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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | NOTES | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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getrlimit(2) System Calls Manual getrlimit(2)
getrlimit, setrlimit, prlimit - get/set resource limits
Standard C library (libc, -lc)
#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 *_Nullable new_limit,
struct rlimit *_Nullable old_limit);
struct rlimit {
rlim_t rlim_cur; /* Soft limit */
rlim_t rlim_max; /* Hard limit (ceiling for rlim_cur) */
};
typedef /* ... */ rlim_t; /* Unsigned integer type */
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
prlimit():
_GNU_SOURCE
The getrlimit() and setrlimit() system calls get and set resource
limits. Each resource has an associated soft and hard limit, as
defined by the rlimit structure.
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 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 in the initial
user namespace) may make arbitrary changes to either limit value.
The value RLIM_INFINITY denotes no limit on a resource (both in
the structure returned by getrlimit() and in the structure passed
to setrlimit()).
The resource argument must be one of:
RLIMIT_AS
This is the maximum size of the process's virtual memory
(address space). The limit is specified in bytes, and is
rounded down to the system page size. This limit affects
calls to brk(2), mmap(2), and mremap(2), which fail with
the error ENOMEM upon exceeding this limit. In addition,
automatic stack expansion fails (and generates 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.
RLIMIT_CORE
This is the maximum size of a core file (see core(5)) in
bytes that the process may dump. When 0 no core dump
files are created. When nonzero, larger dumps are
truncated to this size.
RLIMIT_CPU
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 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.)
RLIMIT_DATA
This is the maximum size of the process's data segment
(initialized data, uninitialized data, and heap). The
limit is specified in bytes, and is rounded down to the
system page size. This limit affects calls to brk(2),
sbrk(2), and (since Linux 4.7) mmap(2), which fail with
the error ENOMEM upon encountering the soft limit of this
resource.
RLIMIT_FSIZE
This is the maximum size in bytes 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 (Linux 2.4.0 to Linux 2.4.24)
This is a limit on the combined number of flock(2) locks
and fcntl(2) leases that this process may establish.
RLIMIT_MEMLOCK
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.
Before Linux 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 messages nevertheless each consume some
system memory for bookkeeping 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 typically have special
meanings. For example, RLIM_INFINITY typically is the
same as -1. For more detail on the nice value, see
sched(7).
RLIMIT_NOFILE
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 processes, by being passed across UNIX
domain sockets. This limit applies to the sendmsg(2)
system call. For further details, see unix(7).
RLIMIT_NPROC
This is a limit on the number of extant process (or, more
precisely on Linux, threads) for the real user ID of the
calling process. So long as the current number of
processes belonging to this process's real user ID is
greater than or equal to this limit, fork(2) fails with
the error EAGAIN.
The RLIMIT_NPROC limit is not enforced for processes that
have either the CAP_SYS_ADMIN or the CAP_SYS_RESOURCE
capability, or run with real user ID 0.
RLIMIT_RSS
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_setparam(2).
For further details on real-time scheduling policies, see
sched(7)
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 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 sched_yield(2).
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.
For further details on real-time scheduling policies, see
sched(7)
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.
RLIMIT_STACK
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 (sigaltstack(2)).
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).
prlimit()
The Linux-specific prlimit() system call combines and extends the
functionality 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
getrlimit().
If the new_limit argument is 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 not NULL,
then a successful 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, effective, 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 to indicate the error.
EFAULT A pointer argument points to a location outside the
accessible address space.
EINVAL The value specified in resource is not valid; or, for
setrlimit() or prlimit(): rlim->rlim_cur was greater than
rlim->rlim_max.
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.
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├─────────────────────────────────────┼───────────────┼─────────┤
│ getrlimit(), setrlimit(), prlimit() │ Thread safety │ MT-Safe │
└─────────────────────────────────────┴───────────────┴─────────┘
getrlimit()
setrlimit()
POSIX.1-2008.
prlimit()
Linux.
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_MSGQUEUE, RLIMIT_NICE, RLIMIT_RTPRIO,
RLIMIT_RTTIME, and RLIMIT_SIGPENDING are Linux-specific.
getrlimit()
setrlimit()
POSIX.1-2001, SVr4, 4.3BSD.
prlimit()
Linux 2.6.36, glibc 2.13.
A child process created via fork(2) inherits its parent's
resource limits. Resource limits are preserved across execve(2).
Resource limits are per-process attributes that are shared by all
of the threads in a process.
Lowering the soft limit for a resource below the process's
current consumption 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 glibc 2.13, the glibc getrlimit() and setrlimit() wrapper
functions 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 delivered one (CPU) second later than they should have been.
This was fixed in Linux 2.6.8.
In Linux 2.6.x kernels before Linux 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 Linux
2.6.12; the problem is fixed in Linux 2.6.13.
In Linux 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 Linux 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 Linux 2.4.22 did not diagnose the error EINVAL for
setrlimit() when rlim->rlim_cur was greater than rlim->rlim_max.
Linux doesn't return an error when an attempt to set RLIMIT_CPU
has failed, for compatibility reasons.
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, the
kernel 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 _FILE_OFFSET_BITS=64).
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.
Since glibc 2.13, glibc works around the limitations of the
getrlimit() 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 <err.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/resource.h>
#include <time.h>
int
main(int argc, char *argv[])
{
pid_t pid;
struct rlimit old, new;
struct rlimit *newp;
if (!(argc == 2 || argc == 4)) {
fprintf(stderr, "Usage: %s <pid> [<new-soft-limit> "
"<new-hard-limit>]\n", argv[0]);
exit(EXIT_FAILURE);
}
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)
err(EXIT_FAILURE, "prlimit-1");
printf("Previous limits: soft=%jd; hard=%jd\n",
(intmax_t) old.rlim_cur, (intmax_t) old.rlim_max);
/* Retrieve and display new CPU time limit */
if (prlimit(pid, RLIMIT_CPU, NULL, &old) == -1)
err(EXIT_FAILURE, "prlimit-2");
printf("New limits: soft=%jd; hard=%jd\n",
(intmax_t) old.rlim_cur, (intmax_t) old.rlim_max);
exit(EXIT_SUCCESS);
}
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), signal(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
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⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
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Linux man-pages 6.9.1 2024-06-17 getrlimit(2)
Pages that refer to this page: homectl(1), prlimit(1), renice(1), strace(1), systemd-nspawn(1), brk(2), dup(2), execve(2), fcntl(2), fork(2), getpriority(2), getrusage(2), io_uring_register(2), io_uring_setup(2), madvise(2), memfd_secret(2), mlock(2), mmap(2), mremap(2), nice(2), open(2), perf_event_open(2), pidfd_getfd(2), pidfd_open(2), PR_SET_MM_START_BRK(2const), quotactl(2), seccomp(2), seccomp_unotify(2), select(2), shmctl(2), sigaltstack(2), syscalls(2), timer_create(2), write(2), errno(3), getdtablesize(3), io_uring_register_files(3), io_uring_register_files_sparse(3), io_uring_register_files_tags(3), io_uring_register_files_update(3), io_uring_register_files_update_tag(3), malloc(3), mq_open(3), pthread_attr_setstacksize(3), pthread_create(3), pthread_getattr_np(3), pthread_setschedparam(3), pthread_setschedprio(3), ulimit(3), core(5), limits.conf(5), lxc.container.conf(5), proc_pid_limits(5), proc_pid_stat(5), proc_pid_status(5), proc_sys_fs(5), proc_sys_kernel(5), systemd.exec(5), systemd-system.conf(5), capabilities(7), cgroups(7), credentials(7), fanotify(7), mq_overview(7), pthreads(7), sched(7), signal(7), time(7), unix(7), systemd-coredump(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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