trip points 4597 4598 thermal.crt= [HW,ACPI] 4599 -1: disable all critical trip points in all thermal zones 4600 <degrees C>: override all critical trip points 4601 4602 thermal.nocrt= [HW,ACPI] 4603 Set to disable actions on ACPI thermal zone 4604 critical and hot trip points. 4605 4606 thermal.off= [HW,ACPI] 4607 1: disable ACPI thermal control 4608 4609 thermal.psv= [HW,ACPI] 4610 -1: disable all passive trip points 4611 <degrees C>: override all passive trip points to this 4612 value 4613 4614 thermal.tzp= [HW,ACPI] 4615 Specify global default ACPI thermal zone polling rate 4616 <deci-seconds>: poll all this frequency 4617 0: no polling (default) 4618 4619 threadirqs [KNL] 4620 Force threading of all interrupt handlers except those 4621 marked explicitly IRQF_NO_THREAD. 4622 4623 tmem [KNL,XEN] 4624 Enable the Transcendent memory driver if built-in. 4625 4626 tmem.cleancache=0|1 [KNL, XEN] 4627 Default is on (1). Disable the usage of the cleancache 4628 API to send anonymous pages to the hypervisor. 4629 4630 tmem.frontswap=0|1 [KNL, XEN] 4631 Default is on (1). Disable the usage of the frontswap 4632 API to send swap pages to the hypervisor. If disabled 4633 the selfballooning and selfshrinking are force disabled. 4634 4635 tmem.selfballooning=0|1 [KNL, XEN] 4636 Default is on (1). Disable the driving of swap pages 4637 to the hypervisor. 4638 4639 tmem.selfshrinking=0|1 [KNL, XEN] 4640 Default is on (1). Partial swapoff that immediately 4641 transfers pages from Xen hypervisor back to the 4642 kernel based on different criteria. 4643 4644 topology= [S390] 4645 Format: {off | on} 4646 Specify if the kernel should make use of the cpu 4647 topology information if the hardware supports this. 4648 The scheduler will make use of this information and 4649 e.g. base its process migration decisions on it. 4650 Default is on. 4651 4652 topology_updates= [KNL, PPC, NUMA] 4653 Format: {off} 4654 Specify if the kernel should ignore (off) 4655 topology updates sent by the hypervisor to this 4656 LPAR. 4657 4658 tp720= [HW,PS2] 4659 4660 tpm_suspend_pcr=[HW,TPM] 4661 Format: integer pcr id 4662 Specify that at suspend time, the tpm driver 4663 should extend the specified pcr with zeros, 4664 as a workaround for some chips which fail to 4665 flush the last written pcr on TPM_SaveState. 4666 This will guarantee that all the other pcrs 4667 are saved. 4668 4669 trace_buf_size=nn[KMG] 4670 [FTRACE] will set tracing buffer size on each cpu. 4671 4672 trace_event=[event-list] 4673 [FTRACE] Set and start specified trace events in order 4674 to facilitate early boot debugging. The event-list is a 4675 comma separated list of trace events to enable. See 4676 also Documentation/trace/events.rst 4677 4678 trace_options=[option-list] 4679 [FTRACE] Enable or disable tracer options at boot. 4680 The option-list is a comma delimited list of options 4681 that can be enabled or disabled just as if you were 4682 to echo the option name into 4683 4684 /sys/kernel/debug/tracing/trace_options 4685 4686 For example, to enable stacktrace option (to dump the 4687 stack trace of each event), add to the command line: 4688 4689 trace_options=stacktrace 4690 4691 See also Documentation/trace/ftrace.rst "trace options" 4692 section. 4693 4694 tp_printk[FTRACE] 4695 Have the tracepoints sent to printk as well as the 4696 tracing ring buffer. This is useful for early boot up 4697 where the system hangs or reboots and does not give the 4698 option for reading the tracing buffer or performing a 4699 ftrace_dump_on_oops. 4700 4701 To turn off having tracepoints sent to printk, 4702 echo 0 > /proc/sys/kernel/tracepoint_printk 4703 Note, echoing 1 into this file without the 4704 tracepoint_printk kernel cmdline option has no effect. 4705 4706 ** CAUTION ** 4707 4708 Having tracepoints sent to printk() and activating high 4709 frequency tracepoints such as irq or sched, can cause 4710 the system to live lock. 4711 4712 traceoff_on_warning 4713 [FTRACE] enable this option to disable tracing when a 4714 warning is hit. This turns off "tracing_on". Tracing can 4715 be enabled again by echoing '1' into the "tracing_on" 4716 file located in /sys/kernel/debug/tracing/ 4717 4718 This option is useful, as it disables the trace before 4719 the WARNING dump is called, which prevents the trace to 4720 be filled with content caused by the warning output. 4721 4722 This option can also be set at run time via the sysctl 4723 option: kernel/traceoff_on_warning 4724 4725 transparent_hugepage= 4726 [KNL] 4727 Format: [always|madvise|never] 4728 Can be used to control the default behavior of the system 4729 with respect to transparent hugepages. 4730 See Documentation/admin-guide/mm/transhuge.rst 4731 for more details. 4732 4733 tsc= Disable clocksource stability checks for TSC. 4734 Format: <string> 4735 [x86] reliable: mark tsc clocksource as reliable, this 4736 disables clocksource verification at runtime, as well 4737 as the stability checks done at bootup. Used to enable 4738 high-resolution timer mode on older hardware, and in 4739 virtualized environment. 4740 [x86] noirqtime: Do not use TSC to do irq accounting. 4741 Used to run time disable IRQ_TIME_ACCOUNTING on any 4742 platforms where RDTSC is slow and this accounting 4743 can add overhead. 4744 [x86] unstable: mark the TSC clocksource as unstable, this 4745 marks the TSC unconditionally unstable at bootup and 4746 avoids any further wobbles once the TSC watchdog notices. 4747 [x86] nowatchdog: disable clocksource watchdog. Used 4748 in situations with strict latency requirements (where 4749 interruptions from clocksource watchdog are not 4750 acceptable). 4751 4752 turbografx.map[2|3]= [HW,JOY] 4753 TurboGraFX parallel port interface 4754 Format: 4755 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4756 See also Documentation/input/devices/joystick-parport.rst 4757 4758 udbg-immortal [PPC] When debugging early kernel crashes that 4759 happen after console_init() and before a proper 4760 console driver takes over, this boot options might 4761 help "seeing" what's going on. 4762 4763 uhash_entries= [KNL,NET] 4764 Set number of hash buckets for UDP/UDP-Lite connections 4765 4766 uhci-hcd.ignore_oc= 4767 [USB] Ignore overcurrent events (default N). 4768 Some badly-designed motherboards generate lots of 4769 bogus events, for ports that aren't wired to 4770 anything. Set this parameter to avoid log spamming. 4771 Note that genuine overcurrent events won't be 4772 reported either. 4773 4774 unknown_nmi_panic 4775 [X86] Cause panic on unknown NMI. 4776 4777 usbcore.authorized_default= 4778 [USB] Default USB device authorization: 4779 (default -1 = authorized except for wireless USB, 4780 0 = not authorized, 1 = authorized, 2 = authorized 4781 if device connected to internal port) 4782 4783 usbcore.autosuspend= 4784 [USB] The autosuspend time delay (in seconds) used 4785 for newly-detected USB devices (default 2). This 4786 is the time required before an idle device will be 4787 autosuspended. Devices for which the delay is set 4788 to a negative value won't be autosuspended at all. 4789 4790 usbcore.usbfs_snoop= 4791 [USB] Set to log all usbfs traffic (default 0 = off). 4792 4793 usbcore.usbfs_snoop_max= 4794 [USB] Maximum number of bytes to snoop in each URB 4795 (default = 65536). 4796 4797 usbcore.blinkenlights= 4798 [USB] Set to cycle leds on hubs (default 0 = off). 4799 4800 usbcore.old_scheme_first= 4801 [USB] Start with the old device initialization 4802 scheme, applies only to low and full-speed devices 4803 (default 0 = off). 4804 4805 usbcore.usbfs_memory_mb= 4806 [USB] Memory limit (in MB) for buffers allocated by 4807 usbfs (default = 16, 0 = max = 2047). 4808 4809 usbcore.use_both_schemes= 4810 [USB] Try the other device initialization scheme 4811 if the first one fails (default 1 = enabled). 4812 4813 usbcore.initial_descriptor_timeout= 4814 [USB] Specifies timeout for the initial 64-byte 4815 USB_REQ_GET_DESCRIPTOR request in milliseconds 4816 (default 5000 = 5.0 seconds). 4817 4818 usbcore.nousb [USB] Disable the USB subsystem 4819 4820 usbcore.quirks= 4821 [USB] A list of quirk entries to augment the built-in 4822 usb core quirk list. List entries are separated by 4823 commas. Each entry has the form 4824 VendorID:ProductID:Flags. The IDs are 4-digit hex 4825 numbers and Flags is a set of letters. Each letter 4826 will change the built-in quirk; setting it if it is 4827 clear and clearing it if it is set. The letters have 4828 the following meanings: 4829 a = USB_QUIRK_STRING_FETCH_255 (string 4830 descriptors must not be fetched using 4831 a 255-byte read); 4832 b = USB_QUIRK_RESET_RESUME (device can't resume 4833 correctly so reset it instead); 4834 c = USB_QUIRK_NO_SET_INTF (device can't handle 4835 Set-Interface requests); 4836 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 4837 handle its Configuration or Interface 4838 strings); 4839 e = USB_QUIRK_RESET (device can't be reset 4840 (e.g morph devices), don't use reset); 4841 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 4842 more interface descriptions than the 4843 bNumInterfaces count, and can't handle 4844 talking to these interfaces); 4845 g = USB_QUIRK_DELAY_INIT (device needs a pause 4846 during initialization, after we read 4847 the device descriptor); 4848 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 4849 high speed and super speed interrupt 4850 endpoints, the USB 2.0 and USB 3.0 spec 4851 require the interval in microframes (1 4852 microframe = 125 microseconds) to be 4853 calculated as interval = 2 ^ 4854 (bInterval-1). 4855 Devices with this quirk report their 4856 bInterval as the result of this 4857 calculation instead of the exponent 4858 variable used in the calculation); 4859 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 4860 handle device_qualifier descriptor 4861 requests); 4862 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 4863 generates spurious wakeup, ignore 4864 remote wakeup capability); 4865 k = USB_QUIRK_NO_LPM (device can't handle Link 4866 Power Management); 4867 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 4868 (Device reports its bInterval as linear 4869 frames instead of the USB 2.0 4870 calculation); 4871 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 4872 to be disconnected before suspend to 4873 prevent spurious wakeup); 4874 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 4875 pause after every control message); 4876 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 4877 delay after resetting its port); 4878 Example: quirks=0781:5580:bk,0a5c:5834:gij 4879 4880 usbhid.mousepoll= 4881 [USBHID] The interval which mice are to be polled at. 4882 4883 usbhid.jspoll= 4884 [USBHID] The interval which joysticks are to be polled at. 4885 4886 usbhid.kbpoll= 4887 [USBHID] The interval which keyboards are to be polled at. 4888 4889 usb-storage.delay_use= 4890 [UMS] The delay in seconds before a new device is 4891 scanned for Logical Units (default 1). 4892 4893 usb-storage.quirks= 4894 [UMS] A list of quirks entries to supplement or 4895 override the built-in unusual_devs list. List 4896 entries are separated by commas. Each entry has 4897 the form VID:PID:Flags where VID and PID are Vendor 4898 and Product ID values (4-digit hex numbers) and 4899 Flags is a set of characters, each corresponding 4900 to a common usb-storage quirk flag as follows: 4901 a = SANE_SENSE (collect more than 18 bytes 4902 of sense data); 4903 b = BAD_SENSE (don't collect more than 18 4904 bytes of sense data); 4905 c = FIX_CAPACITY (decrease the reported 4906 device capacity by one sector); 4907 d = NO_READ_DISC_INFO (don't use 4908 READ_DISC_INFO command); 4909 e = NO_READ_CAPACITY_16 (don't use 4910 READ_CAPACITY_16 command); 4911 f = NO_REPORT_OPCODES (don't use report opcodes 4912 command, uas only); 4913 g = MAX_SECTORS_240 (don't transfer more than 4914 240 sectors at a time, uas only); 4915 h = CAPACITY_HEURISTICS (decrease the 4916 reported device capacity by one 4917 sector if the number is odd); 4918 i = IGNORE_DEVICE (don't bind to this 4919 device); 4920 j = NO_REPORT_LUNS (don't use report luns 4921 command, uas only); 4922 l = NOT_LOCKABLE (don't try to lock and 4923 unlock ejectable media); 4924 m = MAX_SECTORS_64 (don't transfer more 4925 than 64 sectors = 32 KB at a time); 4926 n = INITIAL_READ10 (force a retry of the 4927 initial READ(10) command); 4928 o = CAPACITY_OK (accept the capacity 4929 reported by the device); 4930 p = WRITE_CACHE (the device cache is ON 4931 by default); 4932 r = IGNORE_RESIDUE (the device reports 4933 bogus residue values); 4934 s = SINGLE_LUN (the device has only one 4935 Logical Unit); 4936 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 4937 commands, uas only); 4938 u = IGNORE_UAS (don't bind to the uas driver); 4939 w = NO_WP_DETECT (don't test whether the 4940 medium is write-protected). 4941 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 4942 even if the device claims no cache) 4943 Example: quirks=0419:aaf5:rl,0421:0433:rc 4944 4945 user_debug= [KNL,ARM] 4946 Format: <int> 4947 See arch/arm/Kconfig.debug help text. 4948 1 - undefined instruction events 4949 2 - system calls 4950 4 - invalid data aborts 4951 8 - SIGSEGV faults 4952 16 - SIGBUS faults 4953 Example: user_debug=31 4954 4955 userpte= 4956 [X86] Flags controlling user PTE allocations. 4957 4958 nohigh = do not allocate PTE pages in 4959 HIGHMEM regardless of setting 4960 of CONFIG_HIGHPTE. 4961 4962 vdso= [X86,SH] 4963 On X86_32, this is an alias for vdso32=. Otherwise: 4964 4965 vdso=1: enable VDSO (the default) 4966 vdso=0: disable VDSO mapping 4967 4968 vdso32= [X86] Control the 32-bit vDSO 4969 vdso32=1: enable 32-bit VDSO 4970 vdso32=0 or vdso32=2: disable 32-bit VDSO 4971 4972 See the help text for CONFIG_COMPAT_VDSO for more 4973 details. If CONFIG_COMPAT_VDSO is set, the default is 4974 vdso32=0; otherwise, the default is vdso32=1. 4975 4976 For compatibility with older kernels, vdso32=2 is an 4977 alias for vdso32=0. 4978 4979 Try vdso32=0 if you encounter an error that says: 4980 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 4981 4982 vector= [IA-64,SMP] 4983 vector=percpu: enable percpu vector domain 4984 4985 video= [FB] Frame buffer configuration 4986 See Documentation/fb/modedb.txt. 4987 4988 video.brightness_switch_enabled= [0,1] 4989 If set to 1, on receiving an ACPI notify event 4990 generated by hotkey, video driver will adjust brightness 4991 level and then send out the event to user space through 4992 the allocated input device; If set to 0, video driver 4993 will only send out the event without touching backlight 4994 brightness level. 4995 default: 1 4996 4997 virtio_mmio.device= 4998 [VMMIO] Memory mapped virtio (platform) device. 4999 5000 <size>@<baseaddr>:<irq>[:<id>] 5001 where: 5002 <size> := size (can use standard suffixes 5003 like K, M and G) 5004 <baseaddr> := physical base address 5005 <irq> := interrupt number (as passed to 5006 request_irq()) 5007 <id> := (optional) platform device id 5008 example: 5009 virtio_mmio.device=1K@0x100b0000:48:7 5010 5011 Can be used multiple times for multiple devices. 5012 5013 vga= [BOOT,X86-32] Select a particular video mode 5014 See Documentation/x86/boot.txt and 5015 Documentation/svga.txt. 5016 Use vga=ask for menu. 5017 This is actually a boot loader parameter; the value is 5018 passed to the kernel using a special protocol. 5019 5020 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5021 May slow down system boot speed, especially when 5022 enabled on systems with a large amount of memory. 5023 All options are enabled by default, and this 5024 interface is meant to allow for selectively 5025 enabling or disabling specific virtual memory 5026 debugging features. 5027 5028 Available options are: 5029 P Enable page structure init time poisoning 5030 - Disable all of the above options 5031 5032 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5033 size of <nn>. This can be used to increase the 5034 minimum size (128MB on x86). It can also be used to 5035 decrease the size and leave more room for directly 5036 mapped kernel RAM. 5037 5038 vmcp_cma=nn[MG] [KNL,S390] 5039 Sets the memory size reserved for contiguous memory 5040 allocations for the vmcp device driver. 5041 5042 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5043 Format: <command> 5044 5045 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5046 Format: <command> 5047 5048 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5049 Format: <command> 5050 5051 vsyscall= [X86-64] 5052 Controls the behavior of vsyscalls (i.e. calls to 5053 fixed addresses of 0xffffffffff600x00 from legacy 5054 code). Most statically-linked binaries and older 5055 versions of glibc use these calls. Because these 5056 functions are at fixed addresses, they make nice 5057 targets for exploits that can control RIP. 5058 5059 emulate [default] Vsyscalls turn into traps and are 5060 emulated reasonably safely. 5061 5062 native Vsyscalls are native syscall instructions. 5063 This is a little bit faster than trapping 5064 and makes a few dynamic recompilers work 5065 better than they would in emulation mode. 5066 It also makes exploits much easier to write. 5067 5068 none Vsyscalls don't work at all. This makes 5069 them quite hard to use for exploits but 5070 might break your system. 5071 5072 vt.color= [VT] Default text color. 5073 Format: 0xYX, X = foreground, Y = background. 5074 Default: 0x07 = light gray on black. 5075 5076 vt.cur_default= [VT] Default cursor shape. 5077 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5078 the parameters of the <Esc>[?A;B;Cc escape sequence; 5079 see VGA-softcursor.txt. Default: 2 = underline. 5080 5081 vt.default_blu= [VT] 5082 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5083 Change the default blue palette of the console. 5084 This is a 16-member array composed of values 5085 ranging from 0-255. 5086 5087 vt.default_grn= [VT] 5088 Format: <green0>,<green1>,<green2>,...,<green15> 5089 Change the default green palette of the console. 5090 This is a 16-member array composed of values 5091 ranging from 0-255. 5092 5093 vt.default_red= [VT] 5094 Format: <red0>,<red1>,<red2>,...,<red15> 5095 Change the default red palette of the console. 5096 This is a 16-member array composed of values 5097 ranging from 0-255. 5098 5099 vt.default_utf8= 5100 [VT] 5101 Format=<0|1> 5102 Set system-wide default UTF-8 mode for all tty's. 5103 Default is 1, i.e. UTF-8 mode is enabled for all 5104 newly opened terminals. 5105 5106 vt.global_cursor_default= 5107 [VT] 5108 Format=<-1|0|1> 5109 Set system-wide default for whether a cursor 5110 is shown on new VTs. Default is -1, 5111 i.e. cursors will be created by default unless 5112 overridden by individual drivers. 0 will hide 5113 cursors, 1 will display them. 5114 5115 vt.italic= [VT] Default color for italic text; 0-15. 5116 Default: 2 = green. 5117 5118 vt.underline= [VT] Default color for underlined text; 0-15. 5119 Default: 3 = cyan. 5120 5121 watchdog timers [HW,WDT] For information on watchdog timers, 5122 see Documentation/watchdog/watchdog-parameters.txt 5123 or other driver-specific files in the 5124 Documentation/watchdog/ directory. 5125 5126 watchdog_thresh= 5127 [KNL] 5128 Set the hard lockup detector stall duration 5129 threshold in seconds. The soft lockup detector 5130 threshold is set to twice the value. A value of 0 5131 disables both lockup detectors. Default is 10 5132 seconds. 5133 5134 workqueue.watchdog_thresh= 5135 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5136 warn stall conditions and dump internal state to 5137 help debugging. 0 disables workqueue stall 5138 detection; otherwise, it's the stall threshold 5139 duration in seconds. The default value is 30 and 5140 it can be updated at runtime by writing to the 5141 corresponding sysfs file. 5142 5143 workqueue.disable_numa 5144 By default, all work items queued to unbound 5145 workqueues are affine to the NUMA nodes they're 5146 issued on, which results in better behavior in 5147 general. If NUMA affinity needs to be disabled for 5148 whatever reason, this option can be used. Note 5149 that this also can be controlled per-workqueue for 5150 workqueues visible under /sys/bus/workqueue/. 5151 5152 workqueue.power_efficient 5153 Per-cpu workqueues are generally preferred because 5154 they show better performance thanks to cache 5155 locality; unfortunately, per-cpu workqueues tend to 5156 be more power hungry than unbound workqueues. 5157 5158 Enabling this makes the per-cpu workqueues which 5159 were observed to contribute significantly to power 5160 consumption unbound, leading to measurably lower 5161 power usage at the cost of small performance 5162 overhead. 5163 5164 The default value of this parameter is determined by 5165 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5166 5167 workqueue.debug_force_rr_cpu 5168 Workqueue used to implicitly guarantee that work 5169 items queued without explicit CPU specified are put 5170 on the local CPU. This guarantee is no longer true 5171 and while local CPU is still preferred work items 5172 may be put on foreign CPUs. This debug option 5173 forces round-robin CPU selection to flush out 5174 usages which depend on the now broken guarantee. 5175 When enabled, memory and cache locality will be 5176 impacted. 5177 5178 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5179 default x2apic cluster mode on platforms 5180 supporting x2apic. 5181 5182 x86_intel_mid_timer= [X86-32,APBT] 5183 Choose timer option for x86 Intel MID platform. 5184 Two valid options are apbt timer only and lapic timer 5185 plus one apbt timer for broadcast timer. 5186 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5187 5188 xen_512gb_limit [KNL,X86-64,XEN] 5189 Restricts the kernel running paravirtualized under Xen 5190 to use only up to 512 GB of RAM. The reason to do so is 5191 crash analysis tools and Xen tools for doing domain 5192 save/restore/migration must be enabled to handle larger 5193 domains. 5194 5195 xen_emul_unplug= [HW,X86,XEN] 5196 Unplug Xen emulated devices 5197 Format: [unplug0,][unplug1] 5198 ide-disks -- unplug primary master IDE devices 5199 aux-ide-disks -- unplug non-primary-master IDE devices 5200 nics -- unplug network devices 5201 all -- unplug all emulated devices (NICs and IDE disks) 5202 unnecessary -- unplugging emulated devices is 5203 unnecessary even if the host did not respond to 5204 the unplug protocol 5205 never -- do not unplug even if version check succeeds 5206 5207 xen_nopvspin [X86,XEN] 5208 Disables the ticketlock slowpath using Xen PV 5209 optimizations. 5210 5211 xen_nopv [X86] 5212 Disables the PV optimizations forcing the HVM guest to 5213 run as generic HVM guest with no PV drivers. 5214 5215 xen_scrub_pages= [XEN] 5216 Boolean option to control scrubbing pages before giving them back 5217 to Xen, for use by other domains. Can be also changed at runtime 5218 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5219 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5220 5221 xirc2ps_cs= [NET,PCMCIA] 5222 Format: 5223 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5224 5225 xhci-hcd.quirks [USB,KNL] 5226 A hex value specifying bitmask with supplemental xhci 5227 host controller quirks. Meaning of each bit can be 5228 consulted in header drivers/usb/host/xhci.h. 5229