ultrix man page for socket

socket(2)							System Calls Manual							 socket(2)

Name
       socket - create an endpoint for communication

Syntax
       #include <sys/types.h>
       #include <sys/socket.h>

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

Description
       The system call creates an endpoint for communication and returns a descriptor.

       The  operation  of  sockets  is controlled by socket-level options, defined in the file and explained in the section, Socket-level Options.
       The calls and are used to set and get options.

Arguments
       The af parameter specifies an address format. Addresses specified in later operations using the socket are interpreted according  to  these
       formats.  The formats are defined in the include file

       AF_UNIX	 UNIX path names
       AF_INET	 ARPA Internet addresses
       AF_IMPLINK     IMP "host at IMP" addresses
       AF_DLI	      For access to broadcast devices (Ethernet)

       The type argument specifies the semantics of communication.  The defined types are:

       SOCK_STREAM
       SOCK_DGRAM
       SOCK_RAW
       SOCK_SEQPACKET

       The  SOCK_STREAM  and SOCK_DGRAM types are available only if your system includes the TCP/IP network.  For example, if you can use the com-
       mand to log in to a remote ULTRIX node, your system supports these socket types.

       A SOCK_STREAM type provides sequenced, reliable, 2-way-connection-based byte streams with an out-of-band data  transmission  mechanism.	 A
       SOCK_DGRAM socket supports datagrams (connectionless, unreliable messages of a fixed maximum length, typically small).

       SOCK_RAW sockets provide access to internal network interfaces and are available only to the super-user.

       The SOCK_SEQPACKET type is the socket protocol to request when you want to communicate with other Digital systems using DECnet.

       Socket types are discussed further in following sections.

       The  protocol  argument specifies the protocol to be used with the socket.  Normally, only a single protocol exists to support a particular
       socket type using a given address format.  However, it is possible that many protocols may exist, in which case a particular protocol  must
       be specified in this manner.  The protocol number to use is particular to the communication domain in which communication is to take place.
       For further information, see and

Socket Type SOCK_STREAM
       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
       can  be	sent or received on it.  A connection to another socket is created with a call.  Once connected, data can be transferred using and
       calls or some variant of the and calls.	When a session has been completed, a may be performed.	Out-of-band data can also  be  transmitted
       as described in and received as described in

       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, then  the	connection  is	considered
       broken  and  calls will indicate an error with -1 returns and with ETIMEDOUT as the specific code in the global variable errno.	The proto-
       cols optionally keep sockets "warm" by forcing transmissions roughly every minute in the absence of other activity.  An error is then indi-
       cated  if no response can be elicited on an otherwise idle connection for an extended period (for example, 5 minutes).  A SIGPIPE signal is
       raised if a process sends on a broken stream; this causes processes that do not handle the signal to exit.

Socket Types SOCK_DGRAM and SOCK_RAW
       SOCK_DGRAM and SOCK_RAW sockets allow sending of datagrams to correspondents named in calls.  It is also possible to receive  datagrams	at
       these sockets with

       An call can be used to specify a process group to receive a SIGURG signal when the out-of-band data arrives.

       SOCK_DGRAM sockets are the only type of socket allowed by the Data Link Interface.

Socket Type SOCK_SEQPACKET
       SOCK_SEQPACKET  sockets	are  similar to datagrams except that they are guaranteed to be received in the sequence that they are sent.  They
       are also guaranteed to be error-free.

Socket-Level Options
       The operation of sockets is controlled by socket-level options.	These options are defined in the file, The calls and are used to  set  and
       get options.

       Options	other than SO_LINGER take an integer parameter that should be nonzero, if the option is to be enabled, or zero (0), if it is to be
       disabled.  SO_LINGER uses a ``linger'' structure parameter defined in This structure specifies the desired state  of  the  option  and  the
       linger interval (see the following).

       SO_DEBUG 	    Turn on recording of debugging information
       SO_REUSEADDR	    Allow local address reuse
       SO_KEEPALIVE	    Keep connections alive
       SO_DONTROUTE	    Do not apply routing on outgoing messages
       SO_LINGER	    Linger on close if data present
       SO_BROADCAST	    Permit sending of broadcast messages
       SO_ACCEPTCONN	    Socket has had listen()
       SO_USELOOPBACK	    Bypass hardware when possible
       SO_OOBINLINE	    Leave received OOB data in line

       SO_DEBUG enables debugging in the underlying protocol modules.

       SO_REUSEADDR indicates the rules used in validating addresses supplied in a call should allow reuse of local addresses.

       SO_KEEPALIVE enables the periodic transmission of messages on a connected socket.  Should the connected party fail to respond to these mes-
       sages, the connection is considered broken and processes using the socket are notified through a SIGIO  signal.	 Note  that  in  order	to
       receive signals on a socket the program must first call with a F_SETOWN request to set the process group of the process to receive the sig-
       nal, and with a F_SETFL request to set the FASYNC flag, which enables the SIGIO signal to be sent.

       SO_DONTROUTE indicates that outgoing messages should bypass the standard routing facilities.  Instead, messages are directed to the  appro-
       priate network interface, according to the network portion of the destination address.

       SO_LINGER  controls  the  actions taken when unsent messages are queued on the socket and a is performed.  When using the to set the linger
       values, the option value for the SO_LINGER command is the address of a linger structure:
       struct  linger {
	       int     l_onoff;       /* option on/off */
	       int     l_linger;      /* linger time */
       };
       If the socket promises reliable delivery of data and l_onoff is nonzero, the system blocks the process on the attempt until it is  able	to
       transmit  the data or until it decides it is unable to deliver the information.	A timeout period, termed the linger interval, is specified
       in l_linger in seconds.	If l_onoff is set to zero (0) and a is issued, the system processes the close in a manner that allows the  process
       to continue as quickly as possible.

       SO_BROADCAST is used to enable or disable broadcasting on the socket.

Return Values
       A -1 is returned if an error occurs.   Otherwise, the return value is a descriptor to be used in other calls to refer to the socket.

Diagnostics
       The call fails if:

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

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

       [EPROTONOSUPPORT]
		 The specified protocol is not supported.

       [EPROTOTYPE]
		 Request for a type of socket for which there is no supporting protocol.

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

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

See Also
       accept(2),  bind(2),  close(2),	connect(2),  fcntl(2),	getsockname(2),  getsockopt(2), ioctl(2), listen(2), read (2), recv(2), select(2),
       send(2), setsockopt(2), shutdown(2), socketpair(2), protocols(5), services(5), write(2),
       Guide to Network Programming,
       Guide to the Data Link Interface

																	 socket(2)