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63 lines
2.4 KiB
XML
63 lines
2.4 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-nix-gc">
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<title>Cleaning the Nix Store</title>
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<para>
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Nix has a purely functional model, meaning that packages are never upgraded
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in place. Instead new versions of packages end up in a different location in
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the Nix store (<filename>/nix/store</filename>). You should periodically run
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Nix’s <emphasis>garbage collector</emphasis> to remove old, unreferenced
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packages. This is easy:
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<screen>
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<prompt>$ </prompt>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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<prompt># </prompt>systemctl start nix-gc.service
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</screen>
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You can tell NixOS in <filename>configuration.nix</filename> to run this unit
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automatically at certain points in time, for instance, every night at 03:15:
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<programlisting>
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<xref linkend="opt-nix.gc.automatic"/> = true;
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<xref linkend="opt-nix.gc.dates"/> = "03:15";
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</programlisting>
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</para>
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<para>
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The commands above do not remove garbage collector roots, such as old system
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configurations. Thus they do not remove the ability to roll back to previous
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configurations. The following command deletes old roots, removing the ability
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to roll back to them:
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<screen>
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<prompt>$ </prompt>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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<prompt>$ </prompt>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>.
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</para>
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<para>
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Another way to reclaim disk space (often as much as 40% of the size of the
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Nix store) is to run Nix’s store optimiser, which seeks out identical files
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in the store and replaces them with hard links to a single copy.
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<screen>
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<prompt>$ </prompt>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 quite a
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while to finish.
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</para>
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<section xml:id="sect-nixos-gc-boot-entries">
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<title>NixOS Boot Entries</title>
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<para>
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If your <filename>/boot</filename> partition runs out of space, after
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clearing old profiles you must rebuild your system with
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<literal>nixos-rebuild</literal> to update the <filename>/boot</filename>
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partition and clear space.
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</para>
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</section>
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</chapter>
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