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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
limits 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
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) 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) 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.
RLIMIT_CORE
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.
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). This limit
affects calls to brk(2) and sbrk(2), which fail with the error
ENOMEM upon encountering the soft limit of this resource.
RLIMIT_FSIZE
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.
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.
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 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 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 capability.
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 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
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 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
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.
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
attributes(7).
┌────────────────────────────────────┬───────────────┬─────────┐
│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_MSGQUEUE, RLIMIT_NICE, RLIMIT_RTPRIO, RLIMIT_RTTIME, and
RLIMIT_SIGPENDING are Linux-specific.
A child process created via fork(2) inherits its parent's resource
limits. Resource limits are preserved across execve(2).
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 version 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 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,
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 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 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.
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
values for its resource limit arguments.
Since version 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 <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)
int
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]);
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)
errExit("prlimit-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)
errExit("prlimit-2");
printf("New limits: soft=%lld; hard=%lld\n",
(long long) old.rlim_cur, (long long) 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 release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2017-03-13 GETRLIMIT(2)
Pages that refer to this page: prlimit(1), renice(1), brk(2), dup(2), execve(2), fcntl(2), fork(2), getpriority(2), getrusage(2), madvise(2), mlock(2), mmap(2), mremap(2), nice(2), open(2), perf_event_open(2), prctl(2), quotactl(2), seccomp(2), select(2), shmctl(2), sigaltstack(2), syscalls(2), timer_create(2), write(2), errno(3), getdtablesize(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(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)