GETSOCKOPT(2)							System Calls Manual						     GETSOCKOPT(2)

NAME

       getsockopt, setsockopt - get and set options on sockets

SYNOPSIS

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

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

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

DESCRIPTION

       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 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(3N).

       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 sup-
       plied or returned, optval may be supplied as 0.

       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(4P).

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

       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
	      SO_KEEPALIVE    toggle keep connections alive
	      SO_DONTROUTE    toggle routing bypass for outgoing messages
	      SO_LINGER       linger on close if data 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(2) call should allow reuse of local addresses.  SO_KEEPALIVE enables the periodic transmission of messages on a connected socket.
       Should the connected party fail to respond to these messages, the connection is considered broken and processes using the socket are  noti-
       fied via 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 messags are queued on socket and a close(2) 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.  Broadcast was a	privileged  operation  in  earlier
       versions  of the system.  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	to  adjust  the  normal buffer sizes allocated for output and input buffers, respectively.  The buffer size may be
       increased for high-volume 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 setsockopt.  SO_TYPE returns the type of the socket, such
       as 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

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

ERRORS

       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.

       [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.

SEE ALSO

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

BUGS

       Several of the socket options should be handled at lower levels of the system.

4.2 Berkeley Distribution					   May 23, 1986 						     GETSOCKOPT(2)