NAME
getrlimit,
setrlimit —
control maximum system resource
consumption
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.
The resource parameter is one of the following:
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_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_STACK- The maximum size (in bytes) of the stack segment for a process, which defines how far a process's stack segment may be extended. Stack extension is performed automatically by the system, and is only used by the main thread of a process.
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 superuser 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.
A value of RLIM_SAVED_CUR
or RLIM_SAVED_MAX will be stored in
rlim_cur or rlim_max
respectively by
getrlimit()
if the value for the current or maximum resource limit cannot be stored in
an rlim_t. The values
RLIM_SAVED_CUR and
RLIM_SAVED_MAX should not be used in a call to
setrlimit()
unless they were returned by a previous call to
getrlimit().
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) and ulimit is the
sh(1)
equivalent.
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 than 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. A return value of -1 indicates that an error occurred, and an error code is stored in the global variable errno.
ERRORS
getrlimit() and
setrlimit() will fail if:
- [
EFAULT] - The address specified for rlp is invalid.
- [
EINVAL] - An unrecognized value for resource was specified.
In addition, setrlimit() may return the
following errors:
- [
EINVAL] - The new rlim_cur is greater than the new rlim_max.
- [
EPERM] - The new rlim_max is greater than the current maximum limit value, and the caller is not the superuser.
SEE ALSO
csh(1), sh(1), quotactl(2), sigaction(2), sigaltstack(2), sysctl(3)
STANDARDS
The getrlimit() and
setrlimit() functions conform to
IEEE Std 1003.1-2008 (“POSIX.1”).
The RLIMIT_MEMLOCK,
RLIMIT_NPROC, and RLIMIT_RSS
resources are non-standard extensions.
HISTORY
The getrlimit() and
setrlimit() system calls first appeared in
4.1cBSD.
BUGS
The RLIMIT_AS resource is missing.