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          getrlimit, setrlimit, prlimit - get/set resource limits

          #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
                      struct rlimit *old_limit);

     Feature Test Macro Requirements for glibc (see

          prlimit(): _GNU_SOURCE

          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
          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 privi-
          leged 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 struc-
          ture passed to setrlimit()).

          The resource argument must be one of:

               This is the maximum size of the process's virtual mem-
               ory (address 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

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               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 resource 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 created.  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 pro-
               cess.  However, the signal can be caught, and the han-
               dler 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 lat-
               ter point describes Linux behavior.  Implementations
               vary in how they treat processes which continue to con-
               sume CPU time after reaching the soft limit.  Portable
               applications that need to catch this signal should per-
               form an orderly termination upon first receipt of

               This is the maximum size of the process's data segment
               (initialized 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 encountering 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 result in delivery of a SIGXFSZ signal.  By
               default, this signal terminates a process, but a pro-
               cess 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 (Linux 2.4.0 to 2.4.24)
               This is a limit on the combined number of flock(2)
               locks and fcntl(2) leases that this process may estab-

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               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 seg-
               ments (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 privi-
               leged 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 mem-
               ory 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 accord-
               ing 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

               The "overhead" addend in the formula accounts for

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               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 over-

          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).

               This 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.  (Histori-
               cally, 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

               This is a limit on the number of extant process (or,
               more precisely 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 effect only in Linux 2.4.x, x < 30, and
               there affects only calls to madvise(2) specifying

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          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.

               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

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          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 pro-
          cess 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.

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

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

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

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

               The caller tried to increase the hard RLIMIT_NOFILE
               limit above the maximum defined by /proc/sys/fs/nr_open
               (see proc(5))

               (prlimit()) The calling process did not have permission

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               to set limits for the process specified by pid.

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

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

          For an explanation of the terms used in this section, see
          attributes(7).  allbox; lbw35 lb lb l l l.
          Interface Attribute Value T{ getrlimit(), setrlimit(),
          prlimit() T}   Thread safety  MT-Safe

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

          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_SIGPENDING are Linux-specific.

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

          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 cre-
          ates 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

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          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().

          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 ker-
          nel 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 proba-
          bly 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

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

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        Representation of "large" resource limit values
          The glibc getrlimit() and setrlimit() wrapper functions use
          a 64-bit rlim_t data type, even on 32-bit platforms.  How-
          ever, the rlim_t data type used in the getrlimit() and
          setrlimit() system calls is a (32-bit) unsigned long. Fur-
          thermore, 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 _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 repre-
          sented 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

          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]);

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              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);


          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)

          This page is part of release 5.10 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

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