NAME
sysconf
- get configurable system variables
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
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 maxmimum 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).
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
sysctl(3)
STANDARDS
The
sysconf()
function conforms to
ISO/IEC 9945-1:1990 (``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.