getrlimit,
setrlimit —
control maximum system resource consumption
#include
<sys/resource.h>
int
getrlimit(
int
resource,
struct
rlimit *rlp);
int
setrlimit(
int
resource,
const
struct rlimit *rlp);
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
includes memory allocated via
malloc(3) and all other
anonymous memory mapped via
mmap(2).
-
-
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.
-
-
- The maximum size (in bytes) to which a process's resident set size may
grow. This setting is no longer enforced, but retained for
compatibility.
-
-
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.
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.
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.
csh(1),
sh(1),
quotactl(2),
sigaction(2),
sigaltstack(2),
sysctl(2)
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.
The
getrlimit() and
setrlimit() system calls first appeared in
4.1cBSD.
The
RLIMIT_AS resource is missing.
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