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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 && _FILE_OFFSET_BITS == 64
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).
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.
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. 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.
The prlimit() system call is available since Linux 2.6.36. Library support
is available since glibc 2.13.
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.
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().
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);
}
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.
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)
This page is part of release 3.41 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 2011-09-10 GETRLIMIT(2)
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The Linux Programming Interface,
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