:: RootR ::  Hosting Order Map Login   Secure Inter-Network Operations  
getrlimit(2) - phpMan

Command: man perldoc info search(apropos)  

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 && _FILE_OFFSET_BITS == 64

       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 capabil‐
       ity) 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:

              The  maximum  size  of the process's virtual memory (address space) in bytes.  This
              limit affects calls to brk(2), mmap(2), and mremap(2), which fail  with  the  error
              ENOMEM  upon  exceeding  this limit.  Also automatic stack expansion will fail (and
              generate 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.

              Maximum size of a core file (see core(5)).  When 0 no core dump files are  created.
              When nonzero, larger dumps are truncated to this size.

              CPU  time  limit in seconds.  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 ter‐
              mination upon first receipt of SIGXCPU.)

              The  maximum  size  of  the process's data segment (initialized data, uninitialized
              data, and heap).  This limit affects calls to brk(2) and sbrk(2), which  fail  with
              the error ENOMEM upon encountering the soft limit of this resource.

              The  maximum  size 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)
              A limit on the combined number of flock(2) locks  and  fcntl(2)  leases  that  this
              process may establish.

              The  maximum number of bytes of memory that may be locked into RAM.  In effect this
              limit is rounded down to the nearest multiple of the system page size.  This  limit
              affects mlock(2) and 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), mlock‐
              all(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)
              Specifies  the 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)
              Specifies a ceiling to which the process's nice value can be raised using setprior‐
              ity(2)  or  nice(2).   The  actual  ceiling  for  the  nice  value is calculated as
              20 - rlim_cur.  (This strangeness occurs because negative numbers cannot be  speci‐
              fied  as  resource  limit  values, since they typically have special meanings.  For
              example, RLIM_INFINITY typically is the same as -1.)

              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

              The  maximum number of processes (or, more precisely on Linux, threads) that can be
              created for the real user ID of the calling process.  Upon encountering this limit,
              fork(2) fails with the error EAGAIN.  This limit is not enforced for processes that
              have either the CAP_SYS_ADMIN or the CAP_SYS_RESOURCE capability.

              Specifies the limit (in pages) of 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)
              Specifies a ceiling on the real-time priority that may  be  set  for  this  process
              using sched_setscheduler(2) and sched_setparam(2).

       RLIMIT_RTTIME (since Linux 2.6.25)
              Specifies a limit (in microseconds) on the amount of CPU time that a process sched‐
              uled under a real-time scheduling policy may consume without making a blocking sys‐
              tem call.  For the purpose of this limit, each time a process makes a blocking sys‐
              tem 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.

       RLIMIT_SIGPENDING (since Linux 2.6.8)
              Specifies the 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.

              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  setr‐
       limit()  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 argu‐
       ment 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, 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  capa‐
              bility  is  required  to  do  this.   Or,  the  caller  tried  to increase the hard
              RLIMIT_NOFILE limit above the current kernel maximum (NR_OPEN).   Or,  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.

       getrlimit(), setrlimit(): SVr4, 4.3BSD, POSIX.1-2001.
       prlimit(): Linux-specific.

       RLIMIT_MEMLOCK and RLIMIT_NPROC derive from BSD and are  not  specified  in  POSIX.1-2001;
       they  are  present  on  the  BSDs and Linux, but on few other implementations.  RLIMIT_RSS
       derives from BSD and is not specified in POSIX.1-2001; it is nevertheless present on  most
       implementations.    RLIMIT_MSGQUEUE,   RLIMIT_NICE,   RLIMIT_RTPRIO,   RLIMIT_RTTIME,  and
       RLIMIT_SIGPENDING are Linux-specific.

       A child process created via fork(2) inherits its parent's resource limits.  Resource  lim‐
       its 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  consump‐
       tion 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.

       In older Linux kernels, the SIGXCPU and SIGKILL signals delivered when a  process  encoun‐
       tered  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 setr‐
       limit()  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.   How‐
       ever,  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),  quo‐
       tactl(2), sbrk(2), shmctl(2), malloc(3), sigqueue(3), ulimit(3), core(5), capabilities(7),

       This page is part of release 3.74 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 http://www.kernel.org/doc/man-pages/.

Linux                                       2014-10-02                               GETRLIMIT(2)

rootr.net - man pages