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.\"	@(#)sysconf.3	8.3 (Berkeley) 4/19/94
.\" $FreeBSD: src/lib/libc/gen/sysconf.3,v 1.8.2.6 2001/12/14 18:33:51 ru Exp $
.\"
.Dd August 20, 2021
.Dt SYSCONF 3
.Os
.Sh NAME
.Nm sysconf
.Nd get configurable system variables
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft long
.Fn sysconf "int name"
.Sh DESCRIPTION
This interface is defined by
.St -p1003.1-88 .
A far more complete interface is available using
.Xr sysctl 3 .
.Pp
The
.Fn sysconf
function provides a method for applications to determine the current
value of a configurable system limit or option variable.
The
.Fa name
argument specifies the system variable to be queried.
Symbolic constants for each name value are found in the include file
.In unistd.h .
.Pp
The available values are as follows:
.Bl -tag -width 6n
.It Dv _SC_ADVISORY_INFO
The version of
.St -p1003.1
and its
Advisory Information
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_AIO_LISTIO_MAX
Maximum number of I/O operations in a single list I/O call supported.
.It Dv _SC_AIO_MAX
Maximum number of outstanding asynchronous I/O operations supported.
.It Dv _SC_AIO_PRIO_DELTA_MAX
The maximum amount by which a process can decrease its asynchronous I/O
priority level from its own scheduling priority.
.It Dv _SC_ASYNCHRONOUS_IO
The version of
.St -p1003.1
and its
Asynchronous Input and Output
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_ARG_MAX
The maximum bytes of argument to
.Xr execve 2 .
.It Dv _SC_ATEXIT_MAX
Maximum number of functions that may be registered with
.Fn atexit .
.It Dv _SC_BARRIERS
The version of
.St -p1003.1
and its
Barriers
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_BC_BASE_MAX
The maximum ibase/obase values in the
.Xr bc 1
utility.
.It Dv _SC_BC_DIM_MAX
The maximum array size in the
.Xr bc 1
utility.
.It Dv _SC_BC_SCALE_MAX
The maximum scale value in the
.Xr bc 1
utility.
.It Dv _SC_BC_STRING_MAX
The maximum string length in the
.Xr bc 1
utility.
.It Dv _SC_CHILD_MAX
The maximum number of simultaneous processes per user id.
.It Dv _SC_CLK_TCK
The frequency of the statistics clock in ticks per second.
.It Dv _SC_CLOCK_SELECTION
Return the POSIX version the implementation of the Clock Selection Option
on this system conforms to, or \-1 if unavailable.
.It Dv _SC_COLL_WEIGHTS_MAX
The maximum number of weights that can be assigned to any entry of
the LC_COLLATE order keyword in the locale definition file.
.It Dv _SC_CPUTIME
The
.Dv CLOCK_PROCESS_CPUTIME_ID
clock ID is supported, otherwise \-1.
.It Dv _SC_DELAYTIMER_MAX
Maximum number of timer expiration overruns.
.It Dv _SC_EXPR_NEST_MAX
The maximum number of expressions that can be nested within
parenthesis by the
.Xr expr 1
utility.
.It Dv _SC_FSYNC
Return 1 if the File Synchronization Option is available on this system,
otherwise \-1.
.It Dv _SC_GETGR_R_SIZE_MAX
Suggested initial value for the size of the group entry buffer.
.It Dv _SC_GETPW_R_SIZE_MAX
Suggested initial value for the size of the password entry buffer.
.It Dv _SC_HOST_NAME_MAX
Maximum length of a host name (not including the terminating null) as
returned from the
.Xr gethostname 3 ,
function.
.It Dv _SC_IOV_MAX
The maximum number of elements in the I/O vector used by
.Xr readv 2 ,
.Xr writev 2 ,
.Xr recvmsg 2 ,
and
.Xr sendmsg 2 .
.It Dv _SC_IPV6
The version of
.St -p1003.1
and its
IPv6
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_JOB_CONTROL
Return 1 if job control is available on this system, otherwise \-1.
.It Dv _SC_LINE_MAX
The maximum length in bytes of a text-processing utility's input
line.
.It Dv _SC_LOGIN_NAME_MAX
Maximum length of a login name.
.It Dv _SC_MAPPED_FILES
Return 1 if the Memory Mapped Files Option is available on this system,
otherwise \-1.
.It Dv _SC_MEMLOCK
Return 1 if the Process Memory Locking Option is available on this system,
otherwise \-1.
.It Dv _SC_MEMLOCK_RANGE
Return 1 if the Range Memory Locking Option is available on this system,
otherwise \-1.
.It Dv _SC_MEMORY_PROTECTION
Return 1 if the Memory Protection Option is available on this system,
otherwise \-1.
.It Dv _SC_MESSAGE_PASSING
Whether Message Passing option is supported.
.It Dv _SC_MONOTONIC_CLOCK
Return the POSIX version of the implementation of the Monotonic Clock
option that this system conforms to, or \-1 if unavailable.
.It Dv _SC_MQ_OPEN_MAX
The maximum number of open message queue descriptors per process.
.It Dv _SC_MQ_PRIO_MAX
The maximum number of message priorities supported by the implementation.
.It Dv _SC_NGROUPS_MAX
The maximum number of supplemental groups.
.It Dv _SC_OPEN_MAX
The maximum number of open files per user id.
.It Dv _SC_PAGESIZE
The size of a system page in bytes.
.It Dv _SC_PAGE_SIZE
Equivalent to
.Dv _SC_PAGESIZE .
.It Dv _SC_PRIORITIZED_IO
The version of
.St -p1003.1
and its
Prioritized Input and Output
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_PRIORITY_SCHEDULING
The version of
.St -p1003.1
and its
Process Scheduling
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_RAW_SOCKETS
The version of
.St -p1003.1
and its
Raw Sockets
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_READER_WRITER_LOCKS
The version of
.St -p1003.1
and its
Read-Write Locks
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_REALTIME_SIGNALS
The version of
.St -p1003.1
and its
Realtime Signals Extension
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_RE_DUP_MAX
The maximum number of repeated occurrences of a regular expression
permitted when using interval notation.
.It Dv _SC_REGEXP
Return 1 if the system supports regular expression handling.
.It Dv _SC_RTSIG_MAX
Maximum number of realtime signals reserved for application use.
.It Dv _SC_SAVED_IDS
Return 1 if saved set-group and saved set-user ID is available,
otherwise \-1.
.It Dv _SC_SEMAPHORES
The version of
.St -p1003.1
and its
Semaphores
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_SEM_NSEMS_MAX
Maximum number of semaphores that a process may have.
.It Dv _SC_SEM_VALUE_MAX
The maximum value a semaphore may have.
.It Dv _SC_SHARED_MEMORY_OBJECTS
The version of
.St -p1003.1
and its
Shared Memory Objects
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_SHELL
Return 1 if the system supports the
.Tn POSIX
shell.
.It Dv _SC_SIGQUEUE_MAX
Maximum number of queued signals that a process may send and have pending at
the receiver(s) at any time.
.It Dv _SC_SPAWN
The version of
.St -p1003.1
and its
Spawn
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_SPIN_LOCKS
The version of
.St -p1003.1
and its
Spin Locks
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_SPORADIC_SERVER
The version of
.St -p1003.1
and its
Process Sporadic Server
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_STREAM_MAX
The maximum number of streams that a process may have open at any one time.
.It Dv _SC_SYMLOOP_MAX
Maximum number of symbolic links that can be reliably traversed in the
resolution of a pathname in the absence of a loop.
.It Dv _SC_SYNCHRONIZED_IO
Return 1 if the Synchronized I/O Option is available on this system,
otherwise \-1.
.It Dv _SC_THREAD_ATTR_STACKADDR
The version of
.St -p1003.1
and its
Thread Stack Address Attribute
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_THREAD_ATTR_STACKSIZE
The version of
.St -p1003.1
and its
Thread Stack Size Attribute
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_THREAD_CPUTIME
The
.Dv CLOCK_THREAD_CPUTIME_ID
clock ID is supported, otherwise \-1.
.It Dv _SC_THREAD_PRIO_INHERIT
The version of
.St -p1003.1
and its
Thread Priority Inheritance
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_THREAD_PRIO_PROTECT
Whether the system supports the priority ceiling protocol for POSIX threads.
.It Dv _SC_THREAD_PRIORITY_SCHEDULING
The version of
.St -p1003.1
and its
Thread Execution Scheduling
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_THREAD_PROCESS_SHARED
The version of
.St -p1003.1
and its
Thread Process-Shared Synchronization
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_THREAD_ROBUST_PRIO_INHERIT
The version of
.St -p1003.1
and its
Robust Mutex Priority Inheritance
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_THREAD_ROBUST_PRIO_PROTECT
The version of
.St -p1003.1
and its
Robust Mutex Priority Protection
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_THREADS
The version of
.St -p1003.1
and its
Threads
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_THREAD_SAFE_FUNCTIONS
The level of support for thread-safe (re-entrant) functions.
.It Dv _SC_THREAD_SPORADIC_SERVER
The version of
.St -p1003.1
and its
Thread Sporadic Server
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_THREAD_STACK_MIN
Minimum size in bytes of thread stack storage.
.It Dv _SC_THREAD_THREADS_MAX
Maximum number of threads that can be created per process.
.It Dv _SC_TIMEOUTS
The version of
.St -p1003.1
and its
Timeouts
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_TIMER_MAX
Maximum number of timers per process supported.
.It Dv _SC_TIMERS
The version of
.St -p1003.1
and its
Timers
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_TTY_NAME_MAX
Maximum length of terminal device name.
.It Dv _SC_TYPED_MEMORY_OBJECTS
The version of
.St -p1003.1
and its
Typed Memory Objects
option to which the system attempts to conform,
otherwise \-1.
.It Dv _SC_TZNAME_MAX
The maximum number of bytes supported for the name of a timezone.
.It Dv _SC_VERSION
The version of
.St -p1003.1
with which the system
attempts to comply.
.It Dv _SC_XOPEN_SHM
Return 1 if the system supports the
.St -xpg4.2
Shared Memory Feature
for both compilation and execution, or 0 if only compilation support is
guaranteed.
.It Dv _SC_XOPEN_VERSION
An integer value greater than or equal to 4,
indicating the version of the X/Open Portability Guide to which this
system conforms.
.It Dv _SC_2_C_BIND
Return 1 if the system's C-language development facilities support the
C-Language Bindings Option, otherwise \-1.
.It Dv _SC_2_C_DEV
Return 1 if the system supports the C-Language Development Utilities Option,
otherwise \-1.
.It Dv _SC_2_CHAR_TERM
Return 1 if the system supports at least one terminal type capable of
all operations described in
.St -p1003.2 ,
otherwise \-1.
.It Dv _SC_2_FORT_DEV
Return 1 if the system supports the FORTRAN Development Utilities Option,
otherwise \-1.
.It Dv _SC_2_FORT_RUN
Return 1 if the system supports the FORTRAN Runtime Utilities Option,
otherwise \-1.
.It Dv _SC_2_LOCALEDEF
Return 1 if the system supports the creation of locales, otherwise \-1.
.It Dv _SC_2_SW_DEV
Return 1 if the system supports the Software Development Utilities Option,
otherwise \-1.
.It Dv _SC_2_UPE
Return 1 if the system supports the User Portability Utilities Option,
otherwise \-1.
.It Dv _SC_2_VERSION
The version of
.St -p1003.2
with which the system attempts to comply.
.El
.Pp
These values also exist, but may not be standard:
.Bl -tag -width 6n
.It Dv _SC_LEVEL1_DCACHE_LINESIZE
Returns the L1 cache line size.
.It Dv _SC_NPROCESSORS_CONF
The number of processors configured.
.It Dv _SC_NPROCESSORS_ONLN
The number of processors online.
.It Dv _SC_PHYS_PAGES
The number of pages of physical memory.
.El
.Sh RETURN VALUES
If the call to
.Fn sysconf
is not successful, \-1 is returned and
.Va errno
is set appropriately.
Otherwise, if the variable is associated with functionality that is not
supported, \-1 is returned and
.Va errno
is not modified.
Otherwise, the current variable value is returned.
.Pp
Because \-1 is a valid return value upon success, applications wishing
to check for real error conditions should set
.Va errno
to 0, then call
.Fn sysconf ,
and check
.Va errno
if \-1 is returned.
.Sh ERRORS
The
.Fn sysconf
function may fail and set
.Va errno
for any of the errors specified for the library function
.Xr sysctl 3 .
In addition, the following error may be reported:
.Bl -tag -width Er
.It Bq Er EINVAL
The value of the
.Fa name
argument is invalid.
.El
.Sh SEE ALSO
.Xr getconf 1 ,
.Xr pathconf 2 ,
.Xr confstr 3 ,
.Xr sysctl 3
.Sh STANDARDS
Except for the fact that values returned by
.Fn sysconf
may change over the lifetime of the calling process,
this function conforms to
.St -p1003.1-88 .
.Pp
.Dv _SC_NPROCESSORS_CONF
and
.Dv _SC_NPROCESSORS_ONLN
are nonstandard, but implemented in many systems.
.Sh HISTORY
The
.Fn sysconf
function first appeared in
.Bx 4.4 .