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getsockopt(2)							 getsockopt(2)

NAME
       getsockopt - Get 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 stan‐
       dards as follows:

       getsockopt(): XNS4.0, 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	proto‐
       col  controlling	 the  option.  For example, to indicate that an option
       will be interpreted by the TCP protocol, set level to the protocol num‐
       ber  of	TCP,  as defined in the netinet/in.h header file, or as deter‐
       mined by using  the  getprotobyname()  function.	  Specifies  a	single
       option to be retrieved. The socket level options can be enabled or dis‐
       abled by the setsockopt() function. The getsockopt() function retrieves
       information about the following options: Reports whether socket listen‐
       ing 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 destination 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 pro‐
       cesses using that socket are  notified  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	opera‐
       tion  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 oper‐
       ations 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  pre‐
       vents 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
	      constant across different protocols and implementations. Use the
	      getsockopt(2)  routine to obtain the default values programmati‐
	      cally.  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 call‐
       ing 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 fol‐
       lowing  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  sys‐
       tem  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 opera‐
       tion is not supported by the socket protocol.

SEE ALSO
       Functions: bind(2), close(2), endprotoent(3), getprotobynumber(3), get‐
       protoent(3), setprotoent(3), setsockopt(2), socket(2).

       NetworkInformation: ip(7), tcp(7).

       Standards: standards(5).

       Network Programmer's Guide

								 getsockopt(2)
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