| SOCKET(2) | System Calls Manual | SOCKET(2) | 
socket —
#include <sys/socket.h>
int
  
  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 communication 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 local (previously UNIX) domain protocols PF_INET ARPA Internet protocols PF_INET6 IPv6 (Internet Protocol version 6) protocols PF_NS Xerox Network Systems protocols PF_APPLETALK AppleTalk protocols PF_BLUETOOTH Bluetooth protocols PF_CAN CAN bus protocols
The socket has the indicated type, which specifies the semantics of communication. Currently defined types are:
SOCK_STREAM SOCK_DGRAM SOCK_RAW SOCK_SEQPACKET SOCK_RDM
The following flags can be or'ed to the type to condition the returned file descriptor: The following flags are valid:
| SOCK_CLOEXECSet the close on exec property. | 
| SOCK_NONBLOCKSets non-blocking I/O. | 
| SOCK_NOSIGPIPEReturnEPIPEinstead of raisingSIGPIPE. | 
A SOCK_STREAM type provides sequenced,
    reliable, two-way connection based 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). A SOCK_SEQPACKET socket may provide a
    sequenced, reliable, two-way connection-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 specified 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. 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. 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 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 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 an 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 signal, to exit.
SOCK_SEQPACKET sockets employ the same
    system calls as SOCK_STREAM sockets. 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
    correspondents 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⟩. The setsockopt(2) and getsockopt(2) system calls are used to set and get options, respectively.
socket() call fails if:
EACCES]EAFNOSUPPORT]EMFILE]ENFILE]ENOBUFS]EPROTONOSUPPORT]EPROTOTYPE]Stuart Sechrest, An Introductory 4.4BSD Interprocess Communication Tutorial. (see /usr/share/doc/psd/20.ipctut)
Samuel J. Leffler, Robert S. Fabry, William N. Joy, Phil Lapsley, Steve Miller, and Chris Torek, Advanced 4.4BSD IPC Tutorial. (see /usr/share/doc/psd/21.ipc)
socket() function call appeared in
  4.2BSD.
| April 27, 2017 | NetBSD 9.3 |