9.7. Running Sendmail from InetD

Given Sendmail's apparent memory requirements, it is occasionally tempting to run it "on demand" from the InetD rather than running it all the time as a listener (" sendmail -bd -q30m". This is accomplished by adding an entry such as

smtp stream tcp nowait root /usr/lib/sendmail sendmail -bs

in your /etc/inetd.conf file. We recommend against this practice for the following reasons:

1. A real Sendmail listener will watch the system load average and stop accepting incoming mail when the load average gets too high. You will miss this feature if you don't have it, and InetD doesn't have it.

2. Since the "periodic queue run" function is usually performed by the listener, if you don't run a listener you will need to "run the queue" periodically from your Cron Daemon with something like

   23 * * * * root /usr/lib/sendmail -q

   While not difficult, this does add another place where something can go wrong. Sendmail, however monolithic, has the advantage of either working completely or not it can't fail to run the queue without also failing to do a lot of other very noticeable things.

3. The overhead of exec'ing a new SMTP server is higher than that of just fork'ing a process from the listener. This additional overhead can degrade the performance of your system.

4. Finally, the apparent memory requirements of a Sendmail listener are not as bad as they look. All UNIX-like systems are capable of "swapping out" a process if it...