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<sect1 id="debian-orientation"><title>Orienting Yourself to Debian</title>
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Debian is a little different from other distributions. Even if you're
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familiar with Linux in other distributions, there are things you
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should know about Debian to help you to keep your system in a good,
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clean state. This chapter contains material to help you get oriented;
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it is not intended to be a tutorial for how to use Debian, but just a
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very brief glimpse of the system for the very rushed.
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<sect2><title>Debian Packaging System</title>
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The most important concept to grasp is the Debian packaging system.
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In essence, large parts of your system should be considered under the
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control of the packaging system. These include:
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<filename>/usr</filename> (excluding <filename>/usr/local</filename>)
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<filename>/var</filename> (you could make
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<filename>/var/local</filename> and be safe in there)
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<filename>/bin</filename>
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<filename>/sbin</filename>
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<filename>/lib</filename>
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For instance, if you replace <filename>/usr/bin/perl</filename>, that
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will work, but then if you upgrade your <classname>perl</classname>
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package, the file you put there will be replaced. Experts can get
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around this by putting packages on ``hold'' in
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<command>aptitude</command>.
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One of the best installation methods is apt. You can use the command
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line version <command>apt-get</command> or full-screen text version
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<application>aptitude</application>. Note apt will also let you merge
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main, contrib, and non-free so you can have export-restricted packages
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as well as standard versions.
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<sect2><title>Application Version Management</title>
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Alternative versions of applications are managed by update-alternatives. If
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you are maintaining multiple versions of your applications, read the
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update-alternatives man page.
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<sect2><title>Cron Job Management</title>
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Any jobs under the purview of the system administrator should be in
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<filename>/etc</filename>, since they are configuration files. If you
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have a root cron job for daily, weekly, or nightly runs, put them in
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<filename>/etc/cron.{daily,weekly,monthly}</filename>. These are
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invoked from <filename>/etc/crontab</filename>, and will run in
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alphabetic order, which serializes them.
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On the other hand, if you have a cron job that (a) needs to run as a
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special user, or (b) needs to run at a special time or frequency, you
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can use either <filename>/etc/crontab</filename>, or, better yet,
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<filename>/etc/cron.d/whatever</filename>. These particular files
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also have an extra field that allows you to stipulate the user under
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which the cron job runs.
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In either case, you just edit the files and cron will notice them
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automatically. There is no need to run a special command. For more
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information see cron(8), crontab(5), and
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<filename>/usr/share/doc/cron/README.Debian</filename>.