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       getrlimit, setrlimit - 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);


       getrlimit()  and  setrlimit() get and set resource limits respectively.
       Each resource has an associated soft and hard limit, as defined by  the
       rlimit   structure   (the   rlim   argument  to  both  getrlimit()  and

           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 only set 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

       The value RLIM_INFINITY denotes no limit on a  resource  (both  in  the
       structure  returned  by  getrlimit()  and  in  the  structure passed to

       resource 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  core  file.   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  2.2  through  2.6  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.)

              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), 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)
              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:

                  bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
                          attr.mq_maxmsg * attr.mq_msgsize

              where attr is the mq_attr  structure  specified  as  the  fourth
              argument to mq_open(3).

              The  first  addend  in the formula, which includes sizeof(struct
              msg_msg *) (4 bytes on Linux/i386), 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 setpriority(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  specified
              as  resource  limit  values,  since  they typically have special
              meanings.  For example, RLIM_INFINITY typically is the  same  as

              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.

              Specifies the limit (in pages) of  the  process's  resident  set
              (the  number of virtual pages resident in RAM).  This limit only
              has effect in Linux 2.4.x, x < 30, and there only affects  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

       RLIMIT_RTTIME (Since Linux 2.6.25)
              Specifies  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

              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 only enforced for sigqueue(2);  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

              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).


       On  success,  zero is returned.  On error, -1 is returned, and errno is
       set appropriately.


       EFAULT rlim points outside the accessible address space.

       EINVAL resource is not valid; or, for setrlimit():  rlim->rlim_cur  was
              greater than rlim->rlim_max.

       EPERM  An  unprivileged  process tried to use setrlimit() to increase a
              soft  or  hard  limit  above  the  current   hard   limit;   the
              CAP_SYS_RESOURCE  capability  is  required  to do this.  Or, the
              process tried to use setrlimit() to increase the  soft  or  hard
              RLIMIT_NOFILE limit above the current kernel maximum (NR_OPEN).


       SVr4,  4.3BSD,  POSIX.1-2001.   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,


       A child process created via  fork(2)  inherits  its  parent's  resource
       limits.  Resource limits are preserved across execve(2).

       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.


       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 actual ceiling for the nice value was calculated as 19 - rlim_cur.
       This was fixed in kernel 2.6.13.

       Kernels before 2.4.22 did not diagnose the error EINVAL for setrlimit()
       when rlim->rlim_cur was greater than rlim->rlim_max.


       dup(2), fcntl(2), fork(2), getrusage(2),  mlock(2),  mmap(2),  open(2),
       quotactl(2),  sbrk(2),  shmctl(2),  sigqueue(2),  malloc(3), ulimit(3),
       core(5), capabilities(7), signal(7)


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