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 socket(2)							   socket(2)




 NAME
      socket() - create an endpoint for communication

 SYNOPSIS
      #include <&lt&lt&lt;sys/socket.h>&gt&gt&gt;

    AF_CCITT Only
      #include <&lt&lt&lt;x25/x25ccittproto.h>&gt&gt&gt;

      int socket(int af, int type, int protocol);

 DESCRIPTION
      The socket() system call creates an endpoint for communication and
      returns a descriptor.  The socket descriptor returned is used in all
      subsequent socket-related system calls.

      The af parameter specifies an address family to be used to interpret
      addresses in later operations that specify the socket.  These address
      families are defined in the include files <&lt&lt&lt;sys/socket.h>&gt&gt&gt; and
      <&lt&lt&lt;x25/ccittproto.h>&gt&gt&gt;.  The only currently supported address families
      are:

	   AF_INET	       (DARPA Internet addresses)
	   AF_UNIX	       (path names on a local node)
	   AF_CCITT	       (CCITT X.25 addresses)
	   AF_VME_LINK	       (backplane communications on VMEbus)

      The type specifies the semantics of communication for the socket.
      Currently defined types are:

	   SOCK_STREAM	       Sequenced, reliable, two-way-connection-based
			       byte streams.

	   SOCK_DGRAM	       Datagrams (connectionless, unreliable
			       messages of a fixed, typically small, maximum
			       length; for AF_INET only).

      protocol specifies a particular protocol to be used with the socket.
      Normally, only a single protocol exists to support a particular socket
      type using a given address family.  However, many protocols may exist,
      in which case a particular protocol must be specified.  The protocol
      number to use depends on the communication domain in which
      communication is to take place (see services(4) and protocols(4)).
      protocol can be specified as zero, which causes the system to choose a
      protocol type to use.

      Sockets of type SOCK_STREAM are byte streams similar to pipes, except
      that they are full-duplex instead of half-duplex.	 A stream socket
      must be in a connected state before any data can be sent or received
      on it.  A connection to another socket is created with a connect() or
      accept() call.  Once connected, data can be transferred using some



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 socket(2)							   socket(2)




      variant of the send() and recv() or the read() and write() calls.
      When a session is complete, use close() or shutdown() calls to
      terminate the connection.

      TCP, the communications protocol used to implement SOCK_STREAM for
      AF_INET sockets, ensures that data is not lost or duplicated.  If a
      peer has buffer space for data and the data cannot be successfully
      transmitted within a reasonable length of time, the connection is
      considered broken and the next recv() call indicates an error with
      errno set to [ETIMEDOUT].	 If SO_KEEPALIVE is set and the connection
      has been idle for two hours, the TCP protocol sends "keepalive"
      packets every 75 seconds to determine whether the connection is
      active.  These transmissions are not visible to users and cannot be
      read by a recv() call.  If the remote system does not respond within
      10 minutes (i.e., after 8 "keepalive" packets have been sent), the
      next socket call (e.g., recv()) returns an error with errno set to
      [ETIMEDOUT].  A SIGPIPE signal is raised if a process sends on a
      broken stream.  This causes naive processes that do not handle the
      signal to exit.  An end-of-file condition (zero bytes read) is
      returned if a process tries to read on a broken stream.

      SOCK_DGRAM sockets allow sending of messages to correspondents named
      in send() calls.	It is also possible to receive messages at such a
      socket with recv().

      The operation of sockets is controlled by socket level options set by
      the setsockopt() system call described by the getsockopt(2) manual
      entry.  These options are defined in the file <&lt&lt&lt;sys/socket.h>&gt&gt&gt; and
      explained in the getsockopt(2) manual entry.

    X.25 Only
      Socket endpoints for communication over an X.25/9000 link can be in
      either address family, AF_INET or AF_CCITT.  If the socket is in the
      AF_INET family, the connection behaves as described above.  TCP is
      used if the socket type is SOCK_STREAM.  UDP is used if the socket
      type is SOCK_DGRAM.  In both cases, Internet protocol (IP) and the
      X.25-to-IP interface module are used.

      If the socket is in the AF_CCITT address family, only the SOCK_STREAM
      socket type is supported.	 Refer to the topic "Comparing X.25 Level 3
      Access to IP" in the X.25 Programmer's Guide for more details on the
      difference between programmatic access to X.25 via IP and X.25 Level
      3.

      If the socket is in the AF_CCITT family, the connection and all other
      operations pass data directly from the application to the X.25 Packet
      Level (level 3) without passing through a TCP or UDP protocol.
      Connections of the AF_CCITT family cannot use most of the socket level
      options described in getsockopt(2).  However, AF_CCITT connections can
      use many X.25-specific ioctl() calls, described in socketx25(7).




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 socket(2)							   socket(2)




 DEPENDENCIES
    AF_CCITT and AF_VME_LINK
      Only the SOCK_STREAM type is supported.

 RETURN VALUE
      socket() returns the following values:

	    n	Successful completion.	n is a valid file descriptor
		referring to the socket.
	   -1	Failure.  errno is set to indicate the error.

 ERRORS
      If socket() fails, errno is set to one of the following values.

	   [EAFNOSUPPORT]	    The specified address family is not
				    supported in this version of the system.

	   [EHOSTDOWN]		    The networking subsystem is not up.

	   [EINVAL]		    SOCK_DGRAM sockets are currently not
				    supported for the AF_UNIX or AF_VME_LINK
				    address families.

	   [EMFILE]		    The per-process descriptor table is
				    full.

	   [ENFILE]		    The system's table of open files is
				    temporarily full and no more socket()
				    calls can be accepted.

	   [ENOBUFS]		    No buffer space is available.  The
				    socket cannot be created.

	   [ENOMEM]		    No memory is available.  The socket
				    cannot be created.

	   [EPROTONOSUPPORT]	    The specified protocol is not supported.

	   [EPROTOTYPE]		    The type of socket and protocol do not
				    match.

	   [ESOCKTNOSUPPORT]	    The specified socket type is not
				    supported in this address family.

	   [ETIMEDOUT]		    Connection timed out.

 FUTURE DIRECTION
      Currently, the default behavior is the HP-UX BSD Sockets; however, it
      might be changed to X/Open Sockets in a future release.  At that time,
      any HP-UX BSD Sockets behavior that is incompatible with X/Open
      Sockets might be obsoleted.  Applications that conform to the X/Open



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 socket(2)							   socket(2)




      specification now will avoid migration problems (see
      xopen_networking(7)).

 MULTITHREAD USAGE
      The socket() system call is thread-safe.	It has a cancellation point;
      and it is async-cancel safe, async-signal safe, and fork-safe.

 AUTHOR
      socket() was developed by HP and the University of California,
      Berkeley.

 SEE ALSO
      accept(2), bind(2), connect(2), getsockname(2), getsockopt(2),
      ioctl(2), listen(2), recv(2), select(2), send(2), shutdown(2),
      af_ccitt(7F), af_vme_link(7F), socket(7), socketx25(7), tcp(7P),
      udp(7P), unix(7P), xopen_networking(7).

 STANDARDS CONFORMANCE
      socket(): XPG4



































 Hewlett-Packard Company	    - 4 -   HP-UX Release 11i: November 2000