man pages section 3: Basic Library Functions

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Updated: July 2014
 
 

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_2_C_BIND            _POSIX2_C_BIND             Supports the C lang-
                                                   uage binding option
_SC_2_C_DEV             _POSIX2_C_DEV              Supports the C lang-
                                                   uage development
                                                   utilities option
_SC_2_C_VERSION         _POSIX2_C_VERSION          Integer value
                                                   indicates 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 creation
                                                   of locales by the
                                                   localedef utility
_SC_2_SW_DEV            _POSIX2_SW_DEV             Supports Software
                                                   Development Utility
                                                   Option
_SC_2_UPE               _POSIX2_UPE                Supports User
                                                   Portability
                                                   Utilities Option
_SC_2_VERSION           _POSIX2_VERSION            Integer value
                                                   indicates version
                                                   of ISO POSIX-2
                                                   standard (C language
                                                   binding)
_SC_AIO_LISTIO_MAX      AIO_LISTIO_MAX             Max number of I/O
                                                   operations in a
                                                   single list I/O call
                                                   supported
_SC_AIO_MAX             AIO_MAX                    Max number of
                                                   outstanding
                                                   asynchronous I/O
                                                   operations supported
_SC_AIO_PRIO_DELTA_MAX  AIO_PRIO_DELTA_MAX         Max amount by which
                                                   process can decrease
                                                   its asynchronous
                                                   I/O priority level
                                                   from its own
                                                   scheduling priority
_SC_ARG_MAX             ARG_MAX                    Max size of argv[]
                                                   plus envp[]
_SC_ASYNCHRONOUS_IO     _POSIX_ASYNCHRONOUS_IO     Supports
                                                   Asynchronous I/O
_SC_ATEXIT_MAX          ATEXIT_MAX                 Max number of
                                                   functions that can
                                                   be registered with
                                                   atexit()
_SC_AVPHYS_PAGES                                   Number of physical
                                                   memory pages not
                                                   currently in use by
                                                   system
_SC_BARRIERS            _POSIX_BARRIERS            Supports Barriers
                                                   option
_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_CLOCK_SELECTION     _POSIX_CLOCK_SELECTION     Supports Clock 
                                                   Selection option
_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_CPUID_MAX                                      Max possible 
                                                   processor ID
_SC_DELAYTIMER_MAX      DELAYTIMER_MAX             Max number of timer
                                                   expiration overruns
_SC_EXPR_NEST_MAX       EXPR_NEST_MAX              Max number of
                                                   parentheses by expr
_SC_FSYNC               _POSIX_FSYNC               Supports File
                                                   Synchronization
_SC_GETGR_R_SIZE_MAX                               Max size of group
                                                   entry buffer
_SC_GETPW_R_SIZE_MAX                               Max size of password
                                                   entry buffer
_SC_HOST_NAME_MAX       _POSIX_HOST_NAME_MAX       Maximum length of a
                                                   host name (excluding
                                                   terminating null)
_SC_IOV_MAX             IOV_MAX                    Max number of iovec
                                                   structures available
                                                   to one process for
                                                   use with readv()
                                                   and writev()
_SC_JOB_CONTROL         _POSIX_JOB_CONTROL         Job control
                                                   supported?
_SC_LINE_MAX            LINE_MAX                   Max length of input
                                                   line
_SC_LOGIN_NAME_MAX      LOGNAME_MAX + 1            Max length of login
                                                   name
_SC_LOGNAME_MAX         LOGNAME_MAX
_SC_MAPPED_FILES        _POSIX_MAPPED_FILES        Supports Memory
                                                   Mapped Files
_SC_MAXPID                                         Max pid value
_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_MONOTONIC_CLOCK     _POSIX_MONOTONIC_CLOCK     Supports Monotonic
                                                   Clock option
_SC_MQ_OPEN_MAX         MQ_OPEN_MAX                Max number of open
                                                   message queues a
                                                   process can hold
_SC_MQ_PRIO_MAX         MQ_PRIO_MAX                Max number of
                                                   message priorities
                                                   supported
_SC_NGROUPS_MAX         NGROUPS_MAX                Max simultaneous
                                                   groups to which
                                                   one can belong
_SC_NPROCESSORS_CONF                               Number of processors
                                                   configured
_SC_NPROCESSORS_MAX                                Max number of
                                                   processors supported
                                                   by platform
_SC_NPROCESSORS_ONLN                               Number of processors
                                                   online
_SC_OPEN_MAX            OPEN_MAX                   Max open files per
                                                   process
_SC_PAGESIZE            PAGESIZE                   System memory page
                                                   size
_SC_PAGE_SIZE           PAGESIZE                   Same as _SC_PAGESIZE
_SC_PASS_MAX            PASS_MAX                   Max number of
                                                   significant bytes
                                                   in a password
_SC_PHYS_PAGES                                     Total number of
                                                   pages of physical
                                                   memory in system
_SC_PRIORITIZED_IO      _POSIX_PRIORITIZED_IO      Supports Prioritized
                                                   I/O
_SC_PRIORITY_SCHEDULING _POSIX_PRIORITY_SCHEDULING Supports Process
                                                   Scheduling
_SC_RAW_SOCKETS         _POSIX_RAW_SOCKETS         Supports Raw Sockets
                                                   option
_SC_RE_DUP_MAX          RE_DUP_MAX                 Max number of
                                                   repeated occurrences
                                                   of a regular
                                                   expression permitted
                                                   when using interval
                                                   notation \{m,n\}
_SC_READER_WRITER_LOCKS _POSIX_READER_WRITER_LOCKS Supports IPV6 option
_SC_REALTIME_SIGNALS    _POSIX_REALTIME_SIGNALS    Supports Realtime
                                                   Signals
_SC_REGEXP              _POSIX_REGEXP              Supports Regular
                                                   Expression Handling
                                                   option
_SC_RTSIG_MAX           RTSIG_MAX                  Max number of
                                                   realtime signals
                                                   reserved for
                                                   application use
_SC_SAVED_IDS           _POSIX_SAVED_IDS           Saved IDs
                                                   (seteuid())
                                                   supported?
_SC_SEM_NSEMS_MAX       SEM_NSEMS_MAX              Max number of POSIX
                                                   semaphores a process
                                                   can have
_SC_SEM_VALUE_MAX       SEM_VALUE_MAX              Max value a POSIX
                                                   semaphore can have
_SC_SEMAPHORES          _POSIX_SEMAPHORES          Supports Semaphores
_SC_SHARED_MEMORY_      _POSIX_SHARED_MEMORY_      Supports Shared
   OBJECTS                 OBJECTS                 Memory Objects
_SC_SHELL               _POSIX_SHELL               Supports POSIX shell
_SC_SIGQUEUE_MAX        _SIGQ_MAX                  Max number of queued
                                                   signals that a
                                                   process can send and
                                                   have pending at
                                                   receiver(s) at a
                                                   time
_SC_SPAWN               _POSIX_SPAWN               Supports Spawn option
_SC_SPIN_LOCKS          _POSIX_SPIN_LOCKS          Supports Spin Locks
                                                   option
_SC_STACK_PROT                                     Default stack
                                                   protection
_SC_STREAM_MAX          STREAM_MAX                 Number of streams
                                                   one process can
                                                   have open at a time
_SC_SYMLOOP_MAX         _POSIX_SYMLOOP_MAX         Max number of symbolic
                                                   links that can be
                                                   reliably traversed in
                                                   the resolution of a
                                                   pathname in the absence
                                                   of a loop
_SC_SYNCHRONIZED_IO     _POSIX_SYNCHRONIZED_IO     Supports
                                                   Synchronized I/O
_SC_THREAD_ATTR_        _POSIX_THREAD_ATTR_        Supports Thread
   STACKADDR               STACKADDR               Stack Address
                                                   Attribute option
_SC_THREAD_ATTR_        _POSIX_THREAD_ATTR_        Supports Thread
   STACKSIZE               STACKSIZE               Stack Size
                                                   Attribute option
_SC_THREAD_DESTRUCTOR_  PTHREAD_DESTRUCTOR_        Number attempts made
   ITERATIONS              ITERATIONS              to destroy thread-
                                                   specific data on
                                                   thread exit
_SC_THREAD_KEYS_MAX     PTHREAD_KEYS_MAX           Max number of data
                                                   keys per process
_SC_THREAD_PRIO_        _POSIX_THREAD_PRIO_        Supports Priority
   INHERIT                 INHERIT                 Inheritance option
_SC_THREAD_PRIO_        _POSIX_THREAD_PRIO_        Supports Priority
   PROTECT                 PROTECT                 Protection option
_SC_THREAD_PRIORITY_    _POSIX_THREAD_PRIORITY_    Supports Thread
   SCHEDULING              SCHEDULING              Execution
                                                   Scheduling option
_SC_THREAD_PROCESS_     _POSIX_THREAD_PROCESS_     Supports
   SHARED                  SHARED                  Process-Shared
                                                   Synchronization
                                                   option
_SC_THREAD_SAFE_        _POSIX_THREAD_SAFE_        Supports Thread-Safe
   FUNCTIONS               FUNCTIONS               Functions option
_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_THREADS             _POSIX_THREADS             Supports Threads
                                                   option
_SC_TIMEOUTS            _POSIX_TIMEOUTS            Supports Timeouts
                                                   option
_SC_TIMER_MAX           TIMER_MAX                  Max number of timer
                                                   per process
                                                   supported
_SC_TIMERS              _POSIX_TIMERS              Supports Timers
_SC_TTY_NAME_MAX        TTYNAME_MAX                Max length of tty
                                                   device name
_SC_TZNAME_MAX          TZNAME_MAX                 Max number of bytes
                                                   supported for name
                                                   of a time zone
_SC_V6_ILP32_OFF32      _POSIX_V6_ILP32_OFF32      Supports  X/Open
                                                   ILP32 w/32-bit
                                                   offset build 
                                                   environment
_SC_V6_ILP32_OFFBIG     _POSIX_V6_ILP32_OFFBIG     Supports  X/Open
                                                   ILP32 w/64-bit
                                                   offset build 
                                                   environment
_SC_V6_LP64_OFF64       _POSIX_V6_LP64_OFF64       Supports  X/Open
                                                   LP64 w/64-bit
                                                   offset build 
                                                   environment
_SC_V6_LPBIG_OFFBIG     _POSIX_V6_LPBIG_OFFBIG     Same as 
                                                   _SC_V6_LP64_OFF64
_SC_VERSION             _POSIX_VERSION             POSIX.1 version
                                                   supported
_SC_XBS5_ILP32_OFF32    _XBS_ILP32_OFF32           Indicates support
                                                   for X/Open ILP32
                                                   w/32-bit offset
                                                   build environment
_SC_XBS5_ILP32_OFFBIG   _XBS5_ILP32_OFFBIG         Indicates support
                                                   for X/Open ILP32
                                                   w/64-bit offset
                                                   build environment
_SC_XBS5_LP64_OFF64     _XBS5_LP64_OFF64           Indicates support of
                                                   X/Open LP64,
                                                   64-bit offset
                                                   build environment
_SC_XBS5_LPBIG_OFFBIG   _XBS5_LP64_OFF64           Same as
                                                   _SC_XBS5_LP64_OFF64
_SC_XOPEN_CRYPT         _XOPEN_CRYPT               Supports X/Open
                                                   Encryption Feature
                                                   Group
_SC_XOPEN_ENH_I18N      _XOPEN_ENH_I18N            Supports X/Open
                                                   Enhanced
                                                   Internationalization
                                                   Feature Group
_SC_XOPEN_LEGACY        _XOPEN_LEGACY              Supports X/Open
                                                   Legacy Feature Group
_SC_XOPEN_REALTIME      _XOPEN_REALTIME            Supports X/Open
                                                   POSIX Realtime
                                                   Feature Group
_SC_XOPEN_REALTIME_     _XOPEN_REALTIME_THREADS    Supports X/Open
     THREADS                                       POSIX Realtime
                                                   Threads Feature
                                                   Group
_SC_XOPEN_SHM           _XOPEN_SHM                 Supports X/Open
                                                   Shared Memory
                                                   Feature Group
_SC_XOPEN_STREAMS       _POSIX_XOPEN_STREAMS       Supports XSI Streams
                                                   option group
_SC_XOPEN_UNIX          _XOPEN_UNIX                Supports X/Open CAE
                                                   Specification,
                                                   August 1994, System
                                                   Interfaces and
                                                   Headers, Issue 4,
                                                   Version 2
_SC_XOPEN_VERSION       _XOPEN_VERSION             Integer value
                                                   indicates version of
                                                   X/Open Portability
                                                   Guide to which
                                                   implementation
                                                   conforms
_SC_XOPEN_XCU_VERSION   _XOPEN_XCU_VERSION         Integer value
                                                   indicates version of
                                                   XCU specification to
                                                   which implementation
                                                   conforms

The following options are not supported and return −1:

_SC_2_PBS
_POSIX2_PBS
_SC_2_PBS_ACCOUNTING
_POSIX2_PBS_ACCOUNTING
_SC_2_PBS_CHECKPOINT
_POSIX2_PBS_CHECKPOINT
_SC_2_PBS_LOCATE
_POSIX2_PBS_LOCATE
_SC_2_PBS_MESSAGE
_POSIX2_PBS_MESSAGE
_SC_2_PBS_TRACK
_POSIX2_PBS_TRACK
_SC_ADVISORY_INFO
_POSIX_ADVISORY_INFO
_SC_CPUTIME
_POSIX_CPUTIME
_SC_SPORADIC_SERVER
_POSIX_SPORADIC_SERVER
_SC_SS_REPL_MAX
_POSIX_SS_REPL_MAX
_SC_THREAD_CPUTIME
_POSIX_THREAD_CPUTIME
_SC_THREAD_SPORADIC_SERVER
_POSIX_THREAD_SPORADIC_SERVER
_SC_TRACE
_POSIX_TRACE
_SC_TRACE_EVENT_FILTER
_POSIX_TRACE_EVENT_FILTER
_SC_TRACE_EVENT_NAME_MAX
_POSIX_TRACE_EVENT_NAME_MAX
_SC_TRACE_INHERIT
_POSIX_TRACE_INHERIT
_SC_TRACE_LOG
_POSIX_TRACE_LOG
_SC_TRACE_NAME_MAX
_POSIX_TRACE_NAME_MAX
_SC_TRACE_SYS_MAX
_POSIX_TRACE_SYS_MAX
_SC_TRACE_USER_EVENT_MAX
_POSIX_TRACE_USER_EVENT_MAX
_SC_TYPED_MEMORY_OBJECTS
_POSIX_TYPED_MEMORY_OBJECTS

Return Values

Upon successful completion, 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>. With only a few obvious exceptions such as _SC_AVPHYS_PAGES and _SC_NPROCESSORS_ONLN, the value will not change during the lifetime of the calling process.

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.

Calling sysconf() with the following returns −1 without setting errno, because no maximum limit can be determined. The system supports at least the minimum values and can support higher values depending upon system resources.

Variable                            Minimum supported value
_SC_AIO_MAX                        _POSIX_AIO_MAX
_SC_ATEXIT_MAX                     32
_SC_MQ_OPEN_MAX                    32
_SC_THREAD_THREADS_MAX             _POSIX_THREAD_THREADS_MAX
_SC_THREAD_KEYS_MAX                _POSIX_THREAD_KEYS_MAX
_SC_THREAD_DESTRUCTOR_ITERATIONS   _POSIX_THREAD_DESTRUCTOR_ITERATIONS

The following SPARC and x86 platform variables return EINVAL:

_SC_COHER_BLKSZ        _SC_DCACHE_ASSOC
_SC_DCACHE_BLKSZ       _SC_DCACHE_LINESZ
_SC_DCACHE_SZ          _SC_DCACHE_TBLKSZ
_SC_ICACHE_ASSOC       _SC_ICACHE_BLKSZ
_SC_ICACHE_LINESZ      _SC_ICACHE_SZ
_SC_SPLIT_CACHE

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
Interface Stability
Committed
MT-Level
MT-Safe, Async-Signal-Safe
Standard

See Also

pooladm(1M), zoneadm(1M), fpathconf(2), seteuid(2), setrlimit(2), confstr(3C), attributes(5), standards(5)

Notes

A call to setrlimit() can 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 32–bit signed or unsigned integer.

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

If the caller is in a non-global zone and the pools facility is active, sysconf(_SC_NPROCESSORS_CONF) and sysconf(_SC_NPROCESSORS_ONLN) return the number of processors in the processor set of the pool to which the zone is bound.