osf1 man page for getsockopt

getsockopt(2)							System Calls Manual						     getsockopt(2)

NAME
       getsockopt - Gets socket options

SYNOPSIS
       #include <sys/socket.h>
       int getsockopt (
	    int socket,      int level,      int option_nam,	  void *option_value,	   socklen_t *option_len );

       [XNS4.0]  The  definition  of  the getsockopt() function in XNS4.0 uses a size_t data type instead of a socklen_t data type as specified in
       XNS5.0 (the previous definition).

       [Tru64 UNIX]  The following definition of the getsockopt() function does not conform to current standards and is supported only	for  back-
       ward compatibility (see standards(5)):

       int getsockopt (
	    int socket,      int level,      int option_nam,	  char *option_value,	   int *option_len );

STANDARDS
       Interfaces documented on this reference page conform to industry standards as follows:

       getsockopt():  XNS5.0

       Refer to the standards(5) reference page for more information about industry standards and associated tags.

PARAMETERS
       Specifies the file descriptor for the socket.  Specifies the protocol level at which the option resides.  To retrieve options at the socket
       level, specify the level parameter as SOL_SOCKET.  To retrieve options at other levels, supply the appropriate protocol number for the pro-
       tocol  controlling  the option.	For example, to indicate that an option will be interpreted by the TCP protocol, set level to the protocol
       number of TCP, as defined in the netinet/in.h header file, or as determined by using the getprotobyname()  function.   Specifies  a  single
       option  to  be  retrieved.   The  socket  level options can be enabled or disabled by the setsockopt() function.  The getsockopt() function
       retrieves information about the following options: Reports whether socket listening is enabled.	This option returns an int value.  Reports
       whether	transmission  of  broadcast messages is supported.  This option returns an int value.  [Tru64 UNIX]  In a cluster, reports whether
       the socket will use the default cluster alias as its source address.  [Tru64 UNIX]  In a cluster,  reports  whether  the  socket  can  only
       receive packets addressed to this cluster member.  [Tru64 UNIX]	In a cluster, reports whether the socket must receive packets addressed to
       a cluster alias and will drop any packets that are not addressed to a cluster  alias.   Reports	whether  debugging  information  is  being
       recorded.   This option returns an int value.  Reports whether outgoing messages should bypass the standard routing facilities.	The desti-
       nation must be on a directly-connected network; messages are directed to the appropriate network interface.  The protocol in use determines
       the  effect  of this option.  (Not recommended, for debugging purposes only.)  This option returns an int value.  Reports information about
       error status and clears it.  This option returns an int value.  Reports whether connections are kept active with periodic  transmission	of
       messages.   If  the connected socket fails to respond to these messages, the connection is broken and processes using that socket are noti-
       fied with a SIGPIPE signal.  This option returns an int value.  Reports whether the socket  lingers  on	a  close()  function  if  data	is
       present.   If  SO_LINGER is set, the system blocks the process during the close() function until it can transmit the data or until the time
       expires.  If SO_LINGER is not specified, and a close() function is issued, the system handles the call in a way that allows the process	to
       continue  as quickly as possible.  This option returns an struct linger value.  Reports whether the socket leaves received out-of-band data
       (data marked urgent) in line.  This option returns an int value.  Reports receive buffer size information.   This  option  returns  an  int
       value.	Reports  the minimum number of bytes (low-water mark) for socket receive operations.  The default value is 1.  If the value is set
       to a larger value, blocking receive calls wait until they receive either the low water mark value or  the  requested  value  (whichever	is
       smaller).   The	calls might return less than the water mark if an error occurs, a signal is received, or type of data in the receive queue
       is different than that returned.  This option returns an int value.  Reports receive time-out information.  This option	returns  a  struct
       timeval	value  that  specifies the amount of time to wait for a receive operation to complete.	If a receive operation has blocked for the
       specified amount of time without receiving additional data, it returns with a partial error count or errno  set	to  [EAGAIN]  or  [EWOULD-
       BLOCK].	The default is 0 (zero), which indicates that a receive operation will not time out.  [Tru64 UNIX]   In a cluster, reports whether
       an attempt to bind the socket to a port in the reserved range (512-1024) will fail if the port is marked static.  Reports whether the rules
       used  in  validating  addresses	supplied  by  a  bind() function should allow reuse of local addresses.  This option returns an int value.
       [Tru64 UNIX]  In a cluster, reports whether the socket can reuse a locked cluster alias port.  Reports send buffer size information.   This
       option  returns	an int value.  Reports the minimum number of bytes (low-water mark) for socket transmit operations.  Non-blocking transmit
       operations process no data if flow control does not allow either the send low water mark value or the entire request (whichever is smaller)
       to  be  processed.   This  option returns an int value.	Reports send time-out information. This option returns a struct timeval value that
       specifies the amount of time a transmit function blocks when flow control prevents the transmission  of	data.	If  a  transmit  operation
       blocks  for this amount of time without transmitting data, it returns with a partial error count or errno set to [EAGAIN] or [EWOULDBLOCK].
       The default is 0 (zero), which indicates that a transmit operation will not time out.  Reports the socket type.	This option returns an int
       value.  Only valid for routing sockets.	Reports whether the sender receives a copy of each message.  This option returns an int value.
       [Tru64  UNIX]   Options at other protocol levels vary in format and name.  See the tcp(7) and ip(7) reference pages for more information on
       option names relevant for TCP and IP options respectively.

									      Note
	      [Tru64 UNIX]   The default values for socket level options like  SO_SENDBUF, SO_RCVBUF, SO_SNDLOWAT, and SO_RCVLOWAT  are  not  con-
	      stant across different protocols and implementations.  Use the getsockopt(2) routine to obtain the default values programmatically.
	      The  address  of	a buffer.  Specifies the length of buffer pointed to by option_value.  The option_len parameter initially contains
	      the size of the buffer pointed to by the option_value parameter.	On return, the option_len parameter is modified  to  indicate  the
	      actual size of the value returned.  If no option value is supplied or returned, the option_value parameter can be 0 (zero).
	      Options at other protocol levels vary in format and name.

DESCRIPTION
       The getsockopt() function allows an application program to query socket options.  The calling program specifies the name of the socket, the
       name of the option, and a place to store the requested information.  The operating system gets  the  socket  option  information  from  its
       internal data structures and passes the requested information back to the calling program.

       Options	may  exist  at	multiple protocol levels.  They are always present at the uppermost socket level.  When retrieving socket options,
       specify the level at which the option resides and the name of the option.

RETURN VALUES
       Upon successful completion, the getsockopt() function returns a value of 0 (zero).  Otherwise, a value of -1 is returned, and errno is  set
       to indicate the error.

ERRORS
       If  the getsockopt() function fails, errno may be set to one of the following values: The calling process does not have appropriate permis-
       sions.  The socket parameter is not valid.  [POSIX]  The send and receive timeout values are too large to fit in the timeout fields of  the
       socket  structure.   The  address  pointed  to by the option_value parameter is not in a valid (writable) part of the process space, or the
       option_len parameter is not in a valid part of the process address space.  The option_value or option_len  parameter  is  invalid;  or  the
       socket  is  shut  down.	 Insufficient  resources  are available in the system to complete the call.  The option is unknown.  The available
       STREAMS resources were insufficient for the operation to complete.  The socket parameter refers to a file,  not	a  socket.   [XNS4.0]  The
       operation is not supported by the socket protocol.

RELATED INFORMATION
       Functions: bind(2), close(2), endprotoent(3), getprotobynumber(3), getprotoent(3), setprotoent(3), setsockopt(2), socket(2).

       Network Information: ip(7), tcp(7).

       Standards: standards(5).  delim off

																     getsockopt(2)