13.7 Summary

Daemons are processes that run in the background independent of control from all terminals. Many network servers run as daemons. All output from a daemon is normally sent to the syslogd daemon by calling the syslog function. The administrator then has complete control over what happens to these messages, based on the daemon that sent the message and the severity of the message.

To start an arbitrary program and have it run as a daemon requires a few steps: Call fork to run in the background, call setsid to create a new POSIX session and become the session leader, fork again to avoid obtaining a new controlling terminal, change the working directory and the file mode creation mask, and close all unneeded files. Our daemon_init function handles all these details.

Many Unix servers are started by the inetd daemon. It handles all the required daemonization steps, and when the actual server is started, the socket is open on standard input, standard output, and standard error. This lets us omit calls to socket, bind, listen, and accept, since all these steps are handled by inetd.