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

NAME
       getrlimit, setrlimit, prlimit - get/set resource limits

SYNOPSIS
       #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 struc‐
       ture:

           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 ex‐
              pansion 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  sig‐
              nal.   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 encoun‐
              tering 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  sig‐
              nal.   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 (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 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 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 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  num‐
              ber 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 calcu‐
              lated 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  de‐
              tails, 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 cur‐
              rent 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 be‐
       ing 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 to indicate the error.

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).

       β”Œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”¬β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”¬β”€β”€β”€β”€β”€β”€β”€β”€β”€β”
       β”‚Interface                                                                                                                             β”‚ Attribute     β”‚ Value   β”‚
       β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€
       β”‚getrlimit(), setrlimit(), prlimit()                                                                                                   β”‚ Thread safety β”‚ MT-Safe β”‚
       β””β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”˜

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 increas‐
       ing 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 applica‐
       tions 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 con‐
       formant;  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 getr‐
       limit()  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 offsetsβ€”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 ig‐
       nored.

       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), ca‐
       pabilities(7), cgroups(7), credentials(7), signal(7)

Linux                                                                          2021-03-22                                                                   GETRLIMIT(2)