2014-08-24 18:18:18 +01:00
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<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-nix-gc">
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<title>Cleaning the Nix Store</title>
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<para>Nix has a purely functional model, meaning that packages are
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never upgraded in place. Instead new versions of packages end up in a
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different location in the Nix store (<filename>/nix/store</filename>).
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You should periodically run Nix’s <emphasis>garbage
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collector</emphasis> to remove old, unreferenced packages. This is
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easy:
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<screen>
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$ nix-collect-garbage
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</screen>
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Alternatively, you can use a systemd unit that does the same in the
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background:
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<screen>
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2016-06-01 15:23:32 +01:00
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# systemctl start nix-gc.service
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2014-08-24 18:18:18 +01:00
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</screen>
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You can tell NixOS in <filename>configuration.nix</filename> to run
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this unit automatically at certain points in time, for instance, every
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night at 03:15:
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<programlisting>
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nix.gc.automatic = true;
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nix.gc.dates = "03:15";
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</programlisting>
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</para>
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<para>The commands above do not remove garbage collector roots, such
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as old system configurations. Thus they do not remove the ability to
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roll back to previous configurations. The following command deletes
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old roots, removing the ability to roll back to them:
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<screen>
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$ nix-collect-garbage -d
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</screen>
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You can also do this for specific profiles, e.g.
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<screen>
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$ nix-env -p /nix/var/nix/profiles/per-user/eelco/profile --delete-generations old
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</screen>
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Note that NixOS system configurations are stored in the profile
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<filename>/nix/var/nix/profiles/system</filename>.</para>
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<para>Another way to reclaim disk space (often as much as 40% of the
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size of the Nix store) is to run Nix’s store optimiser, which seeks
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out identical files in the store and replaces them with hard links to
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a single copy.
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<screen>
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$ nix-store --optimise
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</screen>
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Since this command needs to read the entire Nix store, it can take
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quite a while to finish.</para>
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2016-06-01 15:23:32 +01:00
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</chapter>
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