pyrox.dev
1<chapter xmlns="http://docbook.org/ns/docbook"
2 xmlns:xlink="http://www.w3.org/1999/xlink"
3 xmlns:xi="http://www.w3.org/2001/XInclude"
4 version="5.0"
5 xml:id="sec-nix-gc">
6 <title>Cleaning the Nix Store</title>
7 <para>
8 Nix has a purely functional model, meaning that packages are never upgraded
9 in place. Instead new versions of packages end up in a different location in
10 the Nix store (<filename>/nix/store</filename>). You should periodically run
11 Nix’s <emphasis>garbage collector</emphasis> to remove old, unreferenced
12 packages. This is easy:
13<screen>
14$ nix-collect-garbage
15</screen>
16 Alternatively, you can use a systemd unit that does the same in the
17 background:
18<screen>
19# systemctl start nix-gc.service
20</screen>
21 You can tell NixOS in <filename>configuration.nix</filename> to run this unit
22 automatically at certain points in time, for instance, every night at 03:15:
23<programlisting>
24<xref linkend="opt-nix.gc.automatic"/> = true;
25<xref linkend="opt-nix.gc.dates"/> = "03:15";
26</programlisting>
27 </para>
28 <para>
29 The commands above do not remove garbage collector roots, such as old system
30 configurations. Thus they do not remove the ability to roll back to previous
31 configurations. The following command deletes old roots, removing the ability
32 to roll back to them:
33<screen>
34$ nix-collect-garbage -d
35</screen>
36 You can also do this for specific profiles, e.g.
37<screen>
38$ nix-env -p /nix/var/nix/profiles/per-user/eelco/profile --delete-generations old
39</screen>
40 Note that NixOS system configurations are stored in the profile
41 <filename>/nix/var/nix/profiles/system</filename>.
42 </para>
43 <para>
44 Another way to reclaim disk space (often as much as 40% of the size of the
45 Nix store) is to run Nix’s store optimiser, which seeks out identical files
46 in the store and replaces them with hard links to a single copy.
47<screen>
48$ nix-store --optimise
49</screen>
50 Since this command needs to read the entire Nix store, it can take quite a
51 while to finish.
52 </para>
53 <section xml:id="sect-nixos-gc-boot-entries">
54 <title>NixOS Boot Entries</title>
55
56 <para>
57 If your <filename>/boot</filename> partition runs out of space, after
58 clearing old profiles you must rebuild your system with
59 <literal>nixos-rebuild</literal> to update the <filename>/boot</filename>
60 partition and clear space.
61 </para>
62 </section>
63</chapter>