Section (2) getsockopt
getsockopt, setsockopt — get and set options on sockets
#include <sys/types.h> /* See NOTES */ #include <sys/socket.h>
|const void *optval,|
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
level should be set to the
protocol number of
optlen are used to access
option values for
getsockopt() they identify
a buffer in which the value for the requested option(s) are
to be returned. For
optlen is a value-result
argument, initially containing the size of the buffer pointed
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
Optname and any
specified options are passed uninterpreted to the appropriate
protocol module for interpretation. The include file
> 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
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.
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.
sockfdis not a valid file descriptor.
The address pointed to by
optvalis not in a valid part of the process address space. For
getsockopt(), this error may also be returned if
optlenis not in a valid part of the process address space.
setsockopt(). In some cases this error can also occur for an invalid value in
optval(e.g., for the
IP_ADD_MEMBERSHIPoption described in ip(7)).
The option is unknown at the level indicated.
The file descriptor
sockfddoes not refer to a socket.
POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (these system calls first appeared in 4.2BSD).
POSIX.1 does not require the inclusion of
> 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.
For background on the socklen_t type, see accept(2).
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man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
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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 (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.