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8.2. Orienting Yourself to Ubuntu

Ubuntu is a little different from other distributions. Even if you're familiar with Linux in other distributions, there are things you should know about Ubuntu to help you to keep your system in a good, clean state. This chapter contains material to help you get oriented; it is not intended to be a tutorial for how to use Ubuntu, but just a very brief glimpse of the system for the very rushed.

8.2.1. Ubuntu Packaging System

The most important concept to grasp is the Ubuntu packaging system, which may be familiar to those who have already used Debian GNU/Linux. In essence, large parts of your system should be considered under the control of the packaging system. These include:

  • /usr (excluding /usr/local)

  • /var (you could make /var/local and be safe in there)

  • /bin

  • /sbin

  • /lib

For instance, if you replace /usr/bin/perl, that will work, but then if you upgrade your perl package, the file you put there will be replaced. Experts can get around this by putting packages on ``hold'' in aptitude.

One of the best installation methods is apt. You can use the command line version apt-get, the full-screen text version aptitude, or the graphical version synaptic. Note apt will also let you merge main, contrib, and non-free so you can have export-restricted packages as well as standard versions.

8.2.2. Application Version Management

Alternative versions of applications are managed by update-alternatives. If you are maintaining multiple versions of your applications, read the update-alternatives man page.

8.2.3. Cron Job Management

Any jobs under the purview of the system administrator should be in /etc, since they are configuration files. If you have a root cron job for daily, weekly, or nightly runs, put them in /etc/cron.{daily,weekly,monthly}. These are invoked from /etc/crontab, and will run in alphabetic order, which serializes them.

On the other hand, if you have a cron job that (a) needs to run as a special user, or (b) needs to run at a special time or frequency, you can use either /etc/crontab, or, better yet, /etc/cron.d/whatever. These particular files also have an extra field that allows you to stipulate the user under which the cron job runs.

In either case, you just edit the files and cron will notice them automatically. There is no need to run a special command. For more information see cron(8), crontab(5), and /usr/share/doc/cron/README.Debian.