Storage optimization: Difference between revisions
imported>Xav-ie m Add reasoning for why auto-optimise-store is not on automatically and what you can do instead |
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A recurring problem with NixOS is lack of space on <code>/</code>. Even if you only | {{Merge|Nix store}} | ||
A recurring problem with NixOS is lack of space on <code>/</code>. Even if you only occasionally use Nix, it is easy for <code>/nix/store</code> to grow beyond reasonable sizes. What follows are generic notes on how to reduce the growth of the [[Nix store]]. | |||
== Optimising the store == | == Optimising the store == | ||
Here we demonstrate how to configure <code>nix</code> to save space via hardlinking store files. | Here, we demonstrate how to configure <code>nix</code> to save space via hardlinking store files. | ||
=== Automatic === | |||
To turn on | To turn on periodic optimisation of the nix store, set the following option in <code>/etc/nixos/configuration.nix</code>: | ||
{{file|configuration.nix|nix|<nowiki> | {{file|configuration.nix|nix|<nowiki> | ||
nix.optimise.automatic = true; | nix.optimise.automatic = true; | ||
nix.optimise.dates = [ "03:45" ]; # Optional; allows customizing optimisation schedule | |||
</nowiki>}} | |||
Alternatively, the store can be optimised during ''every'' build. This may slow down builds, as discussed [https://github.com/NixOS/nix/issues/6033 here]. To enable this behavior, set the following option: | |||
{{file|configuration.nix|nix|<nowiki> | |||
nix.settings.auto-optimise-store = true; | |||
</nowiki>}} | </nowiki>}} | ||
{{Tip|This option only applies to new files | {{Tip|This option only applies to new files, so we recommend manually optimising your nix store when first setting this option.}} | ||
=== Manual === | |||
Run | |||
{{ic|# nix-store --optimise}}. | |||
This is a potentially long operation. | |||
== Garbage collection == | |||
By default, the Nix store will not remove any entries that are no longer used, thus it can accumulate derivations you might no longer need.<ref group="cf.">[https://nixos.org/nix/manual/#sec-garbage-collection Nix Manual, 11. Garbage Collection]</ref> They can be deleted with {{ic|nix-collect-garbage}} <ref group="cf.">{{man|nix-collect-garbage|sec=1}}</ref> or {{ic|nix-store --gc}}.<ref group="cf.">{{man|nix-store|sec=1}}, under {{ic|OPERATION --GC}}</ref> | |||
=== Removing old generations === | |||
NixOS keeps old configurations of your system around so that you can always rollback to a previous configuration if something goes wrong. You can also select which generation to boot into via GRUB. However these previous generations are [[Storage optimization#Garbage collection roots|GC roots]] (see below) that can keep around old, unnecessary software in your nix store. You can check what system generations you have by:<syntaxhighlight lang="console">$ sudo nix-env -p /nix/var/nix/profiles/system --list-generations | |||
... | |||
58 2021-09-04 02:56:54 | |||
59 2021-09-05 07:12:43 | |||
60 2021-09-05 22:12:13 (current)</syntaxhighlight> | |||
= | You can remove all other NixOS generations besides the current one: | ||
<syntaxhighlight lang="console"> | |||
$ sudo nix-collect-garbage -d | |||
... | |||
4394 store paths deleted, 3467.28 MiB freed | |||
</syntaxhighlight> | |||
= | There are also user-specific generations for different things (eg. home-manager). These can be removed with: | ||
<syntaxhighlight lang="console"> | |||
$ nix-collect-garbage -d | |||
</syntaxhighlight> | |||
=== Garbage collection roots === | |||
Note that if a result file still exists in the file system, and your Nix configuration has both <code>keep-outputs = true</code> and <code>keep-derivations = true</code>, all the dependencies used to build it will be kept. To see which result files prevent garbage collection, run: | Note that if a result file still exists in the file system, and your Nix configuration has both <code>keep-outputs = true</code> and <code>keep-derivations = true</code>, all the dependencies used to build it will be kept. To see which result files prevent garbage collection, run: | ||
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<syntaxhighlight lang="console"> | <syntaxhighlight lang="console"> | ||
$ nix-store --gc --print-roots | $ nix-store --gc --print-roots | ||
... | ... | ||
/nix/var/nix/profiles/per-user/root/channels-4-link -> /nix/store/254b6pkhhnjywvj5c0lp2vdai8nz4p0g-user-environment | /nix/var/nix/profiles/per-user/root/channels-4-link -> /nix/store/254b6pkhhnjywvj5c0lp2vdai8nz4p0g-user-environment | ||
/nix/var/nix/profiles/system-398-link -> /nix/store/wmndyzzrbc9fyjw844jmvzwgwgcinq7s-nixos-system-iron-16.0916.09pre.custom | /nix/var/nix/profiles/system-398-link -> /nix/store/wmndyzzrbc9fyjw844jmvzwgwgcinq7s-nixos-system-iron-16.0916.09pre.custom | ||
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Look for system derivations in particular. Those are created on many occasions, for example when running <code>nixos-rebuild build-vm</code> | Look for system derivations in particular. Those are created on many occasions, for example when running <code>nixos-rebuild build-vm</code> | ||
=== Reboot === | === Reboot === | ||
As you see, the reference in <code>/run/booted-system</code> is a GC root, so it won't be cleared until reboot. If you don't want to reboot, just <code>rm /run/booted-system</code> that link and rerun <code>sudo nix-collect-garbage</code>. | As you see, the reference in <code>/run/booted-system</code> is a GC root, so it won't be cleared until reboot. If you don't want to reboot, just <code>rm /run/booted-system</code> that link and rerun <code>sudo nix-collect-garbage</code>. | ||
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# Create a new partition | # Create a new partition | ||
# Mount this new partition over <code>/mnt</code> <syntaxhighlight lang="console"> | # Mount this new partition over <code>/mnt</code> <syntaxhighlight lang="console"> | ||
# mount /dev/disk/by-label/nix /mnt | # mount -o defaults,noatime /dev/disk/by-label/nix /mnt/nix | ||
</syntaxhighlight> | </syntaxhighlight> | ||
# Copy everything from <code>/nix</code> to <code>/mnt</code> ''Trailing slashes are important'', in that without them, <code>rsync</code> will create an additional directory of the same name at the destination. <syntaxhighlight lang="console"> | # Copy everything from <code>/nix</code> to <code>/mnt</code> ''Trailing slashes are important'', in that without them, <code>rsync</code> will create an additional directory of the same name at the destination. <syntaxhighlight lang="console"> | ||
# rsync --archive -- | # rsync --archive --hard-links --acls --one-file-system --verbose /nix/{store,var} /mnt/nix | ||
</syntaxhighlight> | </syntaxhighlight> | ||
# Mount the new partition as the new <code>/nix</code> <syntaxhighlight lang="console"> | # Mount the new partition as the new <code>/nix</code> <syntaxhighlight lang="console"> | ||
# umount /mnt | # umount /mnt/nix | ||
# mount /dev/disk/by-label/nix /nix | # mount /dev/disk/by-label/nix /nix | ||
</syntaxhighlight> | </syntaxhighlight> | ||
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<references group="cf."/> | <references group="cf."/> | ||
[[Category:NixOS]] | |||
[[Category:Nix]] | |||