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getrlimit(S)


getrlimit, setrlimit -- control maximum system resource consumption

Syntax

cc . . . -lc
#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 a variety of system resources by a process and each process it creates 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 a pair of values: one specifying the current (soft) limit, the other a maximum (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.

Limits may have an infinite value of RLIM_INFINITY. rlp is a pointer to an rlimit structure that includes the following members:

   rlim_t	rlim_cur;	/* current (soft) limit */
   rlim_t	rlim_max;	/* hard limit */
rlim_t is an arithmetic data type to which objects of type int, size_t, and off_t can be cast without loss of information.

The possible resources, their descriptions, and the actions taken when current limit is exceeded, are summarized in the table below:

Resources Description Action
RLIMIT_CORE 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. The writing of a core file will terminate at this size.
RLIMIT_CPU The maximum amount of CPU time in seconds used by a process. SIGXCPU is sent to the process.
RLIMIT_DATA The maximum size of a process's heap in bytes. brk(S) will fail with errno set to ENOMEM.
RLIMIT_FSIZE 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. SIGXFSZ is sent to the process. If the process is holding or ignoring SIGXFSZ, continued attempts to increase the size of a file beyond the limit will fail with errno set to EFBIG.
RLIMIT_NOFILE The maximum number of open file descriptors that the process can have. Functions that create new file descriptors will fail with errno set to EMFILE.
RLIMIT_STACK The maximum size of a process's single autogrow stack in bytes. The system will not automatically grow the stack beyond this limit. SIGSEGV is sent to the offending process. If that process is holding SIGSEGV or if the containing process is ignoring SIGSEGV or is catching SIGSEGV and the process has not made arrangements to use an alternate stack (see sigaltstack(S)), the disposition of SIGSEGV will be set to SIG_DFL before it is sent. Consequently, the containing process is terminated.
RLIMIT_AS The maximum size of a process's mapped address space in bytes. brk(S) and mmap(S) functions will fail with errno set to ENOMEM. In addition, the automatic stack growth will fail with the effects outlined above.

 +--------------+-----------------+-----------------+
 |Resources     | Description     | Action          |
 +--------------+-----------------+-----------------+
 |RLIMIT_CORE   | The maximum     | The writing of  |
 |              | size of a core  | a core file     |
 |              | file in bytes   | will terminate  |
 |              | that may be     | at this size.   |
 |              | created by a    |                 |
 |              | process. A      |                 |
 |              | limit of 0 will |                 |
 |              | prevent the     |                 |
 |              | creation of a   |                 |
 |              | core file.      |                 |
 +--------------+-----------------+-----------------+
 |RLIMIT_CPU    | The maximum     | SIGXCPU is sent |
 |              | amount of CPU   | to the process. |
 |              | time in seconds |                 |
 |              | used by a       |                 |
 |              | process.        |                 |
 +--------------+-----------------+-----------------+
 |RLIMIT_DATA   | The maximum     | brk(S) will     |
 |              | size of a       | fail with errno |
 |              | process's heap  | set to ENOMEM.  |
 |              | in bytes.       |                 |
 +--------------+-----------------+-----------------+
 |RLIMIT_FSIZE  | The maximum     | SIGXFSZ is sent |
 |              | size of a file  | to the process. |
 |              | in bytes that   | If the process  |
 |              | may be created  | is holding or   |
 |              | by a process. A | ignoring        |
 |              | limit of 0 will | SIGXFSZ,        |
 |              | prevent the     | continued       |
 |              | creation of a   | attempts to     |
 |              | file.           | increase the    |
 |              |                 | size of a file  |
 |              |                 | beyond the      |
 |              |                 | limit will fail |
 |              |                 | with errno set  |
 |              |                 | to EFBIG.       |
 +--------------+-----------------+-----------------+
 |RLIMIT_NOFILE | The maximum     | Functions that  |
 |              | number of open  | create new file |
 |              | file            | descriptors     |
 |              | descriptors     | will fail with  |
 |              | that the        | errno set to    |
 |              | process can     | EMFILE.         |
 |              | have.           |                 |
 +--------------+-----------------+-----------------+
 |RLIMIT_STACK  | The maximum     | SIGSEGV is sent |
 |              | size of a       | to the          |
 |              | process's       | offending       |
 |              | single autogrow | process. If     |
 |              | stack in bytes. | that process is |
 |              | The system will | holding SIGSEGV |
 |              | not             | or if the       |
 |              | automatically   | containing      |
 |              | grow the stack  | process is      |
 |              | beyond this     | ignoring        |
 |              | limit.          | SIGSEGV or is   |
 |              |                 | catching        |
 |              |                 | SIGSEGV and the |
 |              |                 | process has not |
 |              |                 | made            |
 |              |                 | arrangements to |
 |              |                 | use an          |
 |              |                 | alternate stack |
 |              |                 | (see            |
 |              |                 | sigaltstack(S)  |
 |              |                 | the disposition |
 |              |                 | of SIGSEGV will |
 |              |                 | be set to       |
 |              |                 | SIG_DFL before  |
 |              |                 | it is sent.     |
 |              |                 | Consequently,   |
 |              |                 | the containing  |
 |              |                 | process is      |
 |              |                 | terminated.     |
 +--------------+-----------------+-----------------+
 |RLIMIT_AS     | The maximum     | brk(S) and      |
 |              | size of a       | mmap(S)         |
 |              | process's       | functions will  |
 |              | mapped address  | fail with errno |
 |              | space in bytes. | set to ENOMEM.  |
 |              |                 | In addition,    |
 |              |                 | the automatic   |
 |              |                 | stack growth    |
 |              |                 | will fail with  |
 |              |                 | the effects     |
 |              |                 | outlined above. |
 +--------------+-----------------+-----------------+
Because limit information is stored in the per-process information, the shell built-in ulimit must directly execute this system call if it is to affect all future processes created by the shell.

The value of the current limit of the following resources affect these implementation defined constants:

Limit Implementation defined constant
RLIMIT_NOFILE {OPEN_MAX}

 +--------------+---------------------------------+
 |Limit         | Implementation defined constant |
 +--------------+---------------------------------+
 |RLIMIT_NOFILE | {OPEN_MAX}                      |
 +--------------+---------------------------------+

Return values

On success, getrlimit returns 0. On failure, getrlimit returns -1 and sets errno to identify the error.

Diagnostics

Under the following conditions, the functions getrlimit and setrlimit fail and set errno to:

[EINVAL]
An invalid resource was specified; or in a setrlimit call, the new rlim_cur exceeds the new rlim_max.

[EPERM]
The limit specified to setrlimit would have raised the maximum limit value and the calling process is not the superuser.

Files


/lib/libc.a
linking library

See also

getrusage(S), malloc(S), open(S), sigaltstack(S), signal(S)

Standards conformance

getrlimit and setrlimit are conformant with:

AT&T SVID Issue 3.


© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003