NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON
GETRLIMIT(2) Linux Programmer's Manual GETRLIMIT(2)
getrlimit, setrlimit - 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);
getrlimit() and setrlimit() get and set resource limits respectively. Each
resource has an associated soft and hard limit, as defined by the rlimit
structure (the rlim argument to both getrlimit() and setrlimit()):
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()).
resource 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 non-zero, 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 2.2 through 2.6 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 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(2); 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).
On success, zero is returned. On error, -1 is returned, and errno is set
appropriately.
EFAULT rlim points outside the accessible address space.
EINVAL resource is not valid; or, for setrlimit(): rlim->rlim_cur was greater
than rlim->rlim_max.
EPERM An unprivileged process tried to use setrlimit() to increase a soft or
hard limit above the current hard limit; the CAP_SYS_RESOURCE
capability is required to do this. Or, the process tried to use
setrlimit() to increase the soft or hard RLIMIT_NOFILE limit above the
current kernel maximum (NR_OPEN).
SVr4, 4.3BSD, POSIX.1-2001. 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.
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.
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 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.
dup(2), fcntl(2), fork(2), getrusage(2), mlock(2), mmap(2), open(2),
quotactl(2), sbrk(2), shmctl(2), sigqueue(2), malloc(3), ulimit(3), core(5),
capabilities(7), signal(7)
This page is part of release 3.21 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2008-10-06 GETRLIMIT(2)