getrlimit(2) — Linux manual page


GETRLIMIT(2)              Linux Programmer's Manual             GETRLIMIT(2)

NAME         top

       getrlimit, setrlimit, prlimit - get/set resource limits

SYNOPSIS         top

       #include <sys/time.h>
       #include <sys/resource.h>

       int getrlimit(int resource, struct rlimit *rlim);
       int setrlimit(int resource, const struct rlimit *rlim);

       int prlimit(pid_t pid, int resource, const struct rlimit *new_limit,
                   struct rlimit *old_limit);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       prlimit(): _GNU_SOURCE

DESCRIPTION         top

       The getrlimit() and setrlimit() system calls get and set resource
       limits.  Each resource has an associated soft and hard limit, as
       defined by the rlimit structure:

           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 set only 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 in the initial user namespace) 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

       The resource argument must be one of:

              This is the maximum size of the process's virtual memory (ad‐
              dress space).  The limit is specified in bytes, and is rounded
              down to the system page size.  This limit affects calls to
              brk(2), mmap(2), and mremap(2), which fail with the error
              ENOMEM upon exceeding this limit.  In addition, automatic
              stack expansion fails (and generates 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 re‐
              source is unlimited.

              This is the maximum size of a core file (see core(5)) in bytes
              that the process may dump.  When 0 no core dump files are cre‐
              ated.  When nonzero, larger dumps are truncated to this size.

              This is a limit, in seconds, on the amount of CPU time that
              the process can consume.  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 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.)

              This is the maximum size of the process's data segment (ini‐
              tialized data, uninitialized data, and heap).  The limit is
              specified in bytes, and is rounded down to the system page
              size.  This limit affects calls to brk(2), sbrk(2), and (since
              Linux 4.7) mmap(2), which fail with the error ENOMEM upon en‐
              countering the soft limit of this resource.

              This is the maximum size in bytes of files that the process
              may create.  Attempts to extend a file beyond this limit re‐
              sult in delivery of a SIGXFSZ signal.  By default, this signal
              terminates a process, but a process can catch this signal in‐
              stead, 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)
              This is a limit on the combined number of flock(2) locks and
              fcntl(2) leases that this process may establish.

              This is the maximum number of bytes of memory that may be
              locked into RAM.  This limit is in effect rounded down to the
              nearest multiple of the system page size.  This limit affects
              mlock(2), mlockall(2), and the mmap(2) MAP_LOCKED operation.
              Since Linux 2.6.9, it also affects the shmctl(2) SHM_LOCK op‐
              eration, 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

              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 mem‐
              ory that a privileged process may lock, and this limit instead
              governs the amount of memory that an unprivileged process may

       RLIMIT_MSGQUEUE (since Linux 2.6.8)
              This is a 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:

                  Since Linux 3.5:

                      bytes = attr.mq_maxmsg * sizeof(struct msg_msg) +
                              min(attr.mq_maxmsg, MQ_PRIO_MAX) *
                                    sizeof(struct posix_msg_tree_node)+
                                              /* For overhead */
                              attr.mq_maxmsg * attr.mq_msgsize;
                                              /* For message data */

                  Linux 3.4 and earlier:

                      bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
                                              /* For overhead */
                              attr.mq_maxmsg * attr.mq_msgsize;
                                              /* For message data */

              where attr is the mq_attr structure specified as the fourth
              argument to mq_open(3), and the msg_msg and
              posix_msg_tree_node structures are kernel-internal structures.

              The "overhead" addend in the formula accounts for overhead
              bytes required by the implementation and 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)
              This 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.  The useful
              range for this limit is thus from 1 (corresponding to a nice
              value of 19) to 40 (corresponding to a nice value of -20).
              This unusual choice of range was necessary because negative
              numbers cannot be specified as resource limit values, since
              they typically have special meanings.  For example, RLIM_IN‐
              FINITY typically is the same as -1.  For more detail on the
              nice value, see sched(7).

              This specifies a value one greater than the maximum file de‐
              scriptor 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.)

              Since Linux 4.5, this limit also defines the maximum number of
              file descriptors that an unprivileged process (one without the
              CAP_SYS_RESOURCE capability) may have "in flight" to other
              processes, by being passed across UNIX domain sockets.  This
              limit applies to the sendmsg(2) system call.  For further de‐
              tails, see unix(7).

              This is a limit on the number of extant process (or, more pre‐
              cisely on Linux, threads) for the real user ID of the calling
              process.  So long as the current number of processes belonging
              to this process's real user ID is greater than or equal to
              this limit, fork(2) fails with the error EAGAIN.

              The RLIMIT_NPROC limit is not enforced for processes that have
              either the CAP_SYS_ADMIN or the CAP_SYS_RESOURCE capability.

              This is a limit (in bytes) on the process's resident set (the
              number of virtual pages resident in RAM).  This limit has ef‐
              fect only in Linux 2.4.x, x < 30, and there affects only calls
              to madvise(2) specifying MADV_WILLNEED.

       RLIMIT_RTPRIO (since Linux 2.6.12, but see BUGS)
              This specifies a ceiling on the real-time priority that may be
              set for this process using sched_setscheduler(2) and

              For further details on real-time scheduling policies, see

       RLIMIT_RTTIME (since Linux 2.6.25)
              This is a limit (in microseconds) 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 contin‐
              ues trying to use the CPU but is preempted, its time slice ex‐
              pires, 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.

              For further details on real-time scheduling policies, see

       RLIMIT_SIGPENDING (since Linux 2.6.8)
              This is a 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 enforced only for
              sigqueue(3); 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.

              This is 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

              Since Linux 2.6.23, this limit also determines the amount of
              space used for the process's command-line arguments and envi‐
              ronment variables; for details, see execve(2).

       The Linux-specific prlimit() system call combines and extends the
       functionality of setrlimit() and getrlimit().  It can be used to both
       set and get the resource limits of an arbitrary process.

       The resource argument has the same meaning as for setrlimit() and

       If the new_limit argument is a not NULL, then the rlimit structure to
       which it points is used to set new values for the soft and hard lim‐
       its for resource.  If the old_limit argument is a not NULL, then a
       successful call to prlimit() places the previous soft and hard limits
       for resource in the rlimit structure pointed to by old_limit.

       The pid argument specifies the ID of the process on which the call is
       to operate.  If pid is 0, then the call applies to the calling
       process.  To set or get the resources of a process other than itself,
       the caller must have the CAP_SYS_RESOURCE capability in the user
       namespace of the process whose resource limits are being changed, or
       the real, effective, and saved set user IDs of the target process
       must match the real user ID of the caller and the real, effective,
       and saved set group IDs of the target process must match the real
       group ID of the caller.

RETURN VALUE         top

       On success, these system calls return 0.  On error, -1 is returned,
       and errno is set appropriately.

ERRORS         top

       EFAULT A pointer argument points to a location outside the accessible
              address space.

       EINVAL The value specified in resource is not valid; or, for
              setrlimit() or prlimit(): rlim->rlim_cur was greater than

       EPERM  An unprivileged process tried to raise the hard limit; the
              CAP_SYS_RESOURCE capability is required to do this.

       EPERM  The caller tried to increase the hard RLIMIT_NOFILE limit
              above the maximum defined by /proc/sys/fs/nr_open (see

       EPERM  (prlimit()) The calling process did not have permission to set
              limits for the process specified by pid.

       ESRCH  Could not find a process with the ID specified in pid.

VERSIONS         top

       The prlimit() system call is available since Linux 2.6.36.  Library
       support is available since glibc 2.13.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface                           Attribute     Value   │
       │getrlimit(), setrlimit(), prlimit() │ Thread safety │ MT-Safe │

CONFORMING TO         top

       getrlimit(), setrlimit(): POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

       prlimit(): Linux-specific.

       RLIMIT_MEMLOCK and RLIMIT_NPROC derive from BSD and are not specified
       in POSIX.1; 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; it is nevertheless present on most implementations.
       RLIMIT_SIGPENDING are Linux-specific.

NOTES         top

       A child process created via fork(2) inherits its parent's resource
       limits.  Resource limits are preserved across execve(2).

       Resource limits are per-process attributes that are shared by all of
       the threads in a process.

       Lowering the soft limit for a resource below the process's current
       consumption of that resource will succeed (but will prevent the
       process from further increasing its consumption of the resource).

       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.

       Since Linux 2.6.24, the resource limits of any process can be
       inspected via /proc/[pid]/limits; see proc(5).

       Ancient systems provided a vlimit() function with a similar purpose
       to setrlimit().  For backward compatibility, glibc also provides
       vlimit().  All new applications should be written using setrlimit().

   C library/kernel ABI differences
       Since version 2.13, the glibc getrlimit() and setrlimit() wrapper
       functions no longer invoke the corresponding system calls, but
       instead employ prlimit(), for the reasons described in BUGS.

       The name of the glibc wrapper function is prlimit(); the underlying
       system call is prlimit64().

BUGS         top

       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 the actual ceiling for the nice value was calculated
       as 19 - rlim_cur.  This was fixed in kernel 2.6.13.

       Since Linux 2.6.12, if a process reaches its soft RLIMIT_CPU limit
       and has a handler installed for SIGXCPU, then, in addition to
       invoking the signal handler, the kernel increases the soft limit by
       one second.  This behavior repeats if the process continues to
       consume CPU time, until the hard limit is reached, at which point the
       process is killed.  Other implementations do not change the
       RLIMIT_CPU soft limit in this manner, and the Linux behavior is
       probably not standards conformant; portable applications should avoid
       relying on this Linux-specific behavior.  The Linux-specific
       RLIMIT_RTTIME limit exhibits the same behavior when the soft limit is

       Kernels before 2.4.22 did not diagnose the error EINVAL for
       setrlimit() when rlim->rlim_cur was greater than rlim->rlim_max.

       Linux doesn't return an error when an attempt to set RLIMIT_CPU has
       failed, for compatibility reasons.

   Representation of "large" resource limit values on 32-bit platforms
       The glibc getrlimit() and setrlimit() wrapper functions use a 64-bit
       rlim_t data type, even on 32-bit platforms.  However, the rlim_t data
       type used in the getrlimit() and setrlimit() system calls is a
       (32-bit) unsigned long.  Furthermore, in Linux, the kernel represents
       resource limits on 32-bit platforms as unsigned long.  However, a
       32-bit data type is not wide enough.  The most pertinent limit here
       is RLIMIT_FSIZE, which specifies the maximum size to which a file can
       grow: to be useful, this limit must be represented using a type that
       is as wide as the type used to represent file offsets—that is, as
       wide as a 64-bit off_t (assuming a program compiled with

       To work around this kernel limitation, if a program tried to set a
       resource limit to a value larger than can be represented in a 32-bit
       unsigned long, then the glibc setrlimit() wrapper function silently
       converted the limit value to RLIM_INFINITY.  In other words, the
       requested resource limit setting was silently ignored.

       Since version 2.13, glibc works around the limitations of the
       getrlimit() and setrlimit() system calls by implementing setrlimit()
       and getrlimit() as wrapper functions that call prlimit().

EXAMPLES         top

       The program below demonstrates the use of prlimit().

       #define _GNU_SOURCE
       #define _FILE_OFFSET_BITS 64
       #include <stdint.h>
       #include <stdio.h>
       #include <time.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <sys/resource.h>

       #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \
                               } while (0)

       main(int argc, char *argv[])
           struct rlimit old, new;
           struct rlimit *newp;
           pid_t pid;

           if (!(argc == 2 || argc == 4)) {
               fprintf(stderr, "Usage: %s <pid> [<new-soft-limit> "
                       "<new-hard-limit>]\n", argv[0]);

           pid = atoi(argv[1]);        /* PID of target process */

           newp = NULL;
           if (argc == 4) {
               new.rlim_cur = atoi(argv[2]);
               new.rlim_max = atoi(argv[3]);
               newp = &new;

           /* Set CPU time limit of target process; retrieve and display
              previous limit */

           if (prlimit(pid, RLIMIT_CPU, newp, &old) == -1)
           printf("Previous limits: soft=%jd; hard=%jd\n",
                   (intmax_t) old.rlim_cur, (intmax_t) old.rlim_max);

           /* Retrieve and display new CPU time limit */

           if (prlimit(pid, RLIMIT_CPU, NULL, &old) == -1)
           printf("New limits: soft=%jd; hard=%jd\n",
                   (intmax_t) old.rlim_cur, (intmax_t) old.rlim_max);


SEE ALSO         top

       prlimit(1), dup(2), fcntl(2), fork(2), getrusage(2), mlock(2),
       mmap(2), open(2), quotactl(2), sbrk(2), shmctl(2), malloc(3),
       sigqueue(3), ulimit(3), core(5), capabilities(7), cgroups(7),
       credentials(7), signal(7)

COLOPHON         top

       This page is part of release 5.09 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2020-11-01                     GETRLIMIT(2)

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