Closing a Socket

In most applications, you do not have to worry about cleaning up your sockets. When you exit your program and your process terminates, the sockets are closed for you. If you need to close a socket while your program is still running, use the close system call.

For example, you may have a daemon process that uses fork to create the server process. The daemon process creates the BSD sockets connection and then passes the socket descriptor to the server. You then have more than one process with the same socket descriptor. The daemon process should do a close of the socket descriptor to avoid keeping the socket open once the server is through with it. Because the server performs the work, the daemon does not use the socket after the fork.

close decrements the file descriptor reference count. Once this occurs, the calling process can no longer use that file descriptor.

When the last close is executed on a socket descriptor, any unsent data are sent before the socket is closed. Any unreceived data are lost. This delay in closing the socket can be controlled by the socket option SO_LINGER. Additional options for closing sockets are discussed in chapter 3, "Advanced Topics for Stream Sockets."

For syntax and details on close, refer to the close(2) man page.