GETRLIMIT(2) BSD System Calls Manual GETRLIMIT(2)
NAME
getrlimit, setrlimit -- control maximum system resource consumption
SYNOPSIS
#include <sys/resource.h>
int
getrlimit(int resource, struct rlimit *rlp);
int
setrlimit(int resource, const struct rlimit *rlp);
DESCRIPTION
Limits on the consumption of system resources by the current process and each process it creates may be
obtained with the getrlimit() call, and set with the setrlimit() call.
The resource parameter is one of the following:
RLIMIT_CORE The largest size (in bytes) core file that may be created.
RLIMIT_CPU The maximum amount of cpu time (in seconds) to be used by each process.
RLIMIT_DATA The maximum size (in bytes) of the data segment for a process; this defines how far a
program may extend its break with the sbrk(2) system call.
RLIMIT_FSIZE The largest size (in bytes) file that may be created.
RLIMIT_MEMLOCK The maximum size (in bytes) which a process may lock into memory using the mlock(2)
function.
RLIMIT_NOFILE The maximum number of open files for this process.
RLIMIT_NPROC The maximum number of simultaneous processes for this user id.
RLIMIT_RSS The maximum size (in bytes) to which a process's resident set size may grow. This
imposes a limit on the amount of physical memory to be given to a process; if memory is
tight, the system will prefer to take memory from processes that are exceeding their
declared resident set size.
RLIMIT_STACK The maximum size (in bytes) of the stack segment for a process; this defines how far a
program's stack segment may be extended. Stack extension is performed automatically by
the system.
A resource limit is specified as a soft limit and a hard limit. When a soft limit is exceeded a
process may receive a signal (for example, if the cpu time or file size is exceeded), but it will be
allowed to continue execution until it reaches the hard limit (or modifies its resource limit). The
rlimit structure is used to specify the hard and soft limits on a resource,
struct rlimit {
rlim_t rlim_cur; /* current (soft) limit */
rlim_t rlim_max; /* hard limit */
};
Only the super-user may raise the maximum limits. Other users may only alter rlim_cur within the range
from 0 to rlim_max or (irreversibly) lower rlim_max.
Because this information is stored in the per-process information, this system call must be executed
directly by the shell if it is to affect all future processes created by the shell; limit is thus a
built-in command to csh(1) and ulimit is the sh(1) equivalent.
The system refuses to extend the data or stack space when the limits would be exceeded in the normal
way: a break call fails if the data space limit is reached. When the stack limit is reached, the
process receives a segmentation fault (SIGSEGV); if this signal is not caught by a handler using the
signal stack, this signal will kill the process.
A file I/O operation that would create a file larger that the process' soft limit will cause the write
to fail and a signal SIGXFSZ to be generated; this normally terminates the process, but may be caught.
When the soft cpu time limit is exceeded, a signal SIGXCPU is sent to the offending process.
RETURN VALUES
A 0 return value indicates that the call succeeded, changing or returning the resource limit. A
return value of -1 indicates that an error occurred, and an error code is stored in the global location
errno.
ERRORS
The getrlimit() and setrlimit() system calls will fail if:
[EFAULT] The address specified for rlp is invalid.
[EINVAL] resource is invalid.
The setrlimit() call will fail if:
[EINVAL] The specified limit is invalid (e.g., RLIM_INFINITY or lower than rlim_cur).
[EPERM] The limit specified would have raised the maximum limit value and the caller is not
the super-user.
LEGACY SYNOPSIS
#include <sys/types.h>
#include <sys/time.h>
#include <sys/resource.h>
The include files <sys/types.h> and <sys/time.h> are necessary.
COMPATIBILITY
setrlimit() now returns with errno set to EINVAL in places that historically succeeded. It no longer
accepts "rlim_cur = RLIM_INFINITY" for RLIM_NOFILE. Use "rlim_cur = min(OPEN_MAX, rlim_max)".
SEE ALSO
csh(1), sh(1), quota(2), sigaction(2), sigaltstack(2), sysctl(3), compat(5)
HISTORY
The getrlimit() function call appeared in 4.2BSD.
4th Berkeley Distribution June 4, 1993 4th Berkeley Distribution
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