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Linux 2.6 - man page for getsockopt (linux section 3posix)

GETSOCKOPT(P)			    POSIX Programmer's Manual			    GETSOCKOPT(P)

NAME
       getsockopt - get the socket options

SYNOPSIS
       #include <sys/socket.h>

       int getsockopt(int socket, int level, int option_name,
	      void *restrict option_value, socklen_t *restrict option_len);

DESCRIPTION
       The getsockopt() function manipulates options associated with a socket.

       The  getsockopt()  function  shall  retrieve  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 shall be silently truncated. Otherwise, the object pointed to by the
       option_len argument shall 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 level identifier for the protocol controlling the
       option. For example, to indicate that an option is interpreted by  the  TCP  (Transmission
       Control Protocol), set level to IPPROTO_TCP as defined in the <netinet/in.h> header.

       The  socket  in use may require the process to have appropriate privileges to use the get-
       sockopt() 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 shall store an
	      int value. This is a Boolean option.

       SO_ACCEPTCONN
	      Reports whether socket listening is enabled. This option shall store an int  value.
	      This is a Boolean option.

       SO_BROADCAST
	      Reports  whether	transmission  of broadcast messages is supported, if this is sup-
	      ported by the protocol. This option shall store an int value.  This  is  a  Boolean
	      option.

       SO_REUSEADDR
	      Reports  whether	the  rules used in validating addresses supplied to bind() should
	      allow reuse of local addresses, if this is supported by the protocol.  This  option
	      shall store 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 shall be broken
       and  threads  writing  to that socket shall be notified with a SIGPIPE signal. This option
       shall store an int value. This is a Boolean option.

       SO_LINGER
	      Reports whether the socket lingers on close() if data is present.  If SO_LINGER  is
	      set, the system blocks the process during close() 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() is issued, the system handles the
	      call in a way that allows the process to continue  as  quickly  as  possible.  This
	      option shall store a linger structure.

       SO_OOBINLINE
	      Reports  whether	the  socket leaves received out-of-band data (data marked urgent)
	      inline. This option shall store an int value. This is a Boolean option.

       SO_SNDBUF
	      Reports send buffer size information. This option shall store an int value.

       SO_RCVBUF
	      Reports receive buffer size information. This option shall store an int value.

       SO_ERROR
	      Reports information about error status and clears it. This option  shall	store  an
	      int value.

       SO_TYPE
	      Reports  the  socket  type. This option shall store an int value.  Socket types are
	      described in Socket Types .

       SO_DONTROUTE
	      Reports whether outgoing messages bypass the standard routing facilities.  The des-
	      tination shall 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 shall store an
	      int value. This is a Boolean option.

       SO_RCVLOWAT
	      Reports the minimum number of bytes to process for socket  input	operations.   The
	      default value for SO_RCVLOWAT is 1. If SO_RCVLOWAT is set to a larger value, block-
	      ing receive calls normally wait until they have received the  smaller  of  the  low
	      water  mark value or the requested amount. (They may return less than the low water
	      mark if an error occurs, a signal is caught, or  the  type  of  data  next  in  the
	      receive queue is different from that returned; for example, out-of-band data.) This
	      option shall store an int value. Note  that  not	all  implementations  allow  this
	      option to be retrieved.

       SO_RCVTIMEO
	      Reports  the  timeout value for input operations. This option shall store a timeval
	      structure with the number of seconds and microseconds specifying the limit  on  how
	      long to wait for an input operation to complete. If a receive operation has blocked
	      for this much time without receiving additional data, it shall return with  a  par-
	      tial  count  or errno set to [EAGAIN] or [EWOULDBLOCK] if no data was received. The
	      default for this option is zero, which indicates that a receive operation shall not
	      time out. Note that not all implementations allow this option to be retrieved.

       SO_SNDLOWAT
	      Reports  the minimum number of bytes to process for socket output operations.  Non-
	      blocking output operations shall process no data if flow control does not allow the
	      smaller  of  the	send  low water mark value or the entire request to be processed.
	      This option shall store an int value. Note that not all implementations allow  this
	      option to be retrieved.

       SO_SNDTIMEO
	      Reports  the  timeout  value  specifying the amount of time that an output function
	      blocks because flow control prevents data from being sent. If a send operation  has
	      blocked  for  this  time, it shall return with a partial count or with errno set to
	      [EAGAIN] or [EWOULDBLOCK] if no data was sent. The default for this option is zero,
	      which  indicates that a send operation shall not time out. The option shall store a
	      timeval structure. Note that not	all  implementations  allow  this  option  to  be
	      retrieved.

       For  Boolean  options,  a  zero value indicates that the option is disabled and a non-zero
       value indicates that the option is enabled.

RETURN VALUE
       Upon successful completion, getsockopt() shall return 0; otherwise, -1 shall  be  returned
       and errno set to indicate the error.

ERRORS
       The getsockopt() function shall fail if:

       EBADF  The socket argument is not a valid file descriptor.

       EINVAL The specified option is invalid at the specified socket level.

       ENOPROTOOPT

	      The option is not supported by the protocol.

       ENOTSOCK
	      The socket argument does not refer to a socket.

       The getsockopt() function may fail if:

       EACCES The calling process does not have the appropriate privileges.

       EINVAL The socket has been shut down.

       ENOBUFS
	      Insufficient resources are available in the system to complete the function.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       bind()  ,  close() , endprotoent() , setsockopt() , socket() , the Base Definitions volume
       of IEEE Std 1003.1-2001, <sys/socket.h>, <netinet/in.h>

COPYRIGHT
       Portions of this text are reprinted and	reproduced  in	electronic  form  from	IEEE  Std
       1003.1,	2003  Edition,	Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  by
       the  Institute  of  Electrical  and  Electronics Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				    GETSOCKOPT(P)


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