bionic (2) setrlimit.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
              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

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