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Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)getrlimit.2 8.1 (Berkeley) 6/4/93 29.\" $FreeBSD$ 30.\" 31.Dd September 30, 2016 32.Dt GETRLIMIT 2 33.Os 34.Sh NAME 35.Nm getrlimit , 36.Nm setrlimit 37.Nd control maximum system resource consumption 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In sys/types.h 42.In sys/time.h 43.In sys/resource.h 44.Ft int 45.Fn getrlimit "int resource" "struct rlimit *rlp" 46.Ft int 47.Fn setrlimit "int resource" "const struct rlimit *rlp" 48.Sh DESCRIPTION 49Limits on the consumption of system resources by the current process 50and each process it creates may be obtained with the 51.Fn getrlimit 52system call, and set with the 53.Fn setrlimit 54system call. 55.Pp 56The 57.Fa resource 58argument is one of the following: 59.Bl -tag -width RLIMIT_FSIZEAA 60.It Dv RLIMIT_AS 61The maximum amount (in bytes) of virtual memory the process is 62allowed to map. 63.It Dv RLIMIT_CORE 64The largest size (in bytes) 65.Xr core 5 66file that may be created. 67.It Dv RLIMIT_CPU 68The maximum amount of cpu time (in seconds) to be used by 69each process. 70.It Dv RLIMIT_DATA 71The maximum size (in bytes) of the data segment for a process; 72this defines how far a program may extend its break with the 73.Xr sbrk 2 74function. 75.It Dv RLIMIT_FSIZE 76The largest size (in bytes) file that may be created. 77.It Dv RLIMIT_KQUEUES 78The maximum number of kqueues this user id is allowed to create. 79.It Dv RLIMIT_MEMLOCK 80The maximum size (in bytes) which a process may lock into memory 81using the 82.Xr mlock 2 83system call. 84.It Dv RLIMIT_NOFILE 85The maximum number of open files for this process. 86.It Dv RLIMIT_NPROC 87The maximum number of simultaneous processes for this user id. 88.It Dv RLIMIT_NPTS 89The maximum number of pseudo-terminals this user id is allowed to create. 90.It Dv RLIMIT_RSS 91When there is memory pressure and swap is available, prioritize eviction of 92a process' resident pages beyond this amount (in bytes). 93When memory is not under pressure, this rlimit is effectively ignored. 94Even when there is memory pressure, the amount of available swap space and some 95sysctl settings like 96.Xr vm.swap_enabled 97and 98.Xr vm.swap_idle_enabled 99can affect what happens to processes that have exceeded this size. 100.Pp 101Processes that exceed their set 102.Dv RLIMIT_RSS 103are not signalled or halted. 104The limit is merely a hint to the VM daemon to prefer to deactivate pages from 105processes that have exceeded their set 106.Dv RLIMIT_RSS . 107.It Dv RLIMIT_SBSIZE 108The maximum size (in bytes) of socket buffer usage for this user. 109This limits the amount of network memory, and hence the amount of 110mbufs, that this user may hold at any time. 111.It Dv RLIMIT_STACK 112The maximum size (in bytes) of the stack segment for a process; 113this defines how far a program's stack segment may be extended. 114Stack extension is performed automatically by the system. 115.It Dv RLIMIT_SWAP 116The maximum size (in bytes) of the swap space that may be reserved or 117used by all of this user id's processes. 118This limit is enforced only if bit 1 of the 119.Va vm.overcommit 120sysctl is set. 121Please see 122.Xr tuning 7 123for a complete description of this sysctl. 124.It Dv RLIMIT_VMEM 125An alias for 126.Dv RLIMIT_AS . 127.El 128.Pp 129A resource limit is specified as a soft limit and a hard limit. 130When a soft limit is exceeded, a process might or might not receive a signal. 131For example, signals are generated when the cpu time or file size is exceeded, 132but not if the address space or RSS limit is exceeded. 133A program that exceeds the soft limit is allowed to continue execution until it 134reaches the hard limit, or modifies its own resource limit. 135Even reaching the hard limit does not necessarily halt a process. 136For example, if the RSS hard limit is exceeded, nothing happens. 137.Pp 138The 139.Vt rlimit 140structure is used to specify the hard and soft limits on a resource. 141.Bd -literal -offset indent 142struct rlimit { 143 rlim_t rlim_cur; /* current (soft) limit */ 144 rlim_t rlim_max; /* maximum value for rlim_cur */ 145}; 146.Ed 147.Pp 148Only the super-user may raise the maximum limits. 149Other users 150may only alter 151.Fa rlim_cur 152within the range from 0 to 153.Fa rlim_max 154or (irreversibly) lower 155.Fa rlim_max . 156.Pp 157An 158.Dq infinite 159value for a limit is defined as 160.Dv RLIM_INFINITY . 161.Pp 162Because this information is stored in the per-process information, 163this system call must be executed directly by the shell if it 164is to affect all future processes created by the shell; 165.Ic limit 166is thus a built-in command to 167.Xr csh 1 . 168.Pp 169The system refuses to extend the data or stack space when the limits 170would be exceeded in the normal way: a 171.Xr brk 2 172function fails if the data space limit is reached. 173When the stack limit is reached, the process receives 174a segmentation fault 175.Pq Dv SIGSEGV ; 176if this signal is not 177caught by a handler using the signal stack, this signal 178will kill the process. 179.Pp 180A file I/O operation that would create a file larger that the process' 181soft limit will cause the write to fail and a signal 182.Dv SIGXFSZ 183to be 184generated; this normally terminates the process, but may be caught. 185When 186the soft cpu time limit is exceeded, a 187.Dv SIGXCPU 188signal is sent to the 189offending process. 190.Pp 191When most operations would allocate more virtual memory than allowed by the 192soft limit of 193.Dv RLIMIT_AS , 194the operation fails with 195.Dv ENOMEM 196and no signal is raised. 197A notable exception is stack extension, described above. 198If stack extension would allocate more virtual memory than allowed by the soft 199limit of 200.Dv RLIMIT_AS , 201a 202.Dv SIGSEGV 203signal will be delivered. 204The caller is free to raise the soft address space limit up to the hard limit 205and retry the allocation. 206.Sh RETURN VALUES 207.Rv -std 208.Sh ERRORS 209The 210.Fn getrlimit 211and 212.Fn setrlimit 213system calls 214will fail if: 215.Bl -tag -width Er 216.It Bq Er EFAULT 217The address specified for 218.Fa rlp 219is invalid. 220.It Bq Er EPERM 221The limit specified to 222.Fn setrlimit 223would have 224raised the maximum limit value, and the caller is not the super-user. 225.El 226.Sh SEE ALSO 227.Xr csh 1 , 228.Xr quota 1 , 229.Xr quotactl 2 , 230.Xr sigaction 2 , 231.Xr sigaltstack 2 , 232.Xr sysctl 3 , 233.Xr ulimit 3 234.Sh HISTORY 235The 236.Fn getrlimit 237system call appeared in 238.Bx 4.2 . 239