setrlimit


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 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
       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

       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-
              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  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-
              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 only enforced 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)).

       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).
       #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);
       }

BUGS
       In  older Linux kernels, the SIGXCPU and SIGKILL signals delivered when
       a process encountered the soft and hard RLIMIT_CPU limits  were  deliv-
       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.

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

SEE ALSO
       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 3.35 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://man7.org/linux/man-pages/.



Linux                             2011-09-10                      GETRLIMIT(2)
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