NAME

sysconf — get configurable system variables

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <unistd.h>

long
sysconf(int name);

DESCRIPTION

This interface is defined by IEEE Std 1003.1-1988 (“POSIX.1”). A far more complete interface is available using sysctl(3).

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 argument to execve(2).

_SC_ATEXIT_MAX

The maximum number of functions that may be registered with atexit(3).

_SC_BARRIERS

The version of IEEE Std 1003.1 (“POSIX.1”) and its Barriers option to which the system attempts to conform, otherwise -1.

_SC_CLOCK_SELECTION

Return the POSIX version the implementation of the Clock Selection Option on this system conforms to, or -1 if unavailable.

_SC_CHILD_MAX

The maximum number of simultaneous processes per user id.

_SC_CLK_TCK

The number of clock ticks per second.

_SC_FSYNC

Return 1 if the File Synchronization Option is available on this system, otherwise -1.

_SC_HOST_NAME_MAX

The maximum size of a hostname, including NULL.

_SC_IOV_MAX

The maximum number of iovec structures that a process has available for use with preadv(2), pwritev(2), readv(2), recvmsg(2), sendmsg(2) or writev(2).

_SC_JOB_CONTROL

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

_SC_LOGIN_NAME_MAX

Returns the size of the storage required for a login name, in bytes, including the terminating NUL.

_SC_MAPPED_FILES

Return 1 if the Memory Mapped Files Option is available on this system, otherwise -1.

_SC_MEMLOCK

Return 1 if the Process Memory Locking Option is available on this system, otherwise -1.

_SC_MEMLOCK_RANGE

Return 1 if the Range Memory Locking Option is available on this system, otherwise -1.

_SC_MEMORY_PROTECTION

Return 1 if the Memory Protection Option is available on this system, otherwise -1.

_SC_MONOTONIC_CLOCK

Return the POSIX version the implementation of the Monotonic Clock Option on this system conforms to, or -1 if unavailable.

_SC_NGROUPS_MAX

The maximum number of supplemental groups.

_SC_OPEN_MAX

The maximum number of open files per process.

_SC_PAGESIZE

The size of a system page in bytes.

_SC_PASS_MAX

The maximum length of the password, not counting NULL.

_SC_READER_WRITER_LOCKS

The version of IEEE Std 1003.1 (“POSIX.1”) and its Read-Write Locks option to which the system attempts to conform, otherwise -1.

_SC_REGEXP

Return 1 if POSIX regular expressions are available on this system, otherwise -1.

_SC_SEMAPHORES

The version of IEEE Std 1003.1 (“POSIX.1”) and its Semaphores option to which the system attempts to conform, otherwise -1.

Availability of the Semaphores option depends on the P1003_1B_SEMAPHORE kernel option.

_SC_SHELL

Return 1 if POSIX shell is available on this system, otherwise -1.

_SC_SPIN_LOCKS

The version of IEEE Std 1003.1 (“POSIX.1”) and its Spin Locks option to which the system attempts to conform, otherwise -1.

_SC_STREAM_MAX

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

_SC_SYMLOOP_MAX

The maximum number of symbolic links that may be expanded in a path name.

_SC_SYNCHRONIZED_IO

Return 1 if the Synchronized I/O Option is available on this system, otherwise -1.

_SC_THREADS

The version of IEEE Std 1003.1 (“POSIX.1”) and its Threads option to which the system attempts to conform, otherwise -1.

_SC_TIMERS

The version of IEEE Std 1003.1 (“POSIX.1”) and its Timers option to which the system attempts to conform, otherwise -1.

_SC_TZNAME_MAX

The minimum maximum number of types supported for the name of a timezone.

_SC_SAVED_IDS

Returns 1 if saved set-group 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_XOPEN_SHM

Return 1 if the X/Open Portability Guide Issue 4, Version 2 (“XPG4.2”) Shared Memory option is available on this system, otherwise -1.

Availability of the Shared Memory option depends on the SYSVSHM kernel option.

_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 parenthesis 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_GETGR_R_SIZE_MAX

The minimum size of the buffer passed to getgrgid_r(3) and getgrnam_r(3).

_SC_GETPW_R_SIZE_MAX

The minimum size of the buffer passed to getpwnam_r(3) and getpwuid_r(3).

_SC_NPROCESSORS_CONF

The number of processors configured.

_SC_NPROCESSORS_ONLN

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

_SC_PHYS_PAGES

The amount of physical memory on the system in _SC_PAGESIZE bytes.

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 functions sysctl(3). In addition, the following error may be reported:

[EINVAL]

The value of the name argument is invalid.

SEE ALSO

getconf(1), limits(3), sysctl(3)

STANDARDS

The sysconf() function conforms to IEEE Std 1003.1-1990 (“POSIX.1”). 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.