Copyright (c) 1980 The Regents of the University of California.
All rights reserved.

%sccs.include.redist.man%

@(#)getrlimit.2 6.6 (Berkeley) 06/23/90

C 4 getrlimit, setrlimit - control maximum system resource consumption

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

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

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

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:

17 RLIMIT_CPU the maximum amount of cpu time (in seconds) to be used by each process.

17 RLIMIT_FSIZE the largest size, in bytes, of any single file that may be created.

17 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.

17 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.

17 RLIMIT_CORE the largest size, in bytes, of a core file that may be created.

17 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.

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 {
 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 \*(lqinfinite\*(rq 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 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.

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. The possible errors are:

15 [EFAULT] The address specified for rlp is invalid.

15 [EPERM] The limit specified to setrlimit would have raised the maximum limit value, and the caller is not the super-user.

csh(1), quota(2), sigvec(2), sigstack(2) There should be limit and unlimit commands in sh (1) as well as in csh.