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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.\" 30.Dd September 30, 2016 31.Dt GETRLIMIT 2 32.Os 33.Sh NAME 34.Nm getrlimit , 35.Nm setrlimit 36.Nd control maximum system resource consumption 37.Sh LIBRARY 38.Lb libc 39.Sh SYNOPSIS 40.In sys/types.h 41.In sys/time.h 42.In sys/resource.h 43.Ft int 44.Fn getrlimit "int resource" "struct rlimit *rlp" 45.Ft int 46.Fn setrlimit "int resource" "const struct rlimit *rlp" 47.Sh DESCRIPTION 48Limits on the consumption of system resources by the current process 49and each process it creates may be obtained with the 50.Fn getrlimit 51system call, and set with the 52.Fn setrlimit 53system call. 54.Pp 55The 56.Fa resource 57argument is one of the following: 58.Bl -tag -width RLIMIT_FSIZEAA 59.It Dv RLIMIT_AS 60The maximum amount (in bytes) of virtual memory the process is 61allowed to map. 62.It Dv RLIMIT_CORE 63The largest size (in bytes) 64.Xr core 5 65file that may be created. 66.It Dv RLIMIT_CPU 67The maximum amount of cpu time (in seconds) to be used by 68each process. 69.It Dv RLIMIT_DATA 70The maximum size (in bytes) of the data segment for a process; 71this defines how far a program may extend its break with the 72.Xr sbrk 2 73function. 74.It Dv RLIMIT_FSIZE 75The largest size (in bytes) file that may be created. 76.It Dv RLIMIT_KQUEUES 77The maximum number of kqueues this user id is allowed to create. 78.It Dv RLIMIT_MEMLOCK 79The maximum size (in bytes) which a process may lock into memory 80using the 81.Xr mlock 2 82system call. 83.It Dv RLIMIT_NOFILE 84The maximum number of open files for this process. 85.It Dv RLIMIT_NPROC 86The maximum number of simultaneous processes for this user id. 87.It Dv RLIMIT_NPTS 88The maximum number of pseudo-terminals this user id is allowed to create. 89.It Dv RLIMIT_RSS 90When there is memory pressure and swap is available, prioritize eviction of 91a process' resident pages beyond this amount (in bytes). 92When memory is not under pressure, this rlimit is effectively ignored. 93Even when there is memory pressure, the amount of available swap space and some 94sysctl settings like 95.Xr vm.swap_enabled 96and 97.Xr vm.swap_idle_enabled 98can affect what happens to processes that have exceeded this size. 99.Pp 100Processes that exceed their set 101.Dv RLIMIT_RSS 102are not signalled or halted. 103The limit is merely a hint to the VM daemon to prefer to deactivate pages from 104processes that have exceeded their set 105.Dv RLIMIT_RSS . 106.It Dv RLIMIT_SBSIZE 107The maximum size (in bytes) of socket buffer usage for this user. 108This limits the amount of network memory, and hence the amount of 109mbufs, that this user may hold at any time. 110.It Dv RLIMIT_STACK 111The maximum size (in bytes) of the stack segment for a process; 112this defines how far a program's stack segment may be extended. 113Stack extension is performed automatically by the system. 114.It Dv RLIMIT_SWAP 115The maximum size (in bytes) of the swap space that may be reserved or 116used by all of this user id's processes. 117This limit is enforced only if bit 1 of the 118.Va vm.overcommit 119sysctl is set. 120Please see 121.Xr tuning 7 122for a complete description of this sysctl. 123.It Dv RLIMIT_VMEM 124An alias for 125.Dv RLIMIT_AS . 126.El 127.Pp 128A resource limit is specified as a soft limit and a hard limit. 129When a soft limit is exceeded, a process might or might not receive a signal. 130For example, signals are generated when the cpu time or file size is exceeded, 131but not if the address space or RSS limit is exceeded. 132A program that exceeds the soft limit is allowed to continue execution until it 133reaches the hard limit, or modifies its own resource limit. 134Even reaching the hard limit does not necessarily halt a process. 135For example, if the RSS hard limit is exceeded, nothing happens. 136.Pp 137The 138.Vt rlimit 139structure is used to specify the hard and soft limits on a resource. 140.Bd -literal -offset indent 141struct rlimit { 142 rlim_t rlim_cur; /* current (soft) limit */ 143 rlim_t rlim_max; /* maximum value for rlim_cur */ 144}; 145.Ed 146.Pp 147Only the super-user may raise the maximum limits. 148Other users 149may only alter 150.Fa rlim_cur 151within the range from 0 to 152.Fa rlim_max 153or (irreversibly) lower 154.Fa rlim_max . 155.Pp 156An 157.Dq infinite 158value for a limit is defined as 159.Dv RLIM_INFINITY . 160.Pp 161Because this information is stored in the per-process information, 162this system call must be executed directly by the shell if it 163is to affect all future processes created by the shell; 164.Ic limit 165is thus a built-in command to 166.Xr csh 1 . 167.Pp 168The system refuses to extend the data or stack space when the limits 169would be exceeded in the normal way: a 170.Xr brk 2 171function fails if the data space limit is reached. 172When the stack limit is reached, the process receives 173a segmentation fault 174.Pq Dv SIGSEGV ; 175if this signal is not 176caught by a handler using the signal stack, this signal 177will kill the process. 178.Pp 179A file I/O operation that would create a file larger that the process' 180soft limit will cause the write to fail and a signal 181.Dv SIGXFSZ 182to be 183generated; this normally terminates the process, but may be caught. 184When 185the soft cpu time limit is exceeded, a 186.Dv SIGXCPU 187signal is sent to the 188offending process. 189.Pp 190When most operations would allocate more virtual memory than allowed by the 191soft limit of 192.Dv RLIMIT_AS , 193the operation fails with 194.Dv ENOMEM 195and no signal is raised. 196A notable exception is stack extension, described above. 197If stack extension would allocate more virtual memory than allowed by the soft 198limit of 199.Dv RLIMIT_AS , 200a 201.Dv SIGSEGV 202signal will be delivered. 203The caller is free to raise the soft address space limit up to the hard limit 204and retry the allocation. 205.Sh RETURN VALUES 206.Rv -std 207.Sh ERRORS 208The 209.Fn getrlimit 210and 211.Fn setrlimit 212system calls 213will fail if: 214.Bl -tag -width Er 215.It Bq Er EFAULT 216The address specified for 217.Fa rlp 218is invalid. 219.It Bq Er EPERM 220The limit specified to 221.Fn setrlimit 222would have 223raised the maximum limit value, and the caller is not the super-user. 224.El 225.Sh SEE ALSO 226.Xr csh 1 , 227.Xr quota 1 , 228.Xr quotactl 2 , 229.Xr sigaction 2 , 230.Xr sigaltstack 2 , 231.Xr sysctl 3 , 232.Xr ulimit 3 233.Sh HISTORY 234The 235.Fn getrlimit 236system call appeared in 237.Bx 4.2 . 238