NAME
getrlimit, setrlimit - control maximum system resource consumption

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

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

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(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 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.

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 "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 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 VALUE
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 possible errors are:

[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), sigvec(2), sigstack(2)

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