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.  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 ar-
       bitrary 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 (ad-
              dress 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 expan-
              sion 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  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 fc-
              ntl(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 ar-
              gument 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  de-
              scriptor  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 re-
       source 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 at-

       |Interface                           | Attribute     | Value   |
       |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.
       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).

       Resource limits are per-process attributes that are shared  by  all  of
       the threads in a process.

       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 em-
       ploy 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, un-
       til  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  be-
       havior.   The  Linux-specific RLIMIT_RTTIME limit exhibits the same be-
       havior 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.

       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 re-
       source limit to a value larger than can be represented in a 32-bit  un-
       signed  long, then the glibc setrlimit() wrapper function silently con-
       verted the limit value to RLIM_INFINITY.  In other words, the requested
       resource limit setting was silently ignored.

       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 <sys/resource.h>

       #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \
                               } while (0)

       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);


       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-

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       description  of  the project, information about reporting bugs, and the
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