man2/getrlimit.2

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   3 .\" Copyright (c) 1992 Drew Eckhardt, March 28, 1992
   4 .\" Copyright (c) 2002 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@gmx.net>
  37 .\" Modified 2002-06-13 by Michael Kerrisk <mtk-manpages@gmx.net>
  38 .\"     Added note on non-standard behaviour when SIGCHLD is ignored.
  39 .\" Modified 2002-07-09 by Michael Kerrisk <mtk-manpages@gmx.net>
  40 .\"     Enhanced descriptions of 'resource' values for [gs]etrlimit()
  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@gmx.net>
  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 .\"
  62 .TH GETRLIMIT 2 2005-09-20 "Linux 2.6.13" "Linux Programmer's Manual"
  63 .SH NAME
  64 getrlimit, setrlimit \- get/set resource limits
  65 .SH SYNOPSIS
  66 .B #include <sys/time.h>
  67 .br
  68 .B #include <sys/resource.h>
  69 .sp
  70 .BI "int getrlimit(int " resource ", struct rlimit *" rlim );
  71 .br
  72 .BI "int setrlimit(int " resource ", const struct rlimit *" rlim );
  73 .SH DESCRIPTION
  74 .BR getrlimit ()
  75 and
  76 .BR setrlimit ()
  77 get and set resource limits respectively.
  78 Each resource has an associated soft and hard limit, as defined by the
  79 .B rlimit
  80 structure (the
  81 .I rlim
  82 argument to both
  83 .BR getrlimit ()
  84 and
  85 .BR setrlimit ()):
  86 .PP
  87 .in +0.5i
  88 .nf
  89 struct rlimit {
  90     rlim_t rlim_cur;  /* Soft limit */
  91     rlim_t rlim_max;  /* Hard limit (ceiling for rlim_cur) */
  92 };
  93
  94 .fi
  95 .in -0.5i
  96 The soft limit is the value that the kernel enforces for the
  97 corresponding resource.
  98 The hard limit acts as a ceiling for the soft limit:
  99 an unprivileged process may only set its soft limit to a value in the
 100 range from 0 up to the hard limit, and (irreversibly) lower its hard limit.
 101 A privileged process (under Linux: one with the
 102 .B CAP_SYS_RESOURCE
 103 capability) may make arbitrary changes to either limit value.
 104 .PP
 105 The value
 106 .B RLIM_INFINITY
 107 denotes no limit on a resource (both in the structure returned by
 108 .BR getrlimit ()
 109 and in the structure passed to
 110 .BR setrlimit ()).
 111 .PP
 112 .I resource
 113 must be one of:
 114 .TP
 115 .B RLIMIT_AS
 116 The maximum size of the process's virtual memory (address space) in bytes.
 117 .\" since 2.0.27 / 2.1.12
 118 This limit affects calls to
 119 .BR brk (2),
 120 .BR mmap (2)
 121 and
 122 .BR mremap (2),
 123 which fail with the error
 124 .B ENOMEM
 125 upon exceeding this limit. Also automatic stack expansion will fail
 126 (and generate a
 127 .B SIGSEGV
 128 that kills the process if no alternate stack
 129 has been made available via
 130 .BR sigaltstack (2)).
 131 Since the value is a \fIlong\fP, on machines with a 32-bit \fIlong\fP
 132 either this limit is at most 2 GiB, or this resource is unlimited.
 133 .TP
 134 .B RLIMIT_CORE
 135 Maximum size of
 136 .I core
 137 file. When 0 no core dump files are created.
 138 When non-zero, larger dumps are truncated to this size.
 139 .TP
 140 .B RLIMIT_CPU
 141 CPU time limit in seconds.
 142 When the process reaches the soft limit, it is sent a
 143 .B SIGXCPU
 144 signal.
 145 The default action for this signal is to terminate the process.
 146 However, the signal can be caught, and the handler can return control to
 147 the main program.
 148 If the process continues to consume CPU time, it will be sent
 149 .B SIGXCPU
 150 once per second until the hard limit is reached, at which time
 151 it is sent
 152 .BR SIGKILL .
 153 (This latter point describes Linux 2.2 through 2.6 behaviour.
 154 Implementations vary in how they treat processes which continue to
 155 consume CPU time after reaching the soft limit.
 156 Portable applications that need to catch this signal should
 157 perform an orderly termination upon first receipt of
 158 .BR SIGXCPU .)
 159 .TP
 160 .B RLIMIT_DATA
 161 The maximum size of the process's data segment (initialized data,
 162 uninitialized data, and heap).
 163 This limit affects calls to
 164 .BR brk ()
 165 and
 166 .BR sbrk (),
 167 which fail with the error
 168 .B ENOMEM
 169 upon encountering the soft limit of this resource.
 170 .TP
 171 .B RLIMIT_FSIZE
 172 The maximum size of files that the process may create.
 173 Attempts to extend a file beyond this limit result in delivery of a
 174 .B SIGXFSZ
 175 signal.
 176 By default, this signal terminates a process, but a process can
 177 catch this signal instead, in which case the relevant system call (e.g.,
 178 .BR write ()
 179 .BR truncate ())
 180 fails with the error
 181 .BR EFBIG .
 182 .TP
 183 .BR RLIMIT_LOCKS " (Early Linux 2.4 only)"
 184 .\" to be precise: Linux 2.4.0-test9; no longer in 2.4.25 / 2.5.65
 185 A limit on the combined number of
 186 .BR flock ()
 187 locks and
 188 .BR fcntl ()
 189 leases that this process may establish.
 190 .TP
 191 .B RLIMIT_MEMLOCK
 192 The maximum number of bytes of memory that may be locked
 193 into RAM.
 194 In effect this limit is rounded down to the nearest multiple
 195 of the system page size.
 196 This limit affects
 197 .BR mlock (2)
 198 and
 199 .BR mlockall (2)
 200 and the
 201 .BR mmap (2)
 202 .B MAP_LOCKED
 203 operation.
 204 Since Linux 2.6.9 it also affects the
 205 .BR shmctl (2)
 206 .B SHM_LOCK
 207 operation, where it sets a maximum on the total bytes in
 208 shared memory segments (see
 209 .BR shmget (2))
 210 that may be locked by the real user ID of the calling process.
 211 The
 212 .BR shmctl (2)
 213 .B SHM_LOCK
 214 locks are accounted for separately from the per-process memory
 215 locks established by
 216 .BR mlock (2),
 217 .BR mlockall (2),
 218 and
 219 .BR mmap (2)
 220 .BR MAP_LOCKED ;
 221 a process can lock bytes up to this limit in each of these
 222 two categories.
 223 In Linux kernels before 2.6.9, this limit controlled the amount of
 224 memory that could be locked by a privileged process.
 225 Since Linux 2.6.9, no limits are placed on the amount of memory
 226 that a privileged process may lock, and this limit instead governs
 227 the amount of memory that an unprivileged process may lock.
 228 .TP
 229 .BR RLIMIT_MSGQUEUE " (Since Linux 2.6.8)"
 230 Specifies the limit on the number of bytes that can be allocated
 231 for POSIX message queues for the real user ID of the calling process.
 232 This limit is enforced for
 233 .BR mq_open (3).
 234 .\" FIXME there is no mq_open.3 page yet
 235 Each message queue that the user creates counts (until it is removed)
 236 against this limit according to the formula:
 237 .nf
 238
 239     bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
 240             attr.mq_maxmsg * attr.mq_msgsize
 241
 242 .fi
 243 where
 244 .I attr
 245 is the
 246 .I mq_attr
 247 structure specified as the fourth argument to
 248 .BR mq_open ().
 249
 250 The first addend in the formula, which includes
 251 .I "sizeof(struct msg_msg *)"
 252 (4 bytes on Linux/x86), ensures that the user cannot
 253 create an unlimited number of zero-length messages (such messages
 254 nevertheless each consume some system memory for bookkeeping overhead).
 255 .TP
 256 .BR RLIMIT_NICE " (since kernel 2.6.12, but see BUGS below)"
 257 Specifies a ceiling to which the process's nice value can be raised using
 258 .BR setpriority (2)
 259 or
 260 .BR nice (2).
 261 The actual ceiling for the nice value is calculated as
 262 .IR "20\ \-\ rlim_cur" .
 263 (This strangeness occurs because negative numbers cannot be specified
 264 as resource limit values, since they typically have special meanings.
 265 For example, RLIM_INFINITY typically is the same as \-1.)
 266 .TP
 267 .B RLIMIT_NOFILE
 268 Specifies a value one greater than the maximum file descriptor number
 269 that can be opened by this process.
 270 Attempts
 271 .RB ( open (),
 272 .BR pipe (),
 273 .BR dup (),
 274 etc.)
 275 to exceed this limit yield the error
 276 .BR EMFILE .
 277 .TP
 278 .B RLIMIT_NPROC
 279 The maximum number of processes that can be created for the real user
 280 ID of the calling process.
 281 Upon encountering this limit,
 282 .BR fork ()
 283 fails with the error
 284 .BR EAGAIN .
 285 .TP
 286 .B RLIMIT_RSS
 287 Specifies the limit (in pages) of the process's resident set
 288 (the number of virtual pages resident in RAM).
 289 This limit only has effect in Linux 2.4.x, x < 30, and there only
 290 affects calls to
 291 .BR madvise ()
 292 specifying
 293 .BR MADV_WILLNEED .
 294 .\" As at kernel 2.6.12, this limit still does nothing in 2.6 though
 295 .\" talk of making it do something has surfaced from time to time in LKML
 296 .\"       -- MTK, Jul 05
 297 .TP
 298 .BR RLIMIT_RTPRIO " (Since Linux 2.6.12, but see BUGS)"
 299 Specifies a ceiling on the real-time priority that may be set for
 300 this process using
 301 .BR sched_setscheduler (2)
 302 and
 303 .BR sched_setparam (2).
 304 .TP
 305 .BR RLIMIT_SIGPENDING " (Since Linux 2.6.8)"
 306 Specifies the limit on the number of signals
 307 that may be queued for the real user ID of the calling process.
 308 Both standard and real-time signals are counted for the purpose of
 309 checking this limit.
 310 However, the limit is only enforced for
 311 .BR sigqueue (2);
 312 it is always possible to use
 313 .BR kill (2)
 314 to queue one instance of any of the signals that are not already
 315 queued to the process.
 316 .\" This replaces the /proc/sys/kernel/rtsig-max system-wide limit
 317 .\" that was present in kernels <= 2.6.7.  MTK Dec 04
 318 .TP
 319 .B RLIMIT_STACK
 320 The maximum size of the process stack, in bytes.
 321 Upon reaching this limit, a
 322 .B SIGSEGV
 323 signal is generated.
 324 To handle this signal, a process must employ an alternate signal stack
 325 .RB ( sigaltstack (2)).
 326 .PP
 327 .B RLIMIT_OFILE
 328 is the BSD name for
 329 .BR RLIMIT_NOFILE .
 330 .SH "RETURN VALUE"
 331 On success, zero is returned.  On error, \-1 is returned, and
 332 .I errno
 333 is set appropriately.
 334 .SH ERRORS
 335 .TP
 336 .B EFAULT
 337 .I rlim
 338 points outside the accessible address space.
 339 .TP
 340 .B EINVAL
 341 .I resource
 342 is not valid;
 343 or, for
 344 .BR setrlimit ():
 345 .IR rlim->rlim_cur
 346 was greater than
 347 .IR rlim->rlim_max .
 348 .TP
 349 .B EPERM
 350 An unprivileged process tried to use \fBsetrlimit\fP() to
 351 increase a soft or hard limit above the current hard limit; the
 352 .B CAP_SYS_RESOURCE
 353 capability is required to do this.
 354 Or, the process tried to use \fBsetrlimit\fP() to increase
 355 the soft or hard RLIMIT_NOFILE limit above the current kernel
 356 maximum (NR_OPEN).
 357 .SH BUGS
 358 In older Linux kernels, the
 359 .B SIGXCPU
 360 and
 361 .B SIGKILL
 362 signals delivered when a process encountered the soft and hard
 363 .B RLIMIT_CPU
 364 limits were delivered one (CPU) second later than they should have been.
 365 This was fixed in kernel 2.6.8.
 366
 367 A kernel bug means that
 368 .B RLIMIT_RTPRIO
 369 does not work in kernel 2.6.12; the problem is fixed in kernel 2.6.13.
 370
 371 In kernel 2.6.12, there was an off-by-one mismatch
 372 between the priority ranges returned by
 373 .BR getpriority (2)
 374 and
 375 .BR RLIMIT_NICE .
 376 This had the effect that actual ceiling for the nice value
 377 was calculated as
 378 .IR "19\ \-\ rlim_cur" .
 379 This was fixed in kernel 2.6.13.
 380 .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=112256338703880&w=2
 381
 382 Kernels before 2.4.22 did not diagnose the error
 383 .B EINVAL
 384 for
 385 .BR setrlimit ()
 386 when
 387 .IR rlim->rlim_cur
 388 was greater than
 389 .IR rlim->rlim_max .
 390 .SH "CONFORMING TO"
 391 SVr4, 4.3BSD.
 392 .BR RLIMIT_MEMLOCK
 393 and
 394 .BR RLIMIT_NPROC
 395 derive from BSD and are not specified in POSIX.1-2001;
 396 they are present on the BSDs and Linux, but on few other implementations.
 397 .BR RLIMIT_RSS
 398 derives from BSD and is not specified in POSIX.1-2001;
 399 it is nevertheless present on most implementations.
 400 .BR RLIMIT_MSGQUEUE ,
 401 .BR RLIMIT_NICE ,
 402 .BR RLIMIT_RTPRIO ,
 403 and
 404 .B RLIMIT_SIGPENDING
 405 are Linux specific.
 406 .SH "SEE ALSO"
 407 .BR dup (2),
 408 .BR fcntl (2),
 409 .BR fork (2),
 410 .BR getrusage (2),
 411 .BR mlock (2),
 412 .BR mmap (2),
 413 .BR open (2),
 414 .BR quotactl (2),
 415 .BR sbrk (2),
 416 .BR shmctl (2),
 417 .BR sigqueue (2),
 418 .BR malloc (3),
 419 .BR ulimit (3),
 420 .BR capabilities (7),
 421 .BR signal (7)