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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 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 auto-
              matic 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 neverthe-
              less 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 mean-
              ings.  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  pro-
              cess.  Attempts (open(2), pipe(2), dup(2), etc.)  to exceed this limit yield the error EMFILE.  (Histor-
              ically, 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_setsched-
              uler(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 pro-
              cess.  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 gener-
              ated.  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 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-10-06                      GETRLIMIT(2)