| blob | e5f9dfa9d9fb0a2d15570c91287bc18abdc7a9f6 |
1 .\" Copyright (c) 1992 Drew Eckhardt, March 28, 1992
2 .\" and Copyright (c) 2002, 2004, 2005, 2008, 2010 Michael Kerrisk
3 .\"
4 .\" %%%LICENSE_START(VERBATIM)
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.
13 .\"
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15 .\" manual page may be incorrect or out-of-date.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.
21 .\"
22 .\" Formatted or processed versions of this manual, if unaccompanied by
23 .\" the source, must acknowledge the copyright and authors of this work.
24 .\" %%%LICENSE_END
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
35 .\" Håvard Lygre <hklygre@online.no>
36 .\" Modified 2001-04-17 by Michael Kerrisk <mtk.manpages@gmail.com>
37 .\" Modified 2002-06-13 by Michael Kerrisk <mtk.manpages@gmail.com>
38 .\" Added note on nonstandard behavior when SIGCHLD is ignored.
39 .\" Modified 2002-07-09 by Michael Kerrisk <mtk.manpages@gmail.com>
40 .\" Enhanced descriptions of 'resource' values
41 .\" Modified 2003-11-28 by aeb, added RLIMIT_CORE
42 .\" Modified 2004-03-26 by aeb, added RLIMIT_AS
43 .\" Modified 2004-06-16 by Michael Kerrisk <mtk.manpages@gmail.com>
44 .\" Added notes on CAP_SYS_RESOURCE
45 .\"
46 .\" 2004-11-16 -- mtk: the getrlimit.2 page, which formally included
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
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
58 .\" 2004-11-03, mtk, Added RLIMIT_SIGPENDING
59 .\" 2005-07-13, mtk, documented RLIMIT_MSGQUEUE limit.
60 .\" 2005-07-28, mtk, Added descriptions of RLIMIT_NICE and RLIMIT_RTPRIO
61 .\" 2008-05-07, mtk / Peter Zijlstra, Added description of RLIMIT_RTTIME
62 .\" 2010-11-06, mtk: Added documentation of prlimit()
63 .\"
64 .TH GETRLIMIT 2 2017-03-13 "Linux" "Linux Programmer's Manual"
65 .SH NAME
66 getrlimit, setrlimit, prlimit \- get/set resource limits
67 .SH SYNOPSIS
68 .B #include <sys/time.h>
69 .br
70 .B #include <sys/resource.h>
71 .sp
72 .BI "int getrlimit(int " resource ", struct rlimit *" rlim );
73 .br
74 .BI "int setrlimit(int " resource ", const struct rlimit *" rlim );
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
82 Feature Test Macro Requirements for glibc (see
83 .BR feature_test_macros (7)):
84 .in
85 .sp
86 .BR prlimit ():
87 _GNU_SOURCE
88 .SH DESCRIPTION
89 The
90 .BR getrlimit ()
91 and
92 .BR setrlimit ()
93 system calls get and set resource limits respectively.
94 Each resource has an associated soft and hard limit, as defined by the
95 .I rlimit
96 structure:
97 .PP
98 .in +4n
99 .nf
100 struct rlimit {
101 rlim_t rlim_cur; /* Soft limit */
102 rlim_t rlim_max; /* Hard limit (ceiling for rlim_cur) */
103 };
105 .fi
106 .in
107 The soft limit is the value that the kernel enforces for the
108 corresponding resource.
109 The hard limit acts as a ceiling for the soft limit:
110 an unprivileged process may set only its soft limit to a value in the
111 range from 0 up to the hard limit, and (irreversibly) lower its hard limit.
112 A privileged process (under Linux: one with the
113 .B CAP_SYS_RESOURCE
114 capability) may make arbitrary changes to either limit value.
115 .PP
116 The value
117 .B RLIM_INFINITY
118 denotes no limit on a resource (both in the structure returned by
119 .BR getrlimit ()
120 and in the structure passed to
121 .BR setrlimit ()).
122 .PP
123 The
124 .I resource
125 argument must be one of:
126 .TP
127 .B RLIMIT_AS
128 This is the maximum size of the process's virtual memory
129 (address space) in bytes.
130 .\" since 2.0.27 / 2.1.12
131 This limit affects calls to
132 .BR brk (2),
133 .BR mmap (2),
134 and
135 .BR mremap (2),
136 which fail with the error
137 .B ENOMEM
138 upon exceeding this limit.
139 Also automatic stack expansion will fail
140 (and generate a
141 .B SIGSEGV
142 that kills the process if no alternate stack
143 has been made available via
144 .BR sigaltstack (2)).
145 Since the value is a \fIlong\fP, on machines with a 32-bit \fIlong\fP
146 either this limit is at most 2 GiB, or this resource is unlimited.
147 .TP
148 .B RLIMIT_CORE
149 This is the maximum size of a
150 .I core
151 file (see
152 .BR core (5))
153 that the process may dump.
154 When 0 no core dump files are created.
155 When nonzero, larger dumps are truncated to this size.
156 .TP
157 .B RLIMIT_CPU
158 This is a limit, in seconds,
159 on the amount of CPU time that the process can consume.
160 When the process reaches the soft limit, it is sent a
161 .B SIGXCPU
162 signal.
163 The default action for this signal is to terminate the process.
164 However, the signal can be caught, and the handler can return control to
165 the main program.
166 If the process continues to consume CPU time, it will be sent
167 .B SIGXCPU
168 once per second until the hard limit is reached, at which time
169 it is sent
170 .BR SIGKILL .
171 (This latter point describes Linux behavior.
172 Implementations vary in how they treat processes which continue to
173 consume CPU time after reaching the soft limit.
174 Portable applications that need to catch this signal should
175 perform an orderly termination upon first receipt of
176 .BR SIGXCPU .)
177 .TP
178 .B RLIMIT_DATA
179 This is the maximum size of the process's data segment (initialized data,
180 uninitialized data, and heap).
181 This limit affects calls to
182 .BR brk (2)
183 and
184 .BR sbrk (2),
185 which fail with the error
186 .B ENOMEM
187 upon encountering the soft limit of this resource.
188 .TP
189 .B RLIMIT_FSIZE
190 This is the maximum size of files that the process may create.
191 Attempts to extend a file beyond this limit result in delivery of a
192 .B SIGXFSZ
193 signal.
194 By default, this signal terminates a process, but a process can
195 catch this signal instead, in which case the relevant system call (e.g.,
196 .BR write (2),
197 .BR truncate (2))
198 fails with the error
199 .BR EFBIG .
200 .TP
201 .BR RLIMIT_LOCKS " (early Linux 2.4 only)"
202 .\" to be precise: Linux 2.4.0-test9; no longer in 2.4.25 / 2.5.65
203 This is a limit on the combined number of
204 .BR flock (2)
205 locks and
206 .BR fcntl (2)
207 leases that this process may establish.
208 .TP
209 .B RLIMIT_MEMLOCK
210 This is the maximum number of bytes of memory that may be locked
211 into RAM.
212 This limit is in effect rounded down to the nearest multiple
213 of the system page size.
214 This limit affects
215 .BR mlock (2),
216 .BR mlockall (2),
217 and the
218 .BR mmap (2)
219 .B MAP_LOCKED
220 operation.
221 Since Linux 2.6.9, it also affects the
222 .BR shmctl (2)
223 .B SHM_LOCK
224 operation, where it sets a maximum on the total bytes in
225 shared memory segments (see
226 .BR shmget (2))
227 that may be locked by the real user ID of the calling process.
228 The
229 .BR shmctl (2)
230 .B SHM_LOCK
231 locks are accounted for separately from the per-process memory
232 locks established by
233 .BR mlock (2),
234 .BR mlockall (2),
235 and
236 .BR mmap (2)
237 .BR MAP_LOCKED ;
238 a process can lock bytes up to this limit in each of these
239 two categories.
241 In Linux kernels before 2.6.9, this limit controlled the amount of
242 memory that could be locked by a privileged process.
243 Since Linux 2.6.9, no limits are placed on the amount of memory
244 that a privileged process may lock, and this limit instead governs
245 the amount of memory that an unprivileged process may lock.
246 .TP
247 .BR RLIMIT_MSGQUEUE " (since Linux 2.6.8)"
248 This is a limit on the number of bytes that can be allocated
249 for POSIX message queues for the real user ID of the calling process.
250 This limit is enforced for
251 .BR mq_open (3).
252 Each message queue that the user creates counts (until it is removed)
253 against this limit according to the formula:
254 .nf
256 Since Linux 3.5:
258 bytes = attr.mq_maxmsg * sizeof(struct msg_msg) +
259 min(attr.mq_maxmsg, MQ_PRIO_MAX) *
260 sizeof(struct posix_msg_tree_node)+
261 /* For overhead */
262 attr.mq_maxmsg * attr.mq_msgsize;
263 /* For message data */
265 Linux 3.4 and earlier:
267 bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
268 /* For overhead */
269 attr.mq_maxmsg * attr.mq_msgsize;
270 /* For message data */
272 .fi
273 where
274 .I attr
275 is the
276 .I mq_attr
277 structure specified as the fourth argument to
278 .BR mq_open (3),
279 and the
280 .I msg_msg
281 and
282 .I posix_msg_tree_node
283 structures are kernel-internal structures.
285 The "overhead" addend in the formula accounts for overhead
286 bytes required by the implementation
287 and ensures that the user cannot
288 create an unlimited number of zero-length messages (such messages
289 nevertheless each consume some system memory for bookkeeping overhead).
290 .TP
291 .BR RLIMIT_NICE " (since Linux 2.6.12, but see BUGS below)"
292 This specifies a ceiling to which the process's nice value can be raised using
293 .BR setpriority (2)
294 or
295 .BR nice (2).
296 The actual ceiling for the nice value is calculated as
297 .IR "20\ \-\ rlim_cur" .
298 The useful range for this limit is thus from 1
299 (corresponding to a nice value of 19) to 40
300 (corresponding to a nice value of -20).
301 This unusual choice of range was necessary
302 because negative numbers cannot be specified
303 as resource limit values, since they typically have special meanings.
304 For example,
305 .B RLIM_INFINITY
306 typically is the same as \-1.
307 For more detail on the nice value, see
308 .BR sched (7).
309 .TP
310 .B RLIMIT_NOFILE
311 This specifies a value one greater than the maximum file descriptor number
312 that can be opened by this process.
313 Attempts
314 .RB ( open (2),
315 .BR pipe (2),
316 .BR dup (2),
317 etc.)
318 to exceed this limit yield the error
319 .BR EMFILE .
320 (Historically, this limit was named
321 .B RLIMIT_OFILE
322 on BSD.)
324 Since Linux 4.5,
325 this limit also defines the maximum number of file descriptors that
326 an unprivileged process (one without the
327 .BR CAP_SYS_RESOURCE
328 capability) may have "in flight" to other processes,
329 by being passed across UNIX domain sockets.
330 This limit applies to the
331 .BR sendmsg (2)
332 system call.
333 For further details, see
334 .BR unix (7).
335 .TP
336 .B RLIMIT_NPROC
337 This is the maximum number of processes
338 (or, more precisely on Linux, threads)
339 that can be created for the real user ID of the calling process.
340 Upon encountering this limit,
341 .BR fork (2)
342 fails with the error
343 .BR EAGAIN .
344 This limit is not enforced for processes that have either the
345 .B CAP_SYS_ADMIN
346 or the
347 .B CAP_SYS_RESOURCE
348 capability.
349 .TP
350 .B RLIMIT_RSS
351 This is a limit (in bytes) on the process's resident set
352 (the number of virtual pages resident in RAM).
353 This limit has effect only in Linux 2.4.x, x < 30, and there
354 affects only calls to
355 .BR madvise (2)
356 specifying
357 .BR MADV_WILLNEED .
358 .\" As at kernel 2.6.12, this limit still does nothing in 2.6 though
359 .\" talk of making it do something has surfaced from time to time in LKML
360 .\" -- MTK, Jul 05
361 .TP
362 .BR RLIMIT_RTPRIO " (since Linux 2.6.12, but see BUGS)"
363 This specifies a ceiling on the real-time priority that may be set for
364 this process using
365 .BR sched_setscheduler (2)
366 and
367 .BR sched_setparam (2).
369 For further details on real-time scheduling policies, see
370 .BR sched (7)
371 .TP
372 .BR RLIMIT_RTTIME " (since Linux 2.6.25)"
373 This is a limit (in microseconds)
374 on the amount of CPU time that a process scheduled
375 under a real-time scheduling policy may consume without making a blocking
376 system call.
377 For the purpose of this limit,
378 each time a process makes a blocking system call,
379 the count of its consumed CPU time is reset to zero.
380 The CPU time count is not reset if the process continues trying to
381 use the CPU but is preempted, its time slice expires, or it calls
382 .BR sched_yield (2).
384 Upon reaching the soft limit, the process is sent a
385 .B SIGXCPU
386 signal.
387 If the process catches or ignores this signal and
388 continues consuming CPU time, then
389 .B SIGXCPU
390 will be generated once each second until the hard limit is reached,
391 at which point the process is sent a
392 .B SIGKILL
393 signal.
395 The intended use of this limit is to stop a runaway
396 real-time process from locking up the system.
398 For further details on real-time scheduling policies, see
399 .BR sched (7)
400 .TP
401 .BR RLIMIT_SIGPENDING " (since Linux 2.6.8)"
402 This is a limit on the number of signals
403 that may be queued for the real user ID of the calling process.
404 Both standard and real-time signals are counted for the purpose of
405 checking this limit.
406 However, the limit is enforced only for
407 .BR sigqueue (3);
408 it is always possible to use
409 .BR kill (2)
410 to queue one instance of any of the signals that are not already
411 queued to the process.
412 .\" This replaces the /proc/sys/kernel/rtsig-max system-wide limit
413 .\" that was present in kernels <= 2.6.7. MTK Dec 04
414 .TP
415 .B RLIMIT_STACK
416 This is the maximum size of the process stack, in bytes.
417 Upon reaching this limit, a
418 .B SIGSEGV
419 signal is generated.
420 To handle this signal, a process must employ an alternate signal stack
421 .RB ( sigaltstack (2)).
423 Since Linux 2.6.23,
424 this limit also determines the amount of space used for the process's
425 command-line arguments and environment variables; for details, see
426 .BR execve (2).
427 .SS prlimit()
428 .\" commit c022a0acad534fd5f5d5f17280f6d4d135e74e81
429 .\" Author: Jiri Slaby <jslaby@suse.cz>
430 .\" Date: Tue May 4 18:03:50 2010 +0200
431 .\"
432 .\" rlimits: implement prlimit64 syscall
433 .\"
434 .\" commit 6a1d5e2c85d06da35cdfd93f1a27675bfdc3ad8c
435 .\" Author: Jiri Slaby <jslaby@suse.cz>
436 .\" Date: Wed Mar 24 17:06:58 2010 +0100
437 .\"
438 .\" rlimits: add rlimit64 structure
439 .\"
440 The Linux-specific
441 .BR prlimit ()
442 system call combines and extends the functionality of
443 .BR setrlimit ()
444 and
445 .BR getrlimit ().
446 It can be used to both set and get the resource limits of an arbitrary process.
448 The
449 .I resource
450 argument has the same meaning as for
451 .BR setrlimit ()
452 and
453 .BR getrlimit ().
455 If the
456 .IR new_limit
457 argument is a not NULL, then the
458 .I rlimit
459 structure to which it points is used to set new values for
460 the soft and hard limits for
461 .IR resource .
462 If the
463 .IR old_limit
464 argument is a not NULL, then a successful call to
465 .BR prlimit ()
466 places the previous soft and hard limits for
467 .I resource
468 in the
469 .I rlimit
470 structure pointed to by
471 .IR old_limit .
473 The
474 .I pid
475 argument specifies the ID of the process on which the call is to operate.
476 If
477 .I pid
478 is 0, then the call applies to the calling process.
479 To set or get the resources of a process other than itself,
480 the caller must have the
481 .B CAP_SYS_RESOURCE
482 capability in the user namespace of the process
483 whose resource limits are being changed, or the
484 real, effective, and saved set user IDs of the target process
485 must match the real user ID of the caller
486 .I and
487 the real, effective, and saved set group IDs of the target process
488 must match the real group ID of the caller.
489 .\" FIXME . this permission check is strange
490 .\" Asked about this on LKML, 7 Nov 2010
491 .\" "Inconsistent credential checking in prlimit() syscall"
492 .SH RETURN VALUE
493 On success, these system calls return 0.
494 On error, \-1 is returned, and
495 .I errno
496 is set appropriately.
497 .SH ERRORS
498 .TP
499 .B EFAULT
500 A pointer argument points to a location
501 outside the accessible address space.
502 .TP
503 .B EINVAL
504 The value specified in
505 .I resource
506 is not valid;
507 or, for
508 .BR setrlimit ()
509 or
510 .BR prlimit ():
511 .I rlim\->rlim_cur
512 was greater than
513 .IR rlim\->rlim_max .
514 .TP
515 .B EPERM
516 An unprivileged process tried to raise the hard limit; the
517 .B CAP_SYS_RESOURCE
518 capability is required to do this.
519 .TP
520 .B EPERM
521 The caller tried to increase the hard
522 .B RLIMIT_NOFILE
523 limit above the maximum defined by
524 .IR /proc/sys/fs/nr_open
525 (see
526 .BR proc (5))
527 .TP
528 .B EPERM
529 .RB ( prlimit ())
530 The calling process did not have permission to set limits
531 for the process specified by
532 .IR pid .
533 .TP
534 .B ESRCH
535 Could not find a process with the ID specified in
536 .IR pid .
537 .SH VERSIONS
538 The
539 .BR prlimit ()
540 system call is available since Linux 2.6.36.
541 Library support is available since glibc 2.13.
542 .SH ATTRIBUTES
543 For an explanation of the terms used in this section, see
544 .BR attributes (7).
545 .TS
546 allbox;
547 lbw35 lb lb
548 l l l.
549 Interface Attribute Value
550 T{
551 .BR getrlimit (),
552 .BR setrlimit (),
553 .BR prlimit ()
554 T} Thread safety MT-Safe
555 .TE
557 .SH CONFORMING TO
558 .BR getrlimit (),
559 .BR setrlimit ():
560 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
561 .br
562 .BR prlimit ():
563 Linux-specific.
565 .B RLIMIT_MEMLOCK
566 and
567 .B RLIMIT_NPROC
568 derive from BSD and are not specified in POSIX.1;
569 they are present on the BSDs and Linux, but on few other implementations.
570 .B RLIMIT_RSS
571 derives from BSD and is not specified in POSIX.1;
572 it is nevertheless present on most implementations.
573 .BR RLIMIT_MSGQUEUE ,
574 .BR RLIMIT_NICE ,
575 .BR RLIMIT_RTPRIO ,
576 .BR RLIMIT_RTTIME ,
577 and
578 .B RLIMIT_SIGPENDING
579 are Linux-specific.
580 .SH NOTES
581 A child process created via
582 .BR fork (2)
583 inherits its parent's resource limits.
584 Resource limits are preserved across
585 .BR execve (2).
587 Lowering the soft limit for a resource below the process's
588 current consumption of that resource will succeed
589 (but will prevent the process from further increasing
590 its consumption of the resource).
592 One can set the resource limits of the shell using the built-in
593 .IR ulimit
594 command
595 .RI ( limit
596 in
597 .BR csh (1)).
598 The shell's resource limits are inherited by the processes that
599 it creates to execute commands.
601 Since Linux 2.6.24, the resource limits of any process can be inspected via
602 .IR /proc/[pid]/limits ;
603 see
604 .BR proc (5).
606 Ancient systems provided a
607 .BR vlimit ()
608 function with a similar purpose to
609 .BR setrlimit ().
610 For backward compatibility, glibc also provides
611 .BR vlimit ().
612 All new applications should be written using
613 .BR setrlimit ().
614 .SS C library/ kernel ABI differences
615 Since version 2.13, the glibc
616 .BR getrlimit ()
617 and
618 .BR setrlimit ()
619 wrapper functions no longer invoke the corresponding system calls,
620 but instead employ
621 .BR prlimit (),
622 for the reasons described in BUGS.
624 The name of the glibc wrapper function is
625 .BR prlimit ();
626 the underlying system call is
627 .BR prlimit64 ().
628 .SH BUGS
629 In older Linux kernels, the
630 .B SIGXCPU
631 and
632 .B SIGKILL
633 signals delivered when a process encountered the soft and hard
634 .B RLIMIT_CPU
635 limits were delivered one (CPU) second later than they should have been.
636 This was fixed in kernel 2.6.8.
638 In 2.6.x kernels before 2.6.17, a
639 .B RLIMIT_CPU
640 limit of 0 is wrongly treated as "no limit" (like
641 .BR RLIM_INFINITY ).
642 Since Linux 2.6.17, setting a limit of 0 does have an effect,
643 but is actually treated as a limit of 1 second.
644 .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=114008066530167&w=2
646 A kernel bug means that
647 .\" See https://lwn.net/Articles/145008/
648 .B RLIMIT_RTPRIO
649 does not work in kernel 2.6.12; the problem is fixed in kernel 2.6.13.
651 In kernel 2.6.12, there was an off-by-one mismatch
652 between the priority ranges returned by
653 .BR getpriority (2)
654 and
655 .BR RLIMIT_NICE .
656 This had the effect that the actual ceiling for the nice value
657 was calculated as
658 .IR "19\ \-\ rlim_cur" .
659 This was fixed in kernel 2.6.13.
660 .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=112256338703880&w=2
662 Since Linux 2.6.12,
663 .\" The relevant patch, sent to LKML, seems to be
664 .\" http://thread.gmane.org/gmane.linux.kernel/273462
665 .\" From: Roland McGrath <roland <at> redhat.com>
666 .\" Subject: [PATCH 7/7] make RLIMIT_CPU/SIGXCPU per-process
667 .\" Date: 2005-01-23 23:27:46 GMT
668 if a process reaches its soft
669 .BR RLIMIT_CPU
670 limit and has a handler installed for
671 .BR SIGXCPU ,
672 then, in addition to invoking the signal handler,
673 the kernel increases the soft limit by one second.
674 This behavior repeats if the process continues to consume CPU time,
675 until the hard limit is reached,
676 at which point the process is killed.
677 Other implementations
678 .\" Tested Solaris 10, FreeBSD 9, OpenBSD 5.0
679 do not change the
680 .BR RLIMIT_CPU
681 soft limit in this manner,
682 and the Linux behavior is probably not standards conformant;
683 portable applications should avoid relying on this Linux-specific behavior.
684 .\" FIXME . https://bugzilla.kernel.org/show_bug.cgi?id=50951
685 The Linux-specific
686 .BR RLIMIT_RTTIME
687 limit exhibits the same behavior when the soft limit is encountered.
689 Kernels before 2.4.22 did not diagnose the error
690 .B EINVAL
691 for
692 .BR setrlimit ()
693 when
694 .I rlim\->rlim_cur
695 was greater than
696 .IR rlim\->rlim_max .
697 .\"
698 .SS Representation of """large""" resource limit values on 32-bit platforms
699 The glibc
700 .BR getrlimit ()
701 and
702 .BR setrlimit ()
703 wrapper functions use a 64-bit
704 .IR rlim_t
705 data type, even on 32-bit platforms.
706 However, the
707 .I rlim_t
708 data type used in the
709 .BR getrlimit ()
710 and
711 .BR setrlimit ()
712 system calls is a (32-bit)
713 .IR "unsigned long" .
714 Furthermore, in Linux versions before 2.6.36,
715 the kernel represents resource limits on 32-bit platforms as
716 .IR "unsigned long" .
717 However, a 32-bit data type is not wide enough.
718 .\" https://bugzilla.kernel.org/show_bug.cgi?id=5042
719 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=12201
720 The most pertinent limit here is
721 .BR RLIMIT_FSIZE ,
722 which specifies the maximum size to which a file can grow:
723 to be useful, this limit must be represented using a type
724 that is as wide as the type used to
725 represent file offsets\(emthat is, as wide as a 64-bit
726 .BR off_t
727 (assuming a program compiled with
728 .IR _FILE_OFFSET_BITS=64 ).
730 To work around this kernel limitation,
731 if a program tried to set a resource limit to a value larger than
732 can be represented in a 32-bit
733 .IR "unsigned long" ,
734 then the glibc
735 .BR setrlimit ()
736 wrapper function silently converted the limit value to
737 .BR RLIM_INFINITY .
738 In other words, the requested resource limit setting was silently ignored.
740 This problem was addressed in Linux 2.6.36 with two principal changes:
741 .IP * 3
742 the addition of a new kernel representation of resource limits that
743 uses 64 bits, even on 32-bit platforms;
744 .IP *
745 the addition of the
746 .BR prlimit ()
747 system call, which employs 64-bit values for its resource limit arguments.
748 .PP
749 Since version 2.13,
750 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=12201
751 glibc works around the limitations of the
752 .BR getrlimit ()
753 and
754 .BR setrlimit ()
755 system calls by implementing
756 .BR setrlimit ()
757 and
758 .BR getrlimit ()
759 as wrapper functions that call
760 .BR prlimit ().
761 .SH EXAMPLE
762 The program below demonstrates the use of
763 .BR prlimit ().
764 .PP
765 .nf
766 #define _GNU_SOURCE
767 #define _FILE_OFFSET_BITS 64
768 #include <stdio.h>
769 #include <time.h>
770 #include <stdlib.h>
771 #include <unistd.h>
772 #include <sys/resource.h>
774 #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \\
775 } while (0)
777 int
778 main(int argc, char *argv[])
779 {
780 struct rlimit old, new;
781 struct rlimit *newp;
782 pid_t pid;
784 if (!(argc == 2 || argc == 4)) {
785 fprintf(stderr, "Usage: %s <pid> [<new\-soft\-limit> "
786 "<new\-hard\-limit>]\\n", argv[0]);
787 exit(EXIT_FAILURE);
788 }
790 pid = atoi(argv[1]); /* PID of target process */
792 newp = NULL;
793 if (argc == 4) {
794 new.rlim_cur = atoi(argv[2]);
795 new.rlim_max = atoi(argv[3]);
796 newp = &new;
797 }
799 /* Set CPU time limit of target process; retrieve and display
800 previous limit */
802 if (prlimit(pid, RLIMIT_CPU, newp, &old) == \-1)
803 errExit("prlimit\-1");
804 printf("Previous limits: soft=%lld; hard=%lld\\n",
805 (long long) old.rlim_cur, (long long) old.rlim_max);
807 /* Retrieve and display new CPU time limit */
809 if (prlimit(pid, RLIMIT_CPU, NULL, &old) == \-1)
810 errExit("prlimit\-2");
811 printf("New limits: soft=%lld; hard=%lld\\n",
812 (long long) old.rlim_cur, (long long) old.rlim_max);
814 exit(EXIT_SUCCESS);
815 }
816 .fi
817 .SH SEE ALSO
818 .BR prlimit (1),
819 .BR dup (2),
820 .BR fcntl (2),
821 .BR fork (2),
822 .BR getrusage (2),
823 .BR mlock (2),
824 .BR mmap (2),
825 .BR open (2),
826 .BR quotactl (2),
827 .BR sbrk (2),
828 .BR shmctl (2),
829 .BR malloc (3),
830 .BR sigqueue (3),
831 .BR ulimit (3),
832 .BR core (5),
833 .BR capabilities (7),
834 .BR cgroups (7),
835 .BR credentials (7),
836 .BR signal (7)