The Purpose of the bind(2) Function

When your socket is created by the socket(2) function, it is nameless. You saw in Chapter 1, "Introducing Sockets," that sockets could be used without addresses when the socketpair(2) function was illustrated. However, this worked only because those sockets were created this way, within one Linux kernel. This cannot be done for sockets that must be joined between two different hosts.

A nameless socket is otherwise difficult to use. No one can send information to your nameless socket, because it is like a telephone without a telephone number. Consequently, programmers must bind a name to the socket to make it reachable by someone else. This is like assigning a telephone number to a new telephone so that it can be called. The bind(2) function call permits you to assign an address to a socket in the same manner.