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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

       The  getrlimit() and setrlimit() system calls get and set resource lim-
       its 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 corre-
       sponding 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

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

       The resource argument must be one of:

	      This  is	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.

	      This is the maximum size of a core file (see core(5))  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 behav-
	      ior.  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 per-
	      form an orderly termination upon first receipt of SIGXCPU.)

	      This is the maximum size of the process's data segment (initial-
	      ized 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.

	      This is 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)
	      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  mes-
	      sages nevertheless each consume some system memory for bookkeep-
	      ing 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	 typi-
	      cally  have  special meanings.  For example, RLIM_INFINITY typi-
	      cally 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 pro-
	      cesses, by being passed across UNIX domain sockets.  This	 limit
	      applies to the sendmsg(2) system call.  For further details, see

	      This is 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 capa-

	      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_set-

	      For  further  details  on	 real-time  scheduling	policies,  see

       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 con-
	      sume  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 sig-
	      nal.   If the process catches or ignores this signal and contin-
	      ues 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

       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

	      Since Linux 2.6.23, this limit also  determines  the  amount  of
	      space used for the process's command-line arguments and environ-
	      ment variables; for details, see execve(2).

       The Linux-specific prlimit() system call combines and extends the func-
       tionality  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 getr-

       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 success-
       ful 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, effec-
       tive, 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 appropriately.

       EFAULT A	 pointer  argument points to a location outside the accessible
	      address space.

       EINVAL The value specified in resource is  not  valid;  or,  for	 setr-
	      limit()	or   prlimit():	  rlim->rlim_cur   was	 greater  than

       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

       |Interface			    | Attribute	    | Value   |
       |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.
       RLIMIT_SIGPENDING are Linux-specific.

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

       Lowering the soft limit for a resource below the process's current con-
       sumption 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 func-
       tions  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().

       In  older Linux kernels, the SIGXCPU and SIGKILL signals delivered when
       a process encountered the soft and hard RLIMIT_CPU limits  were	deliv-
       ered 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, set-
       ting 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  ker-
       nel  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 val-
	  ues for its resource limit arguments.

       Since  version  2.13,  glibc  works around the limitations of the getr-
       limit() and setrlimit() system calls by	implementing  setrlimit()  and
       getrlimit() as wrapper functions that call prlimit().

       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), sig-

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Linux				  2017-03-13			  GETRLIMIT(2)