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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15.\" manual page may be incorrect or out-of-date.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>
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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.\"
5722c835 64.TH GETRLIMIT 2 2015-07-23 "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.
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238In Linux kernels before 2.6.9, this limit controlled the amount of
239memory that could be locked by a privileged process.
240Since Linux 2.6.9, no limits are placed on the amount of memory
241that a privileged process may lock, and this limit instead governs
242the amount of memory that an unprivileged process may lock.
9d8b1d5f 243.TP
31c1f2b0 244.BR RLIMIT_MSGQUEUE " (since Linux 2.6.8)"
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245Specifies the limit on the number of bytes that can be allocated
246for POSIX message queues for the real user ID of the calling process.
247This limit is enforced for
248.BR mq_open (3).
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249Each message queue that the user creates counts (until it is removed)
250against this limit according to the formula:
251.nf
252
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253 Since Linux 3.5:
254 bytes = attr.mq_maxmsg * sizeof(struct msg_msg) +
255 min(attr.mq_maxmsg, MQ_PRIO_MAX) *
6f9e0e57 256 sizeof(struct posix_msg_tree_node)+
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257 /* For overhead */
258 attr.mq_maxmsg * attr.mq_msgsize;
259 /* For message data */
260
261 Linux 3.4 and earlier:
262 bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
263 /* For overhead */
264 attr.mq_maxmsg * attr.mq_msgsize;
265 /* For message data */
9d8b1d5f 266
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267.fi
268where
9d8b1d5f 269.I attr
c13182ef 270is the
9d8b1d5f
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271.I mq_attr
272structure specified as the fourth argument to
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273.BR mq_open (3),
274and the
275.I msg_msg
276and
277.I posix_msg_tree_node
278structures are kernel-internal structures.
9d8b1d5f 279
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280The "overhead" addend in the formula accounts for overhead
281bytes required by the implementation
282and ensures that the user cannot
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283create an unlimited number of zero-length messages (such messages
284nevertheless each consume some system memory for bookkeeping overhead).
a23bf8a3 285.TP
64d6219c 286.BR RLIMIT_NICE " (since Linux 2.6.12, but see BUGS below)"
cedd678f 287Specifies a ceiling to which the process's nice value can be raised using
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288.BR setpriority (2)
289or
290.BR nice (2).
291The actual ceiling for the nice value is calculated as
292.IR "20\ \-\ rlim_cur" .
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293(This strangeness occurs because negative numbers cannot be specified
294as resource limit values, since they typically have special meanings.
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295For example,
296.B RLIM_INFINITY
297typically is the same as \-1.)
1bf844f1 298.TP
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299.B RLIMIT_NOFILE
300Specifies a value one greater than the maximum file descriptor number
301that can be opened by this process.
302Attempts
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303.RB ( open (2),
304.BR pipe (2),
305.BR dup (2),
4a04cd9a 306etc.)
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307to exceed this limit yield the error
308.BR EMFILE .
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309(Historically, this limit was named
310.B RLIMIT_OFILE
311on BSD.)
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312.TP
313.B RLIMIT_NPROC
c13182ef 314The maximum number of processes (or, more precisely on Linux, threads)
ee930c49 315that can be created for the real user ID of the calling process.
c13182ef 316Upon encountering this limit,
0bfa087b 317.BR fork (2)
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318fails with the error
319.BR EAGAIN .
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320This limit is not enforced for processes that have either the
321.B CAP_SYS_ADMIN
322or the
323.B CAP_SYS_RESOURCE
324capability.
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325.TP
326.B RLIMIT_RSS
327Specifies the limit (in pages) of the process's resident set
328(the number of virtual pages resident in RAM).
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329This limit has effect only in Linux 2.4.x, x < 30, and there
330affects only calls to
0bfa087b 331.BR madvise (2)
fea681da 332specifying
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333.BR MADV_WILLNEED .
334.\" As at kernel 2.6.12, this limit still does nothing in 2.6 though
c13182ef 335.\" talk of making it do something has surfaced from time to time in LKML
9426c9dd 336.\" -- MTK, Jul 05
fea681da 337.TP
31c1f2b0 338.BR RLIMIT_RTPRIO " (since Linux 2.6.12, but see BUGS)"
c13182ef 339Specifies a ceiling on the real-time priority that may be set for
cedd678f 340this process using
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341.BR sched_setscheduler (2)
342and
343.BR sched_setparam (2).
344.TP
31c1f2b0 345.BR RLIMIT_RTTIME " (since Linux 2.6.25)"
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346Specifies a limit (in microseconds)
347on the amount of CPU time that a process scheduled
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348under a real-time scheduling policy may consume without making a blocking
349system call.
350For the purpose of this limit,
351each time a process makes a blocking system call,
352the count of its consumed CPU time is reset to zero.
353The CPU time count is not reset if the process continues trying to
354use the CPU but is preempted, its time slice expires, or it calls
355.BR sched_yield (2).
356
357Upon reaching the soft limit, the process is sent a
358.B SIGXCPU
359signal.
360If the process catches or ignores this signal and
361continues consuming CPU time, then
362.B SIGXCPU
363will be generated once each second until the hard limit is reached,
364at which point the process is sent a
365.B SIGKILL
366signal.
367
368The intended use of this limit is to stop a runaway
369real-time process from locking up the system.
370.TP
31c1f2b0 371.BR RLIMIT_SIGPENDING " (since Linux 2.6.8)"
8b6aacb0 372Specifies the limit on the number of signals
e6c5832f 373that may be queued for the real user ID of the calling process.
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374Both standard and real-time signals are counted for the purpose of
375checking this limit.
33a0ccb2 376However, the limit is enforced only for
485ab701 377.BR sigqueue (3);
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378it is always possible to use
379.BR kill (2)
380to queue one instance of any of the signals that are not already
381queued to the process.
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382.\" This replaces the /proc/sys/kernel/rtsig-max system-wide limit
383.\" that was present in kernels <= 2.6.7. MTK Dec 04
384.TP
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385.B RLIMIT_STACK
386The maximum size of the process stack, in bytes.
387Upon reaching this limit, a
388.B SIGSEGV
389signal is generated.
390To handle this signal, a process must employ an alternate signal stack
391.RB ( sigaltstack (2)).
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392
393Since Linux 2.6.23,
394this limit also determines the amount of space used for the process's
395command-line arguments and environment variables; for details, see
396.BR execve (2).
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397.SS prlimit()
398.\" commit c022a0acad534fd5f5d5f17280f6d4d135e74e81
399.\" Author: Jiri Slaby <jslaby@suse.cz>
400.\" Date: Tue May 4 18:03:50 2010 +0200
9bd51977
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401.\"
402.\" rlimits: implement prlimit64 syscall
ef4f4031 403.\"
9bd51977
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404.\" commit 6a1d5e2c85d06da35cdfd93f1a27675bfdc3ad8c
405.\" Author: Jiri Slaby <jslaby@suse.cz>
406.\" Date: Wed Mar 24 17:06:58 2010 +0100
ef4f4031 407.\"
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408.\" rlimits: add rlimit64 structure
409.\"
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410The Linux-specific
411.BR prlimit ()
412system call combines and extends the functionality of
413.BR setrlimit ()
414and
415.BR getrlimit ().
416It can be used to both set and get the resource limits of an arbitrary process.
417
418The
419.I resource
420argument has the same meaning as for
421.BR setrlimit ()
422and
423.BR getrlimit ().
424
425If the
426.IR new_limit
427argument is a not NULL, then the
428.I rlimit
429structure to which it points is used to set new values for
430the soft and hard limits for
431.IR resource .
432If the
433.IR old_limit
434argument is a not NULL, then a successful call to
435.BR prlimit ()
436places the previous soft and hard limits for
437.I resource
98b43b57 438in the
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439.I rlimit
440structure pointed to by
441.IR old_limit .
442
443The
444.I pid
445argument specifies the ID of the process on which the call is to operate.
446If
447.I pid
448is 0, then the call applies to the calling process.
449To set or get the resources of a process other than itself,
450the caller must have the
451.B CAP_SYS_RESOURCE
452capability, or the
453real, effective, and saved set user IDs of the target process
454must match the real user ID of the caller
455.I and
456the real, effective, and saved set group IDs of the target process
457must match the real group ID of the caller.
bea08fec 458.\" FIXME . this permission check is strange
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459.\" Asked about this on LKML, 7 Nov 2010
460.\" "Inconsistent credential checking in prlimit() syscall"
461.SH RETURN VALUE
462On success, these system calls return 0.
c13182ef 463On error, \-1 is returned, and
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464.I errno
465is set appropriately.
466.SH ERRORS
467.TP
468.B EFAULT
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469A pointer argument points to a location
470outside the accessible address space.
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471.TP
472.B EINVAL
1546fe19 473The value specified in
0fc46b5a 474.I resource
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475is not valid;
476or, for
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477.BR setrlimit ()
478or
479.BR prlimit ():
94e9d9fe 480.I rlim\->rlim_cur
b270eba9 481was greater than
94e9d9fe 482.IR rlim\->rlim_max .
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483.TP
484.B EPERM
1546fe19 485An unprivileged process tried to raise the hard limit; the
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486.B CAP_SYS_RESOURCE
487capability is required to do this.
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488.TP
489.B EPERM
490The caller tried to increase the hard
682edefb 491.B RLIMIT_NOFILE
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492limit above the maximum defined by
493.IR /proc/sys/fs/nr_open
494(see
495.BR proc (5))
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496.TP
497.B EPERM
498.RB ( prlimit ())
499The calling process did not have permission to set limits
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500for the process specified by
501.IR pid .
502.TP
503.B ESRCH
504Could not find a process with the ID specified in
505.IR pid .
506.SH VERSIONS
010eefd7 507The
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508.BR prlimit ()
509system call is available since Linux 2.6.36.
510Library support is available since glibc 2.13.
57ba9747
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511.SH ATTRIBUTES
512For an explanation of the terms used in this section, see
513.BR attributes (7).
514.TS
515allbox;
516lbw35 lb lb
517l l l.
518Interface Attribute Value
519T{
520.BR getrlimit (),
521.BR setrlimit (),
522.BR prlimit ()
523T} Thread safety MT-Safe
524.TE
525
a1d5f77c 526.SH CONFORMING TO
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527.BR getrlimit (),
528.BR setrlimit ():
ac17f435 529POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
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530.br
531.BR prlimit ():
532Linux-specific.
533
0daa9e92 534.B RLIMIT_MEMLOCK
a1d5f77c 535and
0daa9e92 536.B RLIMIT_NPROC
ac17f435 537derive from BSD and are not specified in POSIX.1;
a1d5f77c 538they are present on the BSDs and Linux, but on few other implementations.
0daa9e92 539.B RLIMIT_RSS
ac17f435 540derives from BSD and is not specified in POSIX.1;
a1d5f77c
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541it is nevertheless present on most implementations.
542.BR RLIMIT_MSGQUEUE ,
543.BR RLIMIT_NICE ,
544.BR RLIMIT_RTPRIO ,
23ce0537 545.BR RLIMIT_RTTIME ,
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546and
547.B RLIMIT_SIGPENDING
8382f16d 548are Linux-specific.
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549.SH NOTES
550A child process created via
551.BR fork (2)
2c0cfe3c 552inherits its parent's resource limits.
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553Resource limits are preserved across
554.BR execve (2).
835363b2 555
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556Lowering the soft limit for a resource below the process's
557current consumption of that resource will succeed
558(but will prevent the process from further increasing
559its consumption of the resource).
560
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561One can set the resource limits of the shell using the built-in
562.IR ulimit
563command
564.RI ( limit
565in
566.BR csh (1)).
567The shell's resource limits are inherited by the processes that
568it creates to execute commands.
e1695dec 569
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570Since Linux 2.6.24, the resource limits of any process can be inspected via
571.IR /proc/[pid]/limits ;
572see
573.BR proc (5).
574
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575Ancient systems provided a
576.BR vlimit ()
577function with a similar purpose to
578.BR setrlimit ().
579For backward compatibility, glibc also provides
580.BR vlimit ().
581All new applications should be written using
582.BR setrlimit ().
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583.SS C library/ kernel ABI differences
584Since version 2.13, the glibc
585.BR getrlimit ()
586and
587.BR setrlimit ()
588wrapper functions no longer invoke the corresponding system calls,
589but instead employ
590.BR prlimit (),
591for the reasons described in BUGS.
28633770
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592
593The name of the glibc wrapper function is
594.BR prlimit ();
595the underlying system call is call prlimit64 ().
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596.SH BUGS
597In older Linux kernels, the
598.B SIGXCPU
599and
600.B SIGKILL
601signals delivered when a process encountered the soft and hard
9a8a1136 602.B RLIMIT_CPU
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603limits were delivered one (CPU) second later than they should have been.
604This was fixed in kernel 2.6.8.
1bf844f1 605
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606In 2.6.x kernels before 2.6.17, a
607.B RLIMIT_CPU
608limit of 0 is wrongly treated as "no limit" (like
6057e7a9 609.BR RLIM_INFINITY ).
64d6219c 610Since Linux 2.6.17, setting a limit of 0 does have an effect,
6057e7a9 611but is actually treated as a limit of 1 second.
a31272fe 612.\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=114008066530167&w=2
6057e7a9 613
1bf844f1 614A kernel bug means that
ceee84ba 615.\" See https://lwn.net/Articles/145008/
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616.B RLIMIT_RTPRIO
617does not work in kernel 2.6.12; the problem is fixed in kernel 2.6.13.
6151ea9a 618
c13182ef 619In kernel 2.6.12, there was an off-by-one mismatch
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620between the priority ranges returned by
621.BR getpriority (2)
622and
6151ea9a 623.BR RLIMIT_NICE .
11532b16 624This had the effect that the actual ceiling for the nice value
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625was calculated as
626.IR "19\ \-\ rlim_cur" .
cedd678f 627This was fixed in kernel 2.6.13.
6151ea9a 628.\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=112256338703880&w=2
b270eba9 629
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630Since Linux 2.6.12,
631.\" The relevant patch, sent to LKML, seems to be
632.\" http://thread.gmane.org/gmane.linux.kernel/273462
633.\" From: Roland McGrath <roland <at> redhat.com>
634.\" Subject: [PATCH 7/7] make RLIMIT_CPU/SIGXCPU per-process
635.\" Date: 2005-01-23 23:27:46 GMT
636if a process reaches its soft
637.BR RLIMIT_CPU
638limit and has a handler installed for
639.BR SIGXCPU ,
640then, in addition to invoking the signal handler,
641the kernel increases the soft limit by one second.
642This behavior repeats if the process continues to consume CPU time,
643until the hard limit is reached,
644at which point the process is killed.
645Other implementations
646.\" Tested Solaris 10, FreeBSD 9, OpenBSD 5.0
647do not change the
648.BR RLIMIT_CPU
649soft limit in this manner,
650and the Linux behavior is probably not standards conformant;
651portable applications should avoid relying on this Linux-specific behavior.
bea08fec 652.\" FIXME . https://bugzilla.kernel.org/show_bug.cgi?id=50951
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653The Linux-specific
654.BR RLIMIT_RTTIME
655limit exhibits the same behavior when the soft limit is encountered.
656
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657Kernels before 2.4.22 did not diagnose the error
658.B EINVAL
c13182ef 659for
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660.BR setrlimit ()
661when
94e9d9fe 662.I rlim\->rlim_cur
b270eba9 663was greater than
94e9d9fe 664.IR rlim\->rlim_max .
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665.\"
666.SS Representation of """large""" resource limit values on 32-bit platforms
667The glibc
668.BR getrlimit ()
669and
670.BR setrlimit ()
671wrapper functions use a 64-bit
672.IR rlim_t
673data type, even on 32-bit platforms.
674However, the
675.I rlim_t
676data type used in the
677.BR getrlimit ()
678and
679.BR setrlimit ()
680system calls is a (32-bit)
681.IR "unsigned long" .
682Furthermore, in Linux versions before 2.6.36,
683the kernel represents resource limits on 32-bit platforms as
684.IR "unsigned long" .
685However, a 32-bit data type is not wide enough.
686.\" https://bugzilla.kernel.org/show_bug.cgi?id=5042
bea08fec 687.\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=12201
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688The most pertinent limit here is
689.BR RLIMIT_FSIZE ,
690which specifies the maximum size to which a file can grow:
691to be useful, this limit must be represented using a type
ef4f4031 692that is as wide as the type used to
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693represent file offsets\(emthat is, as wide as a 64-bit
694.BR off_t
695(assuming a program compiled with
696.IR _FILE_OFFSET_BITS=64 ).
697
698To work around this kernel limitation,
699if a program tried to set a resource limit to a value larger than
700can be represented in a 32-bit
701.IR "unsigned long" ,
702then the glibc
703.BR setrlimit ()
704wrapper function silently converted the limit value to
705.BR RLIM_INFINITY .
706In other words, the requested resource limit setting was silently ignored.
707
708This problem was addressed in Linux 2.6.36 with two principal changes:
709.IP * 3
710the addition of a new kernel representation of resource limits that
711uses 64 bits, even on 32-bit platforms;
712.IP *
713the addition of the
714.BR prlimit ()
715system call, which employs 64-bit values for its resource limit arguments.
716.PP
717Since version 2.13,
718.\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=12201
719glibc works around the limitations of the
720.BR getrlimit ()
721and
722.BR setrlimit ()
723system calls by implementing
724.BR setrlimit ()
725and
726.BR getrlimit ()
727as wrapper functions that call
728.BR prlimit ().
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729.SH EXAMPLE
730The program below demonstrates the use of
731.BR prlimit ().
732.PP
733.nf
734#define _GNU_SOURCE
735#define _FILE_OFFSET_BITS 64
736#include <stdio.h>
737#include <time.h>
738#include <stdlib.h>
739#include <unistd.h>
740#include <sys/resource.h>
741
742#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \\
743 } while (0)
744
745int
746main(int argc, char *argv[])
747{
748 struct rlimit old, new;
749 struct rlimit *newp;
750 pid_t pid;
751
752 if (!(argc == 2 || argc == 4)) {
753 fprintf(stderr, "Usage: %s <pid> [<new\-soft\-limit> "
754 "<new\-hard\-limit>]\\n", argv[0]);
755 exit(EXIT_FAILURE);
756 }
757
758 pid = atoi(argv[1]); /* PID of target process */
759
760 newp = NULL;
761 if (argc == 4) {
762 new.rlim_cur = atoi(argv[2]);
763 new.rlim_max = atoi(argv[3]);
764 newp = &new;
765 }
766
767 /* Set CPU time limit of target process; retrieve and display
768 previous limit */
769
770 if (prlimit(pid, RLIMIT_CPU, newp, &old) == \-1)
771 errExit("prlimit\-1");
772 printf("Previous limits: soft=%lld; hard=%lld\\n",
773 (long long) old.rlim_cur, (long long) old.rlim_max);
774
775 /* Retrieve and display new CPU time limit */
776
777 if (prlimit(pid, RLIMIT_CPU, NULL, &old) == \-1)
778 errExit("prlimit\-2");
779 printf("New limits: soft=%lld; hard=%lld\\n",
780 (long long) old.rlim_cur, (long long) old.rlim_max);
781
782 exit(EXIT_FAILURE);
783}
784.fi
47297adb 785.SH SEE ALSO
94315587 786.BR prlimit (1),
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787.BR dup (2),
788.BR fcntl (2),
789.BR fork (2),
0fc46b5a 790.BR getrusage (2),
fea681da 791.BR mlock (2),
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792.BR mmap (2),
793.BR open (2),
794.BR quotactl (2),
795.BR sbrk (2),
b4c0e1cb 796.BR shmctl (2),
fea681da 797.BR malloc (3),
485ab701 798.BR sigqueue (3),
fea681da 799.BR ulimit (3),
e1a9bc1b 800.BR core (5),
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801.BR capabilities (7),
802.BR signal (7)