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 2015-07-23 "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 The maximum size of the process's virtual memory (address space) in bytes.
 129 .\" since 2.0.27 / 2.1.12
 130 This limit affects calls to
 131 .BR brk (2),
 132 .BR mmap (2),
 133 and
 134 .BR mremap (2),
 135 which fail with the error
 136 .B ENOMEM
 137 upon exceeding this limit.
 138 Also automatic stack expansion will fail
 139 (and generate a
 140 .B SIGSEGV
 141 that kills the process if no alternate stack
 142 has been made available via
 143 .BR sigaltstack (2)).
 144 Since the value is a \fIlong\fP, on machines with a 32-bit \fIlong\fP
 145 either this limit is at most 2 GiB, or this resource is unlimited.
 146 .TP
 147 .B RLIMIT_CORE
 148 Maximum size of a
 149 .I core
 150 file (see
 151 .BR core (5)).
 152 When 0 no core dump files are created.
 153 When nonzero, larger dumps are truncated to this size.
 154 .TP
 155 .B RLIMIT_CPU
 156 CPU time limit in seconds.
 157 When the process reaches the soft limit, it is sent a
 158 .B SIGXCPU
 159 signal.
 160 The default action for this signal is to terminate the process.
 161 However, the signal can be caught, and the handler can return control to
 162 the main program.
 163 If the process continues to consume CPU time, it will be sent
 164 .B SIGXCPU
 165 once per second until the hard limit is reached, at which time
 166 it is sent
 167 .BR SIGKILL .
 168 (This latter point describes Linux behavior.
 169 Implementations vary in how they treat processes which continue to
 170 consume CPU time after reaching the soft limit.
 171 Portable applications that need to catch this signal should
 172 perform an orderly termination upon first receipt of
 173 .BR SIGXCPU .)
 174 .TP
 175 .B RLIMIT_DATA
 176 The maximum size of the process's data segment (initialized data,
 177 uninitialized data, and heap).
 178 This limit affects calls to
 179 .BR brk (2)
 180 and
 181 .BR sbrk (2),
 182 which fail with the error
 183 .B ENOMEM
 184 upon encountering the soft limit of this resource.
 185 .TP
 186 .B RLIMIT_FSIZE
 187 The maximum size of files that the process may create.
 188 Attempts to extend a file beyond this limit result in delivery of a
 189 .B SIGXFSZ
 190 signal.
 191 By default, this signal terminates a process, but a process can
 192 catch this signal instead, in which case the relevant system call (e.g.,
 193 .BR write (2),
 194 .BR truncate (2))
 195 fails with the error
 196 .BR EFBIG .
 197 .TP
 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
 200 A limit on the combined number of
 201 .BR flock (2)
 202 locks and
 203 .BR fcntl (2)
 204 leases that this process may establish.
 205 .TP
 206 .B RLIMIT_MEMLOCK
 207 The maximum number of bytes of memory that may be locked
 208 into RAM.
 209 In effect this limit is rounded down to the nearest multiple
 210 of the system page size.
 211 This limit affects
 212 .BR mlock (2)
 213 and
 214 .BR mlockall (2)
 215 and the
 216 .BR mmap (2)
 217 .B MAP_LOCKED
 218 operation.
 219 Since Linux 2.6.9 it also affects the
 220 .BR shmctl (2)
 221 .B SHM_LOCK
 222 operation, where it sets a maximum on the total bytes in
 223 shared memory segments (see
 224 .BR shmget (2))
 225 that may be locked by the real user ID of the calling process.
 226 The
 227 .BR shmctl (2)
 228 .B SHM_LOCK
 229 locks are accounted for separately from the per-process memory
 230 locks established by
 231 .BR mlock (2),
 232 .BR mlockall (2),
 233 and
 234 .BR mmap (2)
 235 .BR MAP_LOCKED ;
 236 a process can lock bytes up to this limit in each of these
 237 two categories.
 238 In Linux kernels before 2.6.9, this limit controlled the amount of
 239 memory that could be locked by a privileged process.
 240 Since Linux 2.6.9, no limits are placed on the amount of memory
 241 that a privileged process may lock, and this limit instead governs
 242 the amount of memory that an unprivileged process may lock.
 243 .TP
 244 .BR RLIMIT_MSGQUEUE " (since Linux 2.6.8)"
 245 Specifies the limit on the number of bytes that can be allocated
 246 for POSIX message queues for the real user ID of the calling process.
 247 This limit is enforced for
 248 .BR mq_open (3).
 249 Each message queue that the user creates counts (until it is removed)
 250 against this limit according to the formula:
 251 .nf
 252
 253     Since Linux 3.5:
 254         bytes = attr.mq_maxmsg * sizeof(struct msg_msg) +
 255                 min(attr.mq_maxmsg, MQ_PRIO_MAX) *
 256                       sizeof(struct posix_msg_tree_node)+
 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 */
 266
 267 .fi
 268 where
 269 .I attr
 270 is the
 271 .I mq_attr
 272 structure specified as the fourth argument to
 273 .BR mq_open (3),
 274 and the
 275 .I msg_msg
 276 and
 277 .I posix_msg_tree_node
 278 structures are kernel-internal structures.
 279
 280 The "overhead" addend in the formula accounts for overhead
 281 bytes required by the implementation
 282 and ensures that the user cannot
 283 create an unlimited number of zero-length messages (such messages
 284 nevertheless each consume some system memory for bookkeeping overhead).
 285 .TP
 286 .BR RLIMIT_NICE " (since Linux 2.6.12, but see BUGS below)"
 287 Specifies a ceiling to which the process's nice value can be raised using
 288 .BR setpriority (2)
 289 or
 290 .BR nice (2).
 291 The actual ceiling for the nice value is calculated as
 292 .IR "20\ \-\ rlim_cur" .
 293 (This strangeness occurs because negative numbers cannot be specified
 294 as resource limit values, since they typically have special meanings.
 295 For example,
 296 .B RLIM_INFINITY
 297 typically is the same as \-1.)
 298 .TP
 299 .B RLIMIT_NOFILE
 300 Specifies a value one greater than the maximum file descriptor number
 301 that can be opened by this process.
 302 Attempts
 303 .RB ( open (2),
 304 .BR pipe (2),
 305 .BR dup (2),
 306 etc.)
 307 to exceed this limit yield the error
 308 .BR EMFILE .
 309 (Historically, this limit was named
 310 .B RLIMIT_OFILE
 311 on BSD.)
 312 .TP
 313 .B RLIMIT_NPROC
 314 The maximum number of processes (or, more precisely on Linux, threads)
 315 that can be created for the real user ID of the calling process.
 316 Upon encountering this limit,
 317 .BR fork (2)
 318 fails with the error
 319 .BR EAGAIN .
 320 This limit is not enforced for processes that have either the
 321 .B CAP_SYS_ADMIN
 322 or the
 323 .B CAP_SYS_RESOURCE
 324 capability.
 325 .TP
 326 .B RLIMIT_RSS
 327 Specifies the limit (in pages) of the process's resident set
 328 (the number of virtual pages resident in RAM).
 329 This limit has effect only in Linux 2.4.x, x < 30, and there
 330 affects only calls to
 331 .BR madvise (2)
 332 specifying
 333 .BR MADV_WILLNEED .
 334 .\" As at kernel 2.6.12, this limit still does nothing in 2.6 though
 335 .\" talk of making it do something has surfaced from time to time in LKML
 336 .\"       -- MTK, Jul 05
 337 .TP
 338 .BR RLIMIT_RTPRIO " (since Linux 2.6.12, but see BUGS)"
 339 Specifies a ceiling on the real-time priority that may be set for
 340 this process using
 341 .BR sched_setscheduler (2)
 342 and
 343 .BR sched_setparam (2).
 344 .TP
 345 .BR RLIMIT_RTTIME " (since Linux 2.6.25)"
 346 Specifies a limit (in microseconds)
 347 on the amount of CPU time that a process scheduled
 348 under a real-time scheduling policy may consume without making a blocking
 349 system call.
 350 For the purpose of this limit,
 351 each time a process makes a blocking system call,
 352 the count of its consumed CPU time is reset to zero.
 353 The CPU time count is not reset if the process continues trying to
 354 use the CPU but is preempted, its time slice expires, or it calls
 355 .BR sched_yield (2).
 356
 357 Upon reaching the soft limit, the process is sent a
 358 .B SIGXCPU
 359 signal.
 360 If the process catches or ignores this signal and
 361 continues consuming CPU time, then
 362 .B SIGXCPU
 363 will be generated once each second until the hard limit is reached,
 364 at which point the process is sent a
 365 .B SIGKILL
 366 signal.
 367
 368 The intended use of this limit is to stop a runaway
 369 real-time process from locking up the system.
 370 .TP
 371 .BR RLIMIT_SIGPENDING " (since Linux 2.6.8)"
 372 Specifies the limit on the number of signals
 373 that may be queued for the real user ID of the calling process.
 374 Both standard and real-time signals are counted for the purpose of
 375 checking this limit.
 376 However, the limit is enforced only for
 377 .BR sigqueue (3);
 378 it is always possible to use
 379 .BR kill (2)
 380 to queue one instance of any of the signals that are not already
 381 queued to the process.
 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
 385 .B RLIMIT_STACK
 386 The maximum size of the process stack, in bytes.
 387 Upon reaching this limit, a
 388 .B SIGSEGV
 389 signal is generated.
 390 To handle this signal, a process must employ an alternate signal stack
 391 .RB ( sigaltstack (2)).
 392
 393 Since Linux 2.6.23,
 394 this limit also determines the amount of space used for the process's
 395 command-line arguments and environment variables; for details, see
 396 .BR execve (2).
 397 .SS prlimit()
 398 .\" commit c022a0acad534fd5f5d5f17280f6d4d135e74e81
 399 .\" Author: Jiri Slaby <jslaby@suse.cz>
 400 .\" Date:   Tue May 4 18:03:50 2010 +0200
 401 .\"
 402 .\"     rlimits: implement prlimit64 syscall
 403 .\"
 404 .\" commit 6a1d5e2c85d06da35cdfd93f1a27675bfdc3ad8c
 405 .\" Author: Jiri Slaby <jslaby@suse.cz>
 406 .\" Date:   Wed Mar 24 17:06:58 2010 +0100
 407 .\"
 408 .\"     rlimits: add rlimit64 structure
 409 .\"
 410 The Linux-specific
 411 .BR prlimit ()
 412 system call combines and extends the functionality of
 413 .BR setrlimit ()
 414 and
 415 .BR getrlimit ().
 416 It can be used to both set and get the resource limits of an arbitrary process.
 417
 418 The
 419 .I resource
 420 argument has the same meaning as for
 421 .BR setrlimit ()
 422 and
 423 .BR getrlimit ().
 424
 425 If the
 426 .IR new_limit
 427 argument is a not NULL, then the
 428 .I rlimit
 429 structure to which it points is used to set new values for
 430 the soft and hard limits for
 431 .IR resource .
 432 If the
 433 .IR old_limit
 434 argument is a not NULL, then a successful call to
 435 .BR prlimit ()
 436 places the previous soft and hard limits for
 437 .I resource
 438 in the
 439 .I rlimit
 440 structure pointed to by
 441 .IR old_limit .
 442
 443 The
 444 .I pid
 445 argument specifies the ID of the process on which the call is to operate.
 446 If
 447 .I pid
 448 is 0, then the call applies to the calling process.
 449 To set or get the resources of a process other than itself,
 450 the caller must have the
 451 .B CAP_SYS_RESOURCE
 452 capability, or the
 453 real, effective, and saved set user IDs of the target process
 454 must match the real user ID of the caller
 455 .I and
 456 the real, effective, and saved set group IDs of the target process
 457 must match the real group ID of the caller.
 458 .\" FIXME . this permission check is strange
 459 .\" Asked about this on LKML, 7 Nov 2010
 460 .\"     "Inconsistent credential checking in prlimit() syscall"
 461 .SH RETURN VALUE
 462 On success, these system calls return 0.
 463 On error, \-1 is returned, and
 464 .I errno
 465 is set appropriately.
 466 .SH ERRORS
 467 .TP
 468 .B EFAULT
 469 A pointer argument points to a location
 470 outside the accessible address space.
 471 .TP
 472 .B EINVAL
 473 The value specified in
 474 .I resource
 475 is not valid;
 476 or, for
 477 .BR setrlimit ()
 478 or
 479 .BR prlimit ():
 480 .I rlim\->rlim_cur
 481 was greater than
 482 .IR rlim\->rlim_max .
 483 .TP
 484 .B EPERM
 485 An unprivileged process tried to raise the hard limit; the
 486 .B CAP_SYS_RESOURCE
 487 capability is required to do this.
 488 .TP
 489 .B EPERM
 490 The caller tried to increase the hard
 491 .B RLIMIT_NOFILE
 492 limit above the maximum defined by
 493 .IR /proc/sys/fs/nr_open
 494 (see
 495 .BR proc (5))
 496 .TP
 497 .B EPERM
 498 .RB ( prlimit ())
 499 The calling process did not have permission to set limits
 500 for the process specified by
 501 .IR pid .
 502 .TP
 503 .B ESRCH
 504 Could not find a process with the ID specified in
 505 .IR pid .
 506 .SH VERSIONS
 507 The
 508 .BR prlimit ()
 509 system call is available since Linux 2.6.36.
 510 Library support is available since glibc 2.13.
 511 .SH ATTRIBUTES
 512 For an explanation of the terms used in this section, see
 513 .BR attributes (7).
 514 .TS
 515 allbox;
 516 lbw35 lb lb
 517 l l l.
 518 Interface       Attribute       Value
 519 T{
 520 .BR getrlimit (),
 521 .BR setrlimit (),
 522 .BR prlimit ()
 523 T}      Thread safety   MT-Safe
 524 .TE
 525
 526 .SH CONFORMING TO
 527 .BR getrlimit (),
 528 .BR setrlimit ():
 529 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
 530 .br
 531 .BR prlimit ():
 532 Linux-specific.
 533
 534 .B RLIMIT_MEMLOCK
 535 and
 536 .B RLIMIT_NPROC
 537 derive from BSD and are not specified in POSIX.1;
 538 they are present on the BSDs and Linux, but on few other implementations.
 539 .B RLIMIT_RSS
 540 derives from BSD and is not specified in POSIX.1;
 541 it is nevertheless present on most implementations.
 542 .BR RLIMIT_MSGQUEUE ,
 543 .BR RLIMIT_NICE ,
 544 .BR RLIMIT_RTPRIO ,
 545 .BR RLIMIT_RTTIME ,
 546 and
 547 .B RLIMIT_SIGPENDING
 548 are Linux-specific.
 549 .SH NOTES
 550 A child process created via
 551 .BR fork (2)
 552 inherits its parent's resource limits.
 553 Resource limits are preserved across
 554 .BR execve (2).
 555
 556 Lowering the soft limit for a resource below the process's
 557 current consumption of that resource will succeed
 558 (but will prevent the process from further increasing
 559 its consumption of the resource).
 560
 561 One can set the resource limits of the shell using the built-in
 562 .IR ulimit
 563 command
 564 .RI ( limit
 565 in
 566 .BR csh (1)).
 567 The shell's resource limits are inherited by the processes that
 568 it creates to execute commands.
 569
 570 Since Linux 2.6.24, the resource limits of any process can be inspected via
 571 .IR /proc/[pid]/limits ;
 572 see
 573 .BR proc (5).
 574
 575 Ancient systems provided a
 576 .BR vlimit ()
 577 function with a similar purpose to
 578 .BR setrlimit ().
 579 For backward compatibility, glibc also provides
 580 .BR vlimit ().
 581 All new applications should be written using
 582 .BR setrlimit ().
 583 .SS C library/ kernel ABI differences
 584 Since version 2.13, the glibc
 585 .BR getrlimit ()
 586 and
 587 .BR setrlimit ()
 588 wrapper functions no longer invoke the corresponding system calls,
 589 but instead employ
 590 .BR prlimit (),
 591 for the reasons described in BUGS.
 592
 593 The name of the glibc wrapper function is
 594 .BR prlimit ();
 595 the underlying system call is call prlimit64 ().
 596 .SH BUGS
 597 In older Linux kernels, the
 598 .B SIGXCPU
 599 and
 600 .B SIGKILL
 601 signals delivered when a process encountered the soft and hard
 602 .B RLIMIT_CPU
 603 limits were delivered one (CPU) second later than they should have been.
 604 This was fixed in kernel 2.6.8.
 605
 606 In 2.6.x kernels before 2.6.17, a
 607 .B RLIMIT_CPU
 608 limit of 0 is wrongly treated as "no limit" (like
 609 .BR RLIM_INFINITY ).
 610 Since Linux 2.6.17, setting a limit of 0 does have an effect,
 611 but is actually treated as a limit of 1 second.
 612 .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=114008066530167&w=2
 613
 614 A kernel bug means that
 615 .\" See https://lwn.net/Articles/145008/
 616 .B RLIMIT_RTPRIO
 617 does not work in kernel 2.6.12; the problem is fixed in kernel 2.6.13.
 618
 619 In kernel 2.6.12, there was an off-by-one mismatch
 620 between the priority ranges returned by
 621 .BR getpriority (2)
 622 and
 623 .BR RLIMIT_NICE .
 624 This had the effect that the actual ceiling for the nice value
 625 was calculated as
 626 .IR "19\ \-\ rlim_cur" .
 627 This was fixed in kernel 2.6.13.
 628 .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=112256338703880&w=2
 629
 630 Since 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
 636 if a process reaches its soft
 637 .BR RLIMIT_CPU
 638 limit and has a handler installed for
 639 .BR SIGXCPU ,
 640 then, in addition to invoking the signal handler,
 641 the kernel increases the soft limit by one second.
 642 This behavior repeats if the process continues to consume CPU time,
 643 until the hard limit is reached,
 644 at which point the process is killed.
 645 Other implementations
 646 .\" Tested Solaris 10, FreeBSD 9, OpenBSD 5.0
 647 do not change the
 648 .BR RLIMIT_CPU
 649 soft limit in this manner,
 650 and the Linux behavior is probably not standards conformant;
 651 portable applications should avoid relying on this Linux-specific behavior.
 652 .\" FIXME . https://bugzilla.kernel.org/show_bug.cgi?id=50951
 653 The Linux-specific
 654 .BR RLIMIT_RTTIME
 655 limit exhibits the same behavior when the soft limit is encountered.
 656
 657 Kernels before 2.4.22 did not diagnose the error
 658 .B EINVAL
 659 for
 660 .BR setrlimit ()
 661 when
 662 .I rlim\->rlim_cur
 663 was greater than
 664 .IR rlim\->rlim_max .
 665 .\"
 666 .SS Representation of """large""" resource limit values on 32-bit platforms
 667 The glibc
 668 .BR getrlimit ()
 669 and
 670 .BR setrlimit ()
 671 wrapper functions use a 64-bit
 672 .IR rlim_t
 673 data type, even on 32-bit platforms.
 674 However, the
 675 .I rlim_t
 676 data type used in the
 677 .BR getrlimit ()
 678 and
 679 .BR setrlimit ()
 680 system calls is a (32-bit)
 681 .IR "unsigned long" .
 682 Furthermore, in Linux versions before 2.6.36,
 683 the kernel represents resource limits on 32-bit platforms as
 684 .IR "unsigned long" .
 685 However, a 32-bit data type is not wide enough.
 686 .\" https://bugzilla.kernel.org/show_bug.cgi?id=5042
 687 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=12201
 688 The most pertinent limit here is
 689 .BR RLIMIT_FSIZE ,
 690 which specifies the maximum size to which a file can grow:
 691 to be useful, this limit must be represented using a type
 692 that is as wide as the type used to
 693 represent 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
 698 To work around this kernel limitation,
 699 if a program tried to set a resource limit to a value larger than
 700 can be represented in a 32-bit
 701 .IR "unsigned long" ,
 702 then the glibc
 703 .BR setrlimit ()
 704 wrapper function silently converted the limit value to
 705 .BR RLIM_INFINITY .
 706 In other words, the requested resource limit setting was silently ignored.
 707
 708 This problem was addressed in Linux 2.6.36 with two principal changes:
 709 .IP * 3
 710 the addition of a new kernel representation of resource limits that
 711 uses 64 bits, even on 32-bit platforms;
 712 .IP *
 713 the addition of the
 714 .BR prlimit ()
 715 system call, which employs 64-bit values for its resource limit arguments.
 716 .PP
 717 Since version 2.13,
 718 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=12201
 719 glibc works around the limitations of the
 720 .BR getrlimit ()
 721 and
 722 .BR setrlimit ()
 723 system calls by implementing
 724 .BR setrlimit ()
 725 and
 726 .BR getrlimit ()
 727 as wrapper functions that call
 728 .BR prlimit ().
 729 .SH EXAMPLE
 730 The 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
 745 int
 746 main(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
 785 .SH SEE ALSO
 786 .BR prlimit (1),
 787 .BR dup (2),
 788 .BR fcntl (2),
 789 .BR fork (2),
 790 .BR getrusage (2),
 791 .BR mlock (2),
 792 .BR mmap (2),
 793 .BR open (2),
 794 .BR quotactl (2),
 795 .BR sbrk (2),
 796 .BR shmctl (2),
 797 .BR malloc (3),
 798 .BR sigqueue (3),
 799 .BR ulimit (3),
 800 .BR core (5),
 801 .BR capabilities (7),
 802 .BR signal (7)