getrusage
GETRLIMIT(2) Linux Programmer’s Manual GETRLIMIT(2)
NAME
getrlimit, getrusage, setrlimit - get/set resource limits and usage
SYNOPSIS
#include <sys/time.h>
#include <sys/resource.h>
#include <unistd.h>
int getrlimit(int resource, struct rlimit *rlim);
int getrusage(int who, struct rusage *usage);
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 setr-
limit()):
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 corre-
sponding 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 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 setr-
limit()).
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 gen-
erate a SIGSEGV that kills the process when no alternate stack
has been made available). 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 cre-
ated. 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 2.2 and 2.4 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 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() 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 pro-
cess, 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
A limit on the combined number of flock() locks and fcntl()
leases that this process may establish. (Early Linux 2.4
only.)
RLIMIT_MEMLOCK
The maximum number of bytes of virtual memory that may be
locked into RAM using mlock() and mlockall().
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_STACK
The maximum size of the process stack, in bytes. Upon reaching
this limit, a SIGSEGV signal is generated. To handle this sig-
nal, a process must employ an alternate signal stack (sigalt-
stack(2)).
RLIMIT_OFILE is the BSD name for RLIMIT_NOFILE.
getrusage returns the current resource usages, for a who of either
RUSAGE_SELF or RUSAGE_CHILDREN. The former asks for resources used by
the current process, the latter for resources used by those of its
children that have terminated and have been waited for.
struct rusage {
struct timeval ru_utime; /* user time used */
struct timeval ru_stime; /* system time used */
long ru_maxrss; /* maximum resident set size */
long ru_ixrss; /* integral shared memory size */
long ru_idrss; /* integral unshared data size */
long ru_isrss; /* integral unshared stack size */
long ru_minflt; /* page reclaims */
long ru_majflt; /* page faults */
long ru_nswap; /* swaps */
long ru_inblock; /* block input operations */
long ru_oublock; /* block output operations */
long ru_msgsnd; /* messages sent */
long ru_msgrcv; /* messages received */
long ru_nsignals; /* signals received */
long ru_nvcsw; /* voluntary context switches */
long ru_nivcsw; /* involuntary context switches */
};
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is
set appropriately.
ERRORS
EFAULT rlim or usage points outside the accessible address space.
EINVAL getrlimit or setrlimit is called with a bad resource, or
getrusage is called with a bad who.
EPERM A non-superuser tries to use setrlimit() to increase the soft
or hard limit above the current hard limit, or a superuser
tries to increase RLIMIT_NOFILE above the current kernel maxi-
mum.
CONFORMING TO
SVr4, BSD 4.3
NOTE
Including <sys/time.h> is not required these days, but increases
portability. (Indeed, struct timeval is defined in <sys/time.h>.)
On Linux, if the disposition of SIGCHLD is set to SIG_IGN then the
resource usages of child processes are automatically included in the
value returned by RUSAGE_CHILDREN, although POSIX 1003.1-2001 explic-
itly prohibits this.
The above struct was taken from BSD 4.3 Reno. Not all fields are
meaningful under Linux. Right now (Linux 2.4, 2.6) only the fields
ru_utime, ru_stime, ru_minflt, ru_majflt, and ru_nswap are maintained.
SEE ALSO
dup(2), fcntl(2), fork(2), mlock(2), mlockall(2), mmap(2), open(2),
quotactl(2), sbrk(2), wait3(2), wait4(2), malloc(3), ulimit(3), sig-
nal(7)
Linux 2003-11-28 GETRLIMIT(2)
