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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 && _FILE_OFFSET_BITS == 64

DESCRIPTION

       The  getrlimit()  and  setrlimit()  system  calls  get and set resource
       limits respectively.  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 only set 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) 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
              The maximum size of the process's virtual memory (address space)
              in bytes.  This limit  affects  calls  to  brk(2),  mmap(2)  and
              mremap(2),  which fail with the error ENOMEM upon exceeding this
              limit.  Also automatic stack expansion will fail (and generate 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
              Maximum size of core file.   When  0  no  core  dump  files  are
              created.  When nonzero, larger dumps are truncated to this size.

       RLIMIT_CPU
              CPU  time  limit  in seconds.  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
              The maximum size of  the  process's  data  segment  (initialized
              data,  uninitialized  data, and heap).  This limit affects calls
              to brk(2) and sbrk(2), which fail with  the  error  ENOMEM  upon
              encountering the soft limit of this resource.

       RLIMIT_FSIZE
              The maximum size 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)
              A limit on the combined number of flock(2)  locks  and  fcntl(2)
              leases that this process may establish.

       RLIMIT_MEMLOCK
              The  maximum  number  of bytes of memory that may be locked into
              RAM.  In effect this  limit  is  rounded  down  to  the  nearest
              multiple  of  the system page size.  This limit affects mlock(2)
              and 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)
              Specifies the 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:

                  bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
                          attr.mq_maxmsg * attr.mq_msgsize

              where  attr  is  the  mq_attr  structure specified as the fourth
              argument to mq_open(3).

              The first addend in the formula,  which  includes  sizeof(struct
              msg_msg *) (4 bytes on Linux/i386), 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)
              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.    (This
              strangeness  occurs 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.)

       RLIMIT_NOFILE
              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.)

       RLIMIT_NPROC
              The maximum number of processes (or, more  precisely  on  Linux,
              threads) that can be created for the real user ID of the calling
              process.  Upon encountering this limit, fork(2) fails  with  the
              error EAGAIN.

       RLIMIT_RSS
              Specifies  the  limit  (in  pages) of the process's resident set
              (the number of virtual pages resident in RAM).  This limit  only
              has  effect in Linux 2.4.x, x < 30, and there only affects calls
              to madvise(2) specifying MADV_WILLNEED.

       RLIMIT_RTPRIO (Since Linux 2.6.12, but see BUGS)
              Specifies a ceiling on the real-time priority that  may  be  set
              for     this    process    using    sched_setscheduler(2)    and
              sched_setparam(2).

       RLIMIT_RTTIME (Since Linux 2.6.25)
              Specifies 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.

       RLIMIT_SIGPENDING (Since Linux 2.6.8)
              Specifies the 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 only enforced 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
              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, 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.   Or,  the
              caller  tried to increase the hard RLIMIT_NOFILE limit above the
              current kernel maximum (NR_OPEN).  Or, 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.

CONFORMING TO

       getrlimit(), setrlimit(): SVr4, 4.3BSD, POSIX.1-2001.
       prlimit(): Linux-specific.

       RLIMIT_MEMLOCK  and  RLIMIT_NPROC derive from BSD and are not specified
       in POSIX.1-2001; they are present on the BSDs and  Linux,  but  on  few
       other   implementations.   RLIMIT_RSS  derives  from  BSD  and  is  not
       specified  in  POSIX.1-2001;  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).

       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.

       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().

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_FAILURE);
       }

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.

       Kernels before 2.4.22 did not diagnose the error EINVAL for setrlimit()
       when rlim->rlim_cur was greater than rlim->rlim_max.

SEE ALSO

       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), signal(7)

COLOPHON

       This page is part of release 3.35 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://man7.org/linux/man-pages/.