.\" Copyright (c) 1983, 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     $Id: getsockopt.2,v 1.1 1999/05/24 14:57:04 freitag Exp $
.\"
.\" Modified Sat Jul 24 16:19:32 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Mon Apr 22 02:29:06 1996 by Martin Schulze (joey@infodrom.north.de)
.\" Modified Tue Aug 27 10:52:51 1996 by Andries Brouwer (aeb@cwi.nl)
.\" Modified Thu Jan 23 13:29:34 1997 by Andries Brouwer (aeb@cwi.nl)
.\" Modified Sun Mar 28 21:26:46 1999 by Andries Brouwer (aeb@cwi.nl)
.\" Modified 1999 by Andi Kleen <ak@muc.de>. Removed most stuff because it is in socket.7 
.\" now.
.\"
.TH GETSOCKOPT 2 "24 May 1999" "Linux Man Page" "Linux Programmer's Manual"
.SH NAME
getsockopt, setsockopt \- get and set options on sockets
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <sys/socket.h>
.sp 2
.BI "int getsockopt(int " s ", int " level ", int " optname ,
.BI "void *" optval ", socklen_t *" optlen );
.sp
.BI "int setsockopt(int " s ", int " level ", int " optname ,
.BI "const void *" optval ", socklen_t " optlen );
.SH DESCRIPTION
.B Getsockopt
and
.B setsockopt
manipulate the
.I options
associated with a socket.  Options may exist at multiple
protocol levels; they are always present at the uppermost
.B socket
level.

When manipulating socket options the level at which the
option resides and the name of the option must be specified.
To manipulate options at the socket level,
.I level
is specified as
.BR SOL_SOCKET .
To manipulate options at any
other level the protocol number of the appropriate protocol
controlling the option is supplied.  For example,
to indicate that an option is to be interpreted by the
.B TCP
protocol,
.I level
should be set to the protocol number of
.BR TCP ;
see
.BR getprotoent (3).

The parameters
.I optval
and
.I optlen
are used to access option values for
.BR setsockopt .
For
.B getsockopt
they identify a buffer in which the value for the
requested option(s) are to be returned.  For
.BR getsockopt ,
.I optlen
is a value-result parameter, initially containing the
size of the buffer pointed to by
.IR optval ,
and modified on return to indicate the actual size of
the value returned.  If no option value is
to be supplied or returned,
.I optval
may be NULL.

.I Optname
and any specified options are passed uninterpreted to the appropriate
protocol module for interpretation.  The include file
.I <sys/socket.h>
contains definitions for socket level options, described below.  Options at
other protocol levels vary in format and name; consult the appropriate
entries in section 4 of the manual.

Most socket-level options utilize an
.I int
parameter for
.IR optval .
For
.BR setsockopt ,
the parameter should be non-zero to enable a boolean option, or zero if the
option is to be disabled.

.PP
For a description of the available socket options see
.BR socket (7)
and the appropriate protocol man pages.

.SH "RETURN VALUE"
On success, zero is returned.  On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EBADF
The argument
.I s
is not a valid descriptor.
.TP
.B ENOTSOCK
The argument
.I s
is a file, not a socket.
.TP
.B ENOPROTOOPT
The option is unknown at the level indicated.
.TP
.B EFAULT
The address pointed to by 
.I optval
is not in a valid part of the process address space.  For
.BR getsockopt ,
this error may also be returned if
.I optlen
is not in a valid part of the process address space.
.SH CONFORMING TO
SVr4, 4.4BSD (these system calls first appeared in 4.2BSD).
SVr4 documents additional ENOMEM and ENOSR error codes, but does
not document the 
.BR SO_SNDLOWAT ", " SO_RCVLOWAT ", " SO_SNDTIMEO ", " SO_RCVTIMEO
options
.SH NOTE
The fifth argument of 
.BR getsockopt " and " setsockopt
is in reality an int [*] (and this is what BSD 4.* and libc4 and libc5 have).
Some POSIX confusion resulted in the present socklen_t.
The draft standard has not been adopted yet, but glibc2 already
follows it and also has socklen_t [*]. See also
.BR accept (2).
.SH BUGS
Several of the socket options should be handled at lower levels of the
system.
.SH "SEE ALSO"
.BR ioctl (2),
.BR socket (2),
.BR getprotoent (3),
.BR protocols (5),
.BR socket (7),
.BR unix (7),
.BR tcp (7)