Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
SOCKET(2)                 FreeBSD System Calls Manual                SOCKET(2)

     socket -- create an endpoint for communication

     Standard C Library (libc, -lc)

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

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

     Socket() creates an endpoint for communication and returns a descriptor.

     The domain parameter specifies a communications domain within which com-
     munication will take place; this selects the protocol family which should
     be used.  These families are defined in the include file <sys/socket.h>.
     The currently understood formats are:

           PF_LOCAL        Host-internal protocols, formerly called PF_UNIX,
           PF_UNIX         Host-internal protocols, deprecated, use PF_LOCAL,
           PF_INET         Internet version 4 protocols,
           PF_IMPLINK      ARPAnet IMP addresses,
           PF_PUP          PUP protocols, like BSP,
           PF_CHAOS        MIT CHAOS protocols,
           PF_NS           Xerox Network Systems protocols,
           PF_ISO          ISO protocols,
           PF_OSI          Open Systems Interconnection protocols,
           PF_ECMA         European Computer Manufacturers,
           PF_DATAKIT      Datakit protocols,
           PF_CCITT        ITU-T protocols, like X.25,
           PF_SNA          IBM SNA,
           PF_DECnet       DECnet,
           PF_DLI          DEC Direct Data Link Interface protocol,
           PF_LAT          LAT protocol,
           PF_HYLINK       NSC Hyperchannel,
           PF_APPLETALK    AppleTalk protocols,
           PF_ROUTE        Internal Routing protocol,
           PF_LINK         Link layer interface,
           PF_XTP          eXpress Transfer Protocol,
           PF_COIP         Connection-Oriented IP, aka ST II,
           PF_CNT          Computer Network Technology,
           PF_SIP          Simple Internet Protocol,
           PF_IPX          Novell Internet Packet eXchange protocol,
           PF_RTIP         Help Identify RTIP packets,
           PF_PIP          Help Identify PIP packets,
           PF_ISDN         Integrated Services Digital Network,
           PF_KEY          Internal key-management function,
           PF_INET6        Internet version 6 protocols,
           PF_NATM         Native ATM access,
           PF_ATM          ATM,
           PF_NETGRAPH     Netgraph sockets

     The socket has the indicated type, which specifies the semantics of com-
     munication.  Currently defined types are:

           SOCK_STREAM     Stream socket,
           SOCK_DGRAM      Datagram socket,
           SOCK_RAW        Raw-protocol interface,
           SOCK_RDM        Reliably-delivered packet,
           SOCK_SEQPACKET  Sequenced packet stream

     A SOCK_STREAM type provides sequenced, reliable, two-way connection based
     byte streams.  An out-of-band data transmission mechanism may be sup-
     ported.  A SOCK_DGRAM socket supports datagrams (connectionless, unreli-
     able messages of a fixed (typically small) maximum length).  A
     SOCK_SEQPACKET socket may provide a sequenced, reliable, two-way connec-
     tion-based data transmission path for datagrams of fixed maximum length;
     a consumer may be required to read an entire packet with each read system
     call.  This facility is protocol specific, and presently implemented only
     for PF_NS.  SOCK_RAW sockets provide access to internal network protocols
     and interfaces.  The types SOCK_RAW, which is available only to the
     super-user, and SOCK_RDM, which is planned, but not yet implemented, are
     not described here.

     The protocol specifies a particular 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, it is possible that many
     protocols may exist, in which case a particular protocol must be speci-
     fied in this manner.  The protocol number to use is particular to the
     ``communication domain'' in which communication is to take place; see

     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(2) call.  Once connected, data may be transferred using
     read(2) and write(2) calls or some variant of the send(2) and recv(2)
     calls.  (Some protocol families, such as the Internet family, support the
     notion of an ``implied connect'', which permits data to be sent piggy-
     backed onto a connect operation by using the sendto(2) call.)  When a
     session has been completed a close(2) may be performed.  Out-of-band data
     may also be transmitted as described in send(2) and received as described
     in recv(2).

     The communications protocols used to implement a SOCK_STREAM insure 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 protocols optionally
     keep sockets ``warm'' 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 a extended period
     (e.g. 5 minutes).  A SIGPIPE signal is raised if a process sends on a
     broken stream; this causes naive processes, which do not handle the sig-
     nal, to exit.

     SOCK_SEQPACKET sockets employ the same system calls as SOCK_STREAM sock-
     ets.  The only difference is that read(2) calls will return only the
     amount of data requested, and any remaining in the arriving packet will
     be discarded.

     SOCK_DGRAM and SOCK_RAW sockets allow sending of datagrams to correspon-
     dents named in send(2) calls.  Datagrams are generally received with
     recvfrom(2), which returns the next datagram with its return address.

     An fcntl(2) call can be used to specify a process group to receive a
     SIGURG signal when the out-of-band data arrives.  It may also enable non-
     blocking I/O and asynchronous notification of I/O events via SIGIO.

     The operation of sockets is controlled by socket level options.  These
     options are defined in the file <sys/socket.h>.  Setsockopt(2) and
     getsockopt(2) are used to set and get options, respectively.

     A -1 is returned if an error occurs, otherwise the return value is a
     descriptor referencing the socket.

     The socket() call fails if:

     [EPROTONOSUPPORT]  The protocol type or the specified protocol is not
                        supported within this domain.

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

     [ENFILE]           The system file table is full.

     [EACCES]           Permission to create a socket of the specified type
                        and/or protocol is denied.

     [ENOBUFS]          Insufficient buffer space is available.  The socket
                        cannot be created until sufficient resources are

     accept(2), bind(2), connect(2), getpeername(2), getsockname(2),
     getsockopt(2), ioctl(2), listen(2), read(2), recv(2), select(2), send(2),
     shutdown(2), socketpair(2), write(2), getprotoent(3), netgraph(4),

     "An Introductory 4.3 BSD Interprocess Communication Tutorial", PS1, 7.

     "BSD Interprocess Communication Tutorial", PS1, 8.

     The socket() function call appeared in 4.2BSD.

FreeBSD 4.10                   November 24, 1997                  FreeBSD 4.10


Want to link to this manual page? Use this URL:

home | help