socket(2)                           CLIX                           socket(2)



  NAME

    socket - Creates an endpoint for communication

  LIBRARY

    Berkeley Software Distribution Library (libbsd.a)

  SYNOPSIS

    #include <sys/types.h>

    #include <sys/socket.h>

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

  PARAMETERS

    domain     Represents a communications domain.

    type       Specifies the communication semantics.

    protocol   Represents the protocol for the socket.

  DESCRIPTION

    The socket() function creates an endpoint for communication and returns a
    descriptor.

    The domain parameter specifies a communications domain within which
    communication will occur; this selects the protocol family that should be
    used.  The protocol family generally is the same as the address family for
    the addresses supplied in later operations on the socket.  These families
    are defined in the include file <sys/socket.h>.  The currently understood
    formats are as follows:

    AF_UNIX   (UNIX internal protocols)

    AF_INET   (ARPA Internet protocols)

    The socket has the indicated type, which specifies the semantics of
    communication.  Currently defined types are as follows:

    ⊕  SOCK_STREAM

    ⊕  SOCK_DGRAM

    A SOCK_STREAM type provides sequenced, reliable, two-way connection-based



  2/94 - Intergraph Corporation                                              1

  socket(2)                           CLIX                           socket(2)



    byte streams.  An out-of-band data transmission mechanism may be
    supported.  A SOCK_DGRAM socket supports datagrams (connectionless,
    unreliable messages of a fixed (typically small) maximum length).

    The protocol parameter specifies a protocol to be used with the socket.
    Normally, only a single protocol exists to support a particular socket
    type within a given protocol family.  However, many protocols may exist.
    In this case, a protocol must be specified in this manner.  The protocol
    number to use is particular to the communication domain in which
    communication is to occur.  (See the protocols file.)

    Sockets of type SOCK_STREAM are full-duplex byte streams similar to pipes.
    A stream socket must be in a connected state before any data may be sent
    or received on it.  A connection to another socket is created with a
    connect() call.  Once connected, data may be transferred using read() and
    write() calls, the readv() and writev() calls, or some variant of the
    send() and recv() calls.  When a session has been completed, a close()
    call may be performed.  Out-of-band data may also be transmitted as
    described in send() and received as described in recv().

    The communications protocols used to implement a SOCK_STREAM ensure that
    data is not lost or duplicated.  If a piece of data for which the peer
    protocol has buffer space cannot be successfully transmitted within a
    reasonable length of time, the connection is considered broken.  Also,
    calls will indicate an error with -1 returned and with ETIMEDOUT as the
    specific code in the global variable errno.  The protocols optionally keep
    sockets open by forcing transmissions roughly every minute in the absence
    of other activity.  An error is then indicated if no response can be
    elicited on an otherwise idle connection for an extended period (such as
    five minutes).  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.

    SOCK_DGRAM sockets allow datagrams to be sent to correspondents named in
    send() calls.  Datagrams are generally received with recvfrom(), which
    returns the next datagram with its return address.

    The fcntl() function can be used to specify a process group to receive a
    SIGURG signal (see signal(2)) when the out-of-band data arrives.  It may
    also enable nonblocking I/O and asynchronous notification of I/O events
    with the SIGIO signal.

    The operation of sockets is controlled by socket-level options.  These
    options are defined in the file <sys/socket.h>.  The setsockopt() and
    getsockopt() functions are used to set and get options, respectively.

  EXAMPLES

    To create a connection oriented socket in the Internet domain with a
    default protocol:

    if (socket(AF_INET, SOCK_STREAM, 0) == -1)



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  socket(2)                           CLIX                           socket(2)



         perror("Socket failed");


  NOTES

    Datagram sockets are not supported in the UNIX domain.

  RETURN VALUES

    Upon successful completion, a descriptor referencing the socket is
    returned.  Otherwise, a value of -1 is returned and errno is set to
    indicate the error.

  ERRORS

    The socket() function fails if one or more of the following is true:

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

    [ENFILE]
           The system file table is full.

    [ENOBUFS]
           The resources to support the connection are not available.

    [EPROTONOSUPPORT]
           The specified domain, type or protocol is not supported.

    [ESOCKTNOSUPPORT]
           The socket type is not supported for the specified domain.

    [ENXIO]
           The system cannot access the specified device.

    [EIO]  The protocol was not initialized.

    [EINTR]
           A signal was caught during the socket() function.

  RELATED INFORMATION

    Functions:  read(2), write(2), accept(2), bind(2), connect(2),
    getsockname(2), getsockopt(2), listen(2), readv(2), recv(2), select(2),
    send(2), shutdown(2), socketpair(2), writev(2), signal(2)

    Files:  intro(7)

    CLIX Programming Guide





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