1.\" $NetBSD: getrlimit.2,v 1.29 2004/05/13 10:20:58 wiz Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)getrlimit.2 8.1 (Berkeley) 6/4/93 31.\" 32.Dd April 19, 2004 33.Dt GETRLIMIT 2 34.Os 35.Sh NAME 36.Nm getrlimit , 37.Nm setrlimit 38.Nd control maximum system resource consumption 39.Sh LIBRARY 40.Lb libc 41.Sh SYNOPSIS 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 51call, and set with the 52.Fn setrlimit 53call. 54Resources of an arbitrary process can be obtained/changed using 55.Xr sysctl 3 . 56.. 57.Pp 58The 59.Fa resource 60parameter is one of the following: 61.Bl -tag -width RLIMIT_FSIZEAA 62.It Li RLIMIT_CORE 63The largest size (in bytes) 64.Pa core 65file that may be created. 66.It Li RLIMIT_CPU 67The maximum amount of CPU time (in seconds) to be used by 68each process. 69.It Li 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 73system call. 74.It Li RLIMIT_FSIZE 75The largest size (in bytes) file that may be created. 76.It Li RLIMIT_MEMLOCK 77The maximum size (in bytes) which a process may lock into memory 78using the 79.Xr mlock 2 80function. 81.It Li RLIMIT_NOFILE 82The maximum number of open files for this process. 83.It Li RLIMIT_NPROC 84The maximum number of simultaneous processes for this user id. 85.It Li RLIMIT_RSS 86The maximum size (in bytes) to which a process's resident set size may 87grow. 88This imposes a limit on the amount of physical memory to be given to 89a process; if memory is tight, the system will prefer to take memory 90from processes that are exceeding their declared resident set size. 91.It Li RLIMIT_SBSIZE 92The maximum size (in bytes) of the socket buffers 93set by the 94.Xr setsockopt 2 95.Dv SO_RCVBUF 96and 97.Dv SO_SNDBUF 98options. 99.It Li RLIMIT_STACK 100The maximum size (in bytes) of the stack segment for a process; 101this defines how far a program's stack segment may be extended. 102Stack extension is performed automatically by the system. 103.El 104.Pp 105A resource limit is specified as a soft limit and a hard limit. 106When a soft limit is exceeded a process may receive a signal (for example, 107if the CPU time or file size is exceeded), but it will be allowed to 108continue execution until it reaches the hard limit (or modifies 109its resource limit). 110The 111.Em rlimit 112structure is used to specify the hard and soft limits on a resource, 113.Bd -literal -offset indent 114struct rlimit { 115 rlim_t rlim_cur; /* current (soft) limit */ 116 rlim_t rlim_max; /* hard limit */ 117}; 118.Ed 119.Pp 120Only the super-user may raise the maximum limits. 121Other users may only alter 122.Fa rlim_cur 123within the range from 0 to 124.Fa rlim_max 125or (irreversibly) lower 126.Fa rlim_max . 127.Pp 128An 129.Dq infinite 130value for a limit is defined as 131.Dv RLIM_INFINITY . 132.Pp 133Because this information is stored in the per-process information, 134this system call must be executed directly by the shell if it 135is to affect all future processes created by the shell. 136Thus, shells provide built-in commands to change the limits 137.Ic ( limit 138for 139.Xr csh 1 , 140or 141.Ic ulimit 142for 143.Xr sh 1 ) . 144.Pp 145The system refuses to extend the data or stack space when the limits 146would be exceeded in the normal way: a 147.Xr brk 2 148call fails if the data space limit is reached. 149When the stack limit is reached, the process receives 150a segmentation fault 151.Pq Dv SIGSEGV ; 152if this signal is not 153caught by a handler using the signal stack, this signal 154will kill the process. 155.Pp 156A file I/O operation that would create a file larger that the process' 157soft limit will cause the write to fail and a signal 158.Dv SIGXFSZ 159to be 160generated; this normally terminates the process, but may be caught. 161When the soft CPU time limit is exceeded, a signal 162.Dv SIGXCPU 163is sent to the 164offending process. 165.Sh RETURN VALUES 166A 0 return value indicates that the call succeeded, changing 167or returning the resource limit. 168Otherwise, \-1 is returned and the global variable 169.Va errno 170is set to indicate the error. 171.Sh ERRORS 172The 173.Fn getrlimit 174and 175.Fn setrlimit 176will fail if: 177.Bl -tag -width Er 178.It Bq Er EFAULT 179The address specified for 180.Fa rlp 181is invalid. 182.It Bq Er EINVAL 183Specified 184.Fa resource 185was invalid. 186.It Bq Er EINVAL 187In the 188.Fn setrlimit 189call, the specified 190.Fa rlim_cur 191exceeds the specified 192.Fa rlim_max . 193.It Bq Er EPERM 194The limit specified to 195.Fn setrlimit 196would have 197raised the maximum limit value, and the caller is not the super-user. 198.El 199.Pp 200The 201.Fn setrlimit 202function may fail if: 203.Bl -tag -width Er 204.It Bq Er EINVAL 205The limit specified to 206.Fn setrlimit 207cannot be lowered, because current usage is already higher than the limit. 208.El 209.Sh SEE ALSO 210.Xr csh 1 , 211.Xr sh 1 , 212.Xr mlock 2 , 213.Xr quotactl 2 , 214.Xr setsockopt 2 , 215.Xr sigaction 2 , 216.Xr sigaltstack 2 , 217.Xr sysctl 3 218.\" Sh STANDARDS 219.\" With exception of 220.\" .Li RLIMIT_AS 221.\" (which is not currently supported), the 222.\" .Fn getrlimit 223.\" and 224.\" .Fn setrlimit 225.\" functions conform to 226.\" .St -susv2 . 227.Sh HISTORY 228The 229.Fn getrlimit 230function call appeared in 231.Bx 4.2 . 232