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10.

Debian Packaging System

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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 <quote>hold</quote> in <command>aptitude</command>.

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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.

13.

Application Version Management

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

15.

Cron Job Management

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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 monthly 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.

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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 account under which the cron job runs.

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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>.

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Further Reading and Information