2024-01-25 14:12:00 +00:00
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# `/etc` via overlay filesystem {#sec-etc-overlay}
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::: {.note}
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This is experimental and requires a kernel version >= 6.6 because it uses
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new overlay features and relies on the new mount API.
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:::
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Instead of using a custom perl script to activate `/etc`, you activate it via an
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overlay filesystem:
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```nix
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2024-04-21 15:54:59 +00:00
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{
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system.etc.overlay.enable = true;
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}
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2024-01-25 14:12:00 +00:00
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```
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Using an overlay has two benefits:
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1. it removes a dependency on perl
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2. it makes activation faster (up to a few seconds)
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By default, the `/etc` overlay is mounted writable (i.e. there is a writable
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upper layer). However, you can also mount `/etc` immutably (i.e. read-only) by
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setting:
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```nix
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2024-04-21 15:54:59 +00:00
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{
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system.etc.overlay.mutable = false;
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}
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2024-01-25 14:12:00 +00:00
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```
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The overlay is atomically replaced during system switch. However, files that
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have been modified will NOT be overwritten. This is the biggest change compared
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to the perl-based system.
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If you manually make changes to `/etc` on your system and then switch to a new
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configuration where `system.etc.overlay.mutable = false;`, you will not be able
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to see the previously made changes in `/etc` anymore. However the changes are
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not completely gone, they are still in the upperdir of the previous overlay in
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`/.rw-etc/upper`.
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