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GETRLIMIT(2) Linux Programmer's Manual GETRLIMIT(2)
NAME
getrlimit, setrlimit - 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);
DESCRIPTION
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 behaviour. 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 termi-
nation upon first receipt of SIGXCPU.)
RLIMIT_DATA
The maximum size of the process's data segment (initialized data, uninitial-
ized data, and heap). This limit affects calls to brk() and sbrk(), 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() truncate())
fails with the error EFBIG.
RLIMIT_LOCKS (Early Linux 2.4 only)
A limit on the combined number of flock() locks and fcntl() 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 sepa-
rately from the per-process memory locks established by mlock(2), mlock-
all(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 pro-
cess. 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().
The first addend in the formula, which includes sizeof(struct msg_msg *) (4
bytes on Linux/x86), 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 kernel 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 calcu-
lated as 20 - rlim_cur. (This strangeness occurs because negative numbers
cannot be specified as resource limit values, since they typically have spe-
cial 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(), pipe(), dup(), etc.) to
exceed this limit yield the error EMFILE.
RLIMIT_NPROC
The maximum number of threads that can be created for the real user ID of
the calling process. Upon encountering this limit, fork() 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() 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 pro-
cess using sched_setscheduler(2) and sched_setparam(2).
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)).
RLIMIT_OFILE is the BSD name for RLIMIT_NOFILE.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropri-
ately.
ERRORS
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).
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 kernel 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 ceil-
ing 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.
NOTES
A child process created via fork(2) inherits its parents resource limits. Resource
limits are preserved across execve(2).
CONFORMING TO
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, and RLIMIT_SIGPENDING are Linux specific.
SEE ALSO
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)
Linux 2.6.13 2005-09-20 GETRLIMIT(2)
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