getsockopt() - Unix, Linux System Call
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NAME
getsockopt, setsockopt - get and set options on sockets
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
int getsockopt(int s, int level, int optname, void *optval, socklen_t *optlen);
int setsockopt(int s, int level, int optname, const void *optval, socklen_t optlen); DESCRIPTION
getsockopt() and
setsockopt() manipulate the
options associated with a socket. 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 socket 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 parameters
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 parameter, 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 parameter for
optval. For
setsockopt(), the parameter 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.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and
errno is set appropriately.
ERRORS
Tag | Description |
EBADF |
The argument
s 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(). |
ENOPROTOOPT | |
The option is unknown at the level indicated.
|
ENOTSOCK |
The argument
s is a file, not a socket.
|
CONFORMING TO
SVr4, 4.4BSD (these system calls first appeared in 4.2BSD),
POSIX.1-2001.
NOTE
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).
BUGS
Several of the socket options should be handled at lower levels of the
system.
SEE ALSO
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