xenial (2) getrlimit.2.gz

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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

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 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 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 a core file (see core(5)).  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:

                  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)
              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.  This limit is not enforced for processes  that  have  either  the  CAP_SYS_ADMIN  or  the
              CAP_SYS_RESOURCE capability.

       RLIMIT_RSS
              Specifies the limit (in bytes) of 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)
              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 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
              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.

       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).

       ┌────────────────────────────────────┬───────────────┬─────────┐
       │InterfaceAttributeValue   │
       ├────────────────────────────────────┼───────────────┼─────────┤
       │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).

       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 call 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.

   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  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.

       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  values  for  its  resource  limit
          arguments.

       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_FAILURE);
       }

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), signal(7)

COLOPHON

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       information  about  reporting  bugs,  and  the  latest  version  of  this   page,   can   be   found   at
       http://www.kernel.org/doc/man-pages/.