NAME
getrlimit,
setrlimit —
control maximum system resource consumption
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#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()
call, and set with the
setrlimit() call. Resources of an
arbitrary process can be obtained/changed using
sysctl(3).
The
resource parameter 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 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) system call.
-
-
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)
function.
-
-
RLIMIT_NOFILE
- The maximum number of open files for this process.
-
-
RLIMIT_NPROC
- The maximum number of simultaneous processes for this user
id.
-
-
RLIMIT_NTHR
- The maximum number of simultaneous threads (Lightweight
Processes) for this user id. Kernel threads and the first thread of each
process are not counted against this limit.
-
-
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 the socket buffers set by
the setsockopt(2)
SO_RCVBUF
and SO_SNDBUF
options.
-
-
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.
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; /* 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
.
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. Thus, shells provide built-in commands to
change the limits (
limit for
csh(1), or
ulimit
for
sh(1)).
The system refuses to extend the data or stack space when the limits would be
exceeded in the normal way: a
brk(2) 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 VALUES
A 0 return value indicates that the call succeeded, changing or returning the
resource limit. Otherwise, -1 is returned and the global variable
errno is set to indicate the error.
ERRORS
The
getrlimit() and
setrlimit() will fail
if:
-
-
- [
EFAULT
]
- The address specified for rlp is
invalid.
-
-
- [
EINVAL
]
- Specified resource was invalid; or,
in the setrlimit() call, the specified
rlim_cur exceeds the specified
rlim_max.
-
-
- [
EPERM
]
- The limit specified to setrlimit() would
have raised the maximum limit value, and the caller is not the
super-user.
The
setrlimit() function may fail if:
-
-
- [
EINVAL
]
- The limit specified to setrlimit() cannot
be lowered, because current usage is already higher than the limit.
SEE ALSO
csh(1),
sh(1),
mlock(2),
setsockopt(2),
sigaction(2),
sigaltstack(2),
libquota(3),
sysctl(3)
HISTORY
The
getrlimit() function call appeared in
4.2BSD.
BUGS
The resource limit
RLIMIT_RSS
is not implemented in
uvm(9) which means that process
memory size limits are not enforced.