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GETRLIMIT(2)		   Linux Programmer's Manual		  GETRLIMIT(2)

       getrlimit, setrlimit - get/set resource limits

       #include <sys/time.h>
       #include <sys/resource.h>

       int getrlimit(int resource, struct rlimit *rlim);
       int setrlimit(int resource, const struct rlimit *rlim);

       getrlimit()  and	 setrlimit() get and set resource limits respectively.
       Each resource has an associated soft and hard limit, as defined by  the
       rlimit  structure  (the	rlim  argument	to  both getrlimit() and setr‐

	   struct rlimit {
	       rlim_t rlim_cur;	 /* Soft limit */
	       rlim_t rlim_max;	 /* Hard limit (ceiling for rlim_cur) */

       The soft limit is the value that the kernel  enforces  for  the	corre‐
       sponding	 resource.   The  hard	limit  acts  as a ceiling for the soft
       limit: an unprivileged process may only set its soft limit to  a	 value
       in  the range from 0 up to the hard limit, and (irreversibly) lower its
       hard  limit.   A	 privileged  process  (under  Linux:  one   with   the
       CAP_SYS_RESOURCE capability) may make arbitrary changes to either limit

       The value RLIM_INFINITY denotes no limit on a  resource	(both  in  the
       structure  returned by getrlimit() and in the structure passed to setr‐

       resource must be one of:

	      The maximum size of the process's virtual memory (address space)
	      in  bytes.   This	 limit	affects	 calls	to brk(2), mmap(2) and
	      mremap(2), which fail with the error ENOMEM upon exceeding  this
	      limit.  Also automatic stack expansion will fail (and generate a
	      SIGSEGV that kills the process if no alternate  stack  has  been
	      made  available via sigaltstack(2)).  Since the value is a long,
	      on machines with a 32-bit long either this limit is  at  most  2
	      GiB, or this resource is unlimited.

	      Maximum  size  of core file.  When 0 no core dump files are cre‐
	      ated.  When non-zero, larger dumps are truncated to this size.

	      CPU time limit in seconds.  When the process  reaches  the  soft
	      limit, it is sent a SIGXCPU signal.  The default action for this
	      signal is to terminate the process.  However, the signal can  be
	      caught,  and the handler can return control to the main program.
	      If the process continues to consume CPU time, it	will  be  sent
	      SIGXCPU  once  per  second  until	 the hard limit is reached, at
	      which time it is sent SIGKILL.   (This  latter  point  describes
	      Linux  2.2  through  2.6	behavior.  Implementations vary in how
	      they treat processes which continue to consume  CPU  time	 after
	      reaching	the  soft  limit.   Portable applications that need to
	      catch this signal should perform	an  orderly  termination  upon
	      first receipt of SIGXCPU.)

	      The  maximum  size  of  the  process's data segment (initialized
	      data, uninitialized data, and heap).  This limit	affects	 calls
	      to  brk(2)  and  sbrk(2),	 which fail with the error ENOMEM upon
	      encountering the soft limit of this resource.

	      The maximum size of files that the process may create.  Attempts
	      to  extend  a  file  beyond  this	 limit result in delivery of a
	      SIGXFSZ signal.  By default, this signal terminates  a  process,
	      but  a  process can catch this signal instead, in which case the
	      relevant system call (e.g., write(2),  truncate(2))  fails  with
	      the error EFBIG.

       RLIMIT_LOCKS (Early Linux 2.4 only)
	      A	 limit	on  the combined number of flock(2) locks and fcntl(2)
	      leases that this process may establish.

	      The maximum number of bytes of memory that may  be  locked  into
	      RAM.  In effect this limit is rounded down to the nearest multi‐
	      ple of the system page size.  This limit	affects	 mlock(2)  and
	      mlockall(2)  and	the mmap(2) MAP_LOCKED operation.  Since Linux
	      2.6.9 it also affects the shmctl(2) SHM_LOCK operation, where it
	      sets a maximum on the total bytes in shared memory segments (see
	      shmget(2)) that may be locked by the real user ID of the calling
	      process.	 The  shmctl(2) SHM_LOCK locks are accounted for sepa‐
	      rately  from  the	 per-process  memory  locks   established   by
	      mlock(2),	 mlockall(2),  and  mmap(2)  MAP_LOCKED; a process can
	      lock bytes up to this limit in each of these two categories.  In
	      Linux  kernels before 2.6.9, this limit controlled the amount of
	      memory that could be locked  by  a  privileged  process.	 Since
	      Linux 2.6.9, no limits are placed on the amount of memory that a
	      privileged process may lock, and this limit instead governs  the
	      amount of memory that an unprivileged process may lock.

       RLIMIT_MSGQUEUE (Since Linux 2.6.8)
	      Specifies the limit on the number of bytes that can be allocated
	      for POSIX message queues for the real user  ID  of  the  calling
	      process.	 This  limit is enforced for mq_open(3).  Each message
	      queue that the user creates counts (until it is removed) against
	      this limit according to the formula:

		  bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
			  attr.mq_maxmsg * attr.mq_msgsize

	      where  attr  is  the  mq_attr  structure specified as the fourth
	      argument to mq_open(3).

	      The first addend in the formula,	which  includes	 sizeof(struct
	      msg_msg *) (4 bytes on Linux/i386), ensures that the user cannot
	      create an unlimited number of zero-length	 messages  (such  mes‐
	      sages nevertheless each consume some system memory for bookkeep‐
	      ing overhead).

       RLIMIT_NICE (since Linux 2.6.12, but see BUGS below)
	      Specifies a ceiling to which the process's  nice	value  can  be
	      raised  using setpriority(2) or nice(2).	The actual ceiling for
	      the nice value is calculated as 20 - rlim_cur.   (This  strange‐
	      ness  occurs  because  negative  numbers	cannot be specified as
	      resource limit values, since they typically have	special	 mean‐
	      ings.  For example, RLIM_INFINITY typically is the same as -1.)

	      Specifies	 a  value one greater than the maximum file descriptor
	      number that can be opened by this process.   Attempts  (open(2),
	      pipe(2),	dup(2),	 etc.)	 to  exceed this limit yield the error
	      EMFILE.  (Historically, this limit  was  named  RLIMIT_OFILE  on

	      The  maximum  number  of processes (or, more precisely on Linux,
	      threads) that can be created for the real user ID of the calling
	      process.	 Upon  encountering this limit, fork(2) fails with the
	      error EAGAIN.

	      Specifies the limit (in pages) of	 the  process's	 resident  set
	      (the  number of virtual pages resident in RAM).  This limit only
	      has effect in Linux 2.4.x, x < 30, and there only affects	 calls
	      to madvise(2) specifying MADV_WILLNEED.

       RLIMIT_RTPRIO (Since Linux 2.6.12, but see BUGS)
	      Specifies	 a  ceiling  on the real-time priority that may be set
	      for this	process	 using	sched_setscheduler(2)  and  sched_set‐

       RLIMIT_RTTIME (Since Linux 2.6.25)
	      Specifies	 a  limit  on  the  amount  of CPU time that a process
	      scheduled under a real-time scheduling policy may consume	 with‐
	      out  making  a  blocking	system	call.  For the purpose of this
	      limit, each time a process makes a  blocking  system  call,  the
	      count  of	 its consumed CPU time is reset to zero.  The CPU time
	      count is not reset if the process continues trying  to  use  the
	      CPU  but	is  preempted,	its  time  slice  expires, or it calls

	      Upon reaching the soft limit, the process is sent a SIGXCPU sig‐
	      nal.   If the process catches or ignores this signal and contin‐
	      ues consuming CPU time, then SIGXCPU will be generated once each
	      second  until  the  hard	limit  is  reached, at which point the
	      process is sent a SIGKILL signal.

	      The intended use of this limit is to stop	 a  runaway  real-time
	      process from locking up the system.

       RLIMIT_SIGPENDING (Since Linux 2.6.8)
	      Specifies	 the limit on the number of signals that may be queued
	      for the real user ID of the calling process.  Both standard  and
	      real-time	 signals  are counted for the purpose of checking this
	      limit.  However, the limit is only enforced for sigqueue(2);  it
	      is  always  possible to use kill(2) to queue one instance of any
	      of the signals that are not already queued to the process.

	      The maximum size of the process stack, in bytes.	Upon  reaching
	      this  limit, a SIGSEGV signal is generated.  To handle this sig‐
	      nal, a process must employ an alternate  signal  stack  (sigalt‐

	      Since  Linux  2.6.23,  this  limit also determines the amount of
	      space used for the process's command-line arguments and environ‐
	      ment variables; for details, see execve(2).

       On  success,  zero is returned.	On error, -1 is returned, and errno is
       set appropriately.

       EFAULT rlim points outside the accessible address space.

       EINVAL resource is not valid; or, for setrlimit():  rlim->rlim_cur  was
	      greater than rlim->rlim_max.

       EPERM  An  unprivileged	process tried to use setrlimit() to increase a
	      soft  or	hard  limit  above  the	 current   hard	  limit;   the
	      CAP_SYS_RESOURCE	capability  is	required  to do this.  Or, the
	      process tried to use setrlimit() to increase the	soft  or  hard
	      RLIMIT_NOFILE limit above the current kernel maximum (NR_OPEN).

       SVr4,  4.3BSD,  POSIX.1-2001.   RLIMIT_MEMLOCK  and RLIMIT_NPROC derive
       from BSD and are not specified in POSIX.1-2001; they are present on the
       BSDs  and  Linux, but on few other implementations.  RLIMIT_RSS derives
       from BSD and is not  specified  in  POSIX.1-2001;  it  is  nevertheless
       present	 on   most   implementations.	RLIMIT_MSGQUEUE,  RLIMIT_NICE,

       A child process created via fork(2) inherits its parent's resource lim‐
       its.  Resource limits are preserved across execve(2).

       One  can set the resource limits of the shell using the built-in ulimit
       command (limit in csh(1)).  The shell's resource limits	are  inherited
       by the processes that it creates to execute commands.

       In  older Linux kernels, the SIGXCPU and SIGKILL signals delivered when
       a process encountered the soft and hard RLIMIT_CPU limits  were	deliv‐
       ered one (CPU) second later than they should have been.	This was fixed
       in kernel 2.6.8.

       In 2.6.x kernels before 2.6.17, a RLIMIT_CPU  limit  of	0  is  wrongly
       treated	as  "no limit" (like RLIM_INFINITY).  Since Linux 2.6.17, set‐
       ting a limit of 0 does have an effect, but is  actually	treated	 as  a
       limit of 1 second.

       A  kernel  bug means that RLIMIT_RTPRIO does not work in kernel 2.6.12;
       the problem is fixed in kernel 2.6.13.

       In kernel 2.6.12, there was an off-by-one mismatch between the priority
       ranges returned by getpriority(2) and RLIMIT_NICE.  This had the effect
       that actual ceiling for the nice value was calculated as 19 - rlim_cur.
       This was fixed in kernel 2.6.13.

       Kernels before 2.4.22 did not diagnose the error EINVAL for setrlimit()
       when rlim->rlim_cur was greater than rlim->rlim_max.

       dup(2), fcntl(2), fork(2), getrusage(2),	 mlock(2),  mmap(2),  open(2),
       quotactl(2),  sbrk(2),  shmctl(2),  sigqueue(2),	 malloc(3), ulimit(3),
       core(5), capabilities(7), signal(7)

       This page is part of release 3.22 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at

Linux				  2008-10-06			  GETRLIMIT(2)

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