GETRLIMIT(2) BSD GETRLIMIT(2)
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 Maximum amount of CPU time (in milliseconds) to be used
by each process. A Domain/OS BSD process will receive a
SIGXCPU signal when its CPU usage reaches RLIMIT_CPU.
RLIMIT_FSIZE Largest size, in bytes, of any single file that can be
created.
RLIMIT_DATA 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 Maximum size, in bytes, of the stack segment for child
processes; this defines the size of a program's stack
segment.
RLIMIT_CORE Largest size, in bytes, of a core file that can be
created. Since Domain/OS BSD doesn't create core
images, it doesn't implement this parameter.
RLIMIT_RSS Maximum size, in bytes, to which a process' resident set
size can 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. In Domain/OS BSD, calls to setrlimit specifying
RLIMIT_RSS have no other effect than saving the value
specified. Calls to getrlimit simply return the value
saved.
The above parameters impose operational limits on a process. If it
exceeds a limit (the CPU time, for example), a process may receive a
signal. Processes can change these "soft" limits within the hard limits
imposed by the system.
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 that is too large will
cause 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.
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), sigvec(2), sigstack(2)
DIAGNOSTICS
A successful call returns 0. A failed call returns -1 and sets errno to
indicate the error.
NOTES
There should be limit and unlimit commands in sh(1) as well as in csh.
Some UNIX implementations define RLIMIT_STACK to be the maximum size, in
bytes, of the stack segment for a process.