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       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 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:

              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.

              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.

              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.)

              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.

              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.

              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

              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).

              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.

              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.

              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

       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.


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


       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.


       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 attributes(7).

       │InterfaceAttributeValue   │
       │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.


       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


       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

       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


       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), signal(7)


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