man2/getrlimit.2

   1 .\" Copyright (c) 1992 Drew Eckhardt, March 28, 1992
   2 .\" and Copyright (c) 2002, 2004, 2005, 2008, 2010 Michael Kerrisk
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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
  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 2016-10-08 "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 };
 104
 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 and
 217 .BR mlockall (2)
 218 and the
 219 .BR mmap (2)
 220 .B MAP_LOCKED
 221 operation.
 222 Since Linux 2.6.9 it also affects the
 223 .BR shmctl (2)
 224 .B SHM_LOCK
 225 operation, where it sets a maximum on the total bytes in
 226 shared memory segments (see
 227 .BR shmget (2))
 228 that may be locked by the real user ID of the calling process.
 229 The
 230 .BR shmctl (2)
 231 .B SHM_LOCK
 232 locks are accounted for separately from the per-process memory
 233 locks established by
 234 .BR mlock (2),
 235 .BR mlockall (2),
 236 and
 237 .BR mmap (2)
 238 .BR MAP_LOCKED ;
 239 a process can lock bytes up to this limit in each of these
 240 two categories.
 241
 242 In Linux kernels before 2.6.9, this limit controlled the amount of
 243 memory that could be locked by a privileged process.
 244 Since Linux 2.6.9, no limits are placed on the amount of memory
 245 that a privileged process may lock, and this limit instead governs
 246 the amount of memory that an unprivileged process may lock.
 247 .TP
 248 .BR RLIMIT_MSGQUEUE " (since Linux 2.6.8)"
 249 This is a limit on the number of bytes that can be allocated
 250 for POSIX message queues for the real user ID of the calling process.
 251 This limit is enforced for
 252 .BR mq_open (3).
 253 Each message queue that the user creates counts (until it is removed)
 254 against this limit according to the formula:
 255 .nf
 256
 257     Since Linux 3.5:
 258
 259         bytes = attr.mq_maxmsg * sizeof(struct msg_msg) +
 260                 min(attr.mq_maxmsg, MQ_PRIO_MAX) *
 261                       sizeof(struct posix_msg_tree_node)+
 262                                 /* For overhead */
 263                 attr.mq_maxmsg * attr.mq_msgsize;
 264                                 /* For message data */
 265
 266     Linux 3.4 and earlier:
 267
 268         bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
 269                                 /* For overhead */
 270                 attr.mq_maxmsg * attr.mq_msgsize;
 271                                 /* For message data */
 272
 273 .fi
 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
 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 is 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 .TP
 325 .B RLIMIT_NPROC
 326 This is the maximum number of processes
 327 (or, more precisely on Linux, threads)
 328 that can be created for the real user ID of the calling process.
 329 Upon encountering this limit,
 330 .BR fork (2)
 331 fails with the error
 332 .BR EAGAIN .
 333 This limit is not enforced for processes that have either the
 334 .B CAP_SYS_ADMIN
 335 or the
 336 .B CAP_SYS_RESOURCE
 337 capability.
 338 .TP
 339 .B RLIMIT_RSS
 340 This is a limit (in bytes) on the process's resident set
 341 (the number of virtual pages resident in RAM).
 342 This limit has effect only in Linux 2.4.x, x < 30, and there
 343 affects only calls to
 344 .BR madvise (2)
 345 specifying
 346 .BR MADV_WILLNEED .
 347 .\" As at kernel 2.6.12, this limit still does nothing in 2.6 though
 348 .\" talk of making it do something has surfaced from time to time in LKML
 349 .\"       -- MTK, Jul 05
 350 .TP
 351 .BR RLIMIT_RTPRIO " (since Linux 2.6.12, but see BUGS)"
 352 This specifies a ceiling on the real-time priority that may be set for
 353 this process using
 354 .BR sched_setscheduler (2)
 355 and
 356 .BR sched_setparam (2).
 357
 358 For further details on real-time scheduling policies, see
 359 .BR sched (7)
 360 .TP
 361 .BR RLIMIT_RTTIME " (since Linux 2.6.25)"
 362 This is a limit (in microseconds)
 363 on the amount of CPU time that a process scheduled
 364 under a real-time scheduling policy may consume without making a blocking
 365 system call.
 366 For the purpose of this limit,
 367 each time a process makes a blocking system call,
 368 the count of its consumed CPU time is reset to zero.
 369 The CPU time count is not reset if the process continues trying to
 370 use the CPU but is preempted, its time slice expires, or it calls
 371 .BR sched_yield (2).
 372
 373 Upon reaching the soft limit, the process is sent a
 374 .B SIGXCPU
 375 signal.
 376 If the process catches or ignores this signal and
 377 continues consuming CPU time, then
 378 .B SIGXCPU
 379 will be generated once each second until the hard limit is reached,
 380 at which point the process is sent a
 381 .B SIGKILL
 382 signal.
 383
 384 The intended use of this limit is to stop a runaway
 385 real-time process from locking up the system.
 386
 387 For further details on real-time scheduling policies, see
 388 .BR sched (7)
 389 .TP
 390 .BR RLIMIT_SIGPENDING " (since Linux 2.6.8)"
 391 This is a limit on the number of signals
 392 that may be queued for the real user ID of the calling process.
 393 Both standard and real-time signals are counted for the purpose of
 394 checking this limit.
 395 However, the limit is enforced only for
 396 .BR sigqueue (3);
 397 it is always possible to use
 398 .BR kill (2)
 399 to queue one instance of any of the signals that are not already
 400 queued to the process.
 401 .\" This replaces the /proc/sys/kernel/rtsig-max system-wide limit
 402 .\" that was present in kernels <= 2.6.7.  MTK Dec 04
 403 .TP
 404 .B RLIMIT_STACK
 405 This is the maximum size of the process stack, in bytes.
 406 Upon reaching this limit, a
 407 .B SIGSEGV
 408 signal is generated.
 409 To handle this signal, a process must employ an alternate signal stack
 410 .RB ( sigaltstack (2)).
 411
 412 Since Linux 2.6.23,
 413 this limit also determines the amount of space used for the process's
 414 command-line arguments and environment variables; for details, see
 415 .BR execve (2).
 416 .SS prlimit()
 417 .\" commit c022a0acad534fd5f5d5f17280f6d4d135e74e81
 418 .\" Author: Jiri Slaby <jslaby@suse.cz>
 419 .\" Date:   Tue May 4 18:03:50 2010 +0200
 420 .\"
 421 .\"     rlimits: implement prlimit64 syscall
 422 .\"
 423 .\" commit 6a1d5e2c85d06da35cdfd93f1a27675bfdc3ad8c
 424 .\" Author: Jiri Slaby <jslaby@suse.cz>
 425 .\" Date:   Wed Mar 24 17:06:58 2010 +0100
 426 .\"
 427 .\"     rlimits: add rlimit64 structure
 428 .\"
 429 The Linux-specific
 430 .BR prlimit ()
 431 system call combines and extends the functionality of
 432 .BR setrlimit ()
 433 and
 434 .BR getrlimit ().
 435 It can be used to both set and get the resource limits of an arbitrary process.
 436
 437 The
 438 .I resource
 439 argument has the same meaning as for
 440 .BR setrlimit ()
 441 and
 442 .BR getrlimit ().
 443
 444 If the
 445 .IR new_limit
 446 argument is a not NULL, then the
 447 .I rlimit
 448 structure to which it points is used to set new values for
 449 the soft and hard limits for
 450 .IR resource .
 451 If the
 452 .IR old_limit
 453 argument is a not NULL, then a successful call to
 454 .BR prlimit ()
 455 places the previous soft and hard limits for
 456 .I resource
 457 in the
 458 .I rlimit
 459 structure pointed to by
 460 .IR old_limit .
 461
 462 The
 463 .I pid
 464 argument specifies the ID of the process on which the call is to operate.
 465 If
 466 .I pid
 467 is 0, then the call applies to the calling process.
 468 To set or get the resources of a process other than itself,
 469 the caller must have the
 470 .B CAP_SYS_RESOURCE
 471 capability in the user namespace of the process
 472 whose resource limits are being changed, or the
 473 real, effective, and saved set user IDs of the target process
 474 must match the real user ID of the caller
 475 .I and
 476 the real, effective, and saved set group IDs of the target process
 477 must match the real group ID of the caller.
 478 .\" FIXME . this permission check is strange
 479 .\" Asked about this on LKML, 7 Nov 2010
 480 .\"     "Inconsistent credential checking in prlimit() syscall"
 481 .SH RETURN VALUE
 482 On success, these system calls return 0.
 483 On error, \-1 is returned, and
 484 .I errno
 485 is set appropriately.
 486 .SH ERRORS
 487 .TP
 488 .B EFAULT
 489 A pointer argument points to a location
 490 outside the accessible address space.
 491 .TP
 492 .B EINVAL
 493 The value specified in
 494 .I resource
 495 is not valid;
 496 or, for
 497 .BR setrlimit ()
 498 or
 499 .BR prlimit ():
 500 .I rlim\->rlim_cur
 501 was greater than
 502 .IR rlim\->rlim_max .
 503 .TP
 504 .B EPERM
 505 An unprivileged process tried to raise the hard limit; the
 506 .B CAP_SYS_RESOURCE
 507 capability is required to do this.
 508 .TP
 509 .B EPERM
 510 The caller tried to increase the hard
 511 .B RLIMIT_NOFILE
 512 limit above the maximum defined by
 513 .IR /proc/sys/fs/nr_open
 514 (see
 515 .BR proc (5))
 516 .TP
 517 .B EPERM
 518 .RB ( prlimit ())
 519 The calling process did not have permission to set limits
 520 for the process specified by
 521 .IR pid .
 522 .TP
 523 .B ESRCH
 524 Could not find a process with the ID specified in
 525 .IR pid .
 526 .SH VERSIONS
 527 The
 528 .BR prlimit ()
 529 system call is available since Linux 2.6.36.
 530 Library support is available since glibc 2.13.
 531 .SH ATTRIBUTES
 532 For an explanation of the terms used in this section, see
 533 .BR attributes (7).
 534 .TS
 535 allbox;
 536 lbw35 lb lb
 537 l l l.
 538 Interface       Attribute       Value
 539 T{
 540 .BR getrlimit (),
 541 .BR setrlimit (),
 542 .BR prlimit ()
 543 T}      Thread safety   MT-Safe
 544 .TE
 545
 546 .SH CONFORMING TO
 547 .BR getrlimit (),
 548 .BR setrlimit ():
 549 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
 550 .br
 551 .BR prlimit ():
 552 Linux-specific.
 553
 554 .B RLIMIT_MEMLOCK
 555 and
 556 .B RLIMIT_NPROC
 557 derive from BSD and are not specified in POSIX.1;
 558 they are present on the BSDs and Linux, but on few other implementations.
 559 .B RLIMIT_RSS
 560 derives from BSD and is not specified in POSIX.1;
 561 it is nevertheless present on most implementations.
 562 .BR RLIMIT_MSGQUEUE ,
 563 .BR RLIMIT_NICE ,
 564 .BR RLIMIT_RTPRIO ,
 565 .BR RLIMIT_RTTIME ,
 566 and
 567 .B RLIMIT_SIGPENDING
 568 are Linux-specific.
 569 .SH NOTES
 570 A child process created via
 571 .BR fork (2)
 572 inherits its parent's resource limits.
 573 Resource limits are preserved across
 574 .BR execve (2).
 575
 576 Lowering the soft limit for a resource below the process's
 577 current consumption of that resource will succeed
 578 (but will prevent the process from further increasing
 579 its consumption of the resource).
 580
 581 One can set the resource limits of the shell using the built-in
 582 .IR ulimit
 583 command
 584 .RI ( limit
 585 in
 586 .BR csh (1)).
 587 The shell's resource limits are inherited by the processes that
 588 it creates to execute commands.
 589
 590 Since Linux 2.6.24, the resource limits of any process can be inspected via
 591 .IR /proc/[pid]/limits ;
 592 see
 593 .BR proc (5).
 594
 595 Ancient systems provided a
 596 .BR vlimit ()
 597 function with a similar purpose to
 598 .BR setrlimit ().
 599 For backward compatibility, glibc also provides
 600 .BR vlimit ().
 601 All new applications should be written using
 602 .BR setrlimit ().
 603 .SS C library/ kernel ABI differences
 604 Since version 2.13, the glibc
 605 .BR getrlimit ()
 606 and
 607 .BR setrlimit ()
 608 wrapper functions no longer invoke the corresponding system calls,
 609 but instead employ
 610 .BR prlimit (),
 611 for the reasons described in BUGS.
 612
 613 The name of the glibc wrapper function is
 614 .BR prlimit ();
 615 the underlying system call is
 616 .BR prlimit64 ().
 617 .SH BUGS
 618 In older Linux kernels, the
 619 .B SIGXCPU
 620 and
 621 .B SIGKILL
 622 signals delivered when a process encountered the soft and hard
 623 .B RLIMIT_CPU
 624 limits were delivered one (CPU) second later than they should have been.
 625 This was fixed in kernel 2.6.8.
 626
 627 In 2.6.x kernels before 2.6.17, a
 628 .B RLIMIT_CPU
 629 limit of 0 is wrongly treated as "no limit" (like
 630 .BR RLIM_INFINITY ).
 631 Since Linux 2.6.17, setting a limit of 0 does have an effect,
 632 but is actually treated as a limit of 1 second.
 633 .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=114008066530167&w=2
 634
 635 A kernel bug means that
 636 .\" See https://lwn.net/Articles/145008/
 637 .B RLIMIT_RTPRIO
 638 does not work in kernel 2.6.12; the problem is fixed in kernel 2.6.13.
 639
 640 In kernel 2.6.12, there was an off-by-one mismatch
 641 between the priority ranges returned by
 642 .BR getpriority (2)
 643 and
 644 .BR RLIMIT_NICE .
 645 This had the effect that the actual ceiling for the nice value
 646 was calculated as
 647 .IR "19\ \-\ rlim_cur" .
 648 This was fixed in kernel 2.6.13.
 649 .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=112256338703880&w=2
 650
 651 Since Linux 2.6.12,
 652 .\" The relevant patch, sent to LKML, seems to be
 653 .\" http://thread.gmane.org/gmane.linux.kernel/273462
 654 .\" From: Roland McGrath <roland <at> redhat.com>
 655 .\" Subject: [PATCH 7/7] make RLIMIT_CPU/SIGXCPU per-process
 656 .\" Date: 2005-01-23 23:27:46 GMT
 657 if a process reaches its soft
 658 .BR RLIMIT_CPU
 659 limit and has a handler installed for
 660 .BR SIGXCPU ,
 661 then, in addition to invoking the signal handler,
 662 the kernel increases the soft limit by one second.
 663 This behavior repeats if the process continues to consume CPU time,
 664 until the hard limit is reached,
 665 at which point the process is killed.
 666 Other implementations
 667 .\" Tested Solaris 10, FreeBSD 9, OpenBSD 5.0
 668 do not change the
 669 .BR RLIMIT_CPU
 670 soft limit in this manner,
 671 and the Linux behavior is probably not standards conformant;
 672 portable applications should avoid relying on this Linux-specific behavior.
 673 .\" FIXME . https://bugzilla.kernel.org/show_bug.cgi?id=50951
 674 The Linux-specific
 675 .BR RLIMIT_RTTIME
 676 limit exhibits the same behavior when the soft limit is encountered.
 677
 678 Kernels before 2.4.22 did not diagnose the error
 679 .B EINVAL
 680 for
 681 .BR setrlimit ()
 682 when
 683 .I rlim\->rlim_cur
 684 was greater than
 685 .IR rlim\->rlim_max .
 686 .\"
 687 .SS Representation of """large""" resource limit values on 32-bit platforms
 688 The glibc
 689 .BR getrlimit ()
 690 and
 691 .BR setrlimit ()
 692 wrapper functions use a 64-bit
 693 .IR rlim_t
 694 data type, even on 32-bit platforms.
 695 However, the
 696 .I rlim_t
 697 data type used in the
 698 .BR getrlimit ()
 699 and
 700 .BR setrlimit ()
 701 system calls is a (32-bit)
 702 .IR "unsigned long" .
 703 Furthermore, in Linux versions before 2.6.36,
 704 the kernel represents resource limits on 32-bit platforms as
 705 .IR "unsigned long" .
 706 However, a 32-bit data type is not wide enough.
 707 .\" https://bugzilla.kernel.org/show_bug.cgi?id=5042
 708 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=12201
 709 The most pertinent limit here is
 710 .BR RLIMIT_FSIZE ,
 711 which specifies the maximum size to which a file can grow:
 712 to be useful, this limit must be represented using a type
 713 that is as wide as the type used to
 714 represent file offsets\(emthat is, as wide as a 64-bit
 715 .BR off_t
 716 (assuming a program compiled with
 717 .IR _FILE_OFFSET_BITS=64 ).
 718
 719 To work around this kernel limitation,
 720 if a program tried to set a resource limit to a value larger than
 721 can be represented in a 32-bit
 722 .IR "unsigned long" ,
 723 then the glibc
 724 .BR setrlimit ()
 725 wrapper function silently converted the limit value to
 726 .BR RLIM_INFINITY .
 727 In other words, the requested resource limit setting was silently ignored.
 728
 729 This problem was addressed in Linux 2.6.36 with two principal changes:
 730 .IP * 3
 731 the addition of a new kernel representation of resource limits that
 732 uses 64 bits, even on 32-bit platforms;
 733 .IP *
 734 the addition of the
 735 .BR prlimit ()
 736 system call, which employs 64-bit values for its resource limit arguments.
 737 .PP
 738 Since version 2.13,
 739 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=12201
 740 glibc works around the limitations of the
 741 .BR getrlimit ()
 742 and
 743 .BR setrlimit ()
 744 system calls by implementing
 745 .BR setrlimit ()
 746 and
 747 .BR getrlimit ()
 748 as wrapper functions that call
 749 .BR prlimit ().
 750 .SH EXAMPLE
 751 The program below demonstrates the use of
 752 .BR prlimit ().
 753 .PP
 754 .nf
 755 #define _GNU_SOURCE
 756 #define _FILE_OFFSET_BITS 64
 757 #include <stdio.h>
 758 #include <time.h>
 759 #include <stdlib.h>
 760 #include <unistd.h>
 761 #include <sys/resource.h>
 762
 763 #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \\
 764                         } while (0)
 765
 766 int
 767 main(int argc, char *argv[])
 768 {
 769     struct rlimit old, new;
 770     struct rlimit *newp;
 771     pid_t pid;
 772
 773     if (!(argc == 2 || argc == 4)) {
 774         fprintf(stderr, "Usage: %s <pid> [<new\-soft\-limit> "
 775                 "<new\-hard\-limit>]\\n", argv[0]);
 776         exit(EXIT_FAILURE);
 777     }
 778
 779     pid = atoi(argv[1]);        /* PID of target process */
 780
 781     newp = NULL;
 782     if (argc == 4) {
 783         new.rlim_cur = atoi(argv[2]);
 784         new.rlim_max = atoi(argv[3]);
 785         newp = &new;
 786     }
 787
 788     /* Set CPU time limit of target process; retrieve and display
 789        previous limit */
 790
 791     if (prlimit(pid, RLIMIT_CPU, newp, &old) == \-1)
 792         errExit("prlimit\-1");
 793     printf("Previous limits: soft=%lld; hard=%lld\\n",
 794             (long long) old.rlim_cur, (long long) old.rlim_max);
 795
 796     /* Retrieve and display new CPU time limit */
 797
 798     if (prlimit(pid, RLIMIT_CPU, NULL, &old) == \-1)
 799         errExit("prlimit\-2");
 800     printf("New limits: soft=%lld; hard=%lld\\n",
 801             (long long) old.rlim_cur, (long long) old.rlim_max);
 802
 803     exit(EXIT_FAILURE);
 804 }
 805 .fi
 806 .SH SEE ALSO
 807 .BR prlimit (1),
 808 .BR dup (2),
 809 .BR fcntl (2),
 810 .BR fork (2),
 811 .BR getrusage (2),
 812 .BR mlock (2),
 813 .BR mmap (2),
 814 .BR open (2),
 815 .BR quotactl (2),
 816 .BR sbrk (2),
 817 .BR shmctl (2),
 818 .BR malloc (3),
 819 .BR sigqueue (3),
 820 .BR ulimit (3),
 821 .BR core (5),
 822 .BR capabilities (7),
 823 .BR cgroups (7),
 824 .BR credentials (7),
 825 .BR signal (7)