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().

EXAMPLE
       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
       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 5.01 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                             2018-04-30                      GETRLIMIT(2)