1GETRLIMIT(2) Linux Programmer's Manual GETRLIMIT(2)
2
6 getrlimit, setrlimit - get/set resource limits
7
9 #include <sys/time.h>
10 #include <sys/resource.h>
11 int getrlimit(int resource, struct rlimit *rlim);
13 int setrlimit(int resource, const struct rlimit *rlim);
14
16 getrlimit() and setrlimit() get and set resource limits respectively.
17 Each resource has an associated soft and hard limit, as defined by the
18 rlimit structure (the rlim argument to both getrlimit() and setr‐
19 limit()):
20 struct rlimit {
22 rlim_t rlim_cur; /* Soft limit */
23 rlim_t rlim_max; /* Hard limit (ceiling for rlim_cur) */
24 };
25 The soft limit is the value that the kernel enforces for the corre‐
27 sponding resource. The hard limit acts as a ceiling for the soft
28 limit: an unprivileged process may only set its soft limit to a value
29 in the range from 0 up to the hard limit, and (irreversibly) lower its
30 hard limit. A privileged process (under Linux: one with the
31 CAP_SYS_RESOURCE capability) may make arbitrary changes to either limit
32 value.
33 The value RLIM_INFINITY denotes no limit on a resource (both in the
35 structure returned by getrlimit() and in the structure passed to setr‐
36 limit()).
37 resource must be one of:
39 RLIMIT_AS
41 The maximum size of the process's virtual memory (address space)
42 in bytes. This limit affects calls to brk(2), mmap(2) and
43 mremap(2), which fail with the error ENOMEM upon exceeding this
44 limit. Also automatic stack expansion will fail (and generate a
45 SIGSEGV that kills the process if no alternate stack has been
46 made available via sigaltstack(2)). Since the value is a long,
47 on machines with a 32-bit long either this limit is at most 2
48 GiB, or this resource is unlimited.
49 RLIMIT_CORE
51 Maximum size of core file. When 0 no core dump files are cre‐
52 ated. When non-zero, larger dumps are truncated to this size.
53 RLIMIT_CPU
55 CPU time limit in seconds. When the process reaches the soft
56 limit, it is sent a SIGXCPU signal. The default action for this
57 signal is to terminate the process. However, the signal can be
58 caught, and the handler can return control to the main program.
59 If the process continues to consume CPU time, it will be sent
60 SIGXCPU once per second until the hard limit is reached, at
61 which time it is sent SIGKILL. (This latter point describes
62 Linux 2.2 through 2.6 behavior. Implementations vary in how
63 they treat processes which continue to consume CPU time after
64 reaching the soft limit. Portable applications that need to
65 catch this signal should perform an orderly termination upon
66 first receipt of SIGXCPU.)
67 RLIMIT_DATA
69 The maximum size of the process's data segment (initialized
70 data, uninitialized data, and heap). This limit affects calls
71 to brk(2) and sbrk(2), which fail with the error ENOMEM upon
72 encountering the soft limit of this resource.
73 RLIMIT_FSIZE
75 The maximum size of files that the process may create. Attempts
76 to extend a file beyond this limit result in delivery of a
77 SIGXFSZ signal. By default, this signal terminates a process,
78 but a process can catch this signal instead, in which case the
79 relevant system call (e.g., write(2), truncate(2)) fails with
80 the error EFBIG.
81 RLIMIT_LOCKS (Early Linux 2.4 only)
83 A limit on the combined number of flock(2) locks and fcntl(2)
84 leases that this process may establish.
85 RLIMIT_MEMLOCK
87 The maximum number of bytes of memory that may be locked into
88 RAM. In effect this limit is rounded down to the nearest multi‐
89 ple of the system page size. This limit affects mlock(2) and
90 mlockall(2) and the mmap(2) MAP_LOCKED operation. Since Linux
91 2.6.9 it also affects the shmctl(2) SHM_LOCK operation, where it
92 sets a maximum on the total bytes in shared memory segments (see
93 shmget(2)) that may be locked by the real user ID of the calling
94 process. The shmctl(2) SHM_LOCK locks are accounted for sepa‐
95 rately from the per-process memory locks established by
96 mlock(2), mlockall(2), and mmap(2) MAP_LOCKED; a process can
97 lock bytes up to this limit in each of these two categories. In
98 Linux kernels before 2.6.9, this limit controlled the amount of
99 memory that could be locked by a privileged process. Since
100 Linux 2.6.9, no limits are placed on the amount of memory that a
101 privileged process may lock, and this limit instead governs the
102 amount of memory that an unprivileged process may lock.
103 RLIMIT_MSGQUEUE (Since Linux 2.6.8)
105 Specifies the limit on the number of bytes that can be allocated
106 for POSIX message queues for the real user ID of the calling
107 process. This limit is enforced for mq_open(3). Each message
108 queue that the user creates counts (until it is removed) against
109 this limit according to the formula:
110 bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
112 attr.mq_maxmsg * attr.mq_msgsize
113 where attr is the mq_attr structure specified as the fourth
115 argument to mq_open(3).
116 The first addend in the formula, which includes sizeof(struct
118 msg_msg *) (4 bytes on Linux/i386), ensures that the user cannot
119 create an unlimited number of zero-length messages (such mes‐
120 sages nevertheless each consume some system memory for bookkeep‐
121 ing overhead).
122 RLIMIT_NICE (since Linux 2.6.12, but see BUGS below)
124 Specifies a ceiling to which the process's nice value can be
125 raised using setpriority(2) or nice(2). The actual ceiling for
126 the nice value is calculated as 20 - rlim_cur. (This strange‐
127 ness occurs because negative numbers cannot be specified as
128 resource limit values, since they typically have special mean‐
129 ings. For example, RLIM_INFINITY typically is the same as -1.)
130 RLIMIT_NOFILE
132 Specifies a value one greater than the maximum file descriptor
133 number that can be opened by this process. Attempts (open(2),
134 pipe(2), dup(2), etc.) to exceed this limit yield the error
135 EMFILE. (Historically, this limit was named RLIMIT_OFILE on
136 BSD.)
137 RLIMIT_NPROC
139 The maximum number of processes (or, more precisely on Linux,
140 threads) that can be created for the real user ID of the calling
141 process. Upon encountering this limit, fork(2) fails with the
142 error EAGAIN.
143 RLIMIT_RSS
145 Specifies the limit (in pages) of the process's resident set
146 (the number of virtual pages resident in RAM). This limit only
147 has effect in Linux 2.4.x, x < 30, and there only affects calls
148 to madvise(2) specifying MADV_WILLNEED.
149 RLIMIT_RTPRIO (Since Linux 2.6.12, but see BUGS)
151 Specifies a ceiling on the real-time priority that may be set
152 for this process using sched_setscheduler(2) and sched_set‐
153 param(2).
154 RLIMIT_RTTIME (Since Linux 2.6.25)
156 Specifies a limit on the amount of CPU time that a process
157 scheduled under a real-time scheduling policy may consume with‐
158 out making a blocking system call. For the purpose of this
159 limit, each time a process makes a blocking system call, the
160 count of its consumed CPU time is reset to zero. The CPU time
161 count is not reset if the process continues trying to use the
162 CPU but is preempted, its time slice expires, or it calls
163 sched_yield(2).
164 Upon reaching the soft limit, the process is sent a SIGXCPU sig‐
166 nal. If the process catches or ignores this signal and contin‐
167 ues consuming CPU time, then SIGXCPU will be generated once each
168 second until the hard limit is reached, at which point the
169 process is sent a SIGKILL signal.
170 The intended use of this limit is to stop a runaway real-time
172 process from locking up the system.
173 RLIMIT_SIGPENDING (Since Linux 2.6.8)
175 Specifies the limit on the number of signals that may be queued
176 for the real user ID of the calling process. Both standard and
177 real-time signals are counted for the purpose of checking this
178 limit. However, the limit is only enforced for sigqueue(2); it
179 is always possible to use kill(2) to queue one instance of any
180 of the signals that are not already queued to the process.
181 RLIMIT_STACK
183 The maximum size of the process stack, in bytes. Upon reaching
184 this limit, a SIGSEGV signal is generated. To handle this sig‐
185 nal, a process must employ an alternate signal stack (sigalt‐
186 stack(2)).
187 Since Linux 2.6.23, this limit also determines the amount of
189 space used for the process's command-line arguments and environ‐
190 ment variables; for details, see execve(2).
191
193 On success, zero is returned. On error, -1 is returned, and errno is
194 set appropriately.
195
197 EFAULT rlim points outside the accessible address space.
198 EINVAL resource is not valid; or, for setrlimit(): rlim->rlim_cur was
200 greater than rlim->rlim_max.
201 EPERM An unprivileged process tried to use setrlimit() to increase a
203 soft or hard limit above the current hard limit; the
204 CAP_SYS_RESOURCE capability is required to do this. Or, the
205 process tried to use setrlimit() to increase the soft or hard
206 RLIMIT_NOFILE limit above the current kernel maximum (NR_OPEN).
207
209 SVr4, 4.3BSD, POSIX.1-2001. RLIMIT_MEMLOCK and RLIMIT_NPROC derive
210 from BSD and are not specified in POSIX.1-2001; they are present on the
211 BSDs and Linux, but on few other implementations. RLIMIT_RSS derives
212 from BSD and is not specified in POSIX.1-2001; it is nevertheless
213 present on most implementations. RLIMIT_MSGQUEUE, RLIMIT_NICE,
214 RLIMIT_RTPRIO, RLIMIT_RTTIME, and RLIMIT_SIGPENDING are Linux-specific.
215
217 A child process created via fork(2) inherits its parent's resource lim‐
218 its. Resource limits are preserved across execve(2).
219 One can set the resource limits of the shell using the built-in ulimit
221 command (limit in csh(1)). The shell's resource limits are inherited
222 by the processes that it creates to execute commands.
223
225 In older Linux kernels, the SIGXCPU and SIGKILL signals delivered when
226 a process encountered the soft and hard RLIMIT_CPU limits were deliv‐
227 ered one (CPU) second later than they should have been. This was fixed
228 in kernel 2.6.8.
229 In 2.6.x kernels before 2.6.17, a RLIMIT_CPU limit of 0 is wrongly
231 treated as "no limit" (like RLIM_INFINITY). Since Linux 2.6.17, set‐
232 ting a limit of 0 does have an effect, but is actually treated as a
233 limit of 1 second.
234 A kernel bug means that RLIMIT_RTPRIO does not work in kernel 2.6.12;
236 the problem is fixed in kernel 2.6.13.
237 In kernel 2.6.12, there was an off-by-one mismatch between the priority
239 ranges returned by getpriority(2) and RLIMIT_NICE. This had the effect
240 that actual ceiling for the nice value was calculated as 19 - rlim_cur.
241 This was fixed in kernel 2.6.13.
242 Kernels before 2.4.22 did not diagnose the error EINVAL for setrlimit()
244 when rlim->rlim_cur was greater than rlim->rlim_max.
245
247 dup(2), fcntl(2), fork(2), getrusage(2), mlock(2), mmap(2), open(2),
248 quotactl(2), sbrk(2), shmctl(2), sigqueue(2), malloc(3), ulimit(3),
249 core(5), capabilities(7), signal(7)
250
252 This page is part of release 3.22 of the Linux man-pages project. A
253 description of the project, and information about reporting bugs, can
254 be found at http://www.kernel.org/doc/man-pages/.
255Linux 2008-10-06 GETRLIMIT(2)