Local Name Binding

A socket is created with no name. A remote process has no way to refer to a socket until an address is bound to the socket. Communicating processes are connected through addresses. In the UNIX family, a connection is composed of (usually) one or two path names. UNIX family sockets need not always be bound to a name. If they are, bound, duplicate ordered sets such as local pathname or foreign pathname can never exist. The path names cannot refer to existing files.

The bind(3SOCKET) call enables a process to specify the local address of the socket. This creates the local pathname ordered set, while connect(3SOCKET) and accept(3SOCKET) complete a socket's association by fixing the remote half of the address. Use bind(3SOCKET) as follows:

bind (s, name, namelen);

The socket handle is s. The bound name is a byte string that is interpreted by the supporting protocols. UNIX family names contain a path name and a family. The example shows binding the name /tmp/foo to a UNIX family socket.

#include <sys/un.h>
 ...
struct sockaddr_un addr;
 ...
strcpy(addr.sun_path, "/tmp/foo");
addr.sun_family = AF_UNIX;
bind (s, (struct sockaddr *) &addr,
        strlen(addr.sun_path) + sizeof (addr.sun_family));

When determining the size of an AF_UNIX socket address, null bytes are not counted, which is why you can use strlen(3C).

The file name referred to in addr.sun_path is created as a socket in the system file name space. The caller must have write permission in the directory where addr.sun_path is created. The file should be deleted by the caller when it is no longer needed. Delete AF_UNIX sockets with unlink(1M).