NAME
getrlimit, setrlimit - control maximum system resource consumption
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/types.h>
#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() system call,
and set with the setrlimit() system call.
The resource argument is one of the following:
RLIMIT_AS The maximum amount (in bytes) of virtual memory the
process is allowed to map.
RLIMIT_CORE The largest size (in bytes) core(5) file that may be
created.
RLIMIT_CPU The maximum amount of cpu time (in seconds) to be used by
each process.
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) function.
RLIMIT_FSIZE The largest size (in bytes) file that may be created.
RLIMIT_MEMLOCK The maximum size (in bytes) which a process may lock into
memory using the mlock(2) system call.
RLIMIT_NOFILE The maximum number of open files for this process.
RLIMIT_NPROC The maximum number of simultaneous processes for this
user id.
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_SBSIZE The maximum size (in bytes) of socket buffer usage for
this user. This limits the amount of network memory, and
hence the amount of mbufs, that this user may hold at any
time.
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_SWAP The maximum size (in bytes) of the swap space that may be
reserved or used by all of this user id’s processes.
This limit is enforced only if bit 1 of the vm.overcommit
sysctl is set. Please see tuning(7) for a complete
description of this sysctl.
RLIMIT_NPTS The maximum number of pseudo-terminals created by this
user id.
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 {
rlim_t rlim_cur; /* current (soft) limit */
rlim_t rlim_max; /* maximum value for rlim_cur */
};
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.
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(2) function 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 VALUES
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
ERRORS
The getrlimit() and setrlimit() system calls 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(1), quotactl(2), sigaltstack(2), sigvec(2), sysctl(3),
ulimit(3)
HISTORY
The getrlimit() system call appeared in 4.2BSD.