1GETRLIMIT(2)               Linux Programmer's Manual              GETRLIMIT(2)
2
3
4

NAME

6       getrlimit, setrlimit, prlimit - get/set resource limits
7

SYNOPSIS

9       #include <sys/time.h>
10       #include <sys/resource.h>
11
12       int getrlimit(int resource, struct rlimit *rlim);
13       int setrlimit(int resource, const struct rlimit *rlim);
14
15       int prlimit(pid_t pid, int resource, const struct rlimit *new_limit,
16                   struct rlimit *old_limit);
17
18   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
19
20       prlimit(): _GNU_SOURCE
21

DESCRIPTION

23       The  getrlimit() and setrlimit() system calls get and set resource lim‐
24       its.  Each resource has an associated soft and hard limit,  as  defined
25       by the rlimit structure:
26
27           struct rlimit {
28               rlim_t rlim_cur;  /* Soft limit */
29               rlim_t rlim_max;  /* Hard limit (ceiling for rlim_cur) */
30           };
31
32       The  soft  limit  is  the value that the kernel enforces for the corre‐
33       sponding resource.  The hard limit acts  as  a  ceiling  for  the  soft
34       limit:  an  unprivileged process may set only its soft limit to a value
35       in the range from 0 up to the hard limit, and (irreversibly) lower  its
36       hard   limit.    A  privileged  process  (under  Linux:  one  with  the
37       CAP_SYS_RESOURCE capability in the initial user namespace) may make ar‐
38       bitrary changes to either limit value.
39
40       The  value  RLIM_INFINITY  denotes  no limit on a resource (both in the
41       structure returned by getrlimit() and in the structure passed to  setr‐
42       limit()).
43
44       The resource argument must be one of:
45
46       RLIMIT_AS
47              This  is  the  maximum size of the process's virtual memory (ad‐
48              dress space).  The limit is specified in bytes, and  is  rounded
49              down  to  the  system  page  size.   This limit affects calls to
50              brk(2), mmap(2), and mremap(2), which fail with the error ENOMEM
51              upon  exceeding this limit.  In addition, automatic stack expan‐
52              sion fails (and generates a SIGSEGV that kills the process if no
53              alternate  stack  has  been  made available via sigaltstack(2)).
54              Since the value is a long, on machines with a 32-bit long either
55              this limit is at most 2 GiB, or this resource is unlimited.
56
57       RLIMIT_CORE
58              This  is  the maximum size of a core file (see core(5)) in bytes
59              that the process may dump.  When 0 no core dump files  are  cre‐
60              ated.  When nonzero, larger dumps are truncated to this size.
61
62       RLIMIT_CPU
63              This  is a limit, in seconds, on the amount of CPU time that the
64              process can consume.  When the process reaches the  soft  limit,
65              it is sent a SIGXCPU signal.  The default action for this signal
66              is to terminate the process.  However, the signal can be caught,
67              and  the handler can return control to the main program.  If the
68              process continues to consume CPU time, it will be  sent  SIGXCPU
69              once  per  second until the hard limit is reached, at which time
70              it is sent SIGKILL.  (This latter point describes  Linux  behav‐
71              ior.   Implementations  vary  in  how they treat processes which
72              continue to consume CPU time  after  reaching  the  soft  limit.
73              Portable applications that need to catch this signal should per‐
74              form an orderly termination upon first receipt of SIGXCPU.)
75
76       RLIMIT_DATA
77              This is the maximum size of the process's data segment (initial‐
78              ized  data,  uninitialized data, and heap).  The limit is speci‐
79              fied in bytes, and is rounded down  to  the  system  page  size.
80              This  limit  affects  calls to brk(2), sbrk(2), and (since Linux
81              4.7) mmap(2), which fail with the error ENOMEM upon encountering
82              the soft limit of this resource.
83
84       RLIMIT_FSIZE
85              This  is the maximum size in bytes of files that the process may
86              create.  Attempts to extend a file beyond this limit  result  in
87              delivery  of  a  SIGXFSZ signal.  By default, this signal termi‐
88              nates a process, but a process can catch this signal instead, in
89              which  case  the  relevant  system  call  (e.g., write(2), trun‐
90              cate(2)) fails with the error EFBIG.
91
92       RLIMIT_LOCKS (Linux 2.4.0 to 2.4.24)
93              This is a limit on the combined number of flock(2) locks and fc‐
94              ntl(2) leases that this process may establish.
95
96       RLIMIT_MEMLOCK
97              This is the maximum number of bytes of memory that may be locked
98              into RAM.  This limit is in effect rounded down to  the  nearest
99              multiple  of the system page size.  This limit affects mlock(2),
100              mlockall(2), and the mmap(2) MAP_LOCKED operation.  Since  Linux
101              2.6.9,  it  also affects the shmctl(2) SHM_LOCK operation, where
102              it sets a maximum on the total bytes in shared  memory  segments
103              (see  shmget(2))  that  may be locked by the real user ID of the
104              calling process.  The shmctl(2) SHM_LOCK locks are accounted for
105              separately  from  the  per-process  memory  locks established by
106              mlock(2), mlockall(2), and mmap(2)  MAP_LOCKED;  a  process  can
107              lock bytes up to this limit in each of these two categories.
108
109              In  Linux kernels before 2.6.9, this limit controlled the amount
110              of memory that could be locked by a privileged  process.   Since
111              Linux 2.6.9, no limits are placed on the amount of memory that a
112              privileged process may lock, and this limit instead governs  the
113              amount of memory that an unprivileged process may lock.
114
115       RLIMIT_MSGQUEUE (since Linux 2.6.8)
116              This is a limit on the number of bytes that can be allocated for
117              POSIX message queues  for  the  real  user  ID  of  the  calling
118              process.   This  limit is enforced for mq_open(3).  Each message
119              queue that the user creates counts (until it is removed) against
120              this limit according to the formula:
121
122                  Since Linux 3.5:
123
124                      bytes = attr.mq_maxmsg * sizeof(struct msg_msg) +
125                              min(attr.mq_maxmsg, MQ_PRIO_MAX) *
126                                    sizeof(struct posix_msg_tree_node)+
127                                              /* For overhead */
128                              attr.mq_maxmsg * attr.mq_msgsize;
129                                              /* For message data */
130
131                  Linux 3.4 and earlier:
132
133                      bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
134                                              /* For overhead */
135                              attr.mq_maxmsg * attr.mq_msgsize;
136                                              /* For message data */
137
138              where  attr is the mq_attr structure specified as the fourth ar‐
139              gument to mq_open(3), and the  msg_msg  and  posix_msg_tree_node
140              structures are kernel-internal structures.
141
142              The "overhead" addend in the formula accounts for overhead bytes
143              required by the implementation and ensures that the user  cannot
144              create  an  unlimited  number of zero-length messages (such mes‐
145              sages nevertheless each consume some system memory for bookkeep‐
146              ing overhead).
147
148       RLIMIT_NICE (since Linux 2.6.12, but see BUGS below)
149              This  specifies  a ceiling to which the process's nice value can
150              be raised using setpriority(2) or nice(2).  The  actual  ceiling
151              for  the  nice value is calculated as 20 - rlim_cur.  The useful
152              range for this limit is thus from 1  (corresponding  to  a  nice
153              value of 19) to 40 (corresponding to a nice value of -20).  This
154              unusual choice of range was necessary because  negative  numbers
155              cannot  be  specified as resource limit values, since they typi‐
156              cally have special meanings.  For example,  RLIM_INFINITY  typi‐
157              cally is the same as -1.  For more detail on the nice value, see
158              sched(7).
159
160       RLIMIT_NOFILE
161              This specifies a value one greater than  the  maximum  file  de‐
162              scriptor  number  that  can be opened by this process.  Attempts
163              (open(2), pipe(2), dup(2), etc.)  to exceed this limit yield the
164              error  EMFILE.  (Historically, this limit was named RLIMIT_OFILE
165              on BSD.)
166
167              Since Linux 4.5, this limit also defines the maximum  number  of
168              file  descriptors  that an unprivileged process (one without the
169              CAP_SYS_RESOURCE capability) may have "in flight" to other  pro‐
170              cesses,  by being passed across UNIX domain sockets.  This limit
171              applies to the sendmsg(2) system call.  For further details, see
172              unix(7).
173
174       RLIMIT_NPROC
175              This  is  a limit on the number of extant process (or, more pre‐
176              cisely on Linux, threads) for the real user ID  of  the  calling
177              process.   So  long as the current number of processes belonging
178              to this process's real user ID is greater than or equal to  this
179              limit, fork(2) fails with the error EAGAIN.
180
181              The  RLIMIT_NPROC  limit is not enforced for processes that have
182              either the CAP_SYS_ADMIN or the CAP_SYS_RESOURCE capability.
183
184       RLIMIT_RSS
185              This is a limit (in bytes) on the process's  resident  set  (the
186              number of virtual pages resident in RAM).  This limit has effect
187              only in Linux 2.4.x, x < 30, and there  affects  only  calls  to
188              madvise(2) specifying MADV_WILLNEED.
189
190       RLIMIT_RTPRIO (since Linux 2.6.12, but see BUGS)
191              This  specifies  a ceiling on the real-time priority that may be
192              set for this process using sched_setscheduler(2) and  sched_set‐
193              param(2).
194
195              For  further  details  on  real-time  scheduling  policies,  see
196              sched(7)
197
198       RLIMIT_RTTIME (since Linux 2.6.25)
199              This is a limit (in microseconds) on the amount of CPU time that
200              a process scheduled under a real-time scheduling policy may con‐
201              sume without making a blocking system call.  For the purpose  of
202              this  limit,  each  time a process makes a blocking system call,
203              the count of its consumed CPU time is reset to  zero.   The  CPU
204              time  count  is not reset if the process continues trying to use
205              the CPU but is preempted, its time slice expires,  or  it  calls
206              sched_yield(2).
207
208              Upon reaching the soft limit, the process is sent a SIGXCPU sig‐
209              nal.  If the process catches or ignores this signal and  contin‐
210              ues consuming CPU time, then SIGXCPU will be generated once each
211              second until the hard limit  is  reached,  at  which  point  the
212              process is sent a SIGKILL signal.
213
214              The  intended  use  of this limit is to stop a runaway real-time
215              process from locking up the system.
216
217              For  further  details  on  real-time  scheduling  policies,  see
218              sched(7)
219
220       RLIMIT_SIGPENDING (since Linux 2.6.8)
221              This  is a limit on the number of signals that may be queued for
222              the real user ID of the  calling  process.   Both  standard  and
223              real-time  signals  are counted for the purpose of checking this
224              limit.  However, the limit is enforced only for sigqueue(3);  it
225              is  always  possible to use kill(2) to queue one instance of any
226              of the signals that are not already queued to the process.
227
228       RLIMIT_STACK
229              This is the maximum size of the process stack, in  bytes.   Upon
230              reaching  this  limit, a SIGSEGV signal is generated.  To handle
231              this signal, a process must employ  an  alternate  signal  stack
232              (sigaltstack(2)).
233
234              Since  Linux  2.6.23,  this  limit also determines the amount of
235              space used for the process's command-line arguments and environ‐
236              ment variables; for details, see execve(2).
237
238   prlimit()
239       The Linux-specific prlimit() system call combines and extends the func‐
240       tionality of setrlimit() and getrlimit().  It can be used to  both  set
241       and get the resource limits of an arbitrary process.
242
243       The resource argument has the same meaning as for setrlimit() and getr‐
244       limit().
245
246       If the new_limit argument is a not NULL, then the rlimit  structure  to
247       which  it points is used to set new values for the soft and hard limits
248       for resource.  If the old_limit argument is a not NULL, then a success‐
249       ful  call to prlimit() places the previous soft and hard limits for re‐
250       source in the rlimit structure pointed to by old_limit.
251
252       The pid argument specifies the ID of the process on which the  call  is
253       to operate.  If pid is 0, then the call applies to the calling process.
254       To set or get the resources of a process other than itself, the  caller
255       must  have the CAP_SYS_RESOURCE capability in the user namespace of the
256       process whose resource limits are being changed, or  the  real,  effec‐
257       tive,  and saved set user IDs of the target process must match the real
258       user ID of the caller and the real, effective, and saved set group  IDs
259       of the target process must match the real group ID of the caller.
260

RETURN VALUE

262       On success, these system calls return 0.  On error, -1 is returned, and
263       errno is set appropriately.
264

ERRORS

266       EFAULT A pointer argument points to a location outside  the  accessible
267              address space.
268
269       EINVAL The  value  specified  in  resource  is not valid; or, for setr‐
270              limit()  or   prlimit():   rlim->rlim_cur   was   greater   than
271              rlim->rlim_max.
272
273       EPERM  An  unprivileged  process  tried  to  raise  the hard limit; the
274              CAP_SYS_RESOURCE capability is required to do this.
275
276       EPERM  The caller tried to increase the hard RLIMIT_NOFILE limit  above
277              the maximum defined by /proc/sys/fs/nr_open (see proc(5))
278
279       EPERM  (prlimit())  The  calling process did not have permission to set
280              limits for the process specified by pid.
281
282       ESRCH  Could not find a process with the ID specified in pid.
283

VERSIONS

285       The prlimit() system call is available  since  Linux  2.6.36.   Library
286       support is available since glibc 2.13.
287

ATTRIBUTES

289       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
290       tributes(7).
291
292       ┌────────────────────────────────────┬───────────────┬─────────┐
293Interface                           Attribute     Value   
294       ├────────────────────────────────────┼───────────────┼─────────┤
295getrlimit(), setrlimit(), prlimit() │ Thread safety │ MT-Safe │
296       └────────────────────────────────────┴───────────────┴─────────┘
297

CONFORMING TO

299       getrlimit(), setrlimit(): POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
300
301       prlimit(): Linux-specific.
302
303       RLIMIT_MEMLOCK and RLIMIT_NPROC derive from BSD and are  not  specified
304       in  POSIX.1;  they  are present on the BSDs and Linux, but on few other
305       implementations.  RLIMIT_RSS derives from BSD and is not  specified  in
306       POSIX.1;   it   is   nevertheless   present  on  most  implementations.
307       RLIMIT_MSGQUEUE,   RLIMIT_NICE,   RLIMIT_RTPRIO,   RLIMIT_RTTIME,   and
308       RLIMIT_SIGPENDING are Linux-specific.
309

NOTES

311       A child process created via fork(2) inherits its parent's resource lim‐
312       its.  Resource limits are preserved across execve(2).
313
314       Resource limits are per-process attributes that are shared  by  all  of
315       the threads in a process.
316
317       Lowering the soft limit for a resource below the process's current con‐
318       sumption of that resource will succeed (but will  prevent  the  process
319       from further increasing its consumption of the resource).
320
321       One  can set the resource limits of the shell using the built-in ulimit
322       command (limit in csh(1)).  The shell's resource limits  are  inherited
323       by the processes that it creates to execute commands.
324
325       Since Linux 2.6.24, the resource limits of any process can be inspected
326       via /proc/[pid]/limits; see proc(5).
327
328       Ancient systems provided a vlimit() function with a similar purpose  to
329       setrlimit().  For backward compatibility, glibc also provides vlimit().
330       All new applications should be written using setrlimit().
331
332   C library/kernel ABI differences
333       Since version 2.13, the glibc getrlimit() and setrlimit() wrapper func‐
334       tions  no longer invoke the corresponding system calls, but instead em‐
335       ploy prlimit(), for the reasons described in BUGS.
336
337       The name of the glibc wrapper function  is  prlimit();  the  underlying
338       system call is prlimit64().
339

BUGS

341       In  older Linux kernels, the SIGXCPU and SIGKILL signals delivered when
342       a process encountered the soft and hard RLIMIT_CPU limits  were  deliv‐
343       ered one (CPU) second later than they should have been.  This was fixed
344       in kernel 2.6.8.
345
346       In 2.6.x kernels before 2.6.17, a RLIMIT_CPU  limit  of  0  is  wrongly
347       treated  as  "no limit" (like RLIM_INFINITY).  Since Linux 2.6.17, set‐
348       ting a limit of 0 does have an effect, but is  actually  treated  as  a
349       limit of 1 second.
350
351       A  kernel  bug means that RLIMIT_RTPRIO does not work in kernel 2.6.12;
352       the problem is fixed in kernel 2.6.13.
353
354       In kernel 2.6.12, there was an off-by-one mismatch between the priority
355       ranges returned by getpriority(2) and RLIMIT_NICE.  This had the effect
356       that  the  actual  ceiling  for  the  nice  value  was  calculated   as
357       19 - rlim_cur.  This was fixed in kernel 2.6.13.
358
359       Since  Linux 2.6.12, if a process reaches its soft RLIMIT_CPU limit and
360       has a handler installed for SIGXCPU, then, in addition to invoking  the
361       signal  handler,  the  kernel  increases  the soft limit by one second.
362       This behavior repeats if the process continues to consume CPU time, un‐
363       til  the  hard  limit is reached, at which point the process is killed.
364       Other implementations do not change the RLIMIT_CPU soft limit  in  this
365       manner,  and  the  Linux behavior is probably not standards conformant;
366       portable applications should avoid relying on this  Linux-specific  be‐
367       havior.   The  Linux-specific RLIMIT_RTTIME limit exhibits the same be‐
368       havior when the soft limit is encountered.
369
370       Kernels before 2.4.22 did not diagnose the error EINVAL for setrlimit()
371       when rlim->rlim_cur was greater than rlim->rlim_max.
372
373       Linux  doesn't  return  an  error when an attempt to set RLIMIT_CPU has
374       failed, for compatibility reasons.
375
376   Representation of "large" resource limit values on 32-bit platforms
377       The glibc getrlimit() and setrlimit() wrapper functions  use  a  64-bit
378       rlim_t  data  type, even on 32-bit platforms.  However, the rlim_t data
379       type used in the getrlimit() and setrlimit() system calls is a (32-bit)
380       unsigned  long.   Furthermore, in Linux, the kernel represents resource
381       limits on 32-bit platforms as unsigned long.  However,  a  32-bit  data
382       type   is   not   wide  enough.   The  most  pertinent  limit  here  is
383       RLIMIT_FSIZE, which specifies the maximum size  to  which  a  file  can
384       grow: to be useful, this limit must be represented using a type that is
385       as wide as the type used to represent file offsets—that is, as wide  as
386       a 64-bit off_t (assuming a program compiled with _FILE_OFFSET_BITS=64).
387
388       To  work around this kernel limitation, if a program tried to set a re‐
389       source limit to a value larger than can be represented in a 32-bit  un‐
390       signed  long, then the glibc setrlimit() wrapper function silently con‐
391       verted the limit value to RLIM_INFINITY.  In other words, the requested
392       resource limit setting was silently ignored.
393
394       Since  version  2.13,  glibc  works around the limitations of the getr‐
395       limit() and setrlimit() system calls by  implementing  setrlimit()  and
396       getrlimit() as wrapper functions that call prlimit().
397

EXAMPLES

399       The program below demonstrates the use of prlimit().
400
401       #define _GNU_SOURCE
402       #define _FILE_OFFSET_BITS 64
403       #include <stdint.h>
404       #include <stdio.h>
405       #include <time.h>
406       #include <stdlib.h>
407       #include <unistd.h>
408       #include <sys/resource.h>
409
410       #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \
411                               } while (0)
412
413       int
414       main(int argc, char *argv[])
415       {
416           struct rlimit old, new;
417           struct rlimit *newp;
418           pid_t pid;
419
420           if (!(argc == 2 || argc == 4)) {
421               fprintf(stderr, "Usage: %s <pid> [<new-soft-limit> "
422                       "<new-hard-limit>]\n", argv[0]);
423               exit(EXIT_FAILURE);
424           }
425
426           pid = atoi(argv[1]);        /* PID of target process */
427
428           newp = NULL;
429           if (argc == 4) {
430               new.rlim_cur = atoi(argv[2]);
431               new.rlim_max = atoi(argv[3]);
432               newp = &new;
433           }
434
435           /* Set CPU time limit of target process; retrieve and display
436              previous limit */
437
438           if (prlimit(pid, RLIMIT_CPU, newp, &old) == -1)
439               errExit("prlimit-1");
440           printf("Previous limits: soft=%jd; hard=%jd\n",
441                   (intmax_t) old.rlim_cur, (intmax_t) old.rlim_max);
442
443           /* Retrieve and display new CPU time limit */
444
445           if (prlimit(pid, RLIMIT_CPU, NULL, &old) == -1)
446               errExit("prlimit-2");
447           printf("New limits: soft=%jd; hard=%jd\n",
448                   (intmax_t) old.rlim_cur, (intmax_t) old.rlim_max);
449
450           exit(EXIT_SUCCESS);
451       }
452

SEE ALSO

454       prlimit(1), dup(2), fcntl(2), fork(2), getrusage(2), mlock(2), mmap(2),
455       open(2),  quotactl(2),  sbrk(2),  shmctl(2),  malloc(3),   sigqueue(3),
456       ulimit(3),  core(5),  capabilities(7), cgroups(7), credentials(7), sig‐
457       nal(7)
458

COLOPHON

460       This page is part of release 5.10 of the Linux  man-pages  project.   A
461       description  of  the project, information about reporting bugs, and the
462       latest    version    of    this    page,    can     be     found     at
463       https://www.kernel.org/doc/man-pages/.
464
465
466
467Linux                             2020-11-01                      GETRLIMIT(2)
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