sysconf(3C)

NAME

sysconf − get configurable system variables

SYNOPSIS

#include <unistd.h>

long sysconf(int name);

DESCRIPTION

The sysconf() function provides a method for an 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> and <unistd.h> that can be returned by sysconf() and the symbolic constants defined in <unistd.h> that are the corresponding values used for name on the SPARC and x86 platforms.

Name	Return Value	Meaning
_SC_ARG_MAX	ARG_MAX	Max size of argv[] plus envp[]
_SC_BC_BASE_MAX	BC_BASE_MAX	Maximum obase values allowed
		by bc
_SC_BC_DIM_MAX	BC_DIM_MAX	Max number of elements permitted
		in array by bc
_SC_BC_SCALE_MAX	BC_SCALE_MAX	Max scale value allowed by bc
_SC_BC_STRING_MAX	BC_STRING_MAX	Max length of string constant
		allowed by bc
_SC_CHILD_MAX	CHILD_MAX	Max processes allowed to a UID
_SC_CLK_TCK	CLK_TCK	Ticks per second (clock_t)
_SC_COLL_WEIGHTS_MAX	COLL_WEIGHTS_MAX	Max number of weights that can
		be assigned to entry of the
		LC_COLLATE order keyword in
		locale definition file
_SC_EXPR_NEST_MAX	EXPR_NEST_MAX	Max number of expressions that
		can be listed within parentheses
		by expr
_SC_LINE_MAX	LINE_MAX	Max length of input line
_SC_NGROUPS_MAX	NGROUPS_MAX	Max simultaneous groups to which
		one may belong
_SC_OPEN_MAX	OPEN_MAX	Max open files per process
_SC_PASS_MAX	PASS_MAX	Max number of significant bytes
		in a password
_SC_2_C_BIN	_POSIX2_C_BIND	Supports the C language
		binding option
_SC_2_C_DEV	_POSIX2_C_DEV	Supports the C language
		development utilities option
_SC_2_C_VERSION	_POSIX2_C_VERSION	Integer value indicating version of
		ISO POSIX-2 standard (Commands)
_SC_2_CHAR_TERM	_POSIX2_CHAR_TERM	Supports at least one terminal
_SC_2_FORT_DEV	_POSIX2_FORT_DEV	Supports FORTRAN Development
		Utilities Option
_SC_2_FORT_RUN	_POSIX2_FORT_RUN	Supports FORTRAN Run-time
		Utilities Option
_SC_2_LOCALEDEF	_POSIX2_LOCALEDEF	Supports the creation of locales
		by the localedef utility
_SC_2_SW_DEV	_POSIX2_SW_DEV	Supports the Software
		Development Utility Option
_SC_2_UPE	_POSIX2_UPE	Supports the User Portability
		Utilities Option
_SC_2_VERSION	_POSIX2_VERSION	Integer value indicating version of
		ISO POSIX-2 standard (C language
		binding)
_SC_JOB_CONTROL	_POSIX_JOB_CONTROL	Job control supported?
_SC_SAVED_IDS	_POSIX_SAVED_IDS	Saved IDs (seteuid()) supported?
_SC_VERSION	_POSIX_VERSION	POSIX.1 version supported
_SC_RE_DUP_MAX	RE_DUP_MAX	Max number of repeated
		occurrences of a regular
		expression permitted when using
		the interval notation \{m,n\}
_SC_STREAM_MAX	STREAM_MAX	Number of streams one processed
		can have open at a time
_SC_TZNAME_MAX	TZNAME_MAX	Max number of bytes supported
		for name of a time zone
_SC_XOPEN_CRYPT	_XOPEN_CRYPT	Supports X/Open Encryption
		Feature Group
_SC_XOPEN_ENH_I18N	_XOPEN_ENH_I18N	Supports X/Open Enhance
		Internationalization Feature Group
_SC_XOPEN_SHM	_XOPEN_SHM	Supports X/Open Shared Memory
		Feature Group
_SC_XOPEN_VERSION	_XOPEN_VERSION	Integer value indicating version of
		X/Open Portability Guide to which
		implementation conforms
_SC_XOPEN_XCU_VERSION	_XOPEN_XCU_VERSION	Integer value indicating version of
		XCU specification to which
		implementation conforms
_SC_ATEXIT_MAX	ATEXIT_MAX	Max number of functions that may
		be registered with atexit()
_SC_IOV_MAX	IOV_MAX	Max number of iovec structures
		that one process has available for
		use with readv() and writev()
_SC_PAGESIZE	PAGESIZE	System memory page size
_SC_PAGE_SIZE	PAGESIZE	Same as _SC_PAGESIZE
_SC_XOPEN_UNIX	_XOPEN_UNIX	Supports X/Open CAE
		Specification, August 1994,
		System Interfaces and Headers,
		Issue 4, Version 2
_SC_LOGNAME_MAX	LOGNAME_MAX
_SC_NPROCESSORS_CONF		Number of processors configured
_SC_NPROCESSORS_ONLN		Number of processors online
_SC_PHYS_PAGES		Total number of pages of
		physical memory in system
_SC_AVPHYS_PAGES		Number physical memory pages
		not currently in use by system
_SC_AIO_LISTIO_MAX	AIO_LISTIO_MAX	Max number of I/O operations
		in a single list I/O call
		supported by implementation
_SC_AIO_MAX	AIO_MAX	Max number of outstanding
		asynchronous I/O operations
		supported by implementation
_SC_AIO_PRIO_DELTA_MAX	AIO_PRIO_DELTA_MAX	Max amount by which a process
		can decrease its asynchronous
		I/O priority level from its own
		scheduling priority
_SC_DELAYTIMER_MAX	DELAYTIMER_MAX	Max number of timer
		expiration overruns
_SC_GETGR_R_SIZE_MAX	NSS_BUFLEN_GROUP	Max size of group entry buffer.
_SC_GETPW_R_SIZE_MAX	NSS_BUFLEN_PASSWD	Max size of password entry buffer.
_SC_LOGIN_NAME_MAX	LOGNAME_MAX + 1	Max length of login name.
_SC_MQ_OPEN_MAX	MQ_OPEN_MAX	Max number of open message
		queues a process may hold.
_SC_MQ_PRIO_MAX	MQ_PRIO_MAX	Max number of message priorities
		supported by implementation.
_SC_RTSIG_MAX	RTSIG_MAX	Max number of realtime signals
		reserved for application use
		in this implementation.
_SC_SEM_NSEMS_MAX	SEM_NSEMS_MAX	Max number of semaphores
		that a process may have.
_SC_SEM_VALUE_MAX	SEM_VALUE_MAX	Max value a semaphore may have.
_SC_SIGQUEUE_MAX	SIGQUEUE_MAX	Max number of queued signals
		that a process may send and have
		pending at receiver(s) at a time.
_SC_TIMER_MAX	TIMER_MAX	Max number of timers per process
		supported by implementation.
_SC_ASYNCHRONOUS_IO	_POSIX_ASYNCHRONOUS_IO	Supports Asynchronous I/O.
_SC_FSYNC	_POSIX_FSYNC	Supports File Synchronization.
_SC_MAPPED_FILES	_POSIX_MAPPED_FILES	Supports Memory Mapped Files.
_SC_MEMLOCK	_POSIX_MEMLOCK	Supports Process Memory Locking.
_SC_MEMLOCK_RANGE	_POSIX_MEMLOCK_RANGE	Supports Range Memory Locking.
_SC_MEMORY_PROTECTION	_POSIX_MEMORY_PROTECTION	Supports Memory Protection.
_SC_MESSAGE_PASSING	_POSIX_MESSAGE_PASSING	Supports Message Passing.
_SC_PRIORITIZED_IO	_POSIX_PRIORITIZED_IO	Supports Prioritized I/O.
_SC_PRIORITY_SCHEDULING	_POSIX_PRIORITY_SCHEDULING	Supports Process Scheduling
_SC_REALTIME_SIGNALS	_POSIX_REALTIME_SIGNALS	Supports Realtime Signals.
_SC_SEMAPHORES	_POSIX_SEMAPHORES	Supports Semaphores.
_SC_SHARED_MEMORY_	_POSIX_SHARED_MEMORY_	Supports Shared Memory
OBJECTS	OBJECTS	Objects.
_SC_SYNCHRONIZED_IO	_POSIX_SYNCHRONIZED_IO	Supports Synchronized I/O.
_SC_TIMERS	_POSIX_TIMERS	Supports Timers.
_SC_THREAD_DESTRUCTOR_	PTHREAD_DESTRUCTOR_	Number attempts made to destroy
ITERATIONS	ITERATIONS	thread-specific data on thread exit.
_SC_THREAD_KEYS_MAX	PTHREAD_KEYS_MAX	Max number of data keys
		per process.
_SC_THREAD_STACK_MIN	PTHREAD_STACK_MIN	Min byte size of thread
		stack storage.
_SC_THREAD_THREADS_MAX	PTHREAD_THREADS_MAX	Max number of threads per process.
_SC_TTY_NAME_MAX	TTYNAME_MAX	Max length of tty device name.
_SC_THREADS	_POSIX_THREADS	Supports Threads option.

_SC_THREAD_ATTR_STACKADDR	_POSIX_THREAD_ATTR_STACKADDR
	Supports Thread Stack Address Attribute option.
_SC_THREAD_ATTR_STACKSIZE	_POSIX_THREAD_ATTR_STACKSIZE
	Supports Thread Stack Size Attribute option.
_SC_THREAD_PRIORITY_SCHEDULING	_POSIX_THREAD_PRIORITY_SCHEDULING
	Supports Thread Execution Scheduling option.
_SC_THREAD_PRIO_INHERIT	_POSIX_THREAD_PRIO_INHERIT
	Supports Priority Inheritance option.
_SC_THREAD_PRIO_PROTECT	_POSIX_THREAD_PRIO_PROTECT
	Supports Priority Protection option.
_SC_THREAD_PROCESS_SHARED	_POSIX_THREAD_PROCESS_SHARED
	Supports Process-Shared Synchronization option.
_SC_THREAD_SAFE_FUNCTIONS	_POSIX_THREAD_SAFE_FUNCTIONS
	Supports Thread-Safe Functions option.

The following table lists the names and return values for SPARC and x86 platform variables.

Name	Return Value
	SPARC, x86
_SC_COHER_BLKSZ	EINVAL
_SC_SPLIT_CACHE	EINVAL
_SC_ICACHE_SZ	EINVAL
_SC_DCACHE_SZ	EINVAL
_SC_ICACHE_LINESZ	EINVAL
_SC_DCACHE_LINESZ	EINVAL
_SC_ICACHE_BLKSZ	EINVAL
_SC_DCACHE_BLKSZ	EINVAL
_SC_DCACHE_TBLKSZ	EINVAL
_SC_ICACHE_ASSOC	EINVAL
_SC_DCACHE_ASSOC	EINVAL

RETURN VALUES

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.

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Architecture	SPARC and x86
MT-Level	MT-Safe, Async-Signal-Safe

NOTES

A call to setrlimit() may cause the value of OPEN_MAX to change.

Multiplying sysconf(_SC_PHYS_PAGES) or sysconf(_SC_AVPHYS_PAGES) by sysconf(_SC_PAGESIZE) to determine memory amount in bytes can exceed the maximum values representable in a long or unsigned long.

_SC_PHYS_PAGES and _SC_AVPHYS_PAGES are specific to Solaris 2.3 and later releases.

The value of CLK_TCK may be variable and it should not be assumed that CLK_TCK is a compile-time constant.

Calling sysconf() with _SC_THREAD_KEYS_MAX or _SC_THREAD_THREADS_MAX returns −1, because no maximum limit can be determined. The system supports at least the minimum values defined by _POSIX_THREAD_KEYS_MAX and _POSIX_THREAD_THREADS_MAX and can support higher values depending upon system resources.

The _SC_THREAD_PRIO_INHERIT and _SC_THREAD_PRIO_PROTECT variables are currently not supported. A call to sysconf() with these variables as arguments returns −1.

SunOS 5.6 — Last change: 20 Mar 1997

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