getrlimit(2)
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
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 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
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 a core file (see core(5)). 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:
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)
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 is 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
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. This limit is not enforced for processes that
have either the CAP_SYS_ADMIN or the CAP_SYS_RESOURCE
capability.
RLIMIT_RSS
Specifies the limit (in bytes) of 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)
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)
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.
For further details on real-time scheduling policies, see
sched(7)
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 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
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.
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.
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.
VERSIONS
The prlimit() system call is available since Linux 2.6.36. Library support is available since glibc 2.13.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7). Interface Attribute Value getrlimit(), setrlimit(), prlimit() Thread safety MT-Safe
CONFORMING TO
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.
NOTES
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().
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. 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().
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);
}
SEE ALSO
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), credentials(7), cgroups(7), signal(7)
COLOPHON
This page is part of release 4.09 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/.
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