https://github.com/noteed/toplevels

NixOS toplevels
https://github.com/noteed/toplevels

Last synced: about 2 months ago
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NixOS toplevels

• Host: GitHub
• URL: https://github.com/noteed/toplevels
• Owner: noteed
• Created: 2020-12-09T05:40:08.000Z (about 4 years ago)
• Default Branch: main
• Last Pushed: 2024-11-06T22:53:28.000Z (2 months ago)
• Last Synced: 2024-11-06T23:31:46.320Z (2 months ago)
• Language: Nix
• Size: 26.4 KB
• Stars: 0
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# Toplevels

In NixOS parlance, the `toplevel` is a complete system, and is really "just" a

path in the Nix store. In a NixOS machine, `/run/current-system` points to the

current toplevel, which is usually built by `nixos-rebuild`.

In Nixpkgs, the `nixos/default.nix` file exposes the toplevel as the `system`

attribute.

This repository contains a Nix expression to define a test toplevel, together

with a GitHub action to build it and cache it to Backblaze B2.

In addition to the toplevel content, a file containing the latest toplevel (as

a path in the Nix store) is uploaded to

https://f003.backblazeb2.com/file/hypered-store/toplevels/test.txt.

The test toplevel contains an `update-system` script which check the above

file, downloads the corresponding Nix paths, then activate the toplevel.

# Notes

Building, including downloading from cache.nixos.org, takes about 100 seconds.

Uploading everything to B2 took about 14 minutes the first time. Next uploads

take about 50 seconds.

Playing with a binary cache may reuse cached data in `/root/.cache/nix`,

resulting in `does not contain a valid signature`, even though `nix path-info

--sigs ... --store ...` seems fine. Deleting the cache solves the problem.

Backblaze "Daily Class B Transactions Caps" seems to be impacted by simply

uploading the narinfos to it (I guess that some metadata are downloaded to

check if the uploads should actually happen).

Downloading the toplevel on a different machine downloads about 500MB,

resulting in 2GB once unpacked. If it is a minor change, it can take around 5

seconds for about 5MB. If nothing has changed, it takes less than a second.

# Hosts

In addition of the above experiment (in `default.nix`), I'm starting to keep my

NixOS configurations in the `hosts/` directory.