sysconf
—
get configurable system variables
Standard C Library (libc, -lc)
#include <unistd.h>
long
sysconf
(int
name);
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
.
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.
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.
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.
The sysconf
function first appeared in
4.4BSD.
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.