socket(2)

DESCRIPTION

The socket() system call creates an endpoint for communication and returns a descriptor. The socket descriptor returned is used in all subsequent socket-related system calls.

The af parameter specifies an address family to be used to interpret addresses in later operations that specify the socket. These address families are defined in the include files <sys/socket.h> and <x25/ccittproto.h>. The only currently supported address families are:

The type specifies the semantics of communication for the socket. Currently defined types are:

protocol specifies a particular protocol to be used with the socket. Normally, only a single protocol exists to support a particular socket type using a given address family. However, many protocols may exist, in which case a particular protocol must be specified. The protocol number to use depends on the communication domain in which communication is to take place (see services(4) and protocols(4)). protocol can be specified as zero, which causes the system to choose a protocol type to use.

Sockets of type SOCK_STREAM are byte streams similar to pipes, except that they are full-duplex instead of half-duplex. 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 connect() or accept() call. Once connected, data can be transferred using some variant of the send() and recv() or the read() and write() calls. When a session is complete, use close() or shutdown() calls to terminate the connection.

TCP, the communications protocol used to implement SOCK_STREAM for AF_INET sockets, ensures that data is not lost or duplicated. If a peer has buffer space for data and the data cannot be successfully transmitted within a reasonable length of time, the connection is considered broken and the next recv() call indicates an error with errno set to [ETIMEDOUT]. If SO_KEEPALIVE is set and the connection has been idle for two hours, the TCP protocol sends "keepalive" packets every 75 seconds to determine whether the connection is active. These transmissions are not visible to users and cannot be read by a recv() call. If the remote system does not respond within 10 minutes (i.e., after 8 "keepalive" packets have been sent), the next socket call (e.g., recv()) returns an error with errno set to [ETIMEDOUT]. 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. An end-of-file condition (zero bytes read) is returned if a process tries to read on a broken stream.

SOCK_DGRAM sockets allow sending of messages to correspondents named in send() calls. It is also possible to receive messages at such a socket with recv().

The operation of sockets is controlled by socket level options set by the setsockopt() system call described by the getsockopt(2) manual entry. These options are defined in the file <sys/socket.h> and explained in the getsockopt(2) manual entry.

DEPENDENCIES

RETURN VALUE

socket() returns the following values:

ERRORS

If socket() fails, errno is set to one of the following values.

FUTURE DIRECTION

Currently, the default behavior is the HP-UX BSD Sockets; however, it might be changed to X/Open Sockets in a future release. At that time, any HP-UX BSD Sockets behavior that is incompatible with X/Open Sockets might be obsoleted. Applications that conform to the X/Open specification now will avoid migration problems (see xopen_networking(7))

MULTITHREAD USAGE

The socket() system call is thread-safe. It has a cancellation point; and it is async-cancel safe, async-signal safe, and fork-safe.

AUTHOR

socket() was developed by HP and the University of California, Berkeley.

SEE ALSO

accept(2), bind(2), connect(2), getsockname(2), getsockopt(2), ioctl(2), listen(2), recv(2), select(2), send(2), shutdown(2), af_ccitt(7F), af_vme_link(7F), socket(7), socketx25(7), tcp(7P), udp(7P), unix(7P), xopen_networking(7).

STANDARDS CONFORMANCE

socket(): XPG4