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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 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 setrlimit()).

       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  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
              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 created.  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 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
              This  is  the  maximum  size  of  the  process's  data  segment  (initialized data,
              uninitialized data, and heap).  The limit is specified 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  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)
              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  messages  nevertheless each consume some system memory for
              bookkeeping 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 typically have special meanings.  For example,
              RLIM_INFINITY typically 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 processes, 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 precisely 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_setparam(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 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.

              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  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  in  the
       user  namespace  of  the  process  whose  resource  limits are being changed, 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
       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_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), signal(7)

COLOPHON

       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 https://www.kernel.org/doc/man-pages/.