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

NAME
       getrlimit, setrlimit, prlimit - get/set resource limits

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

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

       int prlimit(pid_t pid, int resource, const struct rlimit *new_limit,
		   struct rlimit *old_limit);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       prlimit(): _GNU_SOURCE && _FILE_OFFSET_BITS == 64

DESCRIPTION
       The  getrlimit() and setrlimit() system calls get and set resource lim‐
       its respectively.  Each resource has an associated soft and hard limit,
       as defined by the rlimit structure:

	   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 set only 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
       value.

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

       The resource argument must be one of:

       RLIMIT_AS
	      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.

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

       RLIMIT_CPU
	      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 behavior.  Implementations vary in	how  they  treat  pro‐
	      cesses  which  continue  to  consume CPU time after reaching the
	      soft limit.  Portable applications that need to catch this  sig‐
	      nal  should perform an orderly termination upon first receipt of
	      SIGXCPU.)

       RLIMIT_DATA
	      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.

       RLIMIT_FSIZE
	      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.

       RLIMIT_MEMLOCK
	      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.)

       RLIMIT_NOFILE
	      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
	      BSD.)

       RLIMIT_NPROC
	      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.

       RLIMIT_RSS
	      Specifies	 the  limit  (in  pages) of the process's resident set
	      (the number of virtual pages resident in RAM).  This  limit  has
	      effect only in Linux 2.4.x, x < 30, and there affects only 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‐
	      param(2).

       RLIMIT_RTTIME (since Linux 2.6.25)
	      Specifies a limit (in microseconds) on the amount	 of  CPU  time
	      that a process scheduled under a real-time scheduling policy may
	      consume without 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
	      sched_yield(2).

	      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 enforced only for sigqueue(3); 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.

       RLIMIT_STACK
	      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‐
	      stack(2)).

	      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).

   prlimit()
       The Linux-specific prlimit() system call combines and extends the func‐
       tionality  of  setrlimit() and getrlimit().  It can be used to both set
       and get the resource limits of an arbitrary process.

       The resource argument has the same meaning as for setrlimit() and getr‐
       limit().

       If  the	new_limit argument is a not NULL, then the rlimit structure to
       which it points is used to set new values for the soft and hard	limits
       for resource.  If the old_limit argument is a not NULL, then a success‐
       ful call to prlimit() places the previous  soft	and  hard  limits  for
       resource in the rlimit structure pointed to by old_limit.

       The  pid	 argument specifies the ID of the process on which the call is
       to operate.  If pid is 0, then the call applies to the calling process.
       To  set or get the resources of a process other than itself, the caller
       must have the CAP_SYS_RESOURCE capability, or the real, effective,  and
       saved set user IDs of the target process must match the real user ID of
       the caller and the real, effective, and saved set group IDs of the tar‐
       get process must match the real group ID of the caller.

RETURN VALUE
       On success, these system calls return 0.	 On error, -1 is returned, and
       errno is set appropriately.

ERRORS
       EFAULT A pointer argument points to a location outside  the  accessible
	      address space.

       EINVAL The  value  specified  in	 resource  is not valid; or, for setr‐
	      limit()  or   prlimit():	 rlim->rlim_cur	  was	greater	  than
	      rlim->rlim_max.

       EPERM  An  unprivileged	process	 tried	to  raise  the hard limit; the
	      CAP_SYS_RESOURCE capability is required to  do  this.   Or,  the
	      caller  tried to increase the hard RLIMIT_NOFILE limit above the
	      current kernel maximum (NR_OPEN).	 Or, the calling  process  did
	      not  have	 permission to set limits for the process specified by
	      pid.

       ESRCH  Could not find a process with the ID specified in pid.

VERSIONS
       The prlimit() system call is available  since  Linux  2.6.36.   Library
       support is available since glibc 2.13.

CONFORMING TO
       getrlimit(), setrlimit(): SVr4, 4.3BSD, POSIX.1-2001.
       prlimit(): Linux-specific.

       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 speci‐
       fied in POSIX.1-2001; it is nevertheless present	 on  most  implementa‐
       tions.  RLIMIT_MSGQUEUE, RLIMIT_NICE, RLIMIT_RTPRIO, RLIMIT_RTTIME, and
       RLIMIT_SIGPENDING are Linux-specific.

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

       Lowering the soft limit for a resource below the process's current con‐
       sumption of that resource will succeed (but will	 prevent  the  process
       from further increasing its consumption of the resource).

       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.

       Since Linux 2.6.24, the resource limits of any process can be inspected
       via /proc/[pid]/limits; see proc(5).

       Ancient systems provided a vlimit() function with a similar purpose  to
       setrlimit().  For backward compatibility, glibc also provides vlimit().
       All new applications should be written using setrlimit().

BUGS
       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   the  actual  ceiling  for	 the  nice  value  was	calculated  as
       19 - rlim_cur.  This was fixed in kernel 2.6.13.

       Since Linux 2.6.12, if a process reaches its soft RLIMIT_CPU limit  and
       has  a handler installed for SIGXCPU, then, in addition to invoking the
       signal handler, the kernel increases the	 soft  limit  by  one  second.
       This  behavior  repeats	if  the process continues to consume CPU time,
       until the hard limit is reached, at which point the process is  killed.
       Other  implementations  do not change the RLIMIT_CPU soft limit in this
       manner, and the Linux behavior is probably  not	standards  conformant;
       portable	 applications  should  avoid  relying  on  this Linux-specific
       behavior.  The Linux-specific RLIMIT_RTTIME  limit  exhibits  the  same
       behavior when the soft limit is encountered.

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

EXAMPLE
       The program below demonstrates the use of prlimit().

       #define _GNU_SOURCE
       #define _FILE_OFFSET_BITS 64
       #include <stdio.h>
       #include <time.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <sys/resource.h>

       #define errExit(msg)	do { perror(msg); exit(EXIT_FAILURE); \
			       } while (0)

       int
       main(int argc, char *argv[])
       {
	   struct rlimit old, new;
	   struct rlimit *newp;
	   pid_t pid;

	   if (!(argc == 2 || argc == 4)) {
	       fprintf(stderr, "Usage: %s <pid> [<new-soft-limit> "
		       "<new-hard-limit>]\n", argv[0]);
	       exit(EXIT_FAILURE);
	   }

	   pid = atoi(argv[1]);	       /* PID of target process */

	   newp = NULL;
	   if (argc == 4) {
	       new.rlim_cur = atoi(argv[2]);
	       new.rlim_max = atoi(argv[3]);
	       newp = &new;
	   }

	   /* Set CPU time limit of target process; retrieve and display
	      previous limit */

	   if (prlimit(pid, RLIMIT_CPU, newp, &old) == -1)
	       errExit("prlimit-1");
	   printf("Previous limits: soft=%lld; hard=%lld\n",
		   (long long) old.rlim_cur, (long long) old.rlim_max);

	   /* Retrieve and display new CPU time limit */

	   if (prlimit(pid, RLIMIT_CPU, NULL, &old) == -1)
	       errExit("prlimit-2");
	   printf("New limits: soft=%lld; hard=%lld\n",
		   (long long) old.rlim_cur, (long long) old.rlim_max);

	   exit(EXIT_FAILURE);
       }

SEE ALSO
       prlimit(1), dup(2), fcntl(2), fork(2), getrusage(2), mlock(2), mmap(2),
       open(2),	  quotactl(2),	sbrk(2),  shmctl(2),  malloc(3),  sigqueue(3),
       ulimit(3), core(5), capabilities(7), signal(7)

COLOPHON
       This page is part of release 3.63 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux				  2014-01-22			  GETRLIMIT(2)
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