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.\"     $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 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

getsockopt, setsockopt \- get and set options on sockets

.SH SYNOPSIS

.nf

.BR "#include <sys/types.h>" "          /* See NOTES */"

.B #include <sys/socket.h>

.PP

.BI "int getsockopt(int " sockfd ", int " level ", int " optname ,

.BI "               void *" optval ", socklen_t *" optlen );

.BI "int setsockopt(int " sockfd ", int " level ", int " optname ,

.BI "               const void *" optval ", socklen_t " optlen );

.fi

.SH DESCRIPTION

.BR getsockopt ()

and

.BR setsockopt ()

manipulate options for the socket referred to by the file descriptor

.IR sockfd .

Options may exist at multiple

protocol levels; they are always present at the uppermost

socket level.

.PP

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 sockets API 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).

.PP

The arguments

.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 argument, 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.

.PP

.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.

.PP

Most socket-level options utilize an

.I int

argument for

.IR optval .

For

.BR setsockopt (),

the argument should be nonzero 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 for the standard options.

On error, \-1 is returned, and

.I errno

is set appropriately.

.PP

Netfilter allows the programmer

to define custom socket options with associated handlers; for such

options, the return value on success is the value returned by the handler.

.SH ERRORS

.TP 10

.B EBADF

The argument

.I sockfd

is not a valid file 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 ().

In some cases this error can also occur for an invalid value in

.IR optval

(e.g., for the

.B IP_ADD_MEMBERSHIP

option described in

.BR ip (7)).

.TP

.B ENOPROTOOPT

The option is unknown at the level indicated.

.TP

.B ENOTSOCK

The file descriptor

.I sockfd

does not refer to a socket.

.SH CONFORMING TO

POSIX.1-2001, POSIX.1-2008,

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 NOTES

POSIX.1 does not require the inclusion of

.IR <sys/types.h> ,

and this header file is not required on Linux.

However, some historical (BSD) implementations required this header

file, and portable applications are probably wise to include it.

.PP

For background on the

.I socklen_t

type, see

.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 ip (7),

.BR packet (7),

.BR socket (7),

.BR tcp (7),

.BR udp (7),

.BR unix (7)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.