SYSCONF(3) BSD Library Functions Manual SYSCONF(3)NAMEsysconf — 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 con‐
stants 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 Selec‐
tion 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 avail‐
able 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 sys‐
tem, 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 sys‐
tem, 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, oth‐
erwise -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 expres‐
sion 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 sup‐
port the C-Language Bindings Option, otherwise -1.
_SC_2_C_DEV
Return 1 if the system supports the C-Language Development Utili‐
ties Option, otherwise -1.
_SC_2_CHAR_TERM
Return 1 if the system supports at least one terminal type capa‐
ble 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, other‐
wise -1.
_SC_2_SW_DEV
Return 1 if the system supports the Software Development Utili‐
ties 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 functional‐
ity 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 spec‐
ified for the library functions sysctl(3). In addition, the following
error may be reported:
[EINVAL] The value of the name argument is invalid.
SEE ALSOgetconf(1), limits(3), 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.
BSD August 23, 2011 BSD
