sysconf(3) Library Functions Manual sysconf(3)
NAME
sysconf - Gets configurable system variables
LIBRARY
Standard C Library (libc.so, libc.a)
SYNOPSIS
#include <unistd.h>
long sysconf(
int name);
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
sysconf(): POSIX.1c, XSH4.2
Refer to the standards(5) reference page for more information about industry standards and associated tags.
PARAMETERS
Specifies the system variable to be queried.
DESCRIPTION
The sysconf() function provides a method for the application to determine the current value of a configurable system limit or whether
optional features are supported.
The following is a list of system variables that are returned by the sysconf() function, and the symbolic constants (shown in parentheses)
that are the corresponding values used for the name parameter. The variables come from either the limits.h, unistd.h, or time.h (for
CLK_TCK) header file and the symbolic constants are defined in unistd.h.
[Tru64 UNIX] Integer value indicating the revision of the AES to which the implementation is compliant. Maximum length, in bytes, of the
arguments for one of the exec functions, including environment data. [XSH4.2] Maximum number of functions that can be registered with
atexit() per process. (_SC_ATEXIT_MAX) Maximum value allowed for the obase variable with the bc command. Maximum number of elements per-
mitted in an array by the bc command. Maximum value allowed for the scale variable with the bc command. Maximum length of string con-
stants accepted by the bc command. Maximum number of simultaneous processes for each real user ID. Number of clock ticks per second. The
value of CLK_TCK may be variable, and it should not be assumed that CLK_TCK is a compile-time constant. Maximum number of weights that can
be assigned to an entry in the LC_COLLATE locale-dependent information in a locale-definition file Maximum number of expressions that can
be nested within parentheses by the expr command. [XSH4.2] Maximum number of iovec structures that one process has available for use with
readv() or writev(). Maximum length, in bytes, of a command's input line (either standard input or another file) when the utility is
described as processing text files. The length includes room for the trailing newline character. Maximum number of simultaneous supplemen-
tary group IDs for each process. Maximum number of files that one process can have open at one time.
[Tru64 UNIX] In some cases, the per-process soft descriptor limit is returned instead of the OPEN_MAX value. [XSH4.2] Page size
granularity for memory regions. [XSH4.2] Page size granularity for memory regions. Maximum number of characters returned by get-
pass(), (not including the terminating null character). The variable has a value of 1 if the system supports job control; other-
wise, -1 is returned. [POSIX] The variable has a value of 1 if the system supports POSIX reentrant functions; otherwise, -1 is
returned. The variable has a value of 1 if each process has a saved set user ID and a saved set group ID; otherwise, -1 is
returned. [POSIX] The variable has a value of 1 if the system supports the POSIX.1 Threads option; otherwise, -1 is returned.
[POSIX] The variable has a value of 1 if the system supports the POSIX.1 Threads Stack Size attribute option; otherwise, -1 is
returned. Date of approval of the most current version of the POSIX 1 standard that the system supports. The date is a 6-digit num-
ber, with the first 4 digits signifying the year and the last 2 digits the month. Different versions of the POSIX 1 standard are
periodically approved by the IEEE Standards Board, and the date of approval is used to distinguish between different versions. If
_POSIX_VERSION is defined, it is returned; otherwise, -1 is returned. The variable has a value of 1 if the system supports the C
language binding from POSIX 2; otherwise, -1 is returned.
The variable has a value of 1 if the system supports the optional C Language Development Utilities from POSIX 2; otherwise, -1 is
returned. Date of approval of the most current version of the POSIX 2 ISO C standard that the system supports. The date is a
6-digit number, with the first 4 digits signifying the year and the last 2 digits the month. Different versions of the POSIX 2 ISO C
standard are periodically approved by the IEEE Standards Board, and the date of approval is used to distinguish between different
versions.
The variable has a value of 1 if the system supports at least one terminal; otherwise -1 is returned.
The variable has a value of 1 if the system supports the FORTRAN Development Utilities Option from POSIX 2; otherwise, -1 is
returned.
The variable has a value of 1 if the system supports the FORTRAN Runtime Utilities Option from POSIX 2; otherwise, -1 is returned.
The variable has a value of 1 if the system supports the creation of new locales with the localedef command; otherwise, -1 is
returned. The variable has a value of 1 if the system supports the Software Development Utilities Option from POSIX 2; otherwise,
-1 is returned. The variable has a value of 1 if the system supports the User Portability Environment Option from POSIX 2; other-
wise, -1 is returned. Date of approval of the most current version of the POSIX 2 standard that the system supports. The date is a
6-digit number, with the first 4 digits signifying the year and the last 2 digits the month. Different versions of the POSIX 2 stan-
dard are periodically approved by the IEEE Standards Board, and the date of approval is used to distinguish between different ver-
sions. Maximum number of repeated occurrences of a regular expression permitted when using the interval-notation parameters, such
as the m and n parameters with the ed command. [POSIX] Maximum number of outstanding asynchronous I/O operations. [POSIX] Maxi-
mum number of I/O operations in a single list I/O call. [POSIX] The variable has a value of 1 if the system supports the POSIX
Asynchronous Input and Output option; otherwise -1 is returned. [POSIX] Maximum number of timer expiration overruns. [POSIX] The
variable has a value of 1 if the system supports the POSIX.1 File Synchronization option; otherwise -1 is returned. [POSIX] Maxi-
mum size of data buffers for getgrgid_r and getgrnam_r functions. [POSIX] Maximum size of data buffers for getpwuid_r and getpw-
nam_r functions. [POSIX] Maximum number of I/O operations in a single list I/O call. Avoid using _SC_LISTIO_AIO_MAX, which is
only retained for backward compatibility. Use only the CAE-UNIX98-compliant _SC_AIO_LISTIO_MAX operation. Size in bytes of storage
required for a login name, including the terminating null character. [POSIX] The variable has a value of 1 if the system supports
the POSIX.1 Memory Mapped Files option; otherwise -1 is returned. [POSIX] The variable has a value of 1 if the system supports the
POSIX.1 Process Memory Locking option; otherwise -1 is returned. [POSIX] The variable has a value of 1 if the system supports the
POSIX.1 Range Memory Locking option; otherwise -1 is returned. [POSIX] The variable has a value of 1 if the system supports the
POSIX.1 Memory Protection option; otherwise -1 is returned. [POSIX] The variable has a value of 1 if the system supports the
POSIX.1 Message Passing option; otherwise -1 is returned. [POSIX] Maximum number of open message queue descriptors a process may
hold. [POSIX] Maximum number of message priorities. [POSIX] The variable has a value of 1 if the system supports the POSIX.1
Prioritized Input and Output option; otherwise -1 is returned. [POSIX] The variable has a value of 1 if the system supports the
POSIX.1 Process Scheduling option; otherwise -1 is returned. [POSIX] The variable has a value of 1 if the system supports the
POSIX.1 Realtime Signals Extension option; otherwise -1 is returned. [POSIX] Maximum number of realtime signals reserved for
application use. [POSIX] The variable has a value of 1 if the system supports the POSIX.1 Shared Memory Objects option; otherwise
-1 is returned. [POSIX] The variable has a value of 1 if the system supports the POSIX.1 Semaphores option; otherwise -1 is
returned. [POSIX] Maximum number of semaphores that a process may have. [POSIX] Maximum value a semaphore can have.
[POSIX] Maximum number of queued signals that a process may send and have pending at the receiver(s) at any time. [POSIX] The
variable has a value of 1 if the system supports the POSIX.1 Synchronized Input and Output option; otherwise -1 is returned.
[POSIX] The variable has a value of 1 if the system supports the POSIX.1 Thread Stack Address Attribute option; otherwise -1 is
returned. [POSIX] Maximum number of attempts made to destroy a thread's thread-specific data values on thread exit. [POSIX] Max-
imum number of data keys that can be created per-process. [POSIX] The variable has a value of 1 if the system supports the POSIX.1
Priority Inheritance option; otherwise -1 is returned. [POSIX] The variable has a value of 1 if the system supports the POSIX.1
Priority Protection option; otherwise -1 is returned. [POSIX] The variable has a value of 1 if the system supports the POSIX.1
Thread Execution Scheduling option; otherwise -1 is returned. [POSIX] The variable has a value of 1 if the system supports the
POSIX.1 Process-Shared Synchronization option; otherwise -1 is returned. [POSIX] The variable has a value of 1 if the system sup-
ports the POSIX.1 Thread-Safe Functions option; otherwise -1 is returned. [POSIX] Minimum size in bytes of thread stack storage.
[POSIX] Maximum number of threads that can be created per process. [POSIX] Maximum number of timers per process. [POSIX] The
variable has a value of 1 if the system supports the POSIX.1 Timers option; otherwise -1 is returned. Maximum length of terminal
device name. Number of streams that one process can have open at one time. Maximum number of bytes supported for the name of a
time zone (not the length of the TZ environmental variable). The variable has a value of 1 if the system supports the X/Open
Encryption Feature Group; otherwise, -1 is returned. The variable has a value of 1 if the system supports the X/Open Enhanced
Internationalization Feature Group; otherwise, -1 is returned. The variable has a value of 1 if the system supports the X/Open
Shared Memory Feature Group; otherwise, -1 is returned. [XSH4.2] The variable has a value of 1 if the system supports the X/Open
UNIX Feature Group; otherwise, -1 is returned. Integer indicating the most current version of the X/Open standard that the system
supports. Integer indicating the most current version of the X/Open standard for Commands and Utilities that the system supports.
[Tru64 UNIX] The following values of name are supported as part of the System V Environment for compliance with the System V Release 4.0
with Multiprocessing (SVR4.0MP) standards: Number of processors in the system. Number of processors currently online.
RETURN VALUES
If the name parameter is an invalid value, the sysconf() function returns a value of -1, and sets errno to indicate the error. If the
variable corresponding to name is undefined, the sysconf() function returns a value of -1 without changing the value of errno.
ERRORS
If the following condition occurs, the sysconf() function sets errno to the corresponding value: The value of the name parameter is
invalid.
RELATED INFORMATION
Functions: pathconf(2)
Commands: getconf(1)
Standards: standards(5) delim off
sysconf(3)