lix/doc/manual/packages/garbage-collector-roots.xml

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      xmlns:xlink="http://www.w3.org/1999/xlink"
      xmlns:xi="http://www.w3.org/2001/XInclude"
      version="5.0"
      xml:id="ssec-gc-roots">

<title>Garbage Collector Roots</title>

<para>The roots of the garbage collector are all store paths to which
there are symlinks in the directory
<filename><emphasis>prefix</emphasis>/nix/var/nix/gcroots</filename>.
For instance, the following command makes the path
<filename>/nix/store/d718ef...-foo</filename> a root of the collector:

<screen>
$ ln -s /nix/store/d718ef...-foo /nix/var/nix/gcroots/bar</screen>
	
That is, after this command, the garbage collector will not remove
<filename>/nix/store/d718ef...-foo</filename> or any of its
dependencies.</para>

<para>Subdirectories of
<filename><emphasis>prefix</emphasis>/nix/var/nix/gcroots</filename>
are also searched for symlinks.  Symlinks to non-store paths are
followed and searched for roots, but symlinks to non-store paths
<emphasis>inside</emphasis> the paths reached in that way are not
followed to prevent infinite recursion.</para>

</section>