GETRLIMIT(2)               Linux Programmer's Manual              GETRLIMIT(2)
NAME
       getrlimit, setrlimit - 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);

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
              which time it is sent SIGKILL.   (This  latter  point  describes
              Linux  2.2  through  2.6 behaviour.  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.)

       RLIMIT_DATA
              The  maximum  size  of  the  process's data segment (initialized
              data, uninitialized data, and heap).  This limit  affects  calls
              to  brk()  and  sbrk(),  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() truncate()) fails  with  the
              error EFBIG.

       RLIMIT_LOCKS (Early Linux 2.4 only)
              A  limit  on  the  combined  number of flock() locks and fcntl()
              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().

              The first addend in the formula,  which  includes  sizeof(struct
              msg_msg  *) (4 bytes on Linux/x86), 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 kernel 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
              strangeness  occurs because negative numbers cannot be specified
              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(),
              pipe(), dup(), etc.)  to  exceed  this  limit  yield  the  error
              EMFILE.

       RLIMIT_NPROC
              The  maximum  number of threads that can be created for the real
              user ID of the calling process.  Upon encountering  this  limit,
              fork() 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() 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_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)).

       RLIMIT_OFILE is the BSD name for RLIMIT_NOFILE.

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

ERRORS
       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).

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 kernel 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.

NOTES
       A child process created via fork(2) inherits its parents resource  lim-
       its.  Resource limits are preserved across execve(2).

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, and RLIMIT_SIGPENDING are Linux specific.

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)

Linux 2.6.13                      2005-09-20                      GETRLIMIT(2)