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 2017-03-13 "Linux" "Linux Programmer's Manual"
  65 .SH NAME
  66 getrlimit, setrlimit, prlimit \- get/set resource limits
  67 .SH SYNOPSIS
  68 .B #include <sys/time.h>
  69 .br
  70 .B #include <sys/resource.h>
  71 .PP
  72 .BI "int getrlimit(int " resource ", struct rlimit *" rlim );
  73 .br
  74 .BI "int setrlimit(int " resource ", const struct rlimit *" rlim );
  75 .PP
  76 .BI "int prlimit(pid_t "  pid ", int " resource \
  77 ", const struct rlimit *" new_limit ,
  78 .br
  79 .BI "            struct rlimit *" old_limit );
  80 .PP
  81 .in -4n
  82 Feature Test Macro Requirements for glibc (see
  83 .BR feature_test_macros (7)):
  84 .in
  85 .PP
  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 .EX
 100 struct rlimit {
 101     rlim_t rlim_cur;  /* Soft limit */
 102     rlim_t rlim_max;  /* Hard limit (ceiling for rlim_cur) */
 103 };
 104 .EE
 105 .in
 106 .PP
 107 The soft limit is the value that the kernel enforces for the
 108 corresponding resource.
 109 The hard limit acts as a ceiling for the soft limit:
 110 an unprivileged process may set only its soft limit to a value in the
 111 range from 0 up to the hard limit, and (irreversibly) lower its hard limit.
 112 A privileged process (under Linux: one with the
 113 .B CAP_SYS_RESOURCE
 114 capability) may make arbitrary changes to either limit value.
 115 .PP
 116 The value
 117 .B RLIM_INFINITY
 118 denotes no limit on a resource (both in the structure returned by
 119 .BR getrlimit ()
 120 and in the structure passed to
 121 .BR setrlimit ()).
 122 .PP
 123 The
 124 .I resource
 125 argument must be one of:
 126 .TP
 127 .B RLIMIT_AS
 128 This is the maximum size of the process's virtual memory
 129 (address space) in bytes.
 130 .\" since 2.0.27 / 2.1.12
 131 This limit affects calls to
 132 .BR brk (2),
 133 .BR mmap (2),
 134 and
 135 .BR mremap (2),
 136 which fail with the error
 137 .B ENOMEM
 138 upon exceeding this limit.
 139 Also automatic stack expansion will fail
 140 (and generate a
 141 .B SIGSEGV
 142 that kills the process if no alternate stack
 143 has been made available via
 144 .BR sigaltstack (2)).
 145 Since the value is a \fIlong\fP, on machines with a 32-bit \fIlong\fP
 146 either this limit is at most 2\ GiB, or this resource is unlimited.
 147 .TP
 148 .B RLIMIT_CORE
 149 This is the maximum size of a
 150 .I core
 151 file (see
 152 .BR core (5))
 153 that the process may dump.
 154 When 0 no core dump files are created.
 155 When nonzero, larger dumps are truncated to this size.
 156 .TP
 157 .B RLIMIT_CPU
 158 This is a limit, in seconds,
 159 on the amount of CPU time that the process can consume.
 160 When the process reaches the soft limit, it is sent a
 161 .B SIGXCPU
 162 signal.
 163 The default action for this signal is to terminate the process.
 164 However, the signal can be caught, and the handler can return control to
 165 the main program.
 166 If the process continues to consume CPU time, it will be sent
 167 .B SIGXCPU
 168 once per second until the hard limit is reached, at which time
 169 it is sent
 170 .BR SIGKILL .
 171 (This latter point describes Linux behavior.
 172 Implementations vary in how they treat processes which continue to
 173 consume CPU time after reaching the soft limit.
 174 Portable applications that need to catch this signal should
 175 perform an orderly termination upon first receipt of
 176 .BR SIGXCPU .)
 177 .TP
 178 .B RLIMIT_DATA
 179 This is the maximum size of the process's data segment (initialized data,
 180 uninitialized data, and heap).
 181 This limit affects calls to
 182 .BR brk (2)
 183 and
 184 .BR sbrk (2),
 185 which fail with the error
 186 .B ENOMEM
 187 upon encountering the soft limit of this resource.
 188 .TP
 189 .B RLIMIT_FSIZE
 190 This is the maximum size of files that the process may create.
 191 Attempts to extend a file beyond this limit result in delivery of a
 192 .B SIGXFSZ
 193 signal.
 194 By default, this signal terminates a process, but a process can
 195 catch this signal instead, in which case the relevant system call (e.g.,
 196 .BR write (2),
 197 .BR truncate (2))
 198 fails with the error
 199 .BR EFBIG .
 200 .TP
 201 .BR RLIMIT_LOCKS " (early Linux 2.4 only)"
 202 .\" to be precise: Linux 2.4.0-test9; no longer in 2.4.25 / 2.5.65
 203 This is a limit on the combined number of
 204 .BR flock (2)
 205 locks and
 206 .BR fcntl (2)
 207 leases that this process may establish.
 208 .TP
 209 .B RLIMIT_MEMLOCK
 210 This is the maximum number of bytes of memory that may be locked
 211 into RAM.
 212 This limit is in effect rounded down to the nearest multiple
 213 of the system page size.
 214 This limit affects
 215 .BR mlock (2),
 216 .BR mlockall (2),
 217 and the
 218 .BR mmap (2)
 219 .B MAP_LOCKED
 220 operation.
 221 Since Linux 2.6.9, it also affects the
 222 .BR shmctl (2)
 223 .B SHM_LOCK
 224 operation, where it sets a maximum on the total bytes in
 225 shared memory segments (see
 226 .BR shmget (2))
 227 that may be locked by the real user ID of the calling process.
 228 The
 229 .BR shmctl (2)
 230 .B SHM_LOCK
 231 locks are accounted for separately from the per-process memory
 232 locks established by
 233 .BR mlock (2),
 234 .BR mlockall (2),
 235 and
 236 .BR mmap (2)
 237 .BR MAP_LOCKED ;
 238 a process can lock bytes up to this limit in each of these
 239 two categories.
 240 .IP
 241 In Linux kernels before 2.6.9, this limit controlled the amount of
 242 memory that could be locked by a privileged process.
 243 Since Linux 2.6.9, no limits are placed on the amount of memory
 244 that a privileged process may lock, and this limit instead governs
 245 the amount of memory that an unprivileged process may lock.
 246 .TP
 247 .BR RLIMIT_MSGQUEUE " (since Linux 2.6.8)"
 248 This is a limit on the number of bytes that can be allocated
 249 for POSIX message queues for the real user ID of the calling process.
 250 This limit is enforced for
 251 .BR mq_open (3).
 252 Each message queue that the user creates counts (until it is removed)
 253 against this limit according to the formula:
 254 .IP
 255     Since Linux 3.5:
 256 .IP
 257 .EX
 258         bytes = attr.mq_maxmsg * sizeof(struct msg_msg) +
 259                 min(attr.mq_maxmsg, MQ_PRIO_MAX) *
 260                       sizeof(struct posix_msg_tree_node)+
 261                                 /* For overhead */
 262                 attr.mq_maxmsg * attr.mq_msgsize;
 263                                 /* For message data */
 264 .EE
 265 .IP
 266     Linux 3.4 and earlier:
 267 .IP
 268 .EX
 269         bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
 270                                 /* For overhead */
 271                 attr.mq_maxmsg * attr.mq_msgsize;
 272                                 /* For message data */
 273 .EE
 274 .IP
 275 where
 276 .I attr
 277 is the
 278 .I mq_attr
 279 structure specified as the fourth argument to
 280 .BR mq_open (3),
 281 and the
 282 .I msg_msg
 283 and
 284 .I posix_msg_tree_node
 285 structures are kernel-internal structures.
 286 .IP
 287 The "overhead" addend in the formula accounts for overhead
 288 bytes required by the implementation
 289 and ensures that the user cannot
 290 create an unlimited number of zero-length messages (such messages
 291 nevertheless each consume some system memory for bookkeeping overhead).
 292 .TP
 293 .BR RLIMIT_NICE " (since Linux 2.6.12, but see BUGS below)"
 294 This specifies a ceiling to which the process's nice value can be raised using
 295 .BR setpriority (2)
 296 or
 297 .BR nice (2).
 298 The actual ceiling for the nice value is calculated as
 299 .IR "20\ \-\ rlim_cur" .
 300 The useful range for this limit is thus from 1
 301 (corresponding to a nice value of 19) to 40
 302 (corresponding to a nice value of -20).
 303 This unusual choice of range was necessary
 304 because negative numbers cannot be specified
 305 as resource limit values, since they typically have special meanings.
 306 For example,
 307 .B RLIM_INFINITY
 308 typically is the same as \-1.
 309 For more detail on the nice value, see
 310 .BR sched (7).
 311 .TP
 312 .B RLIMIT_NOFILE
 313 This specifies a value one greater than the maximum file descriptor number
 314 that can be opened by this process.
 315 Attempts
 316 .RB ( open (2),
 317 .BR pipe (2),
 318 .BR dup (2),
 319 etc.)
 320 to exceed this limit yield the error
 321 .BR EMFILE .
 322 (Historically, this limit was named
 323 .B RLIMIT_OFILE
 324 on BSD.)
 325 .IP
 326 Since Linux 4.5,
 327 this limit also defines the maximum number of file descriptors that
 328 an unprivileged process (one without the
 329 .BR CAP_SYS_RESOURCE
 330 capability) may have "in flight" to other processes,
 331 by being passed across UNIX domain sockets.
 332 This limit applies to the
 333 .BR sendmsg (2)
 334 system call.
 335 For further details, see
 336 .BR unix (7).
 337 .TP
 338 .B RLIMIT_NPROC
 339 This is the maximum number of processes
 340 (or, more precisely on Linux, threads)
 341 that can be created for the real user ID of the calling process.
 342 Upon encountering this limit,
 343 .BR fork (2)
 344 fails with the error
 345 .BR EAGAIN .
 346 This limit is not enforced for processes that have either the
 347 .B CAP_SYS_ADMIN
 348 or the
 349 .B CAP_SYS_RESOURCE
 350 capability.
 351 .TP
 352 .B RLIMIT_RSS
 353 This is a limit (in bytes) on the process's resident set
 354 (the number of virtual pages resident in RAM).
 355 This limit has effect only in Linux 2.4.x, x < 30, and there
 356 affects only calls to
 357 .BR madvise (2)
 358 specifying
 359 .BR MADV_WILLNEED .
 360 .\" As at kernel 2.6.12, this limit still does nothing in 2.6 though
 361 .\" talk of making it do something has surfaced from time to time in LKML
 362 .\"       -- MTK, Jul 05
 363 .TP
 364 .BR RLIMIT_RTPRIO " (since Linux 2.6.12, but see BUGS)"
 365 This specifies a ceiling on the real-time priority that may be set for
 366 this process using
 367 .BR sched_setscheduler (2)
 368 and
 369 .BR sched_setparam (2).
 370 .IP
 371 For further details on real-time scheduling policies, see
 372 .BR sched (7)
 373 .TP
 374 .BR RLIMIT_RTTIME " (since Linux 2.6.25)"
 375 This is a limit (in microseconds)
 376 on the amount of CPU time that a process scheduled
 377 under a real-time scheduling policy may consume without making a blocking
 378 system call.
 379 For the purpose of this limit,
 380 each time a process makes a blocking system call,
 381 the count of its consumed CPU time is reset to zero.
 382 The CPU time count is not reset if the process continues trying to
 383 use the CPU but is preempted, its time slice expires, or it calls
 384 .BR sched_yield (2).
 385 .IP
 386 Upon reaching the soft limit, the process is sent a
 387 .B SIGXCPU
 388 signal.
 389 If the process catches or ignores this signal and
 390 continues consuming CPU time, then
 391 .B SIGXCPU
 392 will be generated once each second until the hard limit is reached,
 393 at which point the process is sent a
 394 .B SIGKILL
 395 signal.
 396 .IP
 397 The intended use of this limit is to stop a runaway
 398 real-time process from locking up the system.
 399 .IP
 400 For further details on real-time scheduling policies, see
 401 .BR sched (7)
 402 .TP
 403 .BR RLIMIT_SIGPENDING " (since Linux 2.6.8)"
 404 This is a limit on the number of signals
 405 that may be queued for the real user ID of the calling process.
 406 Both standard and real-time signals are counted for the purpose of
 407 checking this limit.
 408 However, the limit is enforced only for
 409 .BR sigqueue (3);
 410 it is always possible to use
 411 .BR kill (2)
 412 to queue one instance of any of the signals that are not already
 413 queued to the process.
 414 .\" This replaces the /proc/sys/kernel/rtsig-max system-wide limit
 415 .\" that was present in kernels <= 2.6.7.  MTK Dec 04
 416 .TP
 417 .B RLIMIT_STACK
 418 This is the maximum size of the process stack, in bytes.
 419 Upon reaching this limit, a
 420 .B SIGSEGV
 421 signal is generated.
 422 To handle this signal, a process must employ an alternate signal stack
 423 .RB ( sigaltstack (2)).
 424 .IP
 425 Since Linux 2.6.23,
 426 this limit also determines the amount of space used for the process's
 427 command-line arguments and environment variables; for details, see
 428 .BR execve (2).
 429 .SS prlimit()
 430 .\" commit c022a0acad534fd5f5d5f17280f6d4d135e74e81
 431 .\" Author: Jiri Slaby <jslaby@suse.cz>
 432 .\" Date:   Tue May 4 18:03:50 2010 +0200
 433 .\"
 434 .\"     rlimits: implement prlimit64 syscall
 435 .\"
 436 .\" commit 6a1d5e2c85d06da35cdfd93f1a27675bfdc3ad8c
 437 .\" Author: Jiri Slaby <jslaby@suse.cz>
 438 .\" Date:   Wed Mar 24 17:06:58 2010 +0100
 439 .\"
 440 .\"     rlimits: add rlimit64 structure
 441 .\"
 442 The Linux-specific
 443 .BR prlimit ()
 444 system call combines and extends the functionality of
 445 .BR setrlimit ()
 446 and
 447 .BR getrlimit ().
 448 It can be used to both set and get the resource limits of an arbitrary process.
 449 .PP
 450 The
 451 .I resource
 452 argument has the same meaning as for
 453 .BR setrlimit ()
 454 and
 455 .BR getrlimit ().
 456 .PP
 457 If the
 458 .IR new_limit
 459 argument is a not NULL, then the
 460 .I rlimit
 461 structure to which it points is used to set new values for
 462 the soft and hard limits for
 463 .IR resource .
 464 If the
 465 .IR old_limit
 466 argument is a not NULL, then a successful call to
 467 .BR prlimit ()
 468 places the previous soft and hard limits for
 469 .I resource
 470 in the
 471 .I rlimit
 472 structure pointed to by
 473 .IR old_limit .
 474 .PP
 475 The
 476 .I pid
 477 argument specifies the ID of the process on which the call is to operate.
 478 If
 479 .I pid
 480 is 0, then the call applies to the calling process.
 481 To set or get the resources of a process other than itself,
 482 the caller must have the
 483 .B CAP_SYS_RESOURCE
 484 capability in the user namespace of the process
 485 whose resource limits are being changed, or the
 486 real, effective, and saved set user IDs of the target process
 487 must match the real user ID of the caller
 488 .I and
 489 the real, effective, and saved set group IDs of the target process
 490 must match the real group ID of the caller.
 491 .\" FIXME . this permission check is strange
 492 .\" Asked about this on LKML, 7 Nov 2010
 493 .\"     "Inconsistent credential checking in prlimit() syscall"
 494 .SH RETURN VALUE
 495 On success, these system calls return 0.
 496 On error, \-1 is returned, and
 497 .I errno
 498 is set appropriately.
 499 .SH ERRORS
 500 .TP
 501 .B EFAULT
 502 A pointer argument points to a location
 503 outside the accessible address space.
 504 .TP
 505 .B EINVAL
 506 The value specified in
 507 .I resource
 508 is not valid;
 509 or, for
 510 .BR setrlimit ()
 511 or
 512 .BR prlimit ():
 513 .I rlim\->rlim_cur
 514 was greater than
 515 .IR rlim\->rlim_max .
 516 .TP
 517 .B EPERM
 518 An unprivileged process tried to raise the hard limit; the
 519 .B CAP_SYS_RESOURCE
 520 capability is required to do this.
 521 .TP
 522 .B EPERM
 523 The caller tried to increase the hard
 524 .B RLIMIT_NOFILE
 525 limit above the maximum defined by
 526 .IR /proc/sys/fs/nr_open
 527 (see
 528 .BR proc (5))
 529 .TP
 530 .B EPERM
 531 .RB ( prlimit ())
 532 The calling process did not have permission to set limits
 533 for the process specified by
 534 .IR pid .
 535 .TP
 536 .B ESRCH
 537 Could not find a process with the ID specified in
 538 .IR pid .
 539 .SH VERSIONS
 540 The
 541 .BR prlimit ()
 542 system call is available since Linux 2.6.36.
 543 Library support is available since glibc 2.13.
 544 .SH ATTRIBUTES
 545 For an explanation of the terms used in this section, see
 546 .BR attributes (7).
 547 .TS
 548 allbox;
 549 lbw35 lb lb
 550 l l l.
 551 Interface       Attribute       Value
 552 T{
 553 .BR getrlimit (),
 554 .BR setrlimit (),
 555 .BR prlimit ()
 556 T}      Thread safety   MT-Safe
 557 .TE
 558 .sp 1
 559 .SH CONFORMING TO
 560 .BR getrlimit (),
 561 .BR setrlimit ():
 562 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
 563 .br
 564 .BR prlimit ():
 565 Linux-specific.
 566 .PP
 567 .B RLIMIT_MEMLOCK
 568 and
 569 .B RLIMIT_NPROC
 570 derive from BSD and are not specified in POSIX.1;
 571 they are present on the BSDs and Linux, but on few other implementations.
 572 .B RLIMIT_RSS
 573 derives from BSD and is not specified in POSIX.1;
 574 it is nevertheless present on most implementations.
 575 .BR RLIMIT_MSGQUEUE ,
 576 .BR RLIMIT_NICE ,
 577 .BR RLIMIT_RTPRIO ,
 578 .BR RLIMIT_RTTIME ,
 579 and
 580 .B RLIMIT_SIGPENDING
 581 are Linux-specific.
 582 .SH NOTES
 583 A child process created via
 584 .BR fork (2)
 585 inherits its parent's resource limits.
 586 Resource limits are preserved across
 587 .BR execve (2).
 588 .PP
 589 Lowering the soft limit for a resource below the process's
 590 current consumption of that resource will succeed
 591 (but will prevent the process from further increasing
 592 its consumption of the resource).
 593 .PP
 594 One can set the resource limits of the shell using the built-in
 595 .IR ulimit
 596 command
 597 .RI ( limit
 598 in
 599 .BR csh (1)).
 600 The shell's resource limits are inherited by the processes that
 601 it creates to execute commands.
 602 .PP
 603 Since Linux 2.6.24, the resource limits of any process can be inspected via
 604 .IR /proc/[pid]/limits ;
 605 see
 606 .BR proc (5).
 607 .PP
 608 Ancient systems provided a
 609 .BR vlimit ()
 610 function with a similar purpose to
 611 .BR setrlimit ().
 612 For backward compatibility, glibc also provides
 613 .BR vlimit ().
 614 All new applications should be written using
 615 .BR setrlimit ().
 616 .SS C library/ kernel ABI differences
 617 Since version 2.13, the glibc
 618 .BR getrlimit ()
 619 and
 620 .BR setrlimit ()
 621 wrapper functions no longer invoke the corresponding system calls,
 622 but instead employ
 623 .BR prlimit (),
 624 for the reasons described in BUGS.
 625 .PP
 626 The name of the glibc wrapper function is
 627 .BR prlimit ();
 628 the underlying system call is
 629 .BR prlimit64 ().
 630 .SH BUGS
 631 In older Linux kernels, the
 632 .B SIGXCPU
 633 and
 634 .B SIGKILL
 635 signals delivered when a process encountered the soft and hard
 636 .B RLIMIT_CPU
 637 limits were delivered one (CPU) second later than they should have been.
 638 This was fixed in kernel 2.6.8.
 639 .PP
 640 In 2.6.x kernels before 2.6.17, a
 641 .B RLIMIT_CPU
 642 limit of 0 is wrongly treated as "no limit" (like
 643 .BR RLIM_INFINITY ).
 644 Since Linux 2.6.17, setting a limit of 0 does have an effect,
 645 but is actually treated as a limit of 1 second.
 646 .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=114008066530167&w=2
 647 .PP
 648 A kernel bug means that
 649 .\" See https://lwn.net/Articles/145008/
 650 .B RLIMIT_RTPRIO
 651 does not work in kernel 2.6.12; the problem is fixed in kernel 2.6.13.
 652 .PP
 653 In kernel 2.6.12, there was an off-by-one mismatch
 654 between the priority ranges returned by
 655 .BR getpriority (2)
 656 and
 657 .BR RLIMIT_NICE .
 658 This had the effect that the actual ceiling for the nice value
 659 was calculated as
 660 .IR "19\ \-\ rlim_cur" .
 661 This was fixed in kernel 2.6.13.
 662 .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=112256338703880&w=2
 663 .PP
 664 Since Linux 2.6.12,
 665 .\" The relevant patch, sent to LKML, seems to be
 666 .\" http://thread.gmane.org/gmane.linux.kernel/273462
 667 .\" From: Roland McGrath <roland <at> redhat.com>
 668 .\" Subject: [PATCH 7/7] make RLIMIT_CPU/SIGXCPU per-process
 669 .\" Date: 2005-01-23 23:27:46 GMT
 670 if a process reaches its soft
 671 .BR RLIMIT_CPU
 672 limit and has a handler installed for
 673 .BR SIGXCPU ,
 674 then, in addition to invoking the signal handler,
 675 the kernel increases the soft limit by one second.
 676 This behavior repeats if the process continues to consume CPU time,
 677 until the hard limit is reached,
 678 at which point the process is killed.
 679 Other implementations
 680 .\" Tested Solaris 10, FreeBSD 9, OpenBSD 5.0
 681 do not change the
 682 .BR RLIMIT_CPU
 683 soft limit in this manner,
 684 and the Linux behavior is probably not standards conformant;
 685 portable applications should avoid relying on this Linux-specific behavior.
 686 .\" FIXME . https://bugzilla.kernel.org/show_bug.cgi?id=50951
 687 The Linux-specific
 688 .BR RLIMIT_RTTIME
 689 limit exhibits the same behavior when the soft limit is encountered.
 690 .PP
 691 Kernels before 2.4.22 did not diagnose the error
 692 .B EINVAL
 693 for
 694 .BR setrlimit ()
 695 when
 696 .I rlim\->rlim_cur
 697 was greater than
 698 .IR rlim\->rlim_max .
 699 .\"
 700 .SS Representation of """large""" resource limit values on 32-bit platforms
 701 The glibc
 702 .BR getrlimit ()
 703 and
 704 .BR setrlimit ()
 705 wrapper functions use a 64-bit
 706 .IR rlim_t
 707 data type, even on 32-bit platforms.
 708 However, the
 709 .I rlim_t
 710 data type used in the
 711 .BR getrlimit ()
 712 and
 713 .BR setrlimit ()
 714 system calls is a (32-bit)
 715 .IR "unsigned long" .
 716 Furthermore, in Linux versions before 2.6.36,
 717 the kernel represents resource limits on 32-bit platforms as
 718 .IR "unsigned long" .
 719 However, a 32-bit data type is not wide enough.
 720 .\" https://bugzilla.kernel.org/show_bug.cgi?id=5042
 721 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=12201
 722 The most pertinent limit here is
 723 .BR RLIMIT_FSIZE ,
 724 which specifies the maximum size to which a file can grow:
 725 to be useful, this limit must be represented using a type
 726 that is as wide as the type used to
 727 represent file offsets\(emthat is, as wide as a 64-bit
 728 .BR off_t
 729 (assuming a program compiled with
 730 .IR _FILE_OFFSET_BITS=64 ).
 731 .PP
 732 To work around this kernel limitation,
 733 if a program tried to set a resource limit to a value larger than
 734 can be represented in a 32-bit
 735 .IR "unsigned long" ,
 736 then the glibc
 737 .BR setrlimit ()
 738 wrapper function silently converted the limit value to
 739 .BR RLIM_INFINITY .
 740 In other words, the requested resource limit setting was silently ignored.
 741 .PP
 742 This problem was addressed in Linux 2.6.36 with two principal changes:
 743 .IP * 3
 744 the addition of a new kernel representation of resource limits that
 745 uses 64 bits, even on 32-bit platforms;
 746 .IP *
 747 the addition of the
 748 .BR prlimit ()
 749 system call, which employs 64-bit values for its resource limit arguments.
 750 .PP
 751 Since version 2.13,
 752 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=12201
 753 glibc works around the limitations of the
 754 .BR getrlimit ()
 755 and
 756 .BR setrlimit ()
 757 system calls by implementing
 758 .BR setrlimit ()
 759 and
 760 .BR getrlimit ()
 761 as wrapper functions that call
 762 .BR prlimit ().
 763 .SH EXAMPLE
 764 The program below demonstrates the use of
 765 .BR prlimit ().
 766 .PP
 767 .EX
 768 #define _GNU_SOURCE
 769 #define _FILE_OFFSET_BITS 64
 770 #include <stdio.h>
 771 #include <time.h>
 772 #include <stdlib.h>
 773 #include <unistd.h>
 774 #include <sys/resource.h>
 775
 776 #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \\
 777                         } while (0)
 778
 779 int
 780 main(int argc, char *argv[])
 781 {
 782     struct rlimit old, new;
 783     struct rlimit *newp;
 784     pid_t pid;
 785
 786     if (!(argc == 2 || argc == 4)) {
 787         fprintf(stderr, "Usage: %s <pid> [<new\-soft\-limit> "
 788                 "<new\-hard\-limit>]\\n", argv[0]);
 789         exit(EXIT_FAILURE);
 790     }
 791
 792     pid = atoi(argv[1]);        /* PID of target process */
 793
 794     newp = NULL;
 795     if (argc == 4) {
 796         new.rlim_cur = atoi(argv[2]);
 797         new.rlim_max = atoi(argv[3]);
 798         newp = &new;
 799     }
 800
 801     /* Set CPU time limit of target process; retrieve and display
 802        previous limit */
 803
 804     if (prlimit(pid, RLIMIT_CPU, newp, &old) == \-1)
 805         errExit("prlimit\-1");
 806     printf("Previous limits: soft=%lld; hard=%lld\\n",
 807             (long long) old.rlim_cur, (long long) old.rlim_max);
 808
 809     /* Retrieve and display new CPU time limit */
 810
 811     if (prlimit(pid, RLIMIT_CPU, NULL, &old) == \-1)
 812         errExit("prlimit\-2");
 813     printf("New limits: soft=%lld; hard=%lld\\n",
 814             (long long) old.rlim_cur, (long long) old.rlim_max);
 815
 816     exit(EXIT_SUCCESS);
 817 }
 818 .EE
 819 .SH SEE ALSO
 820 .BR prlimit (1),
 821 .BR dup (2),
 822 .BR fcntl (2),
 823 .BR fork (2),
 824 .BR getrusage (2),
 825 .BR mlock (2),
 826 .BR mmap (2),
 827 .BR open (2),
 828 .BR quotactl (2),
 829 .BR sbrk (2),
 830 .BR shmctl (2),
 831 .BR malloc (3),
 832 .BR sigqueue (3),
 833 .BR ulimit (3),
 834 .BR core (5),
 835 .BR capabilities (7),
 836 .BR cgroups (7),
 837 .BR credentials (7),
 838 .BR signal (7)