man2/getrlimit.2

   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  15 .\" manual page may be incorrect or out-of-date.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 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 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
 239 In Linux kernels before 2.6.9, this limit controlled the amount of
 240 memory that could be locked by a privileged process.
 241 Since Linux 2.6.9, no limits are placed on the amount of memory
 242 that a privileged process may lock, and this limit instead governs
 243 the amount of memory that an unprivileged process may lock.
 244 .TP
 245 .BR RLIMIT_MSGQUEUE " (since Linux 2.6.8)"
 246 Specifies the limit on the number of bytes that can be allocated
 247 for POSIX message queues for the real user ID of the calling process.
 248 This limit is enforced for
 249 .BR mq_open (3).
 250 Each message queue that the user creates counts (until it is removed)
 251 against this limit according to the formula:
 252 .nf
 253
 254     Since Linux 3.5:
 255
 256         bytes = attr.mq_maxmsg * sizeof(struct msg_msg) +
 257                 min(attr.mq_maxmsg, MQ_PRIO_MAX) *
 258                       sizeof(struct posix_msg_tree_node)+
 259                                 /* For overhead */
 260                 attr.mq_maxmsg * attr.mq_msgsize;
 261                                 /* For message data */
 262
 263     Linux 3.4 and earlier:
 264
 265         bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
 266                                 /* For overhead */
 267                 attr.mq_maxmsg * attr.mq_msgsize;
 268                                 /* For message data */
 269
 270 .fi
 271 where
 272 .I attr
 273 is the
 274 .I mq_attr
 275 structure specified as the fourth argument to
 276 .BR mq_open (3),
 277 and the
 278 .I msg_msg
 279 and
 280 .I posix_msg_tree_node
 281 structures are kernel-internal structures.
 282
 283 The "overhead" addend in the formula accounts for overhead
 284 bytes required by the implementation
 285 and ensures that the user cannot
 286 create an unlimited number of zero-length messages (such messages
 287 nevertheless each consume some system memory for bookkeeping overhead).
 288 .TP
 289 .BR RLIMIT_NICE " (since Linux 2.6.12, but see BUGS below)"
 290 Specifies a ceiling to which the process's nice value can be raised using
 291 .BR setpriority (2)
 292 or
 293 .BR nice (2).
 294 The actual ceiling for the nice value is calculated as
 295 .IR "20\ \-\ rlim_cur" .
 296 The useful range for this limit is thus from 1
 297 (corresponding to a nice value of 19) to 40
 298 (corresponding to a nice value of -20).
 299 This unusual choice of range is was necessary
 300 because negative numbers cannot be specified
 301 as resource limit values, since they typically have special meanings.
 302 For example,
 303 .B RLIM_INFINITY
 304 typically is the same as \-1.
 305 For more detail on the nice value, see
 306 .BR sched (7).
 307 .TP
 308 .B RLIMIT_NOFILE
 309 Specifies a value one greater than the maximum file descriptor number
 310 that can be opened by this process.
 311 Attempts
 312 .RB ( open (2),
 313 .BR pipe (2),
 314 .BR dup (2),
 315 etc.)
 316 to exceed this limit yield the error
 317 .BR EMFILE .
 318 (Historically, this limit was named
 319 .B RLIMIT_OFILE
 320 on BSD.)
 321 .TP
 322 .B RLIMIT_NPROC
 323 The maximum number of processes (or, more precisely on Linux, threads)
 324 that can be created for the real user ID of the calling process.
 325 Upon encountering this limit,
 326 .BR fork (2)
 327 fails with the error
 328 .BR EAGAIN .
 329 This limit is not enforced for processes that have either the
 330 .B CAP_SYS_ADMIN
 331 or the
 332 .B CAP_SYS_RESOURCE
 333 capability.
 334 .TP
 335 .B RLIMIT_RSS
 336 Specifies the limit (in bytes) of the process's resident set
 337 (the number of virtual pages resident in RAM).
 338 This limit has effect only in Linux 2.4.x, x < 30, and there
 339 affects only calls to
 340 .BR madvise (2)
 341 specifying
 342 .BR MADV_WILLNEED .
 343 .\" As at kernel 2.6.12, this limit still does nothing in 2.6 though
 344 .\" talk of making it do something has surfaced from time to time in LKML
 345 .\"       -- MTK, Jul 05
 346 .TP
 347 .BR RLIMIT_RTPRIO " (since Linux 2.6.12, but see BUGS)"
 348 Specifies a ceiling on the real-time priority that may be set for
 349 this process using
 350 .BR sched_setscheduler (2)
 351 and
 352 .BR sched_setparam (2).
 353
 354 For further details on real-time scheduling policies, see
 355 .BR sched (7)
 356 .TP
 357 .BR RLIMIT_RTTIME " (since Linux 2.6.25)"
 358 Specifies a limit (in microseconds)
 359 on the amount of CPU time that a process scheduled
 360 under a real-time scheduling policy may consume without making a blocking
 361 system call.
 362 For the purpose of this limit,
 363 each time a process makes a blocking system call,
 364 the count of its consumed CPU time is reset to zero.
 365 The CPU time count is not reset if the process continues trying to
 366 use the CPU but is preempted, its time slice expires, or it calls
 367 .BR sched_yield (2).
 368
 369 Upon reaching the soft limit, the process is sent a
 370 .B SIGXCPU
 371 signal.
 372 If the process catches or ignores this signal and
 373 continues consuming CPU time, then
 374 .B SIGXCPU
 375 will be generated once each second until the hard limit is reached,
 376 at which point the process is sent a
 377 .B SIGKILL
 378 signal.
 379
 380 The intended use of this limit is to stop a runaway
 381 real-time process from locking up the system.
 382
 383 For further details on real-time scheduling policies, see
 384 .BR sched (7)
 385 .TP
 386 .BR RLIMIT_SIGPENDING " (since Linux 2.6.8)"
 387 Specifies the limit on the number of signals
 388 that may be queued for the real user ID of the calling process.
 389 Both standard and real-time signals are counted for the purpose of
 390 checking this limit.
 391 However, the limit is enforced only for
 392 .BR sigqueue (3);
 393 it is always possible to use
 394 .BR kill (2)
 395 to queue one instance of any of the signals that are not already
 396 queued to the process.
 397 .\" This replaces the /proc/sys/kernel/rtsig-max system-wide limit
 398 .\" that was present in kernels <= 2.6.7.  MTK Dec 04
 399 .TP
 400 .B RLIMIT_STACK
 401 The maximum size of the process stack, in bytes.
 402 Upon reaching this limit, a
 403 .B SIGSEGV
 404 signal is generated.
 405 To handle this signal, a process must employ an alternate signal stack
 406 .RB ( sigaltstack (2)).
 407
 408 Since Linux 2.6.23,
 409 this limit also determines the amount of space used for the process's
 410 command-line arguments and environment variables; for details, see
 411 .BR execve (2).
 412 .SS prlimit()
 413 .\" commit c022a0acad534fd5f5d5f17280f6d4d135e74e81
 414 .\" Author: Jiri Slaby <jslaby@suse.cz>
 415 .\" Date:   Tue May 4 18:03:50 2010 +0200
 416 .\"
 417 .\"     rlimits: implement prlimit64 syscall
 418 .\"
 419 .\" commit 6a1d5e2c85d06da35cdfd93f1a27675bfdc3ad8c
 420 .\" Author: Jiri Slaby <jslaby@suse.cz>
 421 .\" Date:   Wed Mar 24 17:06:58 2010 +0100
 422 .\"
 423 .\"     rlimits: add rlimit64 structure
 424 .\"
 425 The Linux-specific
 426 .BR prlimit ()
 427 system call combines and extends the functionality of
 428 .BR setrlimit ()
 429 and
 430 .BR getrlimit ().
 431 It can be used to both set and get the resource limits of an arbitrary process.
 432
 433 The
 434 .I resource
 435 argument has the same meaning as for
 436 .BR setrlimit ()
 437 and
 438 .BR getrlimit ().
 439
 440 If the
 441 .IR new_limit
 442 argument is a not NULL, then the
 443 .I rlimit
 444 structure to which it points is used to set new values for
 445 the soft and hard limits for
 446 .IR resource .
 447 If the
 448 .IR old_limit
 449 argument is a not NULL, then a successful call to
 450 .BR prlimit ()
 451 places the previous soft and hard limits for
 452 .I resource
 453 in the
 454 .I rlimit
 455 structure pointed to by
 456 .IR old_limit .
 457
 458 The
 459 .I pid
 460 argument specifies the ID of the process on which the call is to operate.
 461 If
 462 .I pid
 463 is 0, then the call applies to the calling process.
 464 To set or get the resources of a process other than itself,
 465 the caller must have the
 466 .B CAP_SYS_RESOURCE
 467 capability in the user namespace of the process
 468 whose resource limits are being changed, or the
 469 real, effective, and saved set user IDs of the target process
 470 must match the real user ID of the caller
 471 .I and
 472 the real, effective, and saved set group IDs of the target process
 473 must match the real group ID of the caller.
 474 .\" FIXME . this permission check is strange
 475 .\" Asked about this on LKML, 7 Nov 2010
 476 .\"     "Inconsistent credential checking in prlimit() syscall"
 477 .SH RETURN VALUE
 478 On success, these system calls return 0.
 479 On error, \-1 is returned, and
 480 .I errno
 481 is set appropriately.
 482 .SH ERRORS
 483 .TP
 484 .B EFAULT
 485 A pointer argument points to a location
 486 outside the accessible address space.
 487 .TP
 488 .B EINVAL
 489 The value specified in
 490 .I resource
 491 is not valid;
 492 or, for
 493 .BR setrlimit ()
 494 or
 495 .BR prlimit ():
 496 .I rlim\->rlim_cur
 497 was greater than
 498 .IR rlim\->rlim_max .
 499 .TP
 500 .B EPERM
 501 An unprivileged process tried to raise the hard limit; the
 502 .B CAP_SYS_RESOURCE
 503 capability is required to do this.
 504 .TP
 505 .B EPERM
 506 The caller tried to increase the hard
 507 .B RLIMIT_NOFILE
 508 limit above the maximum defined by
 509 .IR /proc/sys/fs/nr_open
 510 (see
 511 .BR proc (5))
 512 .TP
 513 .B EPERM
 514 .RB ( prlimit ())
 515 The calling process did not have permission to set limits
 516 for the process specified by
 517 .IR pid .
 518 .TP
 519 .B ESRCH
 520 Could not find a process with the ID specified in
 521 .IR pid .
 522 .SH VERSIONS
 523 The
 524 .BR prlimit ()
 525 system call is available since Linux 2.6.36.
 526 Library support is available since glibc 2.13.
 527 .SH ATTRIBUTES
 528 For an explanation of the terms used in this section, see
 529 .BR attributes (7).
 530 .TS
 531 allbox;
 532 lbw35 lb lb
 533 l l l.
 534 Interface       Attribute       Value
 535 T{
 536 .BR getrlimit (),
 537 .BR setrlimit (),
 538 .BR prlimit ()
 539 T}      Thread safety   MT-Safe
 540 .TE
 541
 542 .SH CONFORMING TO
 543 .BR getrlimit (),
 544 .BR setrlimit ():
 545 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
 546 .br
 547 .BR prlimit ():
 548 Linux-specific.
 549
 550 .B RLIMIT_MEMLOCK
 551 and
 552 .B RLIMIT_NPROC
 553 derive from BSD and are not specified in POSIX.1;
 554 they are present on the BSDs and Linux, but on few other implementations.
 555 .B RLIMIT_RSS
 556 derives from BSD and is not specified in POSIX.1;
 557 it is nevertheless present on most implementations.
 558 .BR RLIMIT_MSGQUEUE ,
 559 .BR RLIMIT_NICE ,
 560 .BR RLIMIT_RTPRIO ,
 561 .BR RLIMIT_RTTIME ,
 562 and
 563 .B RLIMIT_SIGPENDING
 564 are Linux-specific.
 565 .SH NOTES
 566 A child process created via
 567 .BR fork (2)
 568 inherits its parent's resource limits.
 569 Resource limits are preserved across
 570 .BR execve (2).
 571
 572 Lowering the soft limit for a resource below the process's
 573 current consumption of that resource will succeed
 574 (but will prevent the process from further increasing
 575 its consumption of the resource).
 576
 577 One can set the resource limits of the shell using the built-in
 578 .IR ulimit
 579 command
 580 .RI ( limit
 581 in
 582 .BR csh (1)).
 583 The shell's resource limits are inherited by the processes that
 584 it creates to execute commands.
 585
 586 Since Linux 2.6.24, the resource limits of any process can be inspected via
 587 .IR /proc/[pid]/limits ;
 588 see
 589 .BR proc (5).
 590
 591 Ancient systems provided a
 592 .BR vlimit ()
 593 function with a similar purpose to
 594 .BR setrlimit ().
 595 For backward compatibility, glibc also provides
 596 .BR vlimit ().
 597 All new applications should be written using
 598 .BR setrlimit ().
 599 .SS C library/ kernel ABI differences
 600 Since version 2.13, the glibc
 601 .BR getrlimit ()
 602 and
 603 .BR setrlimit ()
 604 wrapper functions no longer invoke the corresponding system calls,
 605 but instead employ
 606 .BR prlimit (),
 607 for the reasons described in BUGS.
 608
 609 The name of the glibc wrapper function is
 610 .BR prlimit ();
 611 the underlying system call is
 612 .BR prlimit64 ().
 613 .SH BUGS
 614 In older Linux kernels, the
 615 .B SIGXCPU
 616 and
 617 .B SIGKILL
 618 signals delivered when a process encountered the soft and hard
 619 .B RLIMIT_CPU
 620 limits were delivered one (CPU) second later than they should have been.
 621 This was fixed in kernel 2.6.8.
 622
 623 In 2.6.x kernels before 2.6.17, a
 624 .B RLIMIT_CPU
 625 limit of 0 is wrongly treated as "no limit" (like
 626 .BR RLIM_INFINITY ).
 627 Since Linux 2.6.17, setting a limit of 0 does have an effect,
 628 but is actually treated as a limit of 1 second.
 629 .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=114008066530167&w=2
 630
 631 A kernel bug means that
 632 .\" See https://lwn.net/Articles/145008/
 633 .B RLIMIT_RTPRIO
 634 does not work in kernel 2.6.12; the problem is fixed in kernel 2.6.13.
 635
 636 In kernel 2.6.12, there was an off-by-one mismatch
 637 between the priority ranges returned by
 638 .BR getpriority (2)
 639 and
 640 .BR RLIMIT_NICE .
 641 This had the effect that the actual ceiling for the nice value
 642 was calculated as
 643 .IR "19\ \-\ rlim_cur" .
 644 This was fixed in kernel 2.6.13.
 645 .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=112256338703880&w=2
 646
 647 Since Linux 2.6.12,
 648 .\" The relevant patch, sent to LKML, seems to be
 649 .\" http://thread.gmane.org/gmane.linux.kernel/273462
 650 .\" From: Roland McGrath <roland <at> redhat.com>
 651 .\" Subject: [PATCH 7/7] make RLIMIT_CPU/SIGXCPU per-process
 652 .\" Date: 2005-01-23 23:27:46 GMT
 653 if a process reaches its soft
 654 .BR RLIMIT_CPU
 655 limit and has a handler installed for
 656 .BR SIGXCPU ,
 657 then, in addition to invoking the signal handler,
 658 the kernel increases the soft limit by one second.
 659 This behavior repeats if the process continues to consume CPU time,
 660 until the hard limit is reached,
 661 at which point the process is killed.
 662 Other implementations
 663 .\" Tested Solaris 10, FreeBSD 9, OpenBSD 5.0
 664 do not change the
 665 .BR RLIMIT_CPU
 666 soft limit in this manner,
 667 and the Linux behavior is probably not standards conformant;
 668 portable applications should avoid relying on this Linux-specific behavior.
 669 .\" FIXME . https://bugzilla.kernel.org/show_bug.cgi?id=50951
 670 The Linux-specific
 671 .BR RLIMIT_RTTIME
 672 limit exhibits the same behavior when the soft limit is encountered.
 673
 674 Kernels before 2.4.22 did not diagnose the error
 675 .B EINVAL
 676 for
 677 .BR setrlimit ()
 678 when
 679 .I rlim\->rlim_cur
 680 was greater than
 681 .IR rlim\->rlim_max .
 682 .\"
 683 .SS Representation of """large""" resource limit values on 32-bit platforms
 684 The glibc
 685 .BR getrlimit ()
 686 and
 687 .BR setrlimit ()
 688 wrapper functions use a 64-bit
 689 .IR rlim_t
 690 data type, even on 32-bit platforms.
 691 However, the
 692 .I rlim_t
 693 data type used in the
 694 .BR getrlimit ()
 695 and
 696 .BR setrlimit ()
 697 system calls is a (32-bit)
 698 .IR "unsigned long" .
 699 Furthermore, in Linux versions before 2.6.36,
 700 the kernel represents resource limits on 32-bit platforms as
 701 .IR "unsigned long" .
 702 However, a 32-bit data type is not wide enough.
 703 .\" https://bugzilla.kernel.org/show_bug.cgi?id=5042
 704 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=12201
 705 The most pertinent limit here is
 706 .BR RLIMIT_FSIZE ,
 707 which specifies the maximum size to which a file can grow:
 708 to be useful, this limit must be represented using a type
 709 that is as wide as the type used to
 710 represent file offsets\(emthat is, as wide as a 64-bit
 711 .BR off_t
 712 (assuming a program compiled with
 713 .IR _FILE_OFFSET_BITS=64 ).
 714
 715 To work around this kernel limitation,
 716 if a program tried to set a resource limit to a value larger than
 717 can be represented in a 32-bit
 718 .IR "unsigned long" ,
 719 then the glibc
 720 .BR setrlimit ()
 721 wrapper function silently converted the limit value to
 722 .BR RLIM_INFINITY .
 723 In other words, the requested resource limit setting was silently ignored.
 724
 725 This problem was addressed in Linux 2.6.36 with two principal changes:
 726 .IP * 3
 727 the addition of a new kernel representation of resource limits that
 728 uses 64 bits, even on 32-bit platforms;
 729 .IP *
 730 the addition of the
 731 .BR prlimit ()
 732 system call, which employs 64-bit values for its resource limit arguments.
 733 .PP
 734 Since version 2.13,
 735 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=12201
 736 glibc works around the limitations of the
 737 .BR getrlimit ()
 738 and
 739 .BR setrlimit ()
 740 system calls by implementing
 741 .BR setrlimit ()
 742 and
 743 .BR getrlimit ()
 744 as wrapper functions that call
 745 .BR prlimit ().
 746 .SH EXAMPLE
 747 The program below demonstrates the use of
 748 .BR prlimit ().
 749 .PP
 750 .nf
 751 #define _GNU_SOURCE
 752 #define _FILE_OFFSET_BITS 64
 753 #include <stdio.h>
 754 #include <time.h>
 755 #include <stdlib.h>
 756 #include <unistd.h>
 757 #include <sys/resource.h>
 758
 759 #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \\
 760                         } while (0)
 761
 762 int
 763 main(int argc, char *argv[])
 764 {
 765     struct rlimit old, new;
 766     struct rlimit *newp;
 767     pid_t pid;
 768
 769     if (!(argc == 2 || argc == 4)) {
 770         fprintf(stderr, "Usage: %s <pid> [<new\-soft\-limit> "
 771                 "<new\-hard\-limit>]\\n", argv[0]);
 772         exit(EXIT_FAILURE);
 773     }
 774
 775     pid = atoi(argv[1]);        /* PID of target process */
 776
 777     newp = NULL;
 778     if (argc == 4) {
 779         new.rlim_cur = atoi(argv[2]);
 780         new.rlim_max = atoi(argv[3]);
 781         newp = &new;
 782     }
 783
 784     /* Set CPU time limit of target process; retrieve and display
 785        previous limit */
 786
 787     if (prlimit(pid, RLIMIT_CPU, newp, &old) == \-1)
 788         errExit("prlimit\-1");
 789     printf("Previous limits: soft=%lld; hard=%lld\\n",
 790             (long long) old.rlim_cur, (long long) old.rlim_max);
 791
 792     /* Retrieve and display new CPU time limit */
 793
 794     if (prlimit(pid, RLIMIT_CPU, NULL, &old) == \-1)
 795         errExit("prlimit\-2");
 796     printf("New limits: soft=%lld; hard=%lld\\n",
 797             (long long) old.rlim_cur, (long long) old.rlim_max);
 798
 799     exit(EXIT_FAILURE);
 800 }
 801 .fi
 802 .SH SEE ALSO
 803 .BR prlimit (1),
 804 .BR dup (2),
 805 .BR fcntl (2),
 806 .BR fork (2),
 807 .BR getrusage (2),
 808 .BR mlock (2),
 809 .BR mmap (2),
 810 .BR open (2),
 811 .BR quotactl (2),
 812 .BR sbrk (2),
 813 .BR shmctl (2),
 814 .BR malloc (3),
 815 .BR sigqueue (3),
 816 .BR ulimit (3),
 817 .BR core (5),
 818 .BR capabilities (7),
 819 .BR credentials (7),
 820 .BR cgroups (7),
 821 .BR signal (7)