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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 limits 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 corresponding 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 capabil-
       ity) 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 setrlimit()).

       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 created.   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  processes	which continue to consume CPU time after reaching the soft limit.
	      Portable applications that need to catch this signal should perform an orderly ter-
	      mination 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 multiple 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  separately  from  the per-process memory locks established by mlock(2), mlock-
	      all(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 messages nevertheless each consume	some  system  memory  for
	      bookkeeping 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 setprior-
	      ity(2) or nice(2).  The  actual  ceiling	for  the  nice	value  is  calculated  as
	      20 - rlim_cur.   (This strangeness occurs because negative numbers cannot be speci-
	      fied as resource limit values, since they typically  have  special  meanings.   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_setparam(2).

       RLIMIT_RTTIME (Since Linux 2.6.25)
	      Specifies a limit (in microseconds) on the amount of CPU time that a process sched-
	      uled under a real-time scheduling policy may consume without making a blocking sys-
	      tem call.  For the purpose of this limit, each time a process makes a blocking sys-
	      tem 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 signal.  If the process
	      catches  or ignores this signal and continues 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 signal, a process must employ an
	      alternate signal stack (sigaltstack(2)).

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

   prlimit()
       The Linux-specific prlimit() system call combines and extends the functionality	of  setr-
       limit()	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 getrlimit().

       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 argu-
       ment is a not NULL, then a successful 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 target 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 setrlimit() 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  capa-
	      bility  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 specified in POSIX.1-2001; it is nevertheless present on  most
       implementations.    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 limits.  Resource  lim-
       its 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.

       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  encoun-
       tered  the soft and hard RLIMIT_CPU limits were delivered 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, setting 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), quo-
       tactl(2), sbrk(2), shmctl(2), malloc(3), sigqueue(3), ulimit(3), core(5), capabilities(7),
       signal(7)

COLOPHON
       This  page  is  part of release 3.53 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					    2013-02-11				     GETRLIMIT(2)
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