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Standard C Library Functions 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
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Standard C Library Functions SYSCONF(3C)
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
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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
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_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 SIGQUEUE_MAX Max number of queued
signals that a
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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
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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
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_SC_XOPEN_REALTIME_ _XOPEN_REALTIME_THREADS Supports X/Open
THREADS POSIX Reatime
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
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_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 sup-
ported by the system, sysconf() returns -1 without changing
the value of errno.
Calling sysconf() with the following returns -1 without set-
ting 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 EIN-
VAL:
_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:
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EINVAL
The value of the name argument is invalid.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
__________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|____________________|____________________________|
| Architecture | SPARC and x86 |
|____________________|____________________________|
| Interface Stability| Committed |
|____________________|____________________________|
| MT-Level | MT-Safe, Async-Signal-Safe|
|____________________|____________________________|
| Standard | See standards(5). |
|____________________|____________________________|
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 deter-
mine 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 proces-
sors in the processor set of the pool to which the zone is
bound.
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