NAME
sysconf
—
get configurable system
variables
LIBRARY
library “libc”
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.
_SC_SEM_NSEMS_MAX
- The maximum number of semaphores that one process can have open at a time, otherwise -1.
_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_THREAD_PRIO_PROTECT
- System supports the priority ceiling protocol for POSIX threads.
_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_CPUTIME
- The clockID CLOCK_PROCESS_CPUTIME_ID is supported, otherwise -1.
_SC_THREAD_CPUTIME
- The clockID CLOCK_THREAD_CPUTIME_ID is supported, otherwise -1.
_SC_DELAYTIMER_MAX
- The maximum number of overrun for a specific timer, 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. _SC_TIMER_MAX
- The number of timers available for
timer_create(2). This is also known as
_POSIX_TIMER_MAX
.
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
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.