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* Section about garbage collection.

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Eelco Dolstra 2004-11-01 16:03:35 +00:00
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doc/manual/package-management.xml
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@ -332,8 +332,70 @@ This will <emphasis>not</emphasis> change the
<sect1 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 components from the system. All they do (as shown
above) is to make a new user environment that no longer contains
symlinks to the <quote>deleted</quote> components.</para>
<para>Of course, since disk space is not infinite, unused components
should be removed at some point. You can do this by running the Nix
garbage collector. It will remove from the Nix store any component
not used (directly or indirectly) by any generation of any
profile.</para>
<para>Note however that as long as old generations reference a
component, 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-collect-garbage</screen>
You can alo first view what files would be deleted:
<screen>
$ nix-collect-garbage --print-dead</screen>
Likewise, the option <option>--print-live</option> will show the paths
that <emphasis>won't</emphasis> be deleted.</para>
<sect2><title>Garbage collector roots</title>
<para>TODO</para>
<para>The garbage collector uses as roots all store expressions
mentioned in all files with extension <filename>.gcroot</filename> in
the directory
<filename><replaceable>prefix</replaceable>/var/nix/gcroots/</filename>,
or in any file or directory symlinked to from that directory. E.g.,
by default,
<filename><replaceable>prefix</replaceable>/var/nix/gcroots/</filename>
contains a symlink to
<filename><replaceable>prefix</replaceable>/var/nix/profiles/</filename>,
so all generations of all profiles are also roots of the collector.</para>
</sect2>
</sect1>