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Manual page for SYSCONF(2P)

sysconf - (POSIX only) get configurable system variables

SYNOPSIS

#include <unistd.h>

long sysconf(int name);

DESCRIPTION

The information in this specification applies only to POSIX applications.

The sysconf function provides a method for an application to determined the current value of a configurable system limit or option.

The name argument represents the system variable to be queried. The following variables are supported:

Variable: name Value
{ARG_MAX}: {_SC_ARG_MAX}
{CHILD_MAX}: {_SC_CHILD_MAX}
{clock ticks/second}: {_SC_CLK_TCK}
{NGROUPS_MAX}: {_SC_NGROUPS_MAX}
{OPEN_MAX}: {_SC_OPEN_MAX}
{STREAM_BUF}: {_SC_STREAM_BUF}
{TZNAME_MAX}: {_SC_TZNAME_MAX}
{_POSIX_JOB_CONTROL}: {_SC_JOB_CONTROL}
{_POSIX_SAVED_IDS}: {_SC_SAVED_IDS}
{_POSIX_VERSION}: {_SC_VERSION}

The meaning of each variable is as follows:

Variable: Description
{ARG_MAX}: Maximum length of all arguments + environment strings to exec().
{CHILD_MAX}: Maximum number of simultaneous processes per real user ID.
{clock ticks/second}: The number of clock ticks per second.
{NGROUPS_MAX}: Maximum number of simultaneous supplementary group IDs per process.
{OPEN_MAX}: Maximum number of simultaneous open files per process.
{STREAM_BUF}: The number of streams that one process can have open at one time.
{TZNAME_MAX}: The maximum number of bytes supported for the name of a time zone.
{_POSIX_JOB_CONTROL}: If defined, the system supports POSIX job control.
{_POSIX_SAVED_IDS}: If defined, saved set-user-IDs and set-group-IDS are supported.
{_POSIX_VERSION}: The version of POSIX supported by the system.

The values for the variables above are given in the headers <limits.h> or <unistd.h>. The symbolic constants used as values for name are given in <unistd.h>.

RETURN VALUE

Upon successful completion sysconf returns the current variable value on the system. If name is an invalid value, sysconf returns -1. If the variable corresponding to name is associated with functionality that is not supported by the system, sysconf shall return -1 without changing the value of errno.

ERRORS

If any of the following conditions occur, sysconf returns -1 and set errno to the corresponding value:

[EINVAL]: The value of name is invalid.