getrlimit

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



NAME
       getrlimit, setrlimit, prlimit - 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);

       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
       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 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
       setrlimit()).

       The resource argument must be one of:

       RLIMIT_AS
              This is the maximum size of the process's virtual memory (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 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.

       RLIMIT_CORE
              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.

       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).  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.

       RLIMIT_FSIZE
              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 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 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.

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

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

ATTRIBUTES
       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
       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
       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
       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.

       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 _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.

       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
       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)

       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=%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)
               errExit("prlimit-2");
           printf("New limits: soft=%jd; hard=%jd\n",
                   (intmax_t) old.rlim_cur, (intmax_t) old.rlim_max);

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       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
       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
       https://www.kernel.org/doc/man-pages/.



Linux                              2020-11-01                       GETRLIMIT(2)