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);

DESCRIPTION
       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-
       limit()):

           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()).

       resource 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 non-zero, 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

       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-
              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  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
              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(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.

       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).

RETURN VALUE
              process tried to use setrlimit() to increase the  soft  or  hard
              RLIMIT_NOFILE limit above the current kernel maximum (NR_OPEN).

CONFORMING TO
       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,
       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).

       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.

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 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),  sigqueue(2),  malloc(3), ulimit(3),
       core(5), capabilities(7), signal(7)

COLOPHON
       This page is part of release 3.23 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                             2008-10-06                      GETRLIMIT(2)
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