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The getsockopt() function retrieves the value for the option specified by the option_name argument for the socket specified by the socket argument. If the size of the option value is greater than option_len, the value stored in the object pointed to by the option_value
argument will be silently truncated. Otherwise, the object pointed to by the option_len argument will be modified to indicate the actual length of the value.
The level argument specifies the protocol level at which the option resides. To retrieve options at the socket level, specify the level argument
as SOL_SOCKET. To retrieve options at other levels, supply the appropriate protocol number for the protocol controlling the option. For example, to indicate that an option will be interpreted by the TCP
(Transport Control Protocol), set level to the protocol number of TCP, as defined in the <netinet/in.h> header, or as determined by using getprotobyname(3XNET) function.
The socket in use may require the process to have appropriate privileges to use the getsockopt() function.
The option_name argument specifies a single option to be retrieved. It can be one of the following values defined in <sys/socket.h>:
- SO_DEBUG
- Reports whether debugging information is being recorded. This option stores an int value.
This is a boolean option.
- SO_ACCEPTCONN
- Reports whether socket listening is enabled. This option stores an int value.
- SO_BROADCAST
- Reports whether transmission of broadcast messages is supported, if this is supported by the protocol. This option stores an int
value. This is a boolean option.
- SO_REUSEADDR
- Reports whether the rules used in validating addresses supplied to bind(3XNET) should allow reuse of local addresses, if this is supported by the protocol. This option stores an int value. This is a boolean option.
- SO_KEEPALIVE
- Reports whether connections are kept active with periodic transmission of messages, if this is supported by the protocol.
If the connected socket fails to respond to these messages, the connection is broken and processes writing to that socket are notified with a SIGPIPE signal.
This option stores an int value.
This is a boolean option.
- SO_LINGER
- Reports whether the socket lingers on close(2) if data is present. If SO_LINGER is set, the system blocks the process during close(2) until it can transmit the data or until the end of the interval indicated by the l_linger member, whichever
comes first. If SO_LINGER is not specified, and close(2) is issued,
the system handles the call in a way that allows the process to continue as quickly as possible. This option stores a linger structure.
- SO_OOBINLINE
- Reports whether the socket leaves received out-of-band data (data marked urgent) in line. This option stores an int value. This
is a boolean option.
- SO_SNDBUF
- Reports send buffer size information. This option stores an int value.
- SO_RCVBUF
- Reports receive buffer size information. This option stores an int value.
- SO_ERROR
- Reports information about error status and clears it. This option stores an int value.
- SO_TYPE
- Reports the socket type. This option stores an int value.
- SO_DONTROUTE
- Reports whether outgoing messages bypass the standard routing facilities. The destination must be on a directly-connected network, and messages are
directed to the appropriate network interface according to the destination address. The effect, if any, of this option depends on what protocol is in use. This option stores an int
value. This is a boolean option.
For boolean options, a zero value indicates that the option is disabled and a non-zero value indicates that the option is enabled.
Options at other protocol levels vary in format and name.
The socket in use may require the process to have appropriate privileges to use the getsockopt() function.
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