Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


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


     getrlimit, setrlimit, prlimit - get/set resource limits


     #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


     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 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  setr-
     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 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
            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.
            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.)
            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.
            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.
            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
            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
            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.
            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-
            For  further  details  on  real-time  scheduling  policies,  see
     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
            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
     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
            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).
     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-
     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.


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


     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
     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
     allbox;  lbw35  lb lb l l l.  Interface Attribute Value T{ getrlimit(),
     setrlimit(), prlimit() T}   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.
     RLIMIT_SIGPENDING are Linux-specific.


     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().


     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
     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().


     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
     #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]);
         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)
         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)
         printf("New limits: soft=%lld; hard=%lld\n",
                 (long long) old.rlim_cur, (long long) old.rlim_max);
         exit(EXIT_SUCCESS); }


     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-


     This  page  is  part of release 4.16 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

Linux 2018-04-30 GETRLIMIT(2)

/data/webs/external/dokuwiki/data/pages/man/ugetrlimit.txt · Last modified: 2019/05/17 09:32 by

Was this page helpful?-11+1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki