LPI Linux Certification in a Nutshell, 2nd Edition

Objective 1: Configure and Manage inetd, xinetd, and Related Services

To reduce the number of daemons necessary to service requests, the Internet superdaemon, or inetd, was created. Instead of running individual daemons for each service, inetd runs as a single service listening to all of the desired port numbers. When an inbound request is received, it is handed off to the actual daemon for processing. With this scheme, the real daemons are still used as before, but they run only when needed and are started by inetd, freeing resources for other tasks. In addition, using inetd greatly simplifies the code of the various daemons. Instead of listening for connections and everything else required to be a proper network daemon, daemons run by inetd need to read only from stdin and write only to stdout.

Many Linux distributions have started shipping xinetd as a replacement for inetd. The following information applies to only the original inetd. xinetd configuration is significantly different. Both are discussed in this chapter. For more information on xinetd, see http://www.xinetd.org.

The inetd Configuration File

inetd is usually started during system initialization and continues to run indefinitely (or until the process is stopped). When started (and later in response to signal SIGHUP), inetd reads its configuration file from /etc/inetd.conf, which is nothing more than a plain text file that defines the services managed by inetd. (Commented lines begin with #.) Example 20-1 shows ...