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1 '\" t
2 .\" Copyright (c) 1992 Drew Eckhardt, March 28, 1992
3 .\" and Copyright (c) 2002, 2004, 2005, 2008, 2010 Michael Kerrisk
4 .\"
5 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
6 .\"
7 .\" Modified by Michael Haardt <michael@moria.de>
8 .\" Modified 1993-07-23 by Rik Faith <faith@cs.unc.edu>
9 .\" Modified 1996-01-13 by Arnt Gulbrandsen <agulbra@troll.no>
10 .\" Modified 1996-01-22 by aeb, following a remark by
11 .\" Tigran Aivazian <tigran@sco.com>
12 .\" Modified 1996-04-14 by aeb, following a remark by
13 .\" Robert Bihlmeyer <robbe@orcus.ping.at>
14 .\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
15 .\" Modified 2001-05-04 by aeb, following a remark by
16 .\" Håvard Lygre <hklygre@online.no>
17 .\" Modified 2001-04-17 by Michael Kerrisk <mtk.manpages@gmail.com>
18 .\" Modified 2002-06-13 by Michael Kerrisk <mtk.manpages@gmail.com>
19 .\" Added note on nonstandard behavior when SIGCHLD is ignored.
20 .\" Modified 2002-07-09 by Michael Kerrisk <mtk.manpages@gmail.com>
21 .\" Enhanced descriptions of 'resource' values
22 .\" Modified 2003-11-28 by aeb, added RLIMIT_CORE
23 .\" Modified 2004-03-26 by aeb, added RLIMIT_AS
24 .\" Modified 2004-06-16 by Michael Kerrisk <mtk.manpages@gmail.com>
25 .\" Added notes on CAP_SYS_RESOURCE
26 .\"
27 .\" 2004-11-16 -- mtk: the getrlimit.2 page, which formally included
28 .\" coverage of getrusage(2), has been split, so that the latter
29 .\" is now covered in its own getrusage.2.
30 .\"
31 .\" Modified 2004-11-16, mtk: A few other minor changes
32 .\" Modified 2004-11-23, mtk
33 .\" Added notes on RLIMIT_MEMLOCK, RLIMIT_NPROC, and RLIMIT_RSS
34 .\" to "CONFORMING TO"
35 .\" Modified 2004-11-25, mtk
36 .\" Rewrote discussion on RLIMIT_MEMLOCK to incorporate kernel
37 .\" 2.6.9 changes.
38 .\" Added note on RLIMIT_CPU error in older kernels
39 .\" 2004-11-03, mtk, Added RLIMIT_SIGPENDING
40 .\" 2005-07-13, mtk, documented RLIMIT_MSGQUEUE limit.
41 .\" 2005-07-28, mtk, Added descriptions of RLIMIT_NICE and RLIMIT_RTPRIO
42 .\" 2008-05-07, mtk / Peter Zijlstra, Added description of RLIMIT_RTTIME
43 .\" 2010-11-06, mtk: Added documentation of prlimit()
44 .\"
45 .TH getrlimit 2 (date) "Linux man-pages (unreleased)"
46 .SH NAME
47 getrlimit, setrlimit, prlimit \- get/set resource limits
48 .SH LIBRARY
49 Standard C library
50 .RI ( libc ", " \-lc )
51 .SH SYNOPSIS
52 .nf
53 .B #include <sys/resource.h>
54 .P
55 .BI "int getrlimit(int " resource ", struct rlimit *" rlim );
56 .BI "int setrlimit(int " resource ", const struct rlimit *" rlim );
57 .P
58 .BI "int prlimit(pid_t " pid ", int " resource ,
59 .BI " const struct rlimit *_Nullable " new_limit ,
60 .BI " struct rlimit *_Nullable " old_limit );
61 .fi
62 .P
63 .RS -4
64 Feature Test Macro Requirements for glibc (see
65 .BR feature_test_macros (7)):
66 .RE
67 .P
68 .BR prlimit ():
69 .nf
70 _GNU_SOURCE
71 .fi
72 .SH DESCRIPTION
73 The
74 .BR getrlimit ()
75 and
76 .BR setrlimit ()
77 system calls get and set resource limits.
78 Each resource has an associated soft and hard limit, as defined by the
79 .I rlimit
80 structure:
81 .P
82 .in +4n
83 .EX
84 struct rlimit {
85 rlim_t rlim_cur; /* Soft limit */
86 rlim_t rlim_max; /* Hard limit (ceiling for rlim_cur) */
87 };
88 .EE
89 .in
90 .P
91 The soft limit is the value that the kernel enforces for the
92 corresponding resource.
93 The hard limit acts as a ceiling for the soft limit:
94 an unprivileged process may set only its soft limit to a value in the
95 range from 0 up to the hard limit, and (irreversibly) lower its hard limit.
96 A privileged process (under Linux: one with the
97 .B CAP_SYS_RESOURCE
98 capability in the initial user namespace)
99 may make arbitrary changes to either limit value.
100 .P
101 The value
102 .B RLIM_INFINITY
103 denotes no limit on a resource (both in the structure returned by
104 .BR getrlimit ()
105 and in the structure passed to
106 .BR setrlimit ()).
107 .P
108 The
109 .I resource
110 argument must be one of:
111 .TP
112 .B RLIMIT_AS
113 This is the maximum size of the process's virtual memory
114 (address space).
115 The limit is specified in bytes, and is rounded down to the system page size.
116 .\" since Linux 2.0.27 / Linux 2.1.12
117 This limit affects calls to
118 .BR brk (2),
119 .BR mmap (2),
120 and
121 .BR mremap (2),
122 which fail with the error
123 .B ENOMEM
124 upon exceeding this limit.
125 In addition, automatic stack expansion fails
126 (and generates a
127 .B SIGSEGV
128 that kills the process if no alternate stack
129 has been made available via
130 .BR sigaltstack (2)).
131 Since the value is a \fIlong\fP, on machines with a 32-bit \fIlong\fP
132 either this limit is at most 2\ GiB, or this resource is unlimited.
133 .TP
134 .B RLIMIT_CORE
135 This is the maximum size of a
136 .I core
137 file (see
138 .BR core (5))
139 in bytes that the process may dump.
140 When 0 no core dump files are created.
141 When nonzero, larger dumps are truncated to this size.
142 .TP
143 .B RLIMIT_CPU
144 This is a limit, in seconds,
145 on the amount of CPU time that the process can consume.
146 When the process reaches the soft limit, it is sent a
147 .B SIGXCPU
148 signal.
149 The default action for this signal is to terminate the process.
150 However, the signal can be caught, and the handler can return control to
151 the main program.
152 If the process continues to consume CPU time, it will be sent
153 .B SIGXCPU
154 once per second until the hard limit is reached, at which time
155 it is sent
156 .BR SIGKILL .
157 (This latter point describes Linux behavior.
158 Implementations vary in how they treat processes which continue to
159 consume CPU time after reaching the soft limit.
160 Portable applications that need to catch this signal should
161 perform an orderly termination upon first receipt of
162 .BR SIGXCPU .)
163 .TP
164 .B RLIMIT_DATA
165 This is the maximum size
166 of the process's data segment (initialized data,
167 uninitialized data, and heap).
168 The limit is specified in bytes, and is rounded down to the system page size.
169 This limit affects calls to
170 .BR brk (2),
171 .BR sbrk (2),
172 and (since Linux 4.7)
173 .BR mmap (2),
174 .\" commits 84638335900f1995495838fe1bd4870c43ec1f67
175 .\" ("mm: rework virtual memory accounting"),
176 .\" f4fcd55841fc9e46daac553b39361572453c2b88
177 .\" (mm: enable RLIMIT_DATA by default with workaround for valgrind).
178 which fail with the error
179 .B ENOMEM
180 upon encountering the soft limit of this resource.
181 .TP
182 .B RLIMIT_FSIZE
183 This is the maximum size in bytes of files that the process may create.
184 Attempts to extend a file beyond this limit result in delivery of a
185 .B SIGXFSZ
186 signal.
187 By default, this signal terminates a process, but a process can
188 catch this signal instead, in which case the relevant system call (e.g.,
189 .BR write (2),
190 .BR truncate (2))
191 fails with the error
192 .BR EFBIG .
193 .TP
194 .BR RLIMIT_LOCKS " (Linux 2.4.0 to Linux 2.4.24)"
195 .\" to be precise: Linux 2.4.0-test9; no longer in Linux 2.4.25 / Linux 2.5.65
196 This is a limit on the combined number of
197 .BR flock (2)
198 locks and
199 .BR fcntl (2)
200 leases that this process may establish.
201 .TP
202 .B RLIMIT_MEMLOCK
203 This is the maximum number of bytes of memory that may be locked
204 into RAM.
205 This limit is in effect rounded down to the nearest multiple
206 of the system page size.
207 This limit affects
208 .BR mlock (2),
209 .BR mlockall (2),
210 and the
211 .BR mmap (2)
212 .B MAP_LOCKED
213 operation.
214 Since Linux 2.6.9, it also affects the
215 .BR shmctl (2)
216 .B SHM_LOCK
217 operation, where it sets a maximum on the total bytes in
218 shared memory segments (see
219 .BR shmget (2))
220 that may be locked by the real user ID of the calling process.
221 The
222 .BR shmctl (2)
223 .B SHM_LOCK
224 locks are accounted for separately from the per-process memory
225 locks established by
226 .BR mlock (2),
227 .BR mlockall (2),
228 and
229 .BR mmap (2)
230 .BR MAP_LOCKED ;
231 a process can lock bytes up to this limit in each of these
232 two categories.
233 .IP
234 Before Linux 2.6.9, this limit controlled the amount of
235 memory that could be locked by a privileged process.
236 Since Linux 2.6.9, no limits are placed on the amount of memory
237 that a privileged process may lock, and this limit instead governs
238 the amount of memory that an unprivileged process may lock.
239 .TP
240 .BR RLIMIT_MSGQUEUE " (since Linux 2.6.8)"
241 This is a limit on the number of bytes that can be allocated
242 for POSIX message queues for the real user ID of the calling process.
243 This limit is enforced for
244 .BR mq_open (3).
245 Each message queue that the user creates counts (until it is removed)
246 against this limit according to the formula:
247 .RS 4
248 .IP
249 Since Linux 3.5:
250 .IP
251 .in +4n
252 .EX
253 bytes = attr.mq_maxmsg * sizeof(struct msg_msg) +
254 MIN(attr.mq_maxmsg, MQ_PRIO_MAX) *
255 sizeof(struct posix_msg_tree_node)+
256 /* For overhead */
257 attr.mq_maxmsg * attr.mq_msgsize;
258 /* For message data */
259 .EE
260 .in
261 .IP
262 Linux 3.4 and earlier:
263 .IP
264 .in +4n
265 .EX
266 bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
267 /* For overhead */
268 attr.mq_maxmsg * attr.mq_msgsize;
269 /* For message data */
270 .EE
271 .in
272 .RE
273 .IP
274 where
275 .I attr
276 is the
277 .I mq_attr
278 structure specified as the fourth argument to
279 .BR mq_open (3),
280 and the
281 .I msg_msg
282 and
283 .I posix_msg_tree_node
284 structures are kernel-internal structures.
285 .IP
286 The "overhead" addend in the formula accounts for overhead
287 bytes required by the implementation
288 and ensures that the user cannot
289 create an unlimited number of zero-length messages (such messages
290 nevertheless each consume some system memory for bookkeeping overhead).
291 .TP
292 .BR RLIMIT_NICE " (since Linux 2.6.12, but see BUGS below)"
293 This specifies a ceiling to which the process's nice value can be raised using
294 .BR setpriority (2)
295 or
296 .BR nice (2).
297 The actual ceiling for the nice value is calculated as
298 .IR "20\ \-\ rlim_cur" .
299 The useful range for this limit is thus from 1
300 (corresponding to a nice value of 19) to 40
301 (corresponding to a nice value of \-20).
302 This unusual choice of range was necessary
303 because negative numbers cannot be specified
304 as resource limit values, since they typically have special meanings.
305 For example,
306 .B RLIM_INFINITY
307 typically is the same as \-1.
308 For more detail on the nice value, see
309 .BR sched (7).
310 .TP
311 .B RLIMIT_NOFILE
312 This specifies a value one greater than the maximum file descriptor number
313 that can be opened by this process.
314 Attempts
315 .RB ( open (2),
316 .BR pipe (2),
317 .BR dup (2),
318 etc.)
319 to exceed this limit yield the error
320 .BR EMFILE .
321 (Historically, this limit was named
322 .B RLIMIT_OFILE
323 on BSD.)
324 .IP
325 Since Linux 4.5,
326 this limit also defines the maximum number of file descriptors that
327 an unprivileged process (one without the
328 .B CAP_SYS_RESOURCE
329 capability) may have "in flight" to other processes,
330 by being passed across UNIX domain sockets.
331 This limit applies to the
332 .BR sendmsg (2)
333 system call.
334 For further details, see
335 .BR unix (7).
336 .TP
337 .B RLIMIT_NPROC
338 This is a limit on the number of extant process
339 (or, more precisely on Linux, threads)
340 for the real user ID of the calling process.
341 So long as the current number of processes belonging to this
342 process's real user ID is greater than or equal to this limit,
343 .BR fork (2)
344 fails with the error
345 .BR EAGAIN .
346 .IP
347 The
348 .B RLIMIT_NPROC
349 limit is not enforced for processes that have either the
350 .B CAP_SYS_ADMIN
351 or the
352 .B CAP_SYS_RESOURCE
353 capability,
354 or run with real user ID 0.
355 .TP
356 .B RLIMIT_RSS
357 This is a limit (in bytes) on the process's resident set
358 (the number of virtual pages resident in RAM).
359 This limit has effect only in Linux 2.4.x, x < 30, and there
360 affects only calls to
361 .BR madvise (2)
362 specifying
363 .BR MADV_WILLNEED .
364 .\" As at Linux 2.6.12, this limit still does nothing in Linux 2.6 though
365 .\" talk of making it do something has surfaced from time to time in LKML
366 .\" -- MTK, Jul 05
367 .TP
368 .BR RLIMIT_RTPRIO " (since Linux 2.6.12, but see BUGS)"
369 This specifies a ceiling on the real-time priority that may be set for
370 this process using
371 .BR sched_setscheduler (2)
372 and
373 .BR sched_setparam (2).
374 .IP
375 For further details on real-time scheduling policies, see
376 .BR sched (7)
377 .TP
378 .BR RLIMIT_RTTIME " (since Linux 2.6.25)"
379 This is a limit (in microseconds)
380 on the amount of CPU time that a process scheduled
381 under a real-time scheduling policy may consume without making a blocking
382 system call.
383 For the purpose of this limit,
384 each time a process makes a blocking system call,
385 the count of its consumed CPU time is reset to zero.
386 The CPU time count is not reset if the process continues trying to
387 use the CPU but is preempted, its time slice expires, or it calls
388 .BR sched_yield (2).
389 .IP
390 Upon reaching the soft limit, the process is sent a
391 .B SIGXCPU
392 signal.
393 If the process catches or ignores this signal and
394 continues consuming CPU time, then
395 .B SIGXCPU
396 will be generated once each second until the hard limit is reached,
397 at which point the process is sent a
398 .B SIGKILL
399 signal.
400 .IP
401 The intended use of this limit is to stop a runaway
402 real-time process from locking up the system.
403 .IP
404 For further details on real-time scheduling policies, see
405 .BR sched (7)
406 .TP
407 .BR RLIMIT_SIGPENDING " (since Linux 2.6.8)"
408 This is a limit on the number of signals
409 that may be queued for the real user ID of the calling process.
410 Both standard and real-time signals are counted for the purpose of
411 checking this limit.
412 However, the limit is enforced only for
413 .BR sigqueue (3);
414 it is always possible to use
415 .BR kill (2)
416 to queue one instance of any of the signals that are not already
417 queued to the process.
418 .\" This replaces the /proc/sys/kernel/rtsig-max system-wide limit
419 .\" that was present in Linux <= 2.6.7. MTK Dec 04
420 .TP
421 .B RLIMIT_STACK
422 This is the maximum size of the process stack, in bytes.
423 Upon reaching this limit, a
424 .B SIGSEGV
425 signal is generated.
426 To handle this signal, a process must employ an alternate signal stack
427 .RB ( sigaltstack (2)).
428 .IP
429 Since Linux 2.6.23,
430 this limit also determines the amount of space used for the process's
431 command-line arguments and environment variables; for details, see
432 .BR execve (2).
433 .SS prlimit()
434 .\" commit c022a0acad534fd5f5d5f17280f6d4d135e74e81
435 .\" Author: Jiri Slaby <jslaby@suse.cz>
436 .\" Date: Tue May 4 18:03:50 2010 +0200
437 .\"
438 .\" rlimits: implement prlimit64 syscall
439 .\"
440 .\" commit 6a1d5e2c85d06da35cdfd93f1a27675bfdc3ad8c
441 .\" Author: Jiri Slaby <jslaby@suse.cz>
442 .\" Date: Wed Mar 24 17:06:58 2010 +0100
443 .\"
444 .\" rlimits: add rlimit64 structure
445 .\"
446 The Linux-specific
447 .BR prlimit ()
448 system call combines and extends the functionality of
449 .BR setrlimit ()
450 and
451 .BR getrlimit ().
452 It can be used to both set and get the resource limits of an arbitrary process.
453 .P
454 The
455 .I resource
456 argument has the same meaning as for
457 .BR setrlimit ()
458 and
459 .BR getrlimit ().
460 .P
461 If the
462 .I new_limit
463 argument is not NULL, then the
464 .I rlimit
465 structure to which it points is used to set new values for
466 the soft and hard limits for
467 .IR resource .
468 If the
469 .I old_limit
470 argument is not NULL, then a successful call to
471 .BR prlimit ()
472 places the previous soft and hard limits for
473 .I resource
474 in the
475 .I rlimit
476 structure pointed to by
477 .IR old_limit .
478 .P
479 The
480 .I pid
481 argument specifies the ID of the process on which the call is to operate.
482 If
483 .I pid
484 is 0, then the call applies to the calling process.
485 To set or get the resources of a process other than itself,
486 the caller must have the
487 .B CAP_SYS_RESOURCE
488 capability in the user namespace of the process
489 whose resource limits are being changed, or the
490 real, effective, and saved set user IDs of the target process
491 must match the real user ID of the caller
492 .I and
493 the real, effective, and saved set group IDs of the target process
494 must match the real group ID of the caller.
495 .\" FIXME . this permission check is strange
496 .\" Asked about this on LKML, 7 Nov 2010
497 .\" "Inconsistent credential checking in prlimit() syscall"
498 .SH RETURN VALUE
499 On success, these system calls return 0.
500 On error, \-1 is returned, and
501 .I errno
502 is set to indicate the error.
503 .SH ERRORS
504 .TP
505 .B EFAULT
506 A pointer argument points to a location
507 outside the accessible address space.
508 .TP
509 .B EINVAL
510 The value specified in
511 .I resource
512 is not valid;
513 or, for
514 .BR setrlimit ()
515 or
516 .BR prlimit ():
517 .I rlim\->rlim_cur
518 was greater than
519 .IR rlim\->rlim_max .
520 .TP
521 .B EPERM
522 An unprivileged process tried to raise the hard limit; the
523 .B CAP_SYS_RESOURCE
524 capability is required to do this.
525 .TP
526 .B EPERM
527 The caller tried to increase the hard
528 .B RLIMIT_NOFILE
529 limit above the maximum defined by
530 .I /proc/sys/fs/nr_open
531 (see
532 .BR proc (5))
533 .TP
534 .B EPERM
535 .RB ( prlimit ())
536 The calling process did not have permission to set limits
537 for the process specified by
538 .IR pid .
539 .TP
540 .B ESRCH
541 Could not find a process with the ID specified in
542 .IR pid .
543 .SH ATTRIBUTES
544 For an explanation of the terms used in this section, see
545 .BR attributes (7).
546 .TS
547 allbox;
548 lbx lb lb
549 l l l.
550 Interface Attribute Value
551 T{
552 .na
553 .nh
554 .BR getrlimit (),
555 .BR setrlimit (),
556 .BR prlimit ()
557 T} Thread safety MT-Safe
558 .TE
559 .SH STANDARDS
560 .TP
561 .BR getrlimit ()
562 .TQ
563 .BR setrlimit ()
564 POSIX.1-2008.
565 .TP
566 .BR prlimit ()
567 Linux.
568 .P
569 .B RLIMIT_MEMLOCK
570 and
571 .B RLIMIT_NPROC
572 derive from BSD and are not specified in POSIX.1;
573 they are present on the BSDs and Linux, but on few other implementations.
574 .B RLIMIT_RSS
575 derives from BSD and is not specified in POSIX.1;
576 it is nevertheless present on most implementations.
577 .BR \%RLIMIT_MSGQUEUE ,
578 .BR RLIMIT_NICE ,
579 .BR RLIMIT_RTPRIO ,
580 .BR RLIMIT_RTTIME ,
581 and
582 .B \%RLIMIT_SIGPENDING
583 are Linux-specific.
584 .SH HISTORY
585 .TP
586 .BR getrlimit ()
587 .TQ
588 .BR setrlimit ()
589 POSIX.1-2001, SVr4, 4.3BSD.
590 .TP
591 .BR prlimit ()
592 Linux 2.6.36,
593 glibc 2.13.
594 .SH NOTES
595 A child process created via
596 .BR fork (2)
597 inherits its parent's resource limits.
598 Resource limits are preserved across
599 .BR execve (2).
600 .P
601 Resource limits are per-process attributes that are shared
602 by all of the threads in a process.
603 .P
604 Lowering the soft limit for a resource below the process's
605 current consumption of that resource will succeed
606 (but will prevent the process from further increasing
607 its consumption of the resource).
608 .P
609 One can set the resource limits of the shell using the built-in
610 .I ulimit
611 command
612 .RI ( limit
613 in
614 .BR csh (1)).
615 The shell's resource limits are inherited by the processes that
616 it creates to execute commands.
617 .P
618 Since Linux 2.6.24, the resource limits of any process can be inspected via
619 .IR /proc/ pid /limits ;
620 see
621 .BR proc (5).
622 .P
623 Ancient systems provided a
624 .BR vlimit ()
625 function with a similar purpose to
626 .BR setrlimit ().
627 For backward compatibility, glibc also provides
628 .BR vlimit ().
629 All new applications should be written using
630 .BR setrlimit ().
631 .SS C library/kernel ABI differences
632 Since glibc 2.13, the glibc
633 .BR getrlimit ()
634 and
635 .BR setrlimit ()
636 wrapper functions no longer invoke the corresponding system calls,
637 but instead employ
638 .BR prlimit (),
639 for the reasons described in BUGS.
640 .P
641 The name of the glibc wrapper function is
642 .BR prlimit ();
643 the underlying system call is
644 .BR prlimit64 ().
645 .SH BUGS
646 In older Linux kernels, the
647 .B SIGXCPU
648 and
649 .B SIGKILL
650 signals delivered when a process encountered the soft and hard
651 .B RLIMIT_CPU
652 limits were delivered one (CPU) second later than they should have been.
653 This was fixed in Linux 2.6.8.
654 .P
655 In Linux 2.6.x kernels before Linux 2.6.17, a
656 .B RLIMIT_CPU
657 limit of 0 is wrongly treated as "no limit" (like
658 .BR RLIM_INFINITY ).
659 Since Linux 2.6.17, setting a limit of 0 does have an effect,
660 but is actually treated as a limit of 1 second.
661 .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=114008066530167&w=2
662 .P
663 A kernel bug means that
664 .\" See https://lwn.net/Articles/145008/
665 .B RLIMIT_RTPRIO
666 does not work in Linux 2.6.12; the problem is fixed in Linux 2.6.13.
667 .P
668 In Linux 2.6.12, there was an off-by-one mismatch
669 between the priority ranges returned by
670 .BR getpriority (2)
671 and
672 .BR RLIMIT_NICE .
673 This had the effect that the actual ceiling for the nice value
674 was calculated as
675 .IR "19\ \-\ rlim_cur" .
676 This was fixed in Linux 2.6.13.
677 .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=112256338703880&w=2
678 .P
679 Since Linux 2.6.12,
680 .\" The relevant patch, sent to LKML, seems to be
681 .\" http://thread.gmane.org/gmane.linux.kernel/273462
682 .\" From: Roland McGrath <roland <at> redhat.com>
683 .\" Subject: [PATCH 7/7] make RLIMIT_CPU/SIGXCPU per-process
684 .\" Date: 2005-01-23 23:27:46 GMT
685 if a process reaches its soft
686 .B RLIMIT_CPU
687 limit and has a handler installed for
688 .BR SIGXCPU ,
689 then, in addition to invoking the signal handler,
690 the kernel increases the soft limit by one second.
691 This behavior repeats if the process continues to consume CPU time,
692 until the hard limit is reached,
693 at which point the process is killed.
694 Other implementations
695 .\" Tested Solaris 10, FreeBSD 9, OpenBSD 5.0
696 do not change the
697 .B RLIMIT_CPU
698 soft limit in this manner,
699 and the Linux behavior is probably not standards conformant;
700 portable applications should avoid relying on this Linux-specific behavior.
701 .\" FIXME . https://bugzilla.kernel.org/show_bug.cgi?id=50951
702 The Linux-specific
703 .B RLIMIT_RTTIME
704 limit exhibits the same behavior when the soft limit is encountered.
705 .P
706 Kernels before Linux 2.4.22 did not diagnose the error
707 .B EINVAL
708 for
709 .BR setrlimit ()
710 when
711 .I rlim\->rlim_cur
712 was greater than
713 .IR rlim\->rlim_max .
714 .\" d3561f78fd379a7110e46c87964ba7aa4120235c
715 .P
716 Linux doesn't return an error when an attempt to set
717 .B RLIMIT_CPU
718 has failed, for compatibility reasons.
719 .\"
720 .SS Representation of \[dq]large\[dq] resource limit values on 32-bit platforms
721 The glibc
722 .BR getrlimit ()
723 and
724 .BR setrlimit ()
725 wrapper functions use a 64-bit
726 .I rlim_t
727 data type, even on 32-bit platforms.
728 However, the
729 .I rlim_t
730 data type used in the
731 .BR getrlimit ()
732 and
733 .BR setrlimit ()
734 system calls is a (32-bit)
735 .IR "unsigned long" .
736 .\" Linux still uses long for limits internally:
737 .\" c022a0acad534fd5f5d5f17280f6d4d135e74e81
738 .\" kernel/sys.c:do_prlimit() still uses struct rlimit which
739 .\" uses kernel_ulong_t for its members, i.e. 32-bit on 32-bit kernel.
740 Furthermore, in Linux,
741 the kernel represents resource limits on 32-bit platforms as
742 .IR "unsigned long" .
743 However, a 32-bit data type is not wide enough.
744 .\" https://bugzilla.kernel.org/show_bug.cgi?id=5042
745 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=12201
746 The most pertinent limit here is
747 .BR \%RLIMIT_FSIZE ,
748 which specifies the maximum size to which a file can grow:
749 to be useful, this limit must be represented using a type
750 that is as wide as the type used to
751 represent file offsets\[em]that is, as wide as a 64-bit
752 .B off_t
753 (assuming a program compiled with
754 .IR _FILE_OFFSET_BITS=64 ).
755 .P
756 To work around this kernel limitation,
757 if a program tried to set a resource limit to a value larger than
758 can be represented in a 32-bit
759 .IR "unsigned long" ,
760 then the glibc
761 .BR setrlimit ()
762 wrapper function silently converted the limit value to
763 .BR RLIM_INFINITY .
764 In other words, the requested resource limit setting was silently ignored.
765 .P
766 Since glibc 2.13,
767 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=12201
768 glibc works around the limitations of the
769 .BR \%getrlimit ()
770 and
771 .BR setrlimit ()
772 system calls by implementing
773 .BR setrlimit ()
774 and
775 .BR \%getrlimit ()
776 as wrapper functions that call
777 .BR prlimit ().
778 .SH EXAMPLES
779 The program below demonstrates the use of
780 .BR prlimit ().
781 .P
782 .\" SRC BEGIN (getrlimit.c)
783 .EX
784 #define _GNU_SOURCE
785 #define _FILE_OFFSET_BITS 64
786 #include <err.h>
787 #include <stdint.h>
788 #include <stdio.h>
789 #include <stdlib.h>
790 #include <sys/resource.h>
791 #include <time.h>
792 \&
793 int
794 main(int argc, char *argv[])
795 {
796 pid_t pid;
797 struct rlimit old, new;
798 struct rlimit *newp;
799 \&
800 if (!(argc == 2 || argc == 4)) {
801 fprintf(stderr, "Usage: %s <pid> [<new\-soft\-limit> "
802 "<new\-hard\-limit>]\en", argv[0]);
803 exit(EXIT_FAILURE);
804 }
805 \&
806 pid = atoi(argv[1]); /* PID of target process */
807 \&
808 newp = NULL;
809 if (argc == 4) {
810 new.rlim_cur = atoi(argv[2]);
811 new.rlim_max = atoi(argv[3]);
812 newp = &new;
813 }
814 \&
815 /* Set CPU time limit of target process; retrieve and display
816 previous limit */
817 \&
818 if (prlimit(pid, RLIMIT_CPU, newp, &old) == \-1)
819 err(EXIT_FAILURE, "prlimit\-1");
820 printf("Previous limits: soft=%jd; hard=%jd\en",
821 (intmax_t) old.rlim_cur, (intmax_t) old.rlim_max);
822 \&
823 /* Retrieve and display new CPU time limit */
824 \&
825 if (prlimit(pid, RLIMIT_CPU, NULL, &old) == \-1)
826 err(EXIT_FAILURE, "prlimit\-2");
827 printf("New limits: soft=%jd; hard=%jd\en",
828 (intmax_t) old.rlim_cur, (intmax_t) old.rlim_max);
829 \&
830 exit(EXIT_SUCCESS);
831 }
832 .EE
833 .\" SRC END
834 .SH SEE ALSO
835 .BR prlimit (1),
836 .BR dup (2),
837 .BR fcntl (2),
838 .BR fork (2),
839 .BR getrusage (2),
840 .BR mlock (2),
841 .BR mmap (2),
842 .BR open (2),
843 .BR quotactl (2),
844 .BR sbrk (2),
845 .BR shmctl (2),
846 .BR malloc (3),
847 .BR sigqueue (3),
848 .BR ulimit (3),
849 .BR core (5),
850 .BR capabilities (7),
851 .BR cgroups (7),
852 .BR credentials (7),
853 .BR signal (7)