getsockopt, setsockopt - get and set options on sockets
#include <sys/types.h> /* See NOTES */
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);
() 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
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
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
should be set to the
protocol number of TCP
; see getprotoent(3)
The arguments optval
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
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.
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 optval
(), 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)
appropriate protocol man pages.
On success, zero is returned. On error, -1 is returned, and errno
- The argument sockfd is not a valid descriptor.
- 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
- 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)).
- The option is unknown at the level indicated.
- 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>
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.
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.
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