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.Dd $Mdocdate: September 26 2012 $
.Dt SYSCONF 3
.Os
.Sh NAME
.Nm sysconf
.Nd get configurable system variables
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft long
.Fn sysconf "int name"
.Sh DESCRIPTION
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
.Aq Pa unistd.h .
.Pp
The available values are as follows:
.Bl -tag -width "123456"
.It Li _SC_ARG_MAX
The maximum bytes of arguments to
.Xr exec 3
(including the environment).
.It Li _SC_CHILD_MAX
The maximum number of simultaneous processes per user ID.
.It Li _SC_CLK_TCK
The number of clock ticks per second.
.It Li _SC_NGROUPS_MAX
The maximum number of supplemental groups.
.It Li _SC_OPEN_MAX
The maximum number of open files per user ID.
.It Li _SC_STREAM_MAX
The minimum maximum number of streams that a process may have open
at any one time.
.It Li _SC_TZNAME_MAX
The minimum maximum number of types supported for the name of a
time zone.
.It Li _SC_JOB_CONTROL
Returns 1 if job control is available on this system, otherwise \-1.
.It Li _SC_SAVED_IDS
Returns 1 if saved set-group-ID and saved set-user-ID is available,
otherwise \-1.
.It Li _SC_VERSION
The version of ISO/IEC 9945 (POSIX 1003.1) with which the system
attempts to comply.
.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_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_EXPR_NEST_MAX
The maximum number of expressions that can be nested within
parentheses by the
.Xr expr 1
utility.
.It Li _SC_LINE_MAX
The maximum length in bytes of a text-processing utility's input
line.
.It Li _SC_RE_DUP_MAX
The maximum number of repeated occurrences of a regular expression
permitted when using interval notation.
.It Li _SC_2_VERSION
The version of POSIX 1003.2 with which the system attempts to comply.
.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 POSIX 1003.2, 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_PAGESIZE
The size of a system page in bytes.
.It Li _SC_FSYNC
Return 1 if the system supports the File Synchronisation Option, otherwise \-1.
.It Li _SC_XOPEN_SHM
Return 1 if the system supports the Shared Memory Option, otherwise \-1.
.It Li _SC_SEM_NSEMS_MAX
The maximum number of semaphores in the system or \-1 if the system
does not support the Semaphores Option.
.It Li _SC_SEM_VALUE_MAX
The maximum value a semaphore may have or \-1 if the system
does not support the Semaphores Option.
.It Li _SC_PHYS_PAGES
The number of pages of physical memory.
.It Li _SC_AVPHYS_PAGES
The number of pages of physical memory not currently in use by the system.
.It Li _SC_GETGR_R_SIZE_MAX
The maximum size of the data buffer for the
.Fn getgrgid_r
and
.Fn getgrnam_r
functions.
.It Li _SC_GETPW_R_SIZE_MAX
The maximum size of the data buffer for the
.Fn getpwuid_r
and
.Fn getpwnam_r
functions.
.It Li _SC_LOGIN_NAME_MAX
The maximum length of a login name.
.It Li _SC_THREAD_SAFE_FUNCTIONS
The level of support for thread-safe (re-entrant) functions.
.It Li _SC_NPROCESSORS_CONF
The number of processors configured.
.It Li _SC_NPROCESSORS_ONLN
The number of processors online (capable of running processes).
.It Li _SC_HOST_NAME_MAX
The maximum size of a hostname, not counting NULL.
.It Li _SC_MONOTONIC_CLOCK
Return the POSIX version of the implementation of the Monotonic Clock
option that this system conforms to, or \-1 if unavailable.
.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 pathconf 2 ,
.Xr sysctl 3
.Sh STANDARDS
The
.Fn sysconf
function conforms to
.St -p1003.1-88 .
The constants
.Li _SC_NPROCESSORS_CONF
and
.Li _SC_NPROCESSORS_ONLN
are not part of the standard, but are provided by many systems.
.Sh HISTORY
The
.Fn sysconf
function first appeared in
.Bx 4.4 .
.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.