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<sect1 id="debian-orientation"><title>Orienting Yourself to Debian</title>
<para>
Debian is a little different from other distributions. Even if you're
familiar with Linux in other distributions, there are things you
should know about Debian 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 Debian, but just a
very brief glimpse of the system for the very rushed.
</para>
<sect2><title>Debian Packaging System</title>
<para>
The most important concept to grasp is the Debian packaging system.
In essence, large parts of your system should be considered under the
control of the packaging system. These include:
<itemizedlist>
<listitem><para>
<filename>/usr</filename> (excluding <filename>/usr/local</filename>)
</para></listitem>
<listitem><para>
<filename>/var</filename> (you could make
<filename>/var/local</filename> and be safe in there)
</para></listitem>
<listitem><para>
<filename>/bin</filename>
</para></listitem>
<listitem><para>
<filename>/sbin</filename>
</para></listitem>
<listitem><para>
<filename>/lib</filename>
</para></listitem>
</itemizedlist>
For instance, if you replace <filename>/usr/bin/perl</filename>, that
will work, but then if you upgrade your <classname>perl</classname>
package, the file you put there will be replaced. Experts can get
around this by putting packages on ``hold'' in
<command>aptitude</command>.
</para><para>
One of the best installation methods is apt. You can use the command
line version <command>apt-get</command> or full-screen text version
<application>aptitude</application>. Note apt will also let you merge
main, contrib, and non-free so you can have export-restricted packages
as well as standard versions.
</para>
</sect2>
<sect2><title>Application Version Management</title>
<para>
Alternative versions of applications are managed by update-alternatives. If
you are maintaining multiple versions of your applications, read the
update-alternatives man page.
</para>
</sect2>
<sect2><title>Cron Job Management</title>
<para>
Any jobs under the purview of the system administrator should be in
<filename>/etc</filename>, since they are configuration files. If you
have a root cron job for daily, weekly, or nightly runs, put them in
<filename>/etc/cron.{daily,weekly,monthly}</filename>. These are
invoked from <filename>/etc/crontab</filename>, and will run in
alphabetic order, which serializes them.
</para><para>
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 <filename>/etc/crontab</filename>, or, better yet,
<filename>/etc/cron.d/whatever</filename>. These particular files
also have an extra field that allows you to stipulate the user under
which the cron job runs.
</para><para>
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
<filename>/usr/share/doc/cron/README.Debian</filename>.
</para>
</sect2>
</sect1>
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