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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.

       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)).

       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).

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  parents  resource
       limits.  Resource limits are preserved across execve(2).

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 3.01 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/.