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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.Dd July 25, 2024 29.Dt GETRLIMIT 2 30.Os 31.Sh NAME 32.Nm getrlimit , 33.Nm setrlimit 34.Nd control maximum system resource consumption 35.Sh LIBRARY 36.Lb libc 37.Sh SYNOPSIS 38.In sys/types.h 39.In sys/time.h 40.In sys/resource.h 41.Ft int 42.Fn getrlimit "int resource" "struct rlimit *rlp" 43.Ft int 44.Fn setrlimit "int resource" "const struct rlimit *rlp" 45.Sh DESCRIPTION 46Limits on the consumption of system resources by the current process 47and each process it creates may be obtained with the 48.Fn getrlimit 49system call, and set with the 50.Fn setrlimit 51system call. 52.Pp 53The 54.Fa resource 55argument is one of the following: 56.Bl -tag -width RLIMIT_FSIZEAA 57.It Dv RLIMIT_AS 58The maximum amount (in bytes) of virtual memory the process is 59allowed to map. 60.It Dv RLIMIT_CORE 61The largest size (in bytes) 62.Xr core 5 63file that may be created. 64.It Dv RLIMIT_CPU 65The maximum amount of cpu time (in seconds) to be used by 66each process. 67.It Dv RLIMIT_DATA 68The maximum size (in bytes) of the data segment for a process; 69this defines how far a program may extend its break with the 70.Xr sbrk 2 71function. 72.It Dv RLIMIT_FSIZE 73The largest size (in bytes) file that may be created. 74.It Dv RLIMIT_KQUEUES 75The maximum number of kqueues this user id is allowed to create. 76.It Dv RLIMIT_MEMLOCK 77The maximum size (in bytes) which a process may lock into memory 78using the 79.Xr mlock 2 80system call. 81.It Dv RLIMIT_NOFILE 82The maximum number of open files for this process. 83.It Dv RLIMIT_NPROC 84The maximum number of simultaneous processes for this user id. 85.It Dv RLIMIT_NPTS 86The maximum number of pseudo-terminals this user id is allowed to create. 87.It Dv RLIMIT_RSS 88When there is memory pressure and swap is available, prioritize eviction of 89a process' resident pages beyond this amount (in bytes). 90When memory is not under pressure, this rlimit is effectively ignored. 91.Pp 92Processes that exceed their set 93.Dv RLIMIT_RSS 94are not signalled or halted. 95The limit is merely a hint to the VM daemon to prefer to deactivate pages from 96processes that have exceeded their set 97.Dv RLIMIT_RSS . 98.It Dv RLIMIT_SBSIZE 99The maximum size (in bytes) of socket buffer usage for this user. 100This limits the amount of network memory, and hence the amount of 101mbufs, that this user may hold at any time. 102.It Dv RLIMIT_STACK 103The maximum size (in bytes) of the stack segment for a process; 104this defines how far a program's stack segment may be extended. 105Stack extension is performed automatically by the system. 106.It Dv RLIMIT_SWAP 107The maximum size (in bytes) of the swap space that may be reserved or 108used by all of this user id's processes. 109This limit is enforced only if bit 1 of the 110.Va vm.overcommit 111sysctl is set. 112Please see 113.Xr tuning 7 114for a complete description of this sysctl. 115.It Dv RLIMIT_UMTXP 116The limit of the number of process-shared posix thread library objects 117allocated by user id. 118.It Dv RLIMIT_VMEM 119An alias for 120.Dv RLIMIT_AS . 121.El 122.Pp 123A resource limit is specified as a soft limit and a hard limit. 124When a soft limit is exceeded, a process might or might not receive a signal. 125For example, signals are generated when the cpu time or file size is exceeded, 126but not if the address space or RSS limit is exceeded. 127A program that exceeds the soft limit is allowed to continue execution until it 128reaches the hard limit, or modifies its own resource limit. 129Even reaching the hard limit does not necessarily halt a process. 130For example, if the RSS hard limit is exceeded, nothing happens. 131.Pp 132The 133.Vt rlimit 134structure is used to specify the hard and soft limits on a resource. 135.Bd -literal -offset indent 136struct rlimit { 137 rlim_t rlim_cur; /* current (soft) limit */ 138 rlim_t rlim_max; /* maximum value for rlim_cur */ 139}; 140.Ed 141.Pp 142Only the super-user may raise the maximum limits. 143Other users 144may only alter 145.Fa rlim_cur 146within the range from 0 to 147.Fa rlim_max 148or (irreversibly) lower 149.Fa rlim_max . 150.Pp 151An 152.Dq infinite 153value for a limit is defined as 154.Dv RLIM_INFINITY . 155.Pp 156Because this information is stored in the per-process information, 157this system call must be executed directly by the shell if it 158is to affect all future processes created by the shell; 159.Ic limit 160is thus a built-in command to 161.Xr csh 1 . 162.Pp 163The system refuses to extend the data or stack space when the limits 164would be exceeded in the normal way: a 165.Xr brk 2 166function fails if the data space limit is reached. 167When the stack limit is reached, the process receives 168a segmentation fault 169.Pq Dv SIGSEGV ; 170if this signal is not 171caught by a handler using the signal stack, this signal 172will kill the process. 173.Pp 174A file I/O operation that would create a file larger that the process' 175soft limit will cause the write to fail and a signal 176.Dv SIGXFSZ 177to be 178generated; this normally terminates the process, but may be caught. 179When 180the soft cpu time limit is exceeded, a 181.Dv SIGXCPU 182signal is sent to the 183offending process. 184.Pp 185When most operations would allocate more virtual memory than allowed by the 186soft limit of 187.Dv RLIMIT_AS , 188the operation fails with 189.Dv ENOMEM 190and no signal is raised. 191A notable exception is stack extension, described above. 192If stack extension would allocate more virtual memory than allowed by the soft 193limit of 194.Dv RLIMIT_AS , 195a 196.Dv SIGSEGV 197signal will be delivered. 198The caller is free to raise the soft address space limit up to the hard limit 199and retry the allocation. 200.Sh RETURN VALUES 201.Rv -std 202.Sh ERRORS 203The 204.Fn getrlimit 205and 206.Fn setrlimit 207system calls 208will fail if: 209.Bl -tag -width Er 210.It Bq Er EFAULT 211The address specified for 212.Fa rlp 213is invalid. 214.It Bq Er EPERM 215The limit specified to 216.Fn setrlimit 217would have 218raised the maximum limit value, and the caller is not the super-user. 219.El 220.Sh SEE ALSO 221.Xr csh 1 , 222.Xr quota 1 , 223.Xr quotactl 2 , 224.Xr sigaction 2 , 225.Xr sigaltstack 2 , 226.Xr sysctl 3 , 227.Xr ulimit 3 228.Sh HISTORY 229The 230.Fn getrlimit 231system call appeared in 232.Bx 4.2 . 233