sysconf - get configurable system variables
#include <unistd.h> long int sysconf(int name);
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
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.
The sysconf() function will fail if:
- [EINVAL]
- The value of the name argument is invalid.
None.
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:
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.sysconf(_SC_2_VERSION)
None.
confstr(), pathconf(), <limits.h>, <time.h>, <unistd.h>, the XCU specification of getconf.
Derived from the POSIX.1-1988 standard.