GETRLIMIT
Section: Linux Programmer's Manual (2)
Updated: 2011-09-10
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NAME
getrlimit, setrlimit, prlimit - get/set resource limits
SYNOPSIS
#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 && _FILE_OFFSET_BITS == 64
DESCRIPTION
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 only set 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
-
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
-
Maximum size of
core
file.
When 0 no core dump files are created.
When nonzero, larger dumps are truncated to this size.
- RLIMIT_CPU
-
CPU time limit in seconds.
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
-
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
-
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)
-
A limit on the combined number of
flock(2)
locks and
fcntl(2)
leases that this process may establish.
- RLIMIT_MEMLOCK
-
The maximum number of bytes of memory that may be locked
into RAM.
In effect this limit is rounded down to the nearest multiple
of the system page size.
This limit affects
mlock(2)
and
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)
-
Specifies the 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:
bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
attr.mq_maxmsg * attr.mq_msgsize
where
attr
is the
mq_attr
structure specified as the fourth argument to
mq_open(3).
The first addend in the formula, which includes
sizeof(struct msg_msg *)
(4 bytes on Linux/i386), 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)
-
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.
(This strangeness occurs 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.)
- RLIMIT_NOFILE
-
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.)
- RLIMIT_NPROC
-
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.
- RLIMIT_RSS
-
Specifies the limit (in pages) of the process's resident set
(the number of virtual pages resident in RAM).
This limit only has effect in Linux 2.4.x, x < 30, and there only
affects calls to
madvise(2)
specifying
MADV_WILLNEED.
- RLIMIT_RTPRIO (Since Linux 2.6.12, but see BUGS)
-
Specifies a ceiling on the real-time priority that may be set for
this process using
sched_setscheduler(2)
and
sched_setparam(2).
- RLIMIT_RTTIME (Since Linux 2.6.25)
-
Specifies 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.
- RLIMIT_SIGPENDING (Since Linux 2.6.8)
-
Specifies the 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 only enforced 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
-
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, 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.
RETURN VALUE
On success, these system calls return 0.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
- 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.
Or, the caller tried to increase the hard
RLIMIT_NOFILE
limit above the current kernel maximum
(NR_OPEN).
Or, 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.
VERSIONS
The
prlimit()
system call is available since Linux 2.6.36.
Library support is available since glibc 2.13.
CONFORMING TO
getrlimit(),
setrlimit():
SVr4, 4.3BSD, POSIX.1-2001.
prlimit():
Linux-specific.
RLIMIT_MEMLOCK
and
RLIMIT_NPROC
derive from BSD and are not specified in POSIX.1-2001;
they are present on the BSDs and Linux, but on few other implementations.
RLIMIT_RSS
derives from BSD and is not specified in POSIX.1-2001;
it is nevertheless present on most implementations.
RLIMIT_MSGQUEUE,
RLIMIT_NICE,
RLIMIT_RTPRIO,
RLIMIT_RTTIME,
and
RLIMIT_SIGPENDING
are Linux-specific.
NOTES
A child process created via
fork(2)
inherits its parent's resource limits.
Resource limits are preserved across
execve(2).
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.
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().
EXAMPLE
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_FAILURE);
}
BUGS
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.
Kernels before 2.4.22 did not diagnose the error
EINVAL
for
setrlimit()
when
rlim->rlim_cur
was greater than
rlim->rlim_max.
SEE ALSO
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),
signal(7)
COLOPHON
This page is part of release 3.35 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://man7.org/linux/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- prlimit()
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- NOTES
-
- EXAMPLE
-
- BUGS
-
- SEE ALSO
-
- COLOPHON
-
© Andrew Scott 2006 -
2024,
All Rights Reserved