NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON
GETSOCKOPT(2) Linux Programmer's Manual GETSOCKOPT(2)
getsockopt, setsockopt - get and set options on sockets
#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);
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 non-zero 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. On error, -1 is returned, and errno is set
appropriately.
EBADF The argument sockfd is not a valid 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 argument sockfd is a file, not a socket.
SVr4, 4.4BSD (these system calls first appeared in 4.2BSD), POSIX.1-2001.
POSIX.1-2001 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).
Several of the socket options should be handled at lower levels of the system.
ioctl(2), socket(2), getprotoent(3), protocols(5), socket(7), tcp(7), unix(7)
This page is part of release 3.23 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2008-12-03 GETSOCKOPT(2)