man-pages/man2/getsockopt.2

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.\"     $Id: getsockopt.2,v 1.1 1999/05/24 14:57:04 freitag Exp $
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.\" 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 1999-05-24 "Linux Man Page" "Linux Programmer's Manual"
.SH NAME
getsockopt, setsockopt \- get and set options on sockets
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.br
.B #include <sys/socket.h>
.sp
.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 );
.fi
.SH DESCRIPTION
.BR getsockopt ()
and
.BR 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
.BR 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 10
.B EBADF
The argument
.I s
is not a valid descriptor.
.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.
.TP
.B EINVAL
.I optlen
invalid in
.BR setsockopt ().
.TP
.B ENOPROTOOPT
The option is unknown at the level indicated.
.TP
.B ENOTSOCK
The argument
.I s
is a file, not a socket.
.SH "CONFORMING TO"
SVr4, 4.4BSD (these system calls first appeared in 4.2BSD),
POSIX.1-2001.
.\" 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
.I optlen
argument of
.BR getsockopt " and " setsockopt
is in reality an
.I "int [*]"
(and this is what 4.x BSD and libc4 and libc5 have).
Some POSIX confusion resulted in the present
.IR socklen_t ,
also used by glibc.
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 tcp (7),
.BR unix (7)