getrlimit(2) getrlimit(2)
NAME [Toc] [Back]
getrlimit(), setrlimit() - control maximum resource consumption
SYNOPSIS [Toc] [Back]
#include <sys/resource.h>
int getrlimit(int resource, struct rlimit *rlp);
int setrlimit(int resource, const struct rlimit *rlp);
DESCRIPTION [Toc] [Back]
Limits on the consumption of a variety of resources by the calling
process may be obtained with getrlimit() and set with setrlimit().
Each call to either getrlimit() or setrlimit() identifies a specific
resource to be operated upon as well as a resource limit. A resource
limit is represented by an rlimit structure, pointed to by the rlp
argument and includes the following members:
rlim_t rlim_cur; /* Current (soft) limit */
rlim_t rlim_max; /* Hard limit */
The rlim_cur member specifies the current or soft limit and the
rlim_max member specifies the maximum or hard limit. Soft limits may
be changed by a process to any value that is less than or equal to the
hard limit. A process may (irreversibly) lower its hard limit to any
value that is greater than or equal to the soft limit. Only a process
with appropriate privileges can raise a hard limit. Both hard and
soft limits can be changed in a single call to setrlimit() subject to
the constraints described above.
The value RLIM_INFINITY, defined in <sys/resource.h>, is considered to
be larger than any other limit value. If a call to getrlimit()
returns RLIM_INFINITY for a resource, it means the implementation does
not enforce limits on that resource. Specifying RLIM_INFINITY as any
resource limit value on a successful call to setrlimit() inhibits
enforcement of that resource limit.
The following resources are defined:
RLIMIT_CORE This is the maximum size of a core file in
bytes that may be created by a process. A
limit of 0 will prevent the creation of a
core file. If this limit is exceeded, the
writing of a core file will terminate at this
size.
RLIMIT_CPU This is the maximum amount of CPU time in
seconds allowed for a UNIX 95 conforming
application. If this limit is exceeded,
SIGXCPU is generated for the application.
The default action for a UNIX 95 conforming
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getrlimit(2) getrlimit(2)
application is to kill the process and leave
a core file. If the process is blocking,
catching or ignoring SIGXCPU, the behavior is
unspecified in UNIX 95 standard. The HP-UX
implementation blocks, catches or ignores
SIGXCPU as specified by the UNIX 95
conforming applications. Be aware that an
application designed with the HP-UX behavior
may not be portable if and when UNIX
standards define a different behavior. If
the application is a Classic HP-UX
application, the kernel will not send the
signal as a result of exceeding the CPU
limit. However, if this signal is sent
explicitly to a Classic HP-UX application by
another application or via the kill -XCPU
command, this signal will be delivered and
the default action will be taken. In order
for an application to be UNIX 95, it must be
linked with unix95.o either directly or
indirectly. For example:
% cc /usr/lib/unix95.o prog.c
Or,
% export UNIX95=1
% cc prog.c
RLIMIT_DATA This is the maximum size of a process data
segment in bytes. If this limit is exceeded,
the brk(), malloc(), and sbrk() functions
will fail with errno set to ENOMEM. Attempts
to set RLIMIT_DATA to RLIM_INFINITY will
always fail. The upper limit is enforced
through the tunable maxdsiz.
RLIMIT_FSIZE This option is only applicable to UNIX 95
conforming applications. Please see
RLIMIT_CPU option above for explanation on
UNIX 95 conforming applications. This is the
maximum size of a file in bytes that may be
created by a process. A limit of 0 will
prevent the creation of a file. If a write
or truncate operation would cause this limit
to be exceeded, SIGXFSZ is generated for the
process. If the process is blocking,
catching or ignoring SIGXFSZ, continued
attempts to increase the size of a file from
end-of-file to beyond the limit will fail
with errno set to [EFBIG].
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getrlimit(2) getrlimit(2)
RLIMIT_NOFILE This is a number one greater than the maximum
value that the system may assign to a newlycreated
descriptor. If this limit is
exceeded, functions that allocate new file
descriptors may fail with errno set to
[EMFILE]. This limit constrains the number
of file descriptors that a process may
allocate.
RLIMIT_STACK This is the maximum size of a process stack
in bytes. The implementation will not
automatically grow the stack beyond this
limit. If this limit is exceeded, SIGSEGV is
generated for the process. If the process is
blocking or ignoring SIGSEGV, or is catching
SIGSEGV and has not made arrangements to use
an alternate stack, the disposition of
SIGSEGV will be set to SIG_DFL before it is
generated. Attempts to set RLIMIT_STACK to
RLIM_INFINITY will always fail. The upper
limit is enforced through the tunable
maxssiz.
RLIMIT_AS This is the maximum size of a process's total
available memory, in bytes. If this limit is
exceeded, the brk(), malloc(), mmap(), and
sbrk() functions will fail with errno set to
[ENOMEM]. In addition, the automatic stack
growth will fail with the effects outlined
above.
RLIMIT_AIO_OPS This is the maximum number of POSIX
Asynchronous I/O operations that a process
can have enqueued simultaneously. If this
limit is exceeded, the aio_read(),
aio_write(), and lio_listio() functions will
fail with errno set to [EAGAIN].
RLIMIT_AIO_MEM This is the maximum number of bytes of memory
that can be locked simultaneously by POSIX
Asynchronous I/O requests from a single
process.
RETURN VALUE [Toc] [Back]
Upon successful completion, getrlimit() and setrlimit() return 0.
Otherwise, these functions return -1 and set errno to indicate the
error.
ERRORS [Toc] [Back]
The getrlimit() and setrlimit() functions will fail if:
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getrlimit(2) getrlimit(2)
[EINVAL] An invalid resource was specified; or in a
setrlimit() call, the new rlim_cur exceeds the new
rlim_max.
[EFAULT] The address specified for rlp is invalid.
Reliable detection of this error is implementation
dependent.
[EPERM] The limit specified to setrlimit() would have
raised the maximum limit value, and the calling
process does not have appropriate privileges.
The setrlimit() function may fail if:
[EINVAL] The limit specified cannot be lowered because
current usage is already higher than the limit.
[EPERM] The rlp argument specified a hard or soft limit
higher than the current hard limit value, and the
caller does not have the appropriate privileges.
[EINVAL] A user with appropriate privileges has attempted
to raise rlp->rlim_cur or rlp->rlim_max to a value
greater than the system is capable of supporting.
[EINVAL] The value of rlp->rlim_cur is less than the number
of file descriptors the process already has
allocated.
[EINVAL] The value of rlp->rlim_max is less than the
current soft limit.
WARNINGS [Toc] [Back]
The maximum size of a file returned by getrlimit() is in terms of
bytes. The maximum size of a file returned by ulimit (see ulimit(2))
with UL_GETFSIZE is in terms of blocks of size 512 bytes. The value
returned by ulimit with UL_GETFSIZE may thus have to be rounded down
to a multiple of 512.
The total address space used by a process depends on the platform it
is run on. When porting applications, limits set by setrlimit() with
RLIMIT_AS may need to be adjusted. For example, programs tend to use
more memory on Itanium-based systems than on PA-RISC systems.
AUTHOR [Toc] [Back]
getrlimit() and setrlimit() were developed by HP, AT&T, and the
University of California, Berkeley.
SEE ALSO [Toc] [Back]
brk(2), exec(2), fork(2), creat64(2), malloc(3C), open(2),
sigaltstack(2), sysconf(2), ulimit(2), maxdsiz(5), maxssiz(5),
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getrlimit(2) getrlimit(2)
<stropts.h>, <sys/resource.h>.
CHANGE HISTORY [Toc] [Back]
First released in Issue 4, Version 2.
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