A page for randomness

In my last post, sendmail was one of the services on my box that was starting when I enter runlevel 2. Maybe I don’t want sendmail to start, or rather, if it is already started, when I enter runlevel 2, I want to kill it. In other words, I don’t want it running for runlevel 2. How can I make this change?

Well, first, I could just delete the soft link from the runlevel directory /etc/rc2.d/:

aaron@kratos:~ 1355 % sudo rm /etc/rc2.d/S21sendmail
Password:

That would definitely keep it from starting when I enter runlevel 2, but what if I wanted to kill it if it was already started from a previous runlevel? Just deleting the soft link won’t do it. I need to turn it into a K-script. Further, deleting and creating soft links in my /etc/rc[0-6].d/ directories by hand is a bit of a pain. This is where the update-rc.d command comes in:

aaron@kratos:~ 1356 % sudo update-rc.d -f sendmail remove
Password:
Removing any system startup links for /etc/init.d/sendmail …
/etc/rc0.d/K19sendmail
/etc/rc1.d/K19sendmail
/etc/rc2.d/S21sendmail
/etc/rc3.d/S21sendmail
/etc/rc4.d/S21sendmail
/etc/rc5.d/S21sendmail
/etc/rc6.d/K19sendmail
aaron@kratos:~ 1357 % sudo update-rc.d sendmail stop 20 0 1 2 3 4 5 6 .
Adding system startup for /etc/init.d/sendmail …
/etc/rc0.d/K20sendmail -> ../init.d/sendmail
/etc/rc1.d/K20sendmail -> ../init.d/sendmail
/etc/rc2.d/K20sendmail -> ../init.d/sendmail
/etc/rc3.d/K20sendmail -> ../init.d/sendmail
/etc/rc4.d/K20sendmail -> ../init.d/sendmail
/etc/rc5.d/K20sendmail -> ../init.d/sendmail
/etc/rc6.d/K20sendmail -> ../init.d/sendmail

We’ll get into the syntax a bit later, but these commands, as observed, removed any existing soft links that previously existed, and created new K-scripts for all of my runlevels.

First off, why two separate commands? Well, by Debian policy, no package upgrade will ever overwrite a previous configuration. This includes updating soft links in the runlevel directories. This also ensures persistent changes and allows the system administrator to prevent daemons from launching. So, if soft links already exist, they first need to be removed, then new links created.

Source: Aaron Toponce : Managing Services in Ubuntu, Part II: Managing Runlevels

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