sysconf - get numeric value of configurable system variable

Syntax

#include <unistd.h>

long int sysconf(int name); 

Description

sysconf() can be used to determine the current value of a configurable system variable

specified by name. These values represent the configurable limits of the operating system.

The table below lists the system variables from the headers limits.h, unistd.h or time.h for which values can be queried using sysconf(). The symbolic constants containing the corresponding values used for name are defined in unistd.h:

System variable	Value of name (constant)
ARG_MAX	_SC_ARG_MAX
AIO_LISTIO_MAX	_SC_AIO_LISTIO_MAX
AIO_MAX	_SC_AIO_MAX
AIO_PRIO_DELTA_MAX	_SC_AIO_PRIO_DELTA_MAX
BC_BASE_MAX	_SC_BC_BASE_MAX
BC_DIM_MAX	_SC_BC_DIM_MAX
BC_SCALE_MAX	_SC_BC_SCALE_MAX
BC_STRING_MAX	_SC_BC_STRING_MAX
CHILD_MAX	_SC_CHILD_MAX
CLK_TCK	_SC_CLK_TCK
COLL_WEIGHTS_MAX	_SC_COLL_WEIGHTS_MAX
DELAYTIMER_MAX	_SC_DELAYTIMER_MAX
EXPR_NEST_MAX	_SC_EXPR_NEST_MAX
LINE_MAX	_SC_LINE_MAX
LOGIN_NAME_MAX	_SC_LOGIN_NAME_MAX
NGROUPS_MAX	_SC_NGROUPS_MAX
MQ_OPEN_MAX	_SC_MQ_OPEN_MAX
MQ_PRIO_MAX	_SC_MQ_PRIO_MAX
OPEN_MAX	_SC_OPEN_MAX
POSIX_ASYNCHRONOUS_IO	_SC_ASYNCHRONOUS_IO
_POSIX_FSYNC	_SC_FSYNC
_POSIX_MAPPED_FILES	_SC_MAPPED_FILES
_POSIX_MEMLOCK	_SC_MEMLOCK
_POSIX_MEMLOCK_RANGE	_SC_MEMLOCK_RANGE
_POSIX_MEMORY_PROTECTION	_SC_MEMORY_PROTECTION
_POSIX_MESSAGE_PASSING	_SC_MESSAGE_PASSING
_POSIX_PRIORITIZED_IO	_SC_PRIORITIZED_IO
_POSIX_PRIORITY_SCHEDULING	_SC_PRIORITY_SCHEDULING
_POSIX_REALTIME_SIGNALS	_SC_REALTIME_SIGNALS
_POSIX_SEMAPHORES	_SC_SEMAPHORES
_POSIX_SHARED_MEMORY_OBJECTS	_SC_SHARED_MEMORY_OBJECTS
_POSIX_SYNCHRONIZED_IO	_SC_SYNCHRONIZED_IO
_POSIX_THREADS	_SC_THREADS
_POSIX_THREAD_ATTR_STACKADDR	_SC_THREAD_ATTR_STACKADDR
_POSIX_THREAD_ATTR_STACKSIZE	_SC_THREAD_ATTR_STACKSIZE
_POSIX_THREAD_PRIORITY_SCHEDULING	_SC_THREAD_PRIORITY_SCHEDULING
_POSIX_THREAD_PRIO_INHERIT	_SC_THREAD_PRIO_INHERIT
_POSIX_THREAD_PRIO_PROTECT	_SC_THREAD_PRIO_PROTECT
_POSIX_THREAD_PROCESS_SHARED	_SC_THREAD_PROCESS_SHARED
_POSIX_THREAD_SAFE_FUNCTIONS	_SC_THREAD_SAFE_FUNCTIONS
_POSIX_TIMERS	_SC_TIMERS
_POSIX2_C_BIND	_SC_2_C_BIND
_POSIX2_C_DEV	_SC_2_C_DEV
_POSIX2_C_VERSION	_SC_2_C_VERSION
_POSIX2_CHAR_TERM	_SC_2_CHAR_TERM
_POSIX2_FORT_DEV	_SC_2_FORT_DEV
_POSIX2_FORT_RUN	_SC_2_FORT_RUN
_POSIX2_LOCALEDEF	_SC_2_LOCALEDEF
_POSIX2_SW_DEV	_SC_2_SW_DEV
_POSIX2_UPE	_SC_2_UPE
_POSIX2_VERSION	_SC_2_VERSION
_POSIX_JOB_CONTROL	_SC_JOB_CONTROL
_POSIX_SAVED_IDS	_SC_SAVED_IDS
_POSIX_VERSION	_SC_VERSION
PTHREAD_DESTRUCTOR_ITERATIONS	_SC_THREAD_DESTRUCTOR_ITERATIONS
PTHREAD_KEYS_MAX	_SC_THREAD_KEYS_MAX
PTHREAD_STACK_MIN	_SC_THREAD_STACK_MIN
PTHREAD_THREADS_MAX	_SC_THREAD_THREADS_MAX
PTHREAD_DESTRUCTOR_ITERATIONS	_SC_THREAD_DESTRUCTOR_ITERATIONS
PTHREAD_KEYS_MAX	_SC_THREAD_KEYS_MAX
PTHREAD_STACK_MIN	_SC_THREAD_STACK_MIN
PTHREAD_THREADS_MAX	_SC_THREAD_THREADS_MAX
RE_DUP_MAX	_SC_RE_DUP_MAX
RTSIG_MAX	_SC_RTSIG_MAX
SEM_NSEMS_MAX	_SC_SEM_NSEMS_MAX
SEM_VALUE_MAX	_SC_SEM_VALUE_MAX
STREAM_MAX	_SC_STREAM_MAX
SIGQUEUE_MAX	_SC_SIGQUEUE_MAX
TIMER_MAX	_SC_TIMER_MAX
TTY_NAME_MAX	_SC_TTY_NAME_MAX
TZNAME_MAX	_SC_TZNAME_MAX
Maximal size of the data buffer of the functions getgrgid_r() and getgrnam_r()	_SC_GETGR_R_SIZE_MAX
Maximal size of the data buffer of the functions getpwnam_r() and getpwuid_r()	_SC_GETPW_R_SIZE_MAX

Return val.

Current numeric value of name

if successful.
The returned value will not be lower than the corresponding value in the application if it were compiled with the implementation ́s limits.h or unistd.h. The value will not change during the lifetime of the calling process.

-1

if name is an invalid value. errno is set to indicate the error.

if name does not have a defined value. In this case, the value of errno is not changed.

Errors

sysconf() will fail if:

EINVAL

The value of the name argument is invalid.

Notes

Since all return values are permitted in a successful situation, applications wishing to check for error situations should set errno to 0, then call sysconf(), and if it returns -1, check to see if errno is non-zero.

If the value of sysconf(_SC_2_VERSION) is not equal to the value of the symbolic constant _POSIX2_VERSION, the commands available via system() or popen() might not behave in conformance with XPG4. The interfaces described in this manual will, however, continue to operate in conformance with XPG4 even if sysconf(_SC_2_VERSION) reports that the commands no longer perform as defined in the standard.

See also

pathconf(), limits.h, time.h, unistd.h.