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.\" Modified Sat Jul 24 17:51:42 1993 by Rik Faith (faith@cs.unc.edu)
.TH SYSCONF 3  "April 18, 1993" "GNU" "Linux Programmer's Manual"
.SH NAME
sysconf \- Get configuration information at runtime
.SH SYNOPSIS
.nf
.B #include <unistd.h>
.sp
.BI "long sysconf(int " "name" ");"
.fi
.SH DESCRIPTION
.B sysconf()
provides a way for the application to determine values for system
limits or options at runtime.
.PP
The equivalent macros defined in
.B <unistd.h>
can only give conservative values; if an application wants to take
advantage of values which may change, a call to
.B sysconf()
can be made, which may yield more liberal results.
.PP
For getting information about a particular file, see
.BR fpathconf() " or " pathconf() .
.PP
The following values are supported for
.IR name .
First, the POSIX.1 compatible values:
.TP
.B _SC_ARG_MAX
The maximum length of the arguments to the
.B exec()
family of functions; the corresponding macro is
.BR ARG_MAX .
.TP
.B _SC_CHILD_MAX
The number of simultaneous processes per user id, the corresponding macro
is
.BR _POSIX_CHILD_MAX .
.TP
.B _SC_CLK_TCK
The number of clock ticks per second; the corresponding macro is
.BR CLK_TCK .
.TP
.B _SC_STREAM_MAX
The maximum number of streams that a process can have open at any
time.
The corresponding POSIX macro is
.BR STREAM_MAX ,
the corresponding standard C macro is
.BR FOPEN_MAX .
.TP
.B _SC_TZNAME_MAX
The maximum number of bytes in a timezone name, the corresponding macro
is
.BR TZNAME_MAX .
.TP
.B _SC_OPEN_MAX
The maximum number of files that a process can have open at any time,
the corresponding macro is
.BR _POSIX_OPEN_MAX .
.TP
.B _SC_JOB_CONTROL
This indicates whether POSIX \- style job control is supported, the
corresponding macro is
.BR _POSIX_JOB_CONTROL .
.TP
.B _SC_SAVED_IDS
This indicates whether a process has a saved set-user-ID and a saved
set-group-ID; the corresponding macro is
.BR _POSIX_SAVED_IDS .
.TP
.B _SC_VERSION
indicates the year and month the POSIX.1 standard was approved in the
format
.BR YYYYMML ; the
value
.B 199009L
indicates the most recent revision, 1990.
.PP
Next, the POSIX.2 values:
.TP
.B _SC_BC_BASE_MAX
indicates the maximum
.I obase
value accepted by the
.BR bc (1)
utility; the corresponding macro is
.BR BC_BASE_MAX .
.TP
.B _SC_BC_DIM_MAX
indicates the maximum value of elements permitted in an array by
.BR bc (1);
the corresponding macro is
.BR BC_DIM_MAX . 
.TP
.B _SC_BC_SCALE_MAX
indicates the maximum
.I scale
value allowed by
.BR bc (1);
the corresponding macro is
.BR BC_SCALE_MAX .
.TP
.B _SC_BC_STRING_MAX
indicates the maximum length of a string accepted by
.BR bc (1);
the corresponding macro is
.BR BC_STRING_MAX .
.TP
.B _SC_COLL_WEIGHTS_MAX
indicates the maximum numbers of weights that can be assigned to an
entry of the
.B LC_COLLATE order
keyword in the locale definition file; the corresponding macro is
.BR COLL_WEIGHTS_MAX .
.TP
.B _SC_EXPR_NEST_MAX
is the maximum number of expressions which can be nested within
parentheses by
.BR expr (1).
The corresponding macro is
.BR EXPR_NEST_MAX .
.TP
.B _SC_LINE_MAX
The maximum length of a utility's input line length, either from
standard input or from a file. This includes length for a trailing
newline.
The corresponding macro is
.BR LINE_MAX .
.TP
.B _SC_RE_DUP_MAX
The maximum number of repeated occurrences of a regular expression when
the interval notation
.B \e{m,n\e}
is used. The value of the corresponding macro is
.BR RE_DUP_MAX .
.TP
.B _SC_2_VERSION
indicates the version of the POSIX.2 standard in the format of
YYYYMML.  The corresponding macro is
.BR POSIX2_VERSION .
.TP
.B _SC_2_DEV
indicates whether the POSIX.2 C language development facilities are
supported.  The corresponding macro is
.BR POSIX2_C_DEV .
.TP
.B _SC_2_FORT_DEV
indicates whether the POSIX.2 FORTRAN development utilities are
supported.  The corresponding macro is
.BR POSIX2_FORT_RUN .
.TP
.B _SC_2_FORT_RUN
indicates whether the POSIX.2 FORTRAN runtime utilities are supported.
The corresponding macro is
.BR POSIX2_FORT_RUN .
.TP
.B _SC_2_LOCALEDEF
indicates whether the POSIX.2 creation of locates via
.BR localedef (1)
is supported.
The corresponding macro is
.BR _POSIX2_LOCALEDEF .
.TP
.B _SC_2_SW_DEV
indicates whether the POSIX.2 software development utilities option is
supported.
The corresponding macro is
.BR POSIX2_SW_DEV .
.SH "RETURN VALUE"
The value returned is the value of the system resource, 1 if a queried
option is available, 0 if it is not, or \-1 on error.  The variable
.I errno
is not set.
.SH "CONFORMING TO"
POSIX.1, proposed POSIX.2
.SH "BUGS"
It is difficult to use
.B ARG_MAX
because it is not specified how much of the argument space for
.B exec()
is consumed by the user's environment variables.
.PP
Some returned values may be huge; they are not suitable for allocating
memory.
.PP
POSIX.2 is not yet an approved standard; the information in this
manpage is subject to change.
.SH "SEE ALSO"
.BR bc "(1), " expr "(1), " locale "(1), " fpathconf "(3), " pathconf (3)