SOCKET(2)                   BSD System Calls Manual                  SOCKET(2)

NAME
     socket -- create an endpoint for communication

SYNOPSIS
     #include <sys/socket.h>

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

DESCRIPTION
     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_ROUTE        Internal Routing protocol,
           PF_KEY          Internal key-management function,
           PF_INET6        Internet version 6 protocols,
           PF_SYSTEM       System domain,
           PF_NDRV         Raw access to network device

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

           SOCK_STREAM
           SOCK_DGRAM
           SOCK_RAW

     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).  SOCK_RAW
     sockets provide access to internal network protocols and interfaces.  The
     type SOCK_RAW, which is available only to the super-user.

     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
     protocols(5).

     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) or connectx(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.  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_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.

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

ERRORS
     The socket() system call fails if:

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

     [EAFNOSUPPORT]     The specified address family is not supported.

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

     [ENFILE]           The system file table is full.

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

     [ENOMEM]           Insufficient memory was available to fulfill the
                        request.

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

     [EPROTOTYPE]       The socket type is not supported by the protocol.

     If a new protocol family is defined, the socreate process is free to
     return any desired error code.  The socket() system call will pass this
     error code along (even if it is undefined).

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

     The include file <sys/types.h> is necessary.

SEE ALSO
     accept(2), bind(2), connect(2), connectx(2), disconnectx(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),
     inet(4), inet6(4), unix(4), compat(5)

     An Introductory 4.3 BSD Interprocess Communication Tutorial, reprinted in
     UNIX Programmer's Supplementary Documents Volume 1.

     BSD Interprocess Communication Tutorial, reprinted in UNIX Programmer's
     Supplementary Documents Volume 1.

HISTORY
     The socket() function call appeared in 4.2BSD.

BSD                             March 18, 2015                             BSD