1getrlimit(2) System Calls Manual getrlimit(2)
2
6 getrlimit, setrlimit, prlimit - get/set resource limits
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9 Standard C library (libc, -lc)
10
12 #include <sys/resource.h>
13 int getrlimit(int resource, struct rlimit *rlim);
15 int setrlimit(int resource, const struct rlimit *rlim);
16 int prlimit(pid_t pid, int resource,
18 const struct rlimit *_Nullable new_limit,
19 struct rlimit *_Nullable old_limit);
20 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
22 prlimit():
24 _GNU_SOURCE
25
27 The getrlimit() and setrlimit() system calls get and set resource lim‐
28 its. Each resource has an associated soft and hard limit, as defined
29 by the rlimit structure:
30 struct rlimit {
32 rlim_t rlim_cur; /* Soft limit */
33 rlim_t rlim_max; /* Hard limit (ceiling for rlim_cur) */
34 };
35 The soft limit is the value that the kernel enforces for the corre‐
37 sponding resource. The hard limit acts as a ceiling for the soft
38 limit: an unprivileged process may set only its soft limit to a value
39 in the range from 0 up to the hard limit, and (irreversibly) lower its
40 hard limit. A privileged process (under Linux: one with the
41 CAP_SYS_RESOURCE capability in the initial user namespace) may make ar‐
42 bitrary changes to either limit value.
43 The value RLIM_INFINITY denotes no limit on a resource (both in the
45 structure returned by getrlimit() and in the structure passed to setr‐
46 limit()).
47 The resource argument must be one of:
49 RLIMIT_AS
51 This is the maximum size of the process's virtual memory (ad‐
52 dress space). The limit is specified in bytes, and is rounded
53 down to the system page size. This limit affects calls to
54 brk(2), mmap(2), and mremap(2), which fail with the error ENOMEM
55 upon exceeding this limit. In addition, automatic stack expan‐
56 sion fails (and generates a SIGSEGV that kills the process if no
57 alternate stack has been made available via sigaltstack(2)).
58 Since the value is a long, on machines with a 32-bit long either
59 this limit is at most 2 GiB, or this resource is unlimited.
60 RLIMIT_CORE
62 This is the maximum size of a core file (see core(5)) in bytes
63 that the process may dump. When 0 no core dump files are cre‐
64 ated. When nonzero, larger dumps are truncated to this size.
65 RLIMIT_CPU
67 This is a limit, in seconds, on the amount of CPU time that the
68 process can consume. When the process reaches the soft limit,
69 it is sent a SIGXCPU signal. The default action for this signal
70 is to terminate the process. However, the signal can be caught,
71 and the handler can return control to the main program. If the
72 process continues to consume CPU time, it will be sent SIGXCPU
73 once per second until the hard limit is reached, at which time
74 it is sent SIGKILL. (This latter point describes Linux behav‐
75 ior. Implementations vary in how they treat processes which
76 continue to consume CPU time after reaching the soft limit.
77 Portable applications that need to catch this signal should per‐
78 form an orderly termination upon first receipt of SIGXCPU.)
79 RLIMIT_DATA
81 This is the maximum size of the process's data segment (initial‐
82 ized data, uninitialized data, and heap). The limit is speci‐
83 fied in bytes, and is rounded down to the system page size.
84 This limit affects calls to brk(2), sbrk(2), and (since Linux
85 4.7) mmap(2), which fail with the error ENOMEM upon encountering
86 the soft limit of this resource.
87 RLIMIT_FSIZE
89 This is the maximum size in bytes of files that the process may
90 create. Attempts to extend a file beyond this limit result in
91 delivery of a SIGXFSZ signal. By default, this signal termi‐
92 nates a process, but a process can catch this signal instead, in
93 which case the relevant system call (e.g., write(2), trun‐
94 cate(2)) fails with the error EFBIG.
95 RLIMIT_LOCKS (Linux 2.4.0 to Linux 2.4.24)
97 This is a limit on the combined number of flock(2) locks and fc‐
98 ntl(2) leases that this process may establish.
99 RLIMIT_MEMLOCK
101 This is the maximum number of bytes of memory that may be locked
102 into RAM. This limit is in effect rounded down to the nearest
103 multiple of the system page size. This limit affects mlock(2),
104 mlockall(2), and the mmap(2) MAP_LOCKED operation. Since Linux
105 2.6.9, it also affects the shmctl(2) SHM_LOCK operation, where
106 it sets a maximum on the total bytes in shared memory segments
107 (see shmget(2)) that may be locked by the real user ID of the
108 calling process. The shmctl(2) SHM_LOCK locks are accounted for
109 separately from the per-process memory locks established by
110 mlock(2), mlockall(2), and mmap(2) MAP_LOCKED; a process can
111 lock bytes up to this limit in each of these two categories.
112 Before Linux 2.6.9, this limit controlled the amount of memory
114 that could be locked by a privileged process. Since Linux
115 2.6.9, no limits are placed on the amount of memory that a priv‐
116 ileged process may lock, and this limit instead governs the
117 amount of memory that an unprivileged process may lock.
118 RLIMIT_MSGQUEUE (since Linux 2.6.8)
120 This is a limit on the number of bytes that can be allocated for
121 POSIX message queues for the real user ID of the calling
122 process. This limit is enforced for mq_open(3). Each message
123 queue that the user creates counts (until it is removed) against
124 this limit according to the formula:
125 Since Linux 3.5:
127 bytes = attr.mq_maxmsg * sizeof(struct msg_msg) +
129 MIN(attr.mq_maxmsg, MQ_PRIO_MAX) *
130 sizeof(struct posix_msg_tree_node)+
131 /* For overhead */
132 attr.mq_maxmsg * attr.mq_msgsize;
133 /* For message data */
134 Linux 3.4 and earlier:
136 bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
138 /* For overhead */
139 attr.mq_maxmsg * attr.mq_msgsize;
140 /* For message data */
141 where attr is the mq_attr structure specified as the fourth ar‐
143 gument to mq_open(3), and the msg_msg and posix_msg_tree_node
144 structures are kernel-internal structures.
145 The "overhead" addend in the formula accounts for overhead bytes
147 required by the implementation and ensures that the user cannot
148 create an unlimited number of zero-length messages (such mes‐
149 sages nevertheless each consume some system memory for bookkeep‐
150 ing overhead).
151 RLIMIT_NICE (since Linux 2.6.12, but see BUGS below)
153 This specifies a ceiling to which the process's nice value can
154 be raised using setpriority(2) or nice(2). The actual ceiling
155 for the nice value is calculated as 20 - rlim_cur. The useful
156 range for this limit is thus from 1 (corresponding to a nice
157 value of 19) to 40 (corresponding to a nice value of -20). This
158 unusual choice of range was necessary because negative numbers
159 cannot be specified as resource limit values, since they typi‐
160 cally have special meanings. For example, RLIM_INFINITY typi‐
161 cally is the same as -1. For more detail on the nice value, see
162 sched(7).
163 RLIMIT_NOFILE
165 This specifies a value one greater than the maximum file de‐
166 scriptor number that can be opened by this process. Attempts
167 (open(2), pipe(2), dup(2), etc.) to exceed this limit yield the
168 error EMFILE. (Historically, this limit was named RLIMIT_OFILE
169 on BSD.)
170 Since Linux 4.5, this limit also defines the maximum number of
172 file descriptors that an unprivileged process (one without the
173 CAP_SYS_RESOURCE capability) may have "in flight" to other pro‐
174 cesses, by being passed across UNIX domain sockets. This limit
175 applies to the sendmsg(2) system call. For further details, see
176 unix(7).
177 RLIMIT_NPROC
179 This is a limit on the number of extant process (or, more pre‐
180 cisely on Linux, threads) for the real user ID of the calling
181 process. So long as the current number of processes belonging
182 to this process's real user ID is greater than or equal to this
183 limit, fork(2) fails with the error EAGAIN.
184 The RLIMIT_NPROC limit is not enforced for processes that have
186 either the CAP_SYS_ADMIN or the CAP_SYS_RESOURCE capability, or
187 run with real user ID 0.
188 RLIMIT_RSS
190 This is a limit (in bytes) on the process's resident set (the
191 number of virtual pages resident in RAM). This limit has effect
192 only in Linux 2.4.x, x < 30, and there affects only calls to
193 madvise(2) specifying MADV_WILLNEED.
194 RLIMIT_RTPRIO (since Linux 2.6.12, but see BUGS)
196 This specifies a ceiling on the real-time priority that may be
197 set for this process using sched_setscheduler(2) and sched_set‐
198 param(2).
199 For further details on real-time scheduling policies, see
201 sched(7)
202 RLIMIT_RTTIME (since Linux 2.6.25)
204 This is a limit (in microseconds) on the amount of CPU time that
205 a process scheduled under a real-time scheduling policy may con‐
206 sume without making a blocking system call. For the purpose of
207 this limit, each time a process makes a blocking system call,
208 the count of its consumed CPU time is reset to zero. The CPU
209 time count is not reset if the process continues trying to use
210 the CPU but is preempted, its time slice expires, or it calls
211 sched_yield(2).
212 Upon reaching the soft limit, the process is sent a SIGXCPU sig‐
214 nal. If the process catches or ignores this signal and contin‐
215 ues consuming CPU time, then SIGXCPU will be generated once each
216 second until the hard limit is reached, at which point the
217 process is sent a SIGKILL signal.
218 The intended use of this limit is to stop a runaway real-time
220 process from locking up the system.
221 For further details on real-time scheduling policies, see
223 sched(7)
224 RLIMIT_SIGPENDING (since Linux 2.6.8)
226 This is a limit on the number of signals that may be queued for
227 the real user ID of the calling process. Both standard and
228 real-time signals are counted for the purpose of checking this
229 limit. However, the limit is enforced only for sigqueue(3); it
230 is always possible to use kill(2) to queue one instance of any
231 of the signals that are not already queued to the process.
232 RLIMIT_STACK
234 This is the maximum size of the process stack, in bytes. Upon
235 reaching this limit, a SIGSEGV signal is generated. To handle
236 this signal, a process must employ an alternate signal stack
237 (sigaltstack(2)).
238 Since Linux 2.6.23, this limit also determines the amount of
240 space used for the process's command-line arguments and environ‐
241 ment variables; for details, see execve(2).
242 prlimit()
244 The Linux-specific prlimit() system call combines and extends the func‐
245 tionality of setrlimit() and getrlimit(). It can be used to both set
246 and get the resource limits of an arbitrary process.
247 The resource argument has the same meaning as for setrlimit() and getr‐
249 limit().
250 If the new_limit argument is not NULL, then the rlimit structure to
252 which it points is used to set new values for the soft and hard limits
253 for resource. If the old_limit argument is not NULL, then a successful
254 call to prlimit() places the previous soft and hard limits for resource
255 in the rlimit structure pointed to by old_limit.
256 The pid argument specifies the ID of the process on which the call is
258 to operate. If pid is 0, then the call applies to the calling process.
259 To set or get the resources of a process other than itself, the caller
260 must have the CAP_SYS_RESOURCE capability in the user namespace of the
261 process whose resource limits are being changed, or the real, effec‐
262 tive, and saved set user IDs of the target process must match the real
263 user ID of the caller and the real, effective, and saved set group IDs
264 of the target process must match the real group ID of the caller.
265
267 On success, these system calls return 0. On error, -1 is returned, and
268 errno is set to indicate the error.
269
271 EFAULT A pointer argument points to a location outside the accessible
272 address space.
273 EINVAL The value specified in resource is not valid; or, for setr‐
275 limit() or prlimit(): rlim->rlim_cur was greater than
276 rlim->rlim_max.
277 EPERM An unprivileged process tried to raise the hard limit; the
279 CAP_SYS_RESOURCE capability is required to do this.
280 EPERM The caller tried to increase the hard RLIMIT_NOFILE limit above
282 the maximum defined by /proc/sys/fs/nr_open (see proc(5))
283 EPERM (prlimit()) The calling process did not have permission to set
285 limits for the process specified by pid.
286 ESRCH Could not find a process with the ID specified in pid.
288
290 For an explanation of the terms used in this section, see at‐
291 tributes(7).
292 ┌────────────────────────────────────────────┬───────────────┬─────────┐
294 │Interface │ Attribute │ Value │
295 ├────────────────────────────────────────────┼───────────────┼─────────┤
296 │getrlimit(), setrlimit(), prlimit() │ Thread safety │ MT-Safe │
297 └────────────────────────────────────────────┴───────────────┴─────────┘
298
300 getrlimit()
301 setrlimit()
302 POSIX.1-2008.
303 prlimit()
305 Linux.
306 RLIMIT_MEMLOCK and RLIMIT_NPROC derive from BSD and are not specified
308 in POSIX.1; they are present on the BSDs and Linux, but on few other
309 implementations. RLIMIT_RSS derives from BSD and is not specified in
310 POSIX.1; it is nevertheless present on most implementations.
311 RLIMIT_MSGQUEUE, RLIMIT_NICE, RLIMIT_RTPRIO, RLIMIT_RTTIME, and
312 RLIMIT_SIGPENDING are Linux-specific.
313
315 getrlimit()
316 setrlimit()
317 POSIX.1-2001, SVr4, 4.3BSD.
318 prlimit()
320 Linux 2.6.36, glibc 2.13.
321
323 A child process created via fork(2) inherits its parent's resource
324 limits. Resource limits are preserved across execve(2).
325 Resource limits are per-process attributes that are shared by all of
327 the threads in a process.
328 Lowering the soft limit for a resource below the process's current
330 consumption of that resource will succeed (but will prevent the process
331 from further increasing its consumption of the resource).
332 One can set the resource limits of the shell using the built-in ulimit
334 command (limit in csh(1)). The shell's resource limits are inherited
335 by the processes that it creates to execute commands.
336 Since Linux 2.6.24, the resource limits of any process can be inspected
338 via /proc/pid/limits; see proc(5).
339 Ancient systems provided a vlimit() function with a similar purpose to
341 setrlimit(). For backward compatibility, glibc also provides vlimit().
342 All new applications should be written using setrlimit().
343 C library/kernel ABI differences
345 Since glibc 2.13, the glibc getrlimit() and setrlimit() wrapper
346 functions no longer invoke the corresponding system calls, but instead
347 employ prlimit(), for the reasons described in BUGS.
348 The name of the glibc wrapper function is prlimit(); the underlying
350 system call is prlimit64().
351
353 In older Linux kernels, the SIGXCPU and SIGKILL signals delivered when
354 a process encountered the soft and hard RLIMIT_CPU limits were
355 delivered one (CPU) second later than they should have been. This was
356 fixed in Linux 2.6.8.
357 In Linux 2.6.x kernels before Linux 2.6.17, a RLIMIT_CPU limit of 0 is
359 wrongly treated as "no limit" (like RLIM_INFINITY). Since Linux
360 2.6.17, setting a limit of 0 does have an effect, but is actually
361 treated as a limit of 1 second.
362 A kernel bug means that RLIMIT_RTPRIO does not work in Linux 2.6.12;
364 the problem is fixed in Linux 2.6.13.
365 In Linux 2.6.12, there was an off-by-one mismatch between the priority
367 ranges returned by getpriority(2) and RLIMIT_NICE. This had the effect
368 that the actual ceiling for the nice value was calculated as
369 19 - rlim_cur. This was fixed in Linux 2.6.13.
370 Since Linux 2.6.12, if a process reaches its soft RLIMIT_CPU limit and
372 has a handler installed for SIGXCPU, then, in addition to invoking the
373 signal handler, the kernel increases the soft limit by one second.
374 This behavior repeats if the process continues to consume CPU time,
375 until the hard limit is reached, at which point the process is killed.
376 Other implementations do not change the RLIMIT_CPU soft limit in this
377 manner, and the Linux behavior is probably not standards conformant;
378 portable applications should avoid relying on this Linux-specific
379 behavior. The Linux-specific RLIMIT_RTTIME limit exhibits the same
380 behavior when the soft limit is encountered.
381 Kernels before Linux 2.4.22 did not diagnose the error EINVAL for
383 setrlimit() when rlim->rlim_cur was greater than rlim->rlim_max.
384 Linux doesn't return an error when an attempt to set RLIMIT_CPU has
386 failed, for compatibility reasons.
387 Representation of "large" resource limit values on 32-bit platforms
389 The glibc getrlimit() and setrlimit() wrapper functions use a 64-bit
390 rlim_t data type, even on 32-bit platforms. However, the rlim_t data
391 type used in the getrlimit() and setrlimit() system calls is a (32-bit)
392 unsigned long. Furthermore, in Linux, the kernel represents resource
393 limits on 32-bit platforms as unsigned long. However, a 32-bit data
394 type is not wide enough. The most pertinent limit here is
395 RLIMIT_FSIZE, which specifies the maximum size to which a file can
396 grow: to be useful, this limit must be represented using a type that is
397 as wide as the type used to represent file offsets—that is, as wide as
398 a 64-bit off_t (assuming a program compiled with _FILE_OFFSET_BITS=64).
399 To work around this kernel limitation, if a program tried to set a
401 resource limit to a value larger than can be represented in a 32-bit
402 unsigned long, then the glibc setrlimit() wrapper function silently
403 converted the limit value to RLIM_INFINITY. In other words, the
404 requested resource limit setting was silently ignored.
405 Since glibc 2.13, glibc works around the limitations of the getrlimit()
407 and setrlimit() system calls by implementing setrlimit() and
408 getrlimit() as wrapper functions that call prlimit().
409
411 The program below demonstrates the use of prlimit().
412 #define _GNU_SOURCE
414 #define _FILE_OFFSET_BITS 64
415 #include <err.h>
416 #include <stdint.h>
417 #include <stdio.h>
418 #include <stdlib.h>
419 #include <sys/resource.h>
420 #include <time.h>
421 int
423 main(int argc, char *argv[])
424 {
425 pid_t pid;
426 struct rlimit old, new;
427 struct rlimit *newp;
428 if (!(argc == 2 || argc == 4)) {
430 fprintf(stderr, "Usage: %s <pid> [<new-soft-limit> "
431 "<new-hard-limit>]\n", argv[0]);
432 exit(EXIT_FAILURE);
433 }
434 pid = atoi(argv[1]); /* PID of target process */
436 newp = NULL;
438 if (argc == 4) {
439 new.rlim_cur = atoi(argv[2]);
440 new.rlim_max = atoi(argv[3]);
441 newp = &new;
442 }
443 /* Set CPU time limit of target process; retrieve and display
445 previous limit */
446 if (prlimit(pid, RLIMIT_CPU, newp, &old) == -1)
448 err(EXIT_FAILURE, "prlimit-1");
449 printf("Previous limits: soft=%jd; hard=%jd\n",
450 (intmax_t) old.rlim_cur, (intmax_t) old.rlim_max);
451 /* Retrieve and display new CPU time limit */
453 if (prlimit(pid, RLIMIT_CPU, NULL, &old) == -1)
455 err(EXIT_FAILURE, "prlimit-2");
456 printf("New limits: soft=%jd; hard=%jd\n",
457 (intmax_t) old.rlim_cur, (intmax_t) old.rlim_max);
458 exit(EXIT_SUCCESS);
460 }
461
463 prlimit(1), dup(2), fcntl(2), fork(2), getrusage(2), mlock(2), mmap(2),
464 open(2), quotactl(2), sbrk(2), shmctl(2), malloc(3), sigqueue(3),
465 ulimit(3), core(5), capabilities(7), cgroups(7), credentials(7), sig‐
466 nal(7)
467Linux man-pages 6.05 2023-07-20 getrlimit(2)