Name

getsockopt, setsockopt — get and set options on sockets

Synopsis

#include <sys/types.h>           /* See NOTES */
#include <sys/socket.h>
int getsockopt( int sockfd,
  int level,
  int optname,
  void *optval,
  socklen_t *optlen);
 
int setsockopt( int sockfd,
  int level,
  int optname,
  const void *optval,
  socklen_t optlen);
 

DESCRIPTION

getsockopt() and setsockopt() manipulate options for the socket referred to by the file descriptor sockfd. Options may exist at multiple protocol levels; they are always present at the uppermost 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 sockets API level, level is specified as 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 TCP protocol, level should be set to the protocol number of TCP; see getprotoent(3).

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

Optname and any specified options are passed uninterpreted to the appropriate protocol module for interpretation. The include file <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 int argument for optval. For setsockopt(), the argument should be nonzero to enable a boolean option, or zero if the option is to be disabled.

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

RETURN VALUE

On success, zero is returned for the standard options. On error, −1 is returned, and errno is set appropriately.

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.

ERRORS

EBADF

The argument sockfd is not a valid file descriptor.

EFAULT

The address pointed to by optval is not in a valid part of the process address space. For getsockopt(), this error may also be returned if optlen is not in a valid part of the process address space.

EINVAL

optlen invalid in setsockopt(). In some cases this error can also occur for an invalid value in optval (e.g., for the IP_ADD_MEMBERSHIP option described in ip(7)).

ENOPROTOOPT

The option is unknown at the level indicated.

ENOTSOCK

The file descriptor sockfd does not refer to a socket.

CONFORMING TO

POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (these system calls first appeared in 4.2BSD).

NOTES

POSIX.1 does not require the inclusion of <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.

The optlen argument of getsockopt() and setsockopt() is in reality an int [*] (and this is what 4.x BSD and libc4 and libc5 have). Some POSIX confusion resulted in the present socklen_t, also used by glibc. See also accept(2).

BUGS

Several of the socket options should be handled at lower levels of the system.

SEE ALSO

ioctl(2), socket(2), getprotoent(3), protocols(5), ip(7), packet(7), socket(7), tcp(7), udp(7), unix(7)

COLOPHON

This page is part of release 4.07 of the Linux 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/.


  Copyright (c) 1983, 1991 The Regents of the University of California.
All rights reserved.

%%%LICENSE_START(BSD_4_CLAUSE_UCB)
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.
%%%LICENSE_END

    $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 (faithcs.unc.edu)
Modified Mon Apr 22 02:29:06 1996 by Martin Schulze (joeyinfodrom.north.de)
Modified Tue Aug 27 10:52:51 1996 by Andries Brouwer (aebcwi.nl)
Modified Thu Jan 23 13:29:34 1997 by Andries Brouwer (aebcwi.nl)
Modified Sun Mar 28 21:26:46 1999 by Andries Brouwer (aebcwi.nl)
Modified 1999 by Andi Kleen <akmuc.de>.
    Removed most stuff because it is in socket.7 now.