The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group

 NAME

sysconf - get configurable system variables

 SYNOPSIS



#include <unistd.h>

long int sysconf(int name);

 DESCRIPTION

The sysconf() function provides a method for the application to determine the current value of a configurable system limit or option (variable).

The name argument represents the system variable to be queried. The following table lists the minimal set of system variables from <limits.h>, <unistd.h> or <time.h> (for CLK_TCK) that can be returned by sysconf(), and the symbolic constants, defined in <unistd.h> that are the corresponding values used for name:

Variable Value of Name
ARG_MAX _SC_ARG_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
EXPR_NEST_MAX _SC_EXPR_NEST_MAX
LINE_MAX _SC_LINE_MAX
NGROUPS_MAX _SC_NGROUPS_MAX
OPEN_MAX _SC_OPEN_MAX
PASS_MAX _SC_PASS_MAX (LEGACY)
_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
RE_DUP_MAX _SC_RE_DUP_MAX
STREAM_MAX _SC_STREAM_MAX
TZNAME_MAX _SC_TZNAME_MAX
_XOPEN_CRYPT _SC_XOPEN_CRYPT
_XOPEN_ENH_I18N _SC_XOPEN_ENH_I18N
_XOPEN_SHM _SC_XOPEN_SHM
_XOPEN_VERSION _SC_XOPEN_VERSION
_XOPEN_XCU_VERSION _SC_XOPEN_XCU_VERSION
_XOPEN_REALTIME _SC_XOPEN_REALTIME
_XOPEN_REALTIME_THREADS _SC_XOPEN_REALTIME_THREADS
_XOPEN_LEGACY _SC_XOPEN_LEGACY
ATEXIT_MAX _SC_ATEXIT_MAX
IOV_MAX _SC_IOV_MAX
PAGESIZE _SC_PAGESIZE
PAGE_SIZE _SC_PAGE_SIZE
_XOPEN_UNIX _SC_XOPEN_UNIX
_XBS5_ILP32_OFF32 _SC_XBS5_ILP32_OFF32
_XBS5_ILP32_OFFBIG _SC_XBS5_ILP32_OFFBIG
_XBS5_LP64_OFF64 _SC_XBS5_LP64_OFF64
_XBS5_LPBIG_OFFBIG _SC_XBS5_LPBIG_OFFBIG
AIO_LISTIO_MAX _SC_AIO_LISTIO_MAX
AIO_MAX _SC_AIO_MAX
AIO_PRIO_DELTA_MAX _SC_AIO_PRIO_DELTA_MAX
DELAYTIMER_MAX _SC_DELAYTIMER_MAX
MQ_OPEN_MAX _SC_MQ_OPEN_MAX
MQ_PRIO_MAX _SC_MQ_PRIO_MAX
RTSIG_MAX _SC_RTSIG_MAX
SEM_NSEMS_MAX _SC_SEM_NSEMS_MAX
SEM_VALUE_MAX _SC_SEM_VALUE_MAX
SIGQUEUE_MAX _SC_SIGQUEUE_MAX
TIMER_MAX _SC_TIMER_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_TIMERS _SC_TIMERS
Maximum size of and data buffers _SC_GETGR_R_SIZE_MAX
Maximum size of and data buffers _SC_GETPW_R_SIZE_MAX
LOGIN_NAME_MAX _SC_LOGIN_NAME_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
TTY_NAME_MAX _SC_TTY_NAME_MAX
_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

 RETURN VALUE

If name is an invalid value, sysconf() returns -1 and sets errno to indicate the error. If the variable corresponding to name is associated with functionality that is not supported by the system, sysconf() returns -1 without changing the value of errno.

Otherwise, sysconf() returns the current variable value on the system. The value returned will not be more restrictive than the corresponding value described to the application when it was compiled with the implementation's <limits.h>, <unistd.h> or <time.h>. The value will not change during the lifetime of the calling process.

 ERRORS

The sysconf() function will fail if:
[EINVAL]
The value of the name argument is invalid.

 EXAMPLES

None.

 APPLICATION USAGE

As -1 is a permissible return value in a successful situation, an application 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 {_POSIX2_VERSION} symbolic constant, the utilities available via system() or popen() might not behave as described in the XCU specification. This would mean that the application is not running in an environment that conforms to the XCU specification. Some applications might be able to deal with this, others might not. However, the interfaces defined in this specification will continue to operate as specified, even if:

sysconf(_SC_2_VERSION)

reports that the utilities no longer perform as specified.

 FUTURE DIRECTIONS

None.

 SEE ALSO

confstr(), pathconf(), <limits.h>, <time.h>, <unistd.h>, the XCU specification of getconf.

DERIVATION

Derived from the POSIX.1-1988 standard.

UNIX ® is a registered Trademark of The Open Group.
Copyright © 1997 The Open Group
[ Main Index | XSH | XCU | XBD | XCURSES | XNS ]