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getsockopt(3N)							getsockopt(3N)

NAME    [Toc]    [Back]

     getsockopt, setsockopt - get and set options on sockets

SYNOPSIS    [Toc]    [Back]

     #include <sys/types.h>
     #include <sys/socket.h>

     int getsockopt(int	s, int level, int optname, char	*optval,
	 int *optlen);
     int setsockopt(int	s, int level, int optname, char	*optval,
	 int optlen);

DESCRIPTION    [Toc]    [Back]

     getsockopt	and setsockopt manipulate 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, level is the protocol number of the protocol
     that controls the option.	For example, to	indicate that an option	is to
     be	interpreted by the TCP protocol, level is set to the TCP protocol
     number [see getprotoent(3N)].

     The parameters optval and optlen are used to access option	values for
     setsockopt.  For getsockopt, they identify	a buffer in which the value(s)
     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,
     a 0 optval	may be supplied.

     optname and any specified options are passed uninterpreted	to the
     appropriate protocol module for interpretation.  The include file
     sys/socket.h contains definitions for the socket-level options described
     below.  Options at	other protocol levels vary in format and name.

     Most socket-level options take an int for optval.	For setsockopt,	the
     optval parameter should be	non-zero to enable a boolean option, or	zero
     if	the option is to be disabled.  SO_LINGER uses a	struct linger
     parameter that specifies the desired state	of the option and the linger
     interval (see below).  struct linger is defined in

     The following options are recognized at the socket	level.	Except as
     noted, each may be	examined with getsockopt and set with setsockopt.

	  SO_DEBUG	      toggle recording of debugging information
	  SO_REUSEADDR	      toggle local address reuse

									Page 1

getsockopt(3N)							getsockopt(3N)

	  SO_KEEPALIVE	      toggle keep connections alive
	  SO_DONTROUTE	      toggle routing bypass for	outgoing messages
	  SO_LINGER	      linger on	close if data is present
	  SO_BROADCAST	      toggle permission	to transmit broadcast messages
	  SO_OOBINLINE	      toggle reception of out-of-band data in band
	  SO_SNDBUF	      set buffer size for output
	  SO_RCVBUF	      set buffer size for input
	  SO_TYPE	      get the type of the socket (get only)
	  SO_ERROR	      get and clear error on the socket	(get only)

     SO_DEBUG enables debugging	in the underlying protocol modules.
     SO_REUSEADDR indicates that the rules used	in validating addresses
     supplied in a bind	call should allow reuse	of local addresses.
     SO_KEEPALIVE enables the periodic transmission of messages	on a connected
     socket.  If the connected party fails to respond to these messages, the
     connection	is considered broken and processes using the socket are
     notified using a SIGPIPE signal.  SO_DONTROUTE indicates that outgoing
     messages should bypass the	standard routing facilities.  Instead,
     messages are directed to the appropriate network interface	according to
     the network portion of the	destination address.

     SO_LINGER controls	the action taken when unsent messages are queued on a
     socket and	a close	is performed.  If the socket promises reliable
     delivery of data and SO_LINGER is set, the	system will block the process
     on	the close attempt until	it is able to transmit the data	or until it
     decides it	is unable to deliver the information (a	timeout	period,	termed
     the linger	interval, is specified in the setsockopt call when SO_LINGER
     is	requested).  If	SO_LINGER is disabled and a close is issued, the
     system will process the close() in	a manner that allows the process to
     continue as quickly as possible.

     The option	SO_BROADCAST requests permission to send broadcast datagrams
     on	the socket.  With protocols that support out-of-band data, the
     SO_OOBINLINE option requests that out-of-band data	be placed in the
     normal data input queue as	received; it will then be accessible with recv
     or	read calls without the MSG_OOB flag.  SO_SNDBUF	and SO_RCVBUF are
     options that adjust the normal buffer sizes allocated for output and
     input buffers, respectively.  The buffer size may be increased for	highvolume
 connections	or may be decreased to limit the possible backlog of
     incoming data.  The system	places an absolute limit on these values.
     Finally, SO_TYPE and SO_ERROR are options used only with getsockopt.
     SO_TYPE returns the type of the socket (for example, SOCK_STREAM).	 It is
     useful for	servers	that inherit sockets on	startup.  SO_ERROR returns any
     pending error on the socket and clears the	error status.  It may be used
     to	check for asynchronous errors on connected datagram sockets or for
     other asynchronous	errors.

RETURN VALUE    [Toc]    [Back]

     A 0 is returned if	the call succeeds, -1 if it fails.

									Page 2

getsockopt(3N)							getsockopt(3N)

ERRORS    [Toc]    [Back]

     The call succeeds unless:

     EBADF		 The argument s	is not a valid descriptor.

     ENOTSOCK		 The argument s	is a file, not a socket.

     ENOPROTOOPT	 The option is unknown at the level indicated.

     ENOMEM		 There was insufficient	user memory available for the
			 operation to complete.

     ENOSR		 There were insufficient STREAMS resources available
			 for the operation to complete.

SEE ALSO    [Toc]    [Back]

     close(2), ioctl(2), read(2), socket(3N), getprotoent(3N)

									PPPPaaaaggggeeee 3333
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