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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
       setrlimit()):

           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 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
       setrlimit()).

       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
              created.  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 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 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
              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), 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
              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 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(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_setparam(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
              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
              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 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
              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).

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).

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
       limits.  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
       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 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 3.15 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/.