prlimit

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 lim-
       its 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 corre-
       sponding 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) 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  setr-
       limit()).

       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 sigalt-
              stack(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 cre-
              ated.  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 behav-
              ior.  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 per-
              form an orderly termination upon first receipt of SIGXCPU.)

       RLIMIT_DATA
              This is the maximum size of the process's data segment (initial-
              ized data, uninitialized data, and heap).  The limit  is  speci-
              fied  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  termi-
              nates a process, but a process can catch this signal instead, in
              which case the  relevant  system  call  (e.g.,  write(2),  trun-
              cate(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  mes-
              sages nevertheless each consume some system memory for bookkeep-
              ing 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  typi-
              cally  have  special meanings.  For example, RLIM_INFINITY typi-
              cally 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 pro-
              cesses, 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  pre-
              cisely  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_set-
              param(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 con-
              sume  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 sig-
              nal.   If the process catches or ignores this signal and contin-
              ues 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 environ-
              ment variables; for details, see execve(2).

   prlimit()
       The Linux-specific prlimit() system call combines and extends the func-
       tionality  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 getr-
       limit().

       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 success-
       ful 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, effec-
       tive, 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  setr-
              limit()   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 lim-
       its.  Resource limits are preserved across execve(2).

       Lowering the soft limit for a resource below the process's current con-
       sumption 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 func-
       tions  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  deliv-
       ered 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, set-
       ting 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.

   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 versions before 2.6.36, the  ker-
       nel  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.

       This problem was addressed in Linux 2.6.36 with two principal changes:

       *  the  addition of a new kernel representation of resource limits that
          uses 64 bits, even on 32-bit platforms;

       *  the addition of the prlimit() system call, which employs 64-bit val-
          ues for its resource limit arguments.

       Since  version  2.13,  glibc  works around the limitations of the getr-
       limit() 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), sig-
       nal(7)

COLOPHON
       This page is part of release 4.15 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                             2017-09-15                      GETRLIMIT(2)
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