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.\"	@(#)sysconf.3	8.3 (Berkeley) 4/19/94
.\" $FreeBSD$
.\"
.Dd June 18, 2001
.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 .
Shell programmers who need access to these parameters should use the
.Xr getconf 1
utility.
.Pp
The available values are as follows:
.Pp
.Bl -tag -width 6n
.Pp
.It Li _SC_2_C_BIND
Return 1 if the system's C-language development facilities support the
C-Language Bindings Option, otherwise \-1.
.It Li _SC_2_C_DEV
Return 1 if the system supports the C-Language Development Utilities Option,
otherwise \-1.
.It Li _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 Li _SC_2_FORT_DEV
Return 1 if the system supports the FORTRAN Development Utilities Option,
otherwise \-1.
.It Li _SC_2_FORT_RUN
Return 1 if the system supports the FORTRAN Runtime Utilities Option,
otherwise \-1.
.It Li _SC_2_LOCALEDEF
Return 1 if the system supports the creation of locales, otherwise \-1.
.It Li _SC_2_SW_DEV
Return 1 if the system supports the Software Development Utilities Option,
otherwise \-1.
.It Li _SC_2_UPE
Return 1 if the system supports the User Portability Utilities Option,
otherwise \-1.
.It Li _SC_2_VERSION
The version of
.St -p1003.2
with which the system attempts to comply.
.It Li _SC_AIO_LISTIO_MAX
The maximum number of POSIX asynchronous I/O operations supported.
.It Li _SC_AIO_MAX
The maximum number of outstanding asynchronous I/O operations supported.
.It Li _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 Li _SC_ARG_MAX
The maximum bytes of argument to
.Xr execve 2 .
.It Li _SC_ASYNCHRONOUS_IO
Return 1 if the system supports Asynchronous I/O facilities as described in
.St -p1003.1 ,
otherwise \-1.
.It Li _SC_ATEXIT_MAX
The maximum number of functions that a process may register with the
.Fn atexit
function.
.It Li _SC_BC_BASE_MAX
The maximum ibase/obase values in the
.Xr bc 1
utility.
.It Li _SC_BC_DIM_MAX
The maximum array size in the
.Xr bc 1
utility.
.It Li _SC_BC_SCALE_MAX
The maximum scale value in the
.Xr bc 1
utility.
.It Li _SC_BC_STRING_MAX
The maximum string length in the
.Xr bc 1
utility.
.It Li _SC_CHILD_MAX
The maximum number of simultaneous processes per user id.
.It Li _SC_CLK_TCK
The frequency of the statistics clock in ticks per second.
.It Li _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 Li _SC_DELAYTIMER_MAX
The maximum number of timer expiration overruns permitted for each process.
.It Li _SC_EXPR_NEST_MAX
The maximum number of expressions that can be nested within
parenthesis by the
.Xr expr 1
utility.
.It Li _SC_FSYNC
Return 1 if the system supports file synchronization, otherwise \-1.
.It Li _SC_IOV_MAX
The maximum number of iovec structures that one process may use with the
.Fn readv
and
.Fn writev
functions.
.It Li _SC_IPV6
Return 1 if the system supports Internet Protocol version 6, otherwise \-1.
.It Li _SC_JOB_CONTROL
Return 1 if job control is available on this system, otherwise \-1.
.It Li _SC_LINE_MAX
The maximum length in bytes of a text-processing utility's input
line.
.It Li _SC_MAPPED_FILES
Return 1 if the system supports memory mapped files, otherwise \-1.
.It Li _SC_MEMLOCK
Return 1 if the system supports process memory locking, otherwise \-1.
.It Li _SC_MEMLOCK_RANGE
Return 1 if the system supports range memory locking, otherwise \-1.
.It Li _SC_MEMORY_PROTECTION
Return 1 if the system supports memory protection, otherwise \-1.
.It Li _SC_MESSAGE_PASSING
Return 1 if the system supports POSIX message queues, otherwise \-1.
.It Li _SC_MQ_OPEN_MAX
The maximum number of open POSIX message queues which a process may hold.
.It Li _SC_NGROUPS_MAX
The maximum number of supplemental groups.
.It Li _SC_NPROCESSORS_CONF
The number of processors configured.
.It Li _SC_NPROCESSORS_ONLN
The number of processors currently online.
.It Li _SC_OPEN_MAX
The maximum number of open files per user id.
.It Li _SC_PAGE_SIZE
This is a synonym for
.Dv _SC_PAGESIZE .
.It Li _SC_PAGESIZE
The system memory page size.
.It Li _SC_PRIORITIZED_IO
Return 1 if the system supports POSIX prioritized I/O, otherwise \-1.
.It Li _SC_PRIORITY_SCHEDULING
Return 1 if the system supports POSIX priority scheduling, otherwise \-1.
.It Li _SC_RAW_SOCKETS
Return 1 if the system supports
.Dv SOCK_RAW
style raw sockets, otherwise \-1.
.It Li _SC_RE_DUP_MAX
The maximum number of repeated occurrences of a regular expression
permitted when using interval notation.
.It Li _SC_REALTIME_SIGNALS
Return 1 if the system supports POSIX realtime signals, otherwise \-1.
.It Li _SC_RTSIG_MAX
The number of the highest POSIX realtime signal supported.
.It Li _SC_SAVED_IDS
Returns 1 if saved set-group and saved set-user ID is available,
otherwise \-1.
.It Li _SC_SEM_NSEMS_MAX
The maximum number of POSIX semaphores that a process may have.
.It Li _SC_SEM_VALUE_MAX
The maximum value that a POSIX semaphore may have.
.It Li _SC_SEMAPHORES
Return 1 if the system supports POSIX semaphores, otherwise \-1.
.It Li _SC_SHARED_MEMORY_OBJECTS
Return 1 if the system supports POSIX shared memory objects, otherwise \-1.
.It Li _SC_SIGQUEUE_MAX
The maximum number of POSIX queued signals that a process may send and
have pending at receiver(s) at any given time.
.It Li _SC_STREAM_MAX
The minimum maximum number of streams that a process may have open
at any one time.
.It Li _SC_SYNCHRONIZED_IO
Return 1 if the system supports POSIX synchronized I/O, otherwise \-1.
.It Li _SC_TIMER_MAX
The maximum number of POSIX timers that a process may request.
.It Li _SC_TIMERS
Return 1 if the system supports POSIX timers, otherwise \-1.
.It Li _SC_TZNAME_MAX
The minimum maximum number of types supported for the name of a
timezone.
.It Li _SC_VERSION
The version of
.St -p1003.1
with which the system
attempts to comply.
.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.
.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 BUGS
The value for _SC_STREAM_MAX is a minimum maximum, and required to be
the same as ANSI C's FOPEN_MAX, so the returned value is a ridiculously
small and misleading number.
.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 .
.Sh HISTORY
The
.Fn sysconf
function first appeared in
.Bx 4.4 .