Section (2) getsockopt
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. Forgetsockopt
(), this error may also be returned ifoptlen
is not in a valid part of the process address space. - EINVAL
-
optlen
invalid insetsockopt
(). In some cases this error can also occur for an invalid value inoptval
(e.g., for theIP_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.
For background on the socklen_t type, see accept(2).
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 4.16 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/.
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