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<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xi="http://www.w3.org/2001/XInclude"
version="5.0"
xml:id='sec-garbage-collection'>
<title>Garbage Collection</title>
<para><command>nix-env</command> operations such as upgrades
(<option>-u</option>) and uninstall (<option>-e</option>) never
actually delete packages from the system. All they do (as shown
above) is to create a new user environment that no longer contains
symlinks to the “deleted” packages.</para>
<para>Of course, since disk space is not infinite, unused packages
should be removed at some point. You can do this by running the Nix
garbage collector. It will remove from the Nix store any package
not used (directly or indirectly) by any generation of any
profile.</para>
<para>Note however that as long as old generations reference a
package, it will not be deleted. After all, we wouldn’t be able to
do a rollback otherwise. So in order for garbage collection to be
effective, you should also delete (some) old generations. Of course,
this should only be done if you are certain that you will not need to
roll back.</para>
<para>To delete all old (non-current) generations of your current
profile:
<screen>
$ nix-env --delete-generations old</screen>
Instead of <literal>old</literal> you can also specify a list of
generations, e.g.,
<screen>
$ nix-env --delete-generations 10 11 14</screen>
</para>
<para>After removing appropriate old generations you can run the
garbage collector as follows:
<screen>
$ nix-store --gc</screen>
If you are feeling uncertain, you can also first view what files would
be deleted:
<screen>
$ nix-store --gc --print-dead</screen>
Likewise, the option <option>--print-live</option> will show the paths
that <emphasis>won’t</emphasis> be deleted.</para>
<para>There is also a convenient little utility
<command>nix-collect-garbage</command>, which when invoked with the
<option>-d</option> (<option>--delete-old</option>) switch deletes all
old generations of all profiles in
<filename>/nix/var/nix/profiles</filename>. So
<screen>
$ nix-collect-garbage -d</screen>
is a quick and easy way to clean up your system.</para>
<xi:include href="garbage-collector-roots.xml" />
</chapter>
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