GETRLIMIT(2) BSD Programmer's Manual GETRLIMIT(2)
NAME
getrlimit, setrlimit - control maximum system resource consumption
SYNOPSIS
#include <sys/time.h>
#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_CPU The maximum amount of cpu time (in seconds) to be used by
each process.
RLIMIT_FSIZE The largest size, in bytes, of any single file that may
be created.
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_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 automati-
cally by the system.
RLIMIT_CORE The largest size, in bytes, of a core file that may be
created.
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 pro-
cesses that are exceeding their declared resident set
size.
RLIMIT_MEMLOCK The maximum size, in bytes, of the amount of memory that
may be locked into memory by a process. (This limit is
not yet used by the system.)
RLIMIT_NPROC The maximum number of processes which may be created by
this user (according to the effective user ID of the pro-
cesses).
RLIMIT_NOFILE The maximum number of files that may be opened by a pro-
gram.
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 contin-
ue execution until it reaches the hard limit (or modifies its resource
limit). Other soft limits (for example RLIMIT_NPROC and RLIMIT_NOFILE)
may not be exceeded without increasing the soft limit; the soft limit may
be increased to a value up to and including the hard limit by any user.
The rlimit structure is used to specify the hard and soft limits on a re-
source:
struct rlimit {
int rlim_cur; /* current (soft) limit */
int rlim_max; /* hard limit */
};
Only the super-user may raise the maximum limits. Other users may only
alter rlimcur within the range from 0 to rlimmax or (irreversibly) low-
er rlimmax.
An ``infinite'' value for a limit is defined as RLIM_INFINITY
(0x7fffffff).
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).
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 gener-
ated; this normally terminates the process, but may be caught. When the
soft cpu time limit is exceeded, a signal SIGXCPU is sent to the offend-
ing 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 oc-
curred, and an error code is stored in the global location errno.
ERRORS
Getrlimit() and setrlimit() will fail if:
[EFAULT] The address specified for rlp is invalid.
[EPERM] The limit specified to setrlimit() would have raised the
maximum limit value, and the caller is not the super-user.
SEE ALSO
csh(1), quota(2), sigaction(2), sigstack(2)
BUGS
There should be limit and unlimit commands in sh(1) as well as in csh.
HISTORY
The getrlimit function call appeared in 4.2BSD.
4th Berkeley Distribution March 26, 1993 2