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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 September 30, 2016 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. 91Even when there is memory pressure, the amount of available swap space and some 92sysctl settings like 93.Xr vm.swap_enabled 94and 95.Xr vm.swap_idle_enabled 96can affect what happens to processes that have exceeded this size. 97.Pp 98Processes that exceed their set 99.Dv RLIMIT_RSS 100are not signalled or halted. 101The limit is merely a hint to the VM daemon to prefer to deactivate pages from 102processes that have exceeded their set 103.Dv RLIMIT_RSS . 104.It Dv RLIMIT_SBSIZE 105The maximum size (in bytes) of socket buffer usage for this user. 106This limits the amount of network memory, and hence the amount of 107mbufs, that this user may hold at any time. 108.It Dv RLIMIT_STACK 109The maximum size (in bytes) of the stack segment for a process; 110this defines how far a program's stack segment may be extended. 111Stack extension is performed automatically by the system. 112.It Dv RLIMIT_SWAP 113The maximum size (in bytes) of the swap space that may be reserved or 114used by all of this user id's processes. 115This limit is enforced only if bit 1 of the 116.Va vm.overcommit 117sysctl is set. 118Please see 119.Xr tuning 7 120for a complete description of this sysctl. 121.It Dv RLIMIT_VMEM 122An alias for 123.Dv RLIMIT_AS . 124.El 125.Pp 126A resource limit is specified as a soft limit and a hard limit. 127When a soft limit is exceeded, a process might or might not receive a signal. 128For example, signals are generated when the cpu time or file size is exceeded, 129but not if the address space or RSS limit is exceeded. 130A program that exceeds the soft limit is allowed to continue execution until it 131reaches the hard limit, or modifies its own resource limit. 132Even reaching the hard limit does not necessarily halt a process. 133For example, if the RSS hard limit is exceeded, nothing happens. 134.Pp 135The 136.Vt rlimit 137structure is used to specify the hard and soft limits on a resource. 138.Bd -literal -offset indent 139struct rlimit { 140 rlim_t rlim_cur; /* current (soft) limit */ 141 rlim_t rlim_max; /* maximum value for rlim_cur */ 142}; 143.Ed 144.Pp 145Only the super-user may raise the maximum limits. 146Other users 147may only alter 148.Fa rlim_cur 149within the range from 0 to 150.Fa rlim_max 151or (irreversibly) lower 152.Fa rlim_max . 153.Pp 154An 155.Dq infinite 156value for a limit is defined as 157.Dv RLIM_INFINITY . 158.Pp 159Because this information is stored in the per-process information, 160this system call must be executed directly by the shell if it 161is to affect all future processes created by the shell; 162.Ic limit 163is thus a built-in command to 164.Xr csh 1 . 165.Pp 166The system refuses to extend the data or stack space when the limits 167would be exceeded in the normal way: a 168.Xr brk 2 169function fails if the data space limit is reached. 170When the stack limit is reached, the process receives 171a segmentation fault 172.Pq Dv SIGSEGV ; 173if this signal is not 174caught by a handler using the signal stack, this signal 175will kill the process. 176.Pp 177A file I/O operation that would create a file larger that the process' 178soft limit will cause the write to fail and a signal 179.Dv SIGXFSZ 180to be 181generated; this normally terminates the process, but may be caught. 182When 183the soft cpu time limit is exceeded, a 184.Dv SIGXCPU 185signal is sent to the 186offending process. 187.Pp 188When most operations would allocate more virtual memory than allowed by the 189soft limit of 190.Dv RLIMIT_AS , 191the operation fails with 192.Dv ENOMEM 193and no signal is raised. 194A notable exception is stack extension, described above. 195If stack extension would allocate more virtual memory than allowed by the soft 196limit of 197.Dv RLIMIT_AS , 198a 199.Dv SIGSEGV 200signal will be delivered. 201The caller is free to raise the soft address space limit up to the hard limit 202and retry the allocation. 203.Sh RETURN VALUES 204.Rv -std 205.Sh ERRORS 206The 207.Fn getrlimit 208and 209.Fn setrlimit 210system calls 211will fail if: 212.Bl -tag -width Er 213.It Bq Er EFAULT 214The address specified for 215.Fa rlp 216is invalid. 217.It Bq Er EPERM 218The limit specified to 219.Fn setrlimit 220would have 221raised the maximum limit value, and the caller is not the super-user. 222.El 223.Sh SEE ALSO 224.Xr csh 1 , 225.Xr quota 1 , 226.Xr quotactl 2 , 227.Xr sigaction 2 , 228.Xr sigaltstack 2 , 229.Xr sysctl 3 , 230.Xr ulimit 3 231.Sh HISTORY 232The 233.Fn getrlimit 234system call appeared in 235.Bx 4.2 . 236