GETRLIMIT(2)

NAME
getrlimit, setrlimit - control maximum system resource consumption

SYNOPSIS
#include <sys/time.h>
#include <sys/resource.h>

int getrlimit(resource, rlp)
int resource;
struct rlimit *rlp;

int setrlimit(resource, rlp)
int resource;
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() (see brk(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 automatically 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 processes that are exceeding their declared resident set size.

RLIMIT_NOFILE
    one more than the maximum value that the system may assign to a newly created descriptor. This limit constrains the number of descriptors that a process may create.

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 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 {
    	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 rlim_cur within the range from 0 to rlim_max or (irreversibly) lower rlim_max.

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 brk() or sbrk() call will fail if the data space limit is reached, or the process will be sent a SIGSEGV when the stack limit is reached which will kill the process unless SIGSEGV is handled on a separate signal stack (since the stack cannot be extended, there is no way to send a signal!).

A file I/O operation that would create a file that is too large generates a signal SIGXFSZ; 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
getrlimit() and setrlimit() return:

0   on success.

-1  on failure and set errno to indicate the error.

ERRORS

EFAULT
    The address specified by rlp was invalid.

EINVAL
    An invalid resource was specified.

In addition to the above, setrlimit() may set errno to:

EINVAL
    The new rlim_cur exceeds the new rlim_max.

EPERM
    The limit specified would have raised the maximum limit value, and the caller was not the super-user.

SEE ALSO
csh(1), sh(1), brk(2), getdtablesize(2), quotactl(2)

BUGS

There should be limit and unlimit commands in sh(1) as well as in csh(1).