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86 lines
3.1 KiB
XML
86 lines
3.1 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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version="5.0"
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xml:id='sec-garbage-collection'>
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<title>Garbage Collection</title>
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<para><command>nix-env</command> operations such as upgrades
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(<option>-u</option>) and uninstall (<option>-e</option>) never
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actually delete packages from the system. All they do (as shown
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above) is to create a new user environment that no longer contains
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symlinks to the “deleted” packages.</para>
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<para>Of course, since disk space is not infinite, unused packages
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should be removed at some point. You can do this by running the Nix
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garbage collector. It will remove from the Nix store any package
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not used (directly or indirectly) by any generation of any
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profile.</para>
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<para>Note however that as long as old generations reference a
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package, it will not be deleted. After all, we wouldn’t be able to
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do a rollback otherwise. So in order for garbage collection to be
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effective, you should also delete (some) old generations. Of course,
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this should only be done if you are certain that you will not need to
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roll back.</para>
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<para>To delete all old (non-current) generations of your current
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profile:
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<screen>
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$ nix-env --delete-generations old</screen>
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Instead of <literal>old</literal> you can also specify a list of
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generations, e.g.,
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<screen>
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$ nix-env --delete-generations 10 11 14</screen>
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To delete all generations older than a specified number of days
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(except the current generation), use the <literal>d</literal>
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suffix. For example,
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<screen>
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$ nix-env --delete-generations 14d</screen>
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deletes all generations older than two weeks.</para>
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<para>After removing appropriate old generations you can run the
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garbage collector as follows:
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<screen>
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$ nix-store --gc</screen>
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The behaviour of the gargage collector is affected by the
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<literal>keep-derivations</literal> (default: true) and <literal>keep-outputs</literal>
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(default: false) options in the Nix configuration file. The defaults will ensure
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that all derivations that are build-time dependencies of garbage collector roots
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will be kept and that all output paths that are runtime dependencies
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will be kept as well. All other derivations or paths will be collected.
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(This is usually what you want, but while you are developing
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it may make sense to keep outputs to ensure that rebuild times are quick.)
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If you are feeling uncertain, you can also first view what files would
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be deleted:
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<screen>
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$ nix-store --gc --print-dead</screen>
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Likewise, the option <option>--print-live</option> will show the paths
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that <emphasis>won’t</emphasis> be deleted.</para>
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<para>There is also a convenient little utility
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<command>nix-collect-garbage</command>, which when invoked with the
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<option>-d</option> (<option>--delete-old</option>) switch deletes all
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old generations of all profiles in
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<filename>/nix/var/nix/profiles</filename>. So
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<screen>
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$ nix-collect-garbage -d</screen>
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is a quick and easy way to clean up your system.</para>
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<xi:include href="garbage-collector-roots.xml" />
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</chapter>
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