NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | BUGS | EXAMPLE | SEE ALSO | COLOPHON

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 respectively.  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
       corresponding 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) 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()).

       The resource argument must be one of:

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

       RLIMIT_CPU
              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.)

       RLIMIT_DATA
              This is 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
              This is 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)
              This is a limit on the combined number of flock(2) locks and
              fcntl(2) leases that this process may establish.

       RLIMIT_MEMLOCK
              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
              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)
              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_INFINITY typically is the same as -1.  For more detail on
              the nice value, see sched(7).

       RLIMIT_NOFILE
              This 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.)

              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
              details, see unix(7).

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

       RLIMIT_RSS
              This is a limit (in bytes) on the process's resident set (the
              number of virtual pages resident in RAM).  This limit has
              effect 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
              sched_setparam(2).

              For further details on real-time scheduling policies, see
              sched(7)

       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
              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.

              For further details on real-time scheduling policies, see
              sched(7)

       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.

       RLIMIT_STACK
              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
              (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).

   prlimit()
       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
       getrlimit().

       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
       limits 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
              rlim->rlim_max.

       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
              proc(5))

       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
       attributes(7).

       ┌────────────────────────────────────┬───────────────┬─────────┐
       │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_MSGQUEUE, RLIMIT_NICE, RLIMIT_RTPRIO, RLIMIT_RTTIME, and
       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).

       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
       encountered.

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

   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 versions before
       2.6.36, 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 _FILE_OFFSET_BITS=64).

       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.

       This problem was addressed in Linux 2.6.36 with two principal
       changes:

       *  the addition of a new kernel representation of resource limits
          that uses 64 bits, even on 32-bit platforms;

       *  the addition of the prlimit() system call, which employs 64-bit
          values for its resource limit arguments.

       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().

EXAMPLE         top

       The program below demonstrates the use of prlimit().

       #define _GNU_SOURCE
       #define _FILE_OFFSET_BITS 64
       #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)

       int
       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]);
               exit(EXIT_FAILURE);
           }

           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)
               errExit("prlimit-1");
           printf("Previous limits: soft=%lld; hard=%lld\n",
                   (long long) old.rlim_cur, (long long) old.rlim_max);

           /* Retrieve and display new CPU time limit */

           if (prlimit(pid, RLIMIT_CPU, NULL, &old) == -1)
               errExit("prlimit-2");
           printf("New limits: soft=%lld; hard=%lld\n",
                   (long long) old.rlim_cur, (long long) old.rlim_max);

           exit(EXIT_SUCCESS);
       }

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 4.11 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
       https://www.kernel.org/doc/man-pages/.

Linux                            2017-03-13                     GETRLIMIT(2)

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