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       getrlimit, setrlimit, prlimit - get/set resource limits


       Standard C library (libc, -lc)


       #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 *_Nullable new_limit,
                   struct rlimit *_Nullable old_limit);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):



       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

       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:

              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.

              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  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.)

              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 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 Linux 2.4.24)
              This  is  a limit on the combined number of flock(2) locks and fcntl(2) leases that
              this process may establish.

              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.

              Before Linux 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

              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).

              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, or run with real user ID 0.

              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.

              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

       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 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  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.


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


       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.


       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).

       │InterfaceAttributeValue   │
       │getrlimit(), setrlimit(), prlimit()                            │ Thread safety │ MT-Safe │


       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.


       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

       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 glibc 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

       The  name  of  the  glibc  wrapper  function  is  prlimit(); the underlying system call is


       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 Linux 2.6.8.

       In Linux 2.6.x kernels before Linux 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 Linux 2.6.12; the problem is  fixed
       in Linux 2.6.13.

       In  Linux 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 Linux 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 Linux 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 glibc 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 <err.h>
       #include <stdint.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <sys/resource.h>
       #include <time.h>

       main(int argc, char *argv[])
           pid_t          pid;
           struct rlimit  old, new;
           struct rlimit  *newp;

           if (!(argc == 2 || argc == 4)) {
               fprintf(stderr, "Usage: %s <pid> [<new-soft-limit> "
                       "<new-hard-limit>]\n", argv[0]);

           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)
               err(EXIT_FAILURE, "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)
               err(EXIT_FAILURE, "prlimit-2");
           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)