GETSOCKOPT
Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
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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.
For background on the
socklen_t
type, see
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 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- BUGS
-
- SEE ALSO
-
- COLOPHON
-
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