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fea681da 1.\" Copyright (c) 1992 Drew Eckhardt, March 28, 1992
658ea3ee 2.\" and Copyright (c) 2002, 2004, 2005, 2008, 2010 Michael Kerrisk
fea681da 3.\"
93015253 4.\" %%%LICENSE_START(VERBATIM)
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5.\" Permission is granted to make and distribute verbatim copies of this
6.\" manual provided the copyright notice and this permission notice are
7.\" preserved on all copies.
8.\"
9.\" Permission is granted to copy and distribute modified versions of this
10.\" manual under the conditions for verbatim copying, provided that the
11.\" entire resulting derived work is distributed under the terms of a
12.\" permission notice identical to this one.
c13182ef 13.\"
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14.\" Since the Linux kernel and libraries are constantly changing, this
15.\" manual page may be incorrect or out-of-date. The author(s) assume no
16.\" responsibility for errors or omissions, or for damages resulting from
17.\" the use of the information contained herein. The author(s) may not
18.\" have taken the same level of care in the production of this manual,
19.\" which is licensed free of charge, as they might when working
20.\" professionally.
c13182ef 21.\"
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22.\" Formatted or processed versions of this manual, if unaccompanied by
23.\" the source, must acknowledge the copyright and authors of this work.
4b72fb64 24.\" %%%LICENSE_END
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25.\"
26.\" Modified by Michael Haardt <michael@moria.de>
27.\" Modified 1993-07-23 by Rik Faith <faith@cs.unc.edu>
28.\" Modified 1996-01-13 by Arnt Gulbrandsen <agulbra@troll.no>
29.\" Modified 1996-01-22 by aeb, following a remark by
30.\" Tigran Aivazian <tigran@sco.com>
31.\" Modified 1996-04-14 by aeb, following a remark by
32.\" Robert Bihlmeyer <robbe@orcus.ping.at>
33.\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
34.\" Modified 2001-05-04 by aeb, following a remark by
e00c3a07 35.\" HÃ¥vard Lygre <hklygre@online.no>
c11b1abf
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36.\" Modified 2001-04-17 by Michael Kerrisk <mtk.manpages@gmail.com>
37.\" Modified 2002-06-13 by Michael Kerrisk <mtk.manpages@gmail.com>
c8f2dd47 38.\" Added note on nonstandard behavior when SIGCHLD is ignored.
c11b1abf 39.\" Modified 2002-07-09 by Michael Kerrisk <mtk.manpages@gmail.com>
1546fe19 40.\" Enhanced descriptions of 'resource' values
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41.\" Modified 2003-11-28 by aeb, added RLIMIT_CORE
42.\" Modified 2004-03-26 by aeb, added RLIMIT_AS
c11b1abf 43.\" Modified 2004-06-16 by Michael Kerrisk <mtk.manpages@gmail.com>
fea681da
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44.\" Added notes on CAP_SYS_RESOURCE
45.\"
c13182ef 46.\" 2004-11-16 -- mtk: the getrlimit.2 page, which formally included
0fc46b5a
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47.\" coverage of getrusage(2), has been split, so that the latter
48.\" is now covered in its own getrusage.2.
49.\"
50.\" Modified 2004-11-16, mtk: A few other minor changes
b4c0e1cb
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51.\" Modified 2004-11-23, mtk
52.\" Added notes on RLIMIT_MEMLOCK, RLIMIT_NPROC, and RLIMIT_RSS
53.\" to "CONFORMING TO"
54.\" Modified 2004-11-25, mtk
55.\" Rewrote discussion on RLIMIT_MEMLOCK to incorporate kernel
56.\" 2.6.9 changes.
57.\" Added note on RLIMIT_CPU error in older kernels
1bf844f1 58.\" 2004-11-03, mtk, Added RLIMIT_SIGPENDING
9d8b1d5f 59.\" 2005-07-13, mtk, documented RLIMIT_MSGQUEUE limit.
1bf844f1 60.\" 2005-07-28, mtk, Added descriptions of RLIMIT_NICE and RLIMIT_RTPRIO
23ce0537 61.\" 2008-05-07, mtk / Peter Zijlstra, Added description of RLIMIT_RTTIME
1546fe19 62.\" 2010-11-06, mtk: Added documentation of prlimit()
0fc46b5a 63.\"
b8efb414 64.TH GETRLIMIT 2 2016-10-08 "Linux" "Linux Programmer's Manual"
fea681da 65.SH NAME
1546fe19 66getrlimit, setrlimit, prlimit \- get/set resource limits
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67.SH SYNOPSIS
68.B #include <sys/time.h>
69.br
70.B #include <sys/resource.h>
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71.sp
72.BI "int getrlimit(int " resource ", struct rlimit *" rlim );
73.br
fea681da 74.BI "int setrlimit(int " resource ", const struct rlimit *" rlim );
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75.sp
76.BI "int prlimit(pid_t " pid ", int " resource \
77", const struct rlimit *" new_limit ,
78.br
79.BI " struct rlimit *" old_limit );
80.sp
81.in -4n
82Feature Test Macro Requirements for glibc (see
83.BR feature_test_macros (7)):
84.in
85.sp
86.BR prlimit ():
abb3258d 87_GNU_SOURCE
fea681da 88.SH DESCRIPTION
1546fe19 89The
0fc46b5a 90.BR getrlimit ()
fea681da 91and
0fc46b5a 92.BR setrlimit ()
0ef19275 93system calls get and set resource limits respectively.
c13182ef 94Each resource has an associated soft and hard limit, as defined by the
8478ee02 95.I rlimit
c805532e 96structure:
fea681da 97.PP
a08ea57c 98.in +4n
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99.nf
100struct rlimit {
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101 rlim_t rlim_cur; /* Soft limit */
102 rlim_t rlim_max; /* Hard limit (ceiling for rlim_cur) */
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103};
104
105.fi
a08ea57c 106.in
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107The soft limit is the value that the kernel enforces for the
108corresponding resource.
109The hard limit acts as a ceiling for the soft limit:
33a0ccb2 110an unprivileged process may set only its soft limit to a value in the
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111range from 0 up to the hard limit, and (irreversibly) lower its hard limit.
112A privileged process (under Linux: one with the
113.B CAP_SYS_RESOURCE
114capability) may make arbitrary changes to either limit value.
115.PP
116The value
117.B RLIM_INFINITY
118denotes no limit on a resource (both in the structure returned by
119.BR getrlimit ()
120and in the structure passed to
121.BR setrlimit ()).
122.PP
0ef19275 123The
fea681da 124.I resource
0ef19275 125argument must be one of:
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126.TP
127.B RLIMIT_AS
128The maximum size of the process's virtual memory (address space) in bytes.
129.\" since 2.0.27 / 2.1.12
130This limit affects calls to
131.BR brk (2),
9af134cd 132.BR mmap (2),
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133and
134.BR mremap (2),
135which fail with the error
136.B ENOMEM
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137upon exceeding this limit.
138Also automatic stack expansion will fail
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139(and generate a
140.B SIGSEGV
141that kills the process if no alternate stack
142has been made available via
143.BR sigaltstack (2)).
4a3f7c5f 144Since the value is a \fIlong\fP, on machines with a 32-bit \fIlong\fP
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145either this limit is at most 2 GiB, or this resource is unlimited.
146.TP
147.B RLIMIT_CORE
4711f722 148Maximum size of a
fea681da 149.I core
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150file (see
151.BR core (5)).
1c44bd5b 152When 0 no core dump files are created.
c7094399 153When nonzero, larger dumps are truncated to this size.
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154.TP
155.B RLIMIT_CPU
156CPU time limit in seconds.
157When the process reaches the soft limit, it is sent a
158.B SIGXCPU
159signal.
160The default action for this signal is to terminate the process.
161However, the signal can be caught, and the handler can return control to
162the main program.
163If the process continues to consume CPU time, it will be sent
164.B SIGXCPU
165once per second until the hard limit is reached, at which time
166it is sent
167.BR SIGKILL .
4f96e450 168(This latter point describes Linux behavior.
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169Implementations vary in how they treat processes which continue to
170consume CPU time after reaching the soft limit.
171Portable applications that need to catch this signal should
172perform an orderly termination upon first receipt of
e6c5832f 173.BR SIGXCPU .)
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174.TP
175.B RLIMIT_DATA
176The maximum size of the process's data segment (initialized data,
177uninitialized data, and heap).
178This limit affects calls to
0bfa087b 179.BR brk (2)
c13182ef 180and
0bfa087b 181.BR sbrk (2),
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182which fail with the error
183.B ENOMEM
184upon encountering the soft limit of this resource.
185.TP
186.B RLIMIT_FSIZE
187The maximum size of files that the process may create.
188Attempts to extend a file beyond this limit result in delivery of a
189.B SIGXFSZ
190signal.
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191By default, this signal terminates a process, but a process can
192catch this signal instead, in which case the relevant system call (e.g.,
2e42dfb3 193.BR write (2),
0bfa087b 194.BR truncate (2))
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195fails with the error
196.BR EFBIG .
197.TP
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198.BR RLIMIT_LOCKS " (Early Linux 2.4 only)"
199.\" to be precise: Linux 2.4.0-test9; no longer in 2.4.25 / 2.5.65
fea681da 200A limit on the combined number of
0bfa087b 201.BR flock (2)
c13182ef 202locks and
0bfa087b 203.BR fcntl (2)
fea681da 204leases that this process may establish.
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205.TP
206.B RLIMIT_MEMLOCK
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207The maximum number of bytes of memory that may be locked
208into RAM.
209In effect this limit is rounded down to the nearest multiple
210of the system page size.
c13182ef 211This limit affects
e1d6264d 212.BR mlock (2)
c13182ef 213and
e1d6264d 214.BR mlockall (2)
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215and the
216.BR mmap (2)
217.B MAP_LOCKED
218operation.
219Since Linux 2.6.9 it also affects the
220.BR shmctl (2)
221.B SHM_LOCK
c13182ef 222operation, where it sets a maximum on the total bytes in
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223shared memory segments (see
224.BR shmget (2))
225that may be locked by the real user ID of the calling process.
c13182ef 226The
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227.BR shmctl (2)
228.B SHM_LOCK
229locks are accounted for separately from the per-process memory
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230locks established by
231.BR mlock (2),
e1d6264d 232.BR mlockall (2),
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233and
234.BR mmap (2)
235.BR MAP_LOCKED ;
236a process can lock bytes up to this limit in each of these
e6c5832f 237two categories.
40cbb640 238
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239In Linux kernels before 2.6.9, this limit controlled the amount of
240memory that could be locked by a privileged process.
241Since Linux 2.6.9, no limits are placed on the amount of memory
242that a privileged process may lock, and this limit instead governs
243the amount of memory that an unprivileged process may lock.
9d8b1d5f 244.TP
31c1f2b0 245.BR RLIMIT_MSGQUEUE " (since Linux 2.6.8)"
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246Specifies the limit on the number of bytes that can be allocated
247for POSIX message queues for the real user ID of the calling process.
248This limit is enforced for
249.BR mq_open (3).
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250Each message queue that the user creates counts (until it is removed)
251against this limit according to the formula:
252.nf
253
e15dc338 254 Since Linux 3.5:
40cbb640 255
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256 bytes = attr.mq_maxmsg * sizeof(struct msg_msg) +
257 min(attr.mq_maxmsg, MQ_PRIO_MAX) *
6f9e0e57 258 sizeof(struct posix_msg_tree_node)+
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259 /* For overhead */
260 attr.mq_maxmsg * attr.mq_msgsize;
261 /* For message data */
262
263 Linux 3.4 and earlier:
40cbb640 264
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265 bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
266 /* For overhead */
267 attr.mq_maxmsg * attr.mq_msgsize;
268 /* For message data */
9d8b1d5f 269
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270.fi
271where
9d8b1d5f 272.I attr
c13182ef 273is the
9d8b1d5f
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274.I mq_attr
275structure specified as the fourth argument to
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276.BR mq_open (3),
277and the
278.I msg_msg
279and
280.I posix_msg_tree_node
281structures are kernel-internal structures.
9d8b1d5f 282
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283The "overhead" addend in the formula accounts for overhead
284bytes required by the implementation
285and ensures that the user cannot
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286create an unlimited number of zero-length messages (such messages
287nevertheless each consume some system memory for bookkeeping overhead).
a23bf8a3 288.TP
64d6219c 289.BR RLIMIT_NICE " (since Linux 2.6.12, but see BUGS below)"
cedd678f 290Specifies a ceiling to which the process's nice value can be raised using
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291.BR setpriority (2)
292or
293.BR nice (2).
294The actual ceiling for the nice value is calculated as
295.IR "20\ \-\ rlim_cur" .
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296(This strangeness occurs because negative numbers cannot be specified
297as resource limit values, since they typically have special meanings.
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298For example,
299.B RLIM_INFINITY
300typically is the same as \-1.)
1bf844f1 301.TP
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302.B RLIMIT_NOFILE
303Specifies a value one greater than the maximum file descriptor number
304that can be opened by this process.
305Attempts
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306.RB ( open (2),
307.BR pipe (2),
308.BR dup (2),
4a04cd9a 309etc.)
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310to exceed this limit yield the error
311.BR EMFILE .
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312(Historically, this limit was named
313.B RLIMIT_OFILE
314on BSD.)
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315.TP
316.B RLIMIT_NPROC
c13182ef 317The maximum number of processes (or, more precisely on Linux, threads)
ee930c49 318that can be created for the real user ID of the calling process.
c13182ef 319Upon encountering this limit,
0bfa087b 320.BR fork (2)
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321fails with the error
322.BR EAGAIN .
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323This limit is not enforced for processes that have either the
324.B CAP_SYS_ADMIN
325or the
326.B CAP_SYS_RESOURCE
327capability.
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328.TP
329.B RLIMIT_RSS
ce3f6039 330Specifies the limit (in bytes) of the process's resident set
fea681da 331(the number of virtual pages resident in RAM).
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332This limit has effect only in Linux 2.4.x, x < 30, and there
333affects only calls to
0bfa087b 334.BR madvise (2)
fea681da 335specifying
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336.BR MADV_WILLNEED .
337.\" As at kernel 2.6.12, this limit still does nothing in 2.6 though
c13182ef 338.\" talk of making it do something has surfaced from time to time in LKML
9426c9dd 339.\" -- MTK, Jul 05
fea681da 340.TP
31c1f2b0 341.BR RLIMIT_RTPRIO " (since Linux 2.6.12, but see BUGS)"
c13182ef 342Specifies a ceiling on the real-time priority that may be set for
cedd678f 343this process using
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344.BR sched_setscheduler (2)
345and
346.BR sched_setparam (2).
347.TP
31c1f2b0 348.BR RLIMIT_RTTIME " (since Linux 2.6.25)"
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349Specifies a limit (in microseconds)
350on the amount of CPU time that a process scheduled
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351under a real-time scheduling policy may consume without making a blocking
352system call.
353For the purpose of this limit,
354each time a process makes a blocking system call,
355the count of its consumed CPU time is reset to zero.
356The CPU time count is not reset if the process continues trying to
357use the CPU but is preempted, its time slice expires, or it calls
358.BR sched_yield (2).
359
360Upon reaching the soft limit, the process is sent a
361.B SIGXCPU
362signal.
363If the process catches or ignores this signal and
364continues consuming CPU time, then
365.B SIGXCPU
366will be generated once each second until the hard limit is reached,
367at which point the process is sent a
368.B SIGKILL
369signal.
370
371The intended use of this limit is to stop a runaway
372real-time process from locking up the system.
373.TP
31c1f2b0 374.BR RLIMIT_SIGPENDING " (since Linux 2.6.8)"
8b6aacb0 375Specifies the limit on the number of signals
e6c5832f 376that may be queued for the real user ID of the calling process.
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377Both standard and real-time signals are counted for the purpose of
378checking this limit.
33a0ccb2 379However, the limit is enforced only for
485ab701 380.BR sigqueue (3);
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381it is always possible to use
382.BR kill (2)
383to queue one instance of any of the signals that are not already
384queued to the process.
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385.\" This replaces the /proc/sys/kernel/rtsig-max system-wide limit
386.\" that was present in kernels <= 2.6.7. MTK Dec 04
387.TP
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388.B RLIMIT_STACK
389The maximum size of the process stack, in bytes.
390Upon reaching this limit, a
391.B SIGSEGV
392signal is generated.
393To handle this signal, a process must employ an alternate signal stack
394.RB ( sigaltstack (2)).
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395
396Since Linux 2.6.23,
397this limit also determines the amount of space used for the process's
398command-line arguments and environment variables; for details, see
399.BR execve (2).
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400.SS prlimit()
401.\" commit c022a0acad534fd5f5d5f17280f6d4d135e74e81
402.\" Author: Jiri Slaby <jslaby@suse.cz>
403.\" Date: Tue May 4 18:03:50 2010 +0200
9bd51977
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404.\"
405.\" rlimits: implement prlimit64 syscall
ef4f4031 406.\"
9bd51977
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407.\" commit 6a1d5e2c85d06da35cdfd93f1a27675bfdc3ad8c
408.\" Author: Jiri Slaby <jslaby@suse.cz>
409.\" Date: Wed Mar 24 17:06:58 2010 +0100
ef4f4031 410.\"
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411.\" rlimits: add rlimit64 structure
412.\"
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413The Linux-specific
414.BR prlimit ()
415system call combines and extends the functionality of
416.BR setrlimit ()
417and
418.BR getrlimit ().
419It can be used to both set and get the resource limits of an arbitrary process.
420
421The
422.I resource
423argument has the same meaning as for
424.BR setrlimit ()
425and
426.BR getrlimit ().
427
428If the
429.IR new_limit
430argument is a not NULL, then the
431.I rlimit
432structure to which it points is used to set new values for
433the soft and hard limits for
434.IR resource .
435If the
436.IR old_limit
437argument is a not NULL, then a successful call to
438.BR prlimit ()
439places the previous soft and hard limits for
440.I resource
98b43b57 441in the
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442.I rlimit
443structure pointed to by
444.IR old_limit .
445
446The
447.I pid
448argument specifies the ID of the process on which the call is to operate.
449If
450.I pid
451is 0, then the call applies to the calling process.
452To set or get the resources of a process other than itself,
453the caller must have the
454.B CAP_SYS_RESOURCE
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455capability in the user namespace of the process
456whose resource limits are being changed, or the
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457real, effective, and saved set user IDs of the target process
458must match the real user ID of the caller
459.I and
460the real, effective, and saved set group IDs of the target process
461must match the real group ID of the caller.
bea08fec 462.\" FIXME . this permission check is strange
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463.\" Asked about this on LKML, 7 Nov 2010
464.\" "Inconsistent credential checking in prlimit() syscall"
465.SH RETURN VALUE
466On success, these system calls return 0.
c13182ef 467On error, \-1 is returned, and
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468.I errno
469is set appropriately.
470.SH ERRORS
471.TP
472.B EFAULT
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473A pointer argument points to a location
474outside the accessible address space.
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475.TP
476.B EINVAL
1546fe19 477The value specified in
0fc46b5a 478.I resource
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479is not valid;
480or, for
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481.BR setrlimit ()
482or
483.BR prlimit ():
94e9d9fe 484.I rlim\->rlim_cur
b270eba9 485was greater than
94e9d9fe 486.IR rlim\->rlim_max .
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487.TP
488.B EPERM
1546fe19 489An unprivileged process tried to raise the hard limit; the
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490.B CAP_SYS_RESOURCE
491capability is required to do this.
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492.TP
493.B EPERM
494The caller tried to increase the hard
682edefb 495.B RLIMIT_NOFILE
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496limit above the maximum defined by
497.IR /proc/sys/fs/nr_open
498(see
499.BR proc (5))
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500.TP
501.B EPERM
502.RB ( prlimit ())
503The calling process did not have permission to set limits
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504for the process specified by
505.IR pid .
506.TP
507.B ESRCH
508Could not find a process with the ID specified in
509.IR pid .
510.SH VERSIONS
010eefd7 511The
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512.BR prlimit ()
513system call is available since Linux 2.6.36.
514Library support is available since glibc 2.13.
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515.SH ATTRIBUTES
516For an explanation of the terms used in this section, see
517.BR attributes (7).
518.TS
519allbox;
520lbw35 lb lb
521l l l.
522Interface Attribute Value
523T{
524.BR getrlimit (),
525.BR setrlimit (),
526.BR prlimit ()
527T} Thread safety MT-Safe
528.TE
529
a1d5f77c 530.SH CONFORMING TO
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531.BR getrlimit (),
532.BR setrlimit ():
ac17f435 533POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
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534.br
535.BR prlimit ():
536Linux-specific.
537
0daa9e92 538.B RLIMIT_MEMLOCK
a1d5f77c 539and
0daa9e92 540.B RLIMIT_NPROC
ac17f435 541derive from BSD and are not specified in POSIX.1;
a1d5f77c 542they are present on the BSDs and Linux, but on few other implementations.
0daa9e92 543.B RLIMIT_RSS
ac17f435 544derives from BSD and is not specified in POSIX.1;
a1d5f77c
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545it is nevertheless present on most implementations.
546.BR RLIMIT_MSGQUEUE ,
547.BR RLIMIT_NICE ,
548.BR RLIMIT_RTPRIO ,
23ce0537 549.BR RLIMIT_RTTIME ,
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550and
551.B RLIMIT_SIGPENDING
8382f16d 552are Linux-specific.
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553.SH NOTES
554A child process created via
555.BR fork (2)
2c0cfe3c 556inherits its parent's resource limits.
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557Resource limits are preserved across
558.BR execve (2).
835363b2 559
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560Lowering the soft limit for a resource below the process's
561current consumption of that resource will succeed
562(but will prevent the process from further increasing
563its consumption of the resource).
564
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565One can set the resource limits of the shell using the built-in
566.IR ulimit
567command
568.RI ( limit
569in
570.BR csh (1)).
571The shell's resource limits are inherited by the processes that
572it creates to execute commands.
e1695dec 573
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574Since Linux 2.6.24, the resource limits of any process can be inspected via
575.IR /proc/[pid]/limits ;
576see
577.BR proc (5).
578
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579Ancient systems provided a
580.BR vlimit ()
581function with a similar purpose to
582.BR setrlimit ().
583For backward compatibility, glibc also provides
584.BR vlimit ().
585All new applications should be written using
586.BR setrlimit ().
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587.SS C library/ kernel ABI differences
588Since version 2.13, the glibc
589.BR getrlimit ()
590and
591.BR setrlimit ()
592wrapper functions no longer invoke the corresponding system calls,
593but instead employ
594.BR prlimit (),
595for the reasons described in BUGS.
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596
597The name of the glibc wrapper function is
598.BR prlimit ();
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599the underlying system call is
600.BR prlimit64 ().
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601.SH BUGS
602In older Linux kernels, the
603.B SIGXCPU
604and
605.B SIGKILL
606signals delivered when a process encountered the soft and hard
9a8a1136 607.B RLIMIT_CPU
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608limits were delivered one (CPU) second later than they should have been.
609This was fixed in kernel 2.6.8.
1bf844f1 610
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611In 2.6.x kernels before 2.6.17, a
612.B RLIMIT_CPU
613limit of 0 is wrongly treated as "no limit" (like
6057e7a9 614.BR RLIM_INFINITY ).
64d6219c 615Since Linux 2.6.17, setting a limit of 0 does have an effect,
6057e7a9 616but is actually treated as a limit of 1 second.
a31272fe 617.\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=114008066530167&w=2
6057e7a9 618
1bf844f1 619A kernel bug means that
ceee84ba 620.\" See https://lwn.net/Articles/145008/
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621.B RLIMIT_RTPRIO
622does not work in kernel 2.6.12; the problem is fixed in kernel 2.6.13.
6151ea9a 623
c13182ef 624In kernel 2.6.12, there was an off-by-one mismatch
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625between the priority ranges returned by
626.BR getpriority (2)
627and
6151ea9a 628.BR RLIMIT_NICE .
11532b16 629This had the effect that the actual ceiling for the nice value
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630was calculated as
631.IR "19\ \-\ rlim_cur" .
cedd678f 632This was fixed in kernel 2.6.13.
6151ea9a 633.\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=112256338703880&w=2
b270eba9 634
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635Since Linux 2.6.12,
636.\" The relevant patch, sent to LKML, seems to be
637.\" http://thread.gmane.org/gmane.linux.kernel/273462
638.\" From: Roland McGrath <roland <at> redhat.com>
639.\" Subject: [PATCH 7/7] make RLIMIT_CPU/SIGXCPU per-process
640.\" Date: 2005-01-23 23:27:46 GMT
641if a process reaches its soft
642.BR RLIMIT_CPU
643limit and has a handler installed for
644.BR SIGXCPU ,
645then, in addition to invoking the signal handler,
646the kernel increases the soft limit by one second.
647This behavior repeats if the process continues to consume CPU time,
648until the hard limit is reached,
649at which point the process is killed.
650Other implementations
651.\" Tested Solaris 10, FreeBSD 9, OpenBSD 5.0
652do not change the
653.BR RLIMIT_CPU
654soft limit in this manner,
655and the Linux behavior is probably not standards conformant;
656portable applications should avoid relying on this Linux-specific behavior.
bea08fec 657.\" FIXME . https://bugzilla.kernel.org/show_bug.cgi?id=50951
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658The Linux-specific
659.BR RLIMIT_RTTIME
660limit exhibits the same behavior when the soft limit is encountered.
661
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662Kernels before 2.4.22 did not diagnose the error
663.B EINVAL
c13182ef 664for
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665.BR setrlimit ()
666when
94e9d9fe 667.I rlim\->rlim_cur
b270eba9 668was greater than
94e9d9fe 669.IR rlim\->rlim_max .
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670.\"
671.SS Representation of """large""" resource limit values on 32-bit platforms
672The glibc
673.BR getrlimit ()
674and
675.BR setrlimit ()
676wrapper functions use a 64-bit
677.IR rlim_t
678data type, even on 32-bit platforms.
679However, the
680.I rlim_t
681data type used in the
682.BR getrlimit ()
683and
684.BR setrlimit ()
685system calls is a (32-bit)
686.IR "unsigned long" .
687Furthermore, in Linux versions before 2.6.36,
688the kernel represents resource limits on 32-bit platforms as
689.IR "unsigned long" .
690However, a 32-bit data type is not wide enough.
691.\" https://bugzilla.kernel.org/show_bug.cgi?id=5042
bea08fec 692.\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=12201
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693The most pertinent limit here is
694.BR RLIMIT_FSIZE ,
695which specifies the maximum size to which a file can grow:
696to be useful, this limit must be represented using a type
ef4f4031 697that is as wide as the type used to
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698represent file offsets\(emthat is, as wide as a 64-bit
699.BR off_t
700(assuming a program compiled with
701.IR _FILE_OFFSET_BITS=64 ).
702
703To work around this kernel limitation,
704if a program tried to set a resource limit to a value larger than
705can be represented in a 32-bit
706.IR "unsigned long" ,
707then the glibc
708.BR setrlimit ()
709wrapper function silently converted the limit value to
710.BR RLIM_INFINITY .
711In other words, the requested resource limit setting was silently ignored.
712
713This problem was addressed in Linux 2.6.36 with two principal changes:
714.IP * 3
715the addition of a new kernel representation of resource limits that
716uses 64 bits, even on 32-bit platforms;
717.IP *
718the addition of the
719.BR prlimit ()
720system call, which employs 64-bit values for its resource limit arguments.
721.PP
722Since version 2.13,
723.\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=12201
724glibc works around the limitations of the
725.BR getrlimit ()
726and
727.BR setrlimit ()
728system calls by implementing
729.BR setrlimit ()
730and
731.BR getrlimit ()
732as wrapper functions that call
733.BR prlimit ().
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734.SH EXAMPLE
735The program below demonstrates the use of
736.BR prlimit ().
737.PP
738.nf
739#define _GNU_SOURCE
740#define _FILE_OFFSET_BITS 64
741#include <stdio.h>
742#include <time.h>
743#include <stdlib.h>
744#include <unistd.h>
745#include <sys/resource.h>
746
747#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \\
748 } while (0)
749
750int
751main(int argc, char *argv[])
752{
753 struct rlimit old, new;
754 struct rlimit *newp;
755 pid_t pid;
756
757 if (!(argc == 2 || argc == 4)) {
758 fprintf(stderr, "Usage: %s <pid> [<new\-soft\-limit> "
759 "<new\-hard\-limit>]\\n", argv[0]);
760 exit(EXIT_FAILURE);
761 }
762
763 pid = atoi(argv[1]); /* PID of target process */
764
765 newp = NULL;
766 if (argc == 4) {
767 new.rlim_cur = atoi(argv[2]);
768 new.rlim_max = atoi(argv[3]);
769 newp = &new;
770 }
771
772 /* Set CPU time limit of target process; retrieve and display
773 previous limit */
774
775 if (prlimit(pid, RLIMIT_CPU, newp, &old) == \-1)
776 errExit("prlimit\-1");
777 printf("Previous limits: soft=%lld; hard=%lld\\n",
778 (long long) old.rlim_cur, (long long) old.rlim_max);
779
780 /* Retrieve and display new CPU time limit */
781
782 if (prlimit(pid, RLIMIT_CPU, NULL, &old) == \-1)
783 errExit("prlimit\-2");
784 printf("New limits: soft=%lld; hard=%lld\\n",
785 (long long) old.rlim_cur, (long long) old.rlim_max);
786
787 exit(EXIT_FAILURE);
788}
789.fi
47297adb 790.SH SEE ALSO
94315587 791.BR prlimit (1),
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792.BR dup (2),
793.BR fcntl (2),
794.BR fork (2),
0fc46b5a 795.BR getrusage (2),
fea681da 796.BR mlock (2),
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797.BR mmap (2),
798.BR open (2),
799.BR quotactl (2),
800.BR sbrk (2),
b4c0e1cb 801.BR shmctl (2),
fea681da 802.BR malloc (3),
485ab701 803.BR sigqueue (3),
fea681da 804.BR ulimit (3),
e1a9bc1b 805.BR core (5),
fea681da 806.BR capabilities (7),
99851d8b 807.BR cgroups (7),
fea681da 808.BR signal (7)