SYSCONF(3)

NAME
sysconf - get configurable system variables

SYNOPSIS
#include <unistd.h>
long
sysconf(int name);

DESCRIPTION
The sysconf() function provides a method for applications to determine the current value of a configurable system limit or option variable. The name argument specifies the system variable to be queried. Symbolic constants for each name value are found in the include file <unistd.h>.

The available values are as follows:

_SC_ARG_MAX
    The maximum bytes of arguments to exec(3) (including the environment).

_SC_CHILD_MAX
    The maximum number of simultaneous processes per user ID.

_SC_CLK_TCK
    The number of clock ticks per second.

_SC_NGROUPS_MAX
    The maximum number of supplemental groups.

_SC_OPEN_MAX
    The maximum number of open files per user ID.

_SC_STREAM_MAX
    The minimum maximum number of streams that a process may have open at any one time.

_SC_TZNAME_MAX
    The minimum maximum number of types supported for the name of a time zone.

_SC_JOB_CONTROL
    Returns 1 if job control is available on this system, otherwise -1.

_SC_SAVED_IDS
    Returns 1 if saved set-group-ID and saved set-user-ID is available, otherwise -1.

_SC_VERSION
    The version of ISO/IEC 9945 (POSIX 1003.1) with which the system attempts to comply.

_SC_BC_BASE_MAX
    The maximum ibase/obase values in the bc(1) utility.

_SC_BC_DIM_MAX
    The maximum array size in the bc(1) utility.

_SC_BC_SCALE_MAX
    The maximum scale value in the bc(1) utility.

_SC_BC_STRING_MAX
    The maximum string length in the bc(1) utility.

_SC_COLL_WEIGHTS_MAX
    The maximum number of weights that can be assigned to any entry of the LC_COLLATE order keyword in the locale definition file.

_SC_EXPR_NEST_MAX
    The maximum number of expressions that can be nested within parentheses by the expr(1) utility.

_SC_LINE_MAX
    The maximum length in bytes of a text-processing utility's input line.

_SC_RE_DUP_MAX
    The maximum number of repeated occurrences of a regular expression permitted when using interval notation.

_SC_2_VERSION
    The version of POSIX 1003.2 with which the system attempts to comply.

_SC_2_C_BIND
    Return 1 if the system's C-language development facilities support the C-Language Bindings Option, otherwise -1.

_SC_2_C_DEV
    Return 1 if the system supports the C-Language Development Utilities Option, otherwise -1.

_SC_2_CHAR_TERM
    Return 1 if the system supports at least one terminal type capable of all operations described in POSIX 1003.2, otherwise -1.

_SC_2_FORT_DEV
    Return 1 if the system supports the FORTRAN Development Utilities Option, otherwise -1.

_SC_2_FORT_RUN
    Return 1 if the system supports the FORTRAN Runtime Utilities Option, otherwise -1.

_SC_2_LOCALEDEF
    Return 1 if the system supports the creation of locales, otherwise -1.

_SC_2_SW_DEV
    Return 1 if the system supports the Software Development Utilities Option, otherwise -1.

_SC_2_UPE
    Return 1 if the system supports the User Portability Utilities Option, otherwise -1.

_SC_PAGESIZE
    The size of a system page in bytes.

_SC_FSYNC
    Return 1 if the system supports the File Synchronisation Option, otherwise -1.

_SC_XOPEN_SHM
    Return 1 if the system supports the Shared Memory Option, otherwise -1.

_SC_SEM_NSEMS_MAX
    The maximum number of semaphores in the system or -1 if the system does not support the Semaphores Option.

_SC_SEM_VALUE_MAX
    The maximum value a semaphore may have or -1 if the system does not support the Semaphores Option.

_SC_PHYS_PAGES
    The number of pages of physical memory.

_SC_AVPHYS_PAGES
    The number of pages of physical memory not currently in use by the system.

_SC_GETGR_R_SIZE_MAX
    The maximum size of the data buffer for the getgrgid_r() and getgrnam_r() functions.

_SC_GETPW_R_SIZE_MAX
    The maximum size of the data buffer for the getpwuid_r() and getpwnam_r() functions.

_SC_LOGIN_NAME_MAX
    The maximum length of a login name.

_SC_THREAD_SAFE_FUNCTIONS
    The level of support for thread-safe (re-entrant) functions.

_SC_NPROCESSORS_CONF
    The number of processors configured.

_SC_NPROCESSORS_ONLN
    The number of processors online (capable of running processes).

_SC_HOST_NAME_MAX
    The maximum size of a hostname, not counting NULL.

_SC_MONOTONIC_CLOCK
    Return the POSIX version of the implementation of the Monotonic Clock option that this system conforms to, or -1 if unavailable.

RETURN VALUES
If the call to sysconf() is not successful, -1 is returned and errno is set appropriately. Otherwise, if the variable is associated with functionality that is not supported, -1 is returned and errno is not modified. Otherwise, the current variable value is returned.

ERRORS
The sysconf() function may fail and set errno for any of the errors specified for the library function sysctl(2). In addition, the following error may be reported:

[EINVAL]
    The value of the name argument is invalid.

SEE ALSO
pathconf(2), sysctl(2)

STANDARDS
The sysconf() function conforms to p1003.1-88. The constants _SC_NPROCESSORS_CONF and _SC_NPROCESSORS_ONLN are not part of the standard, but are provided by many systems.

HISTORY
The sysconf() function first appeared in 4.4BSD.

BUGS
The value for _SC_STREAM_MAX is a minimum maximum, and required to be the same as ANSI C's FOPEN_MAX, so the returned value is a ridiculously small and misleading number.