Selfhosted @lemmy.world ericjmorey @lemmy.world 1y ago

NixOS and Lemmy

Anyone with experience using NixOS to create a Lemmy instance, please share any caveats and troubleshooting tips you have.

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Oh hello, my instance is on NixOS!
There's a NixOS module for lemmy, but it's kind of broken right now and in the middle of a PR. If you want, you can replace the current nix package with the one from the fork, and successfully deploy it, however, if I were you, I'd just wait a week or so.

The configuration right now requires a bunch of hacks, and even doing some non-reproducible stuff.
- That PR link returns a 404.
  
  This is my way of learning Nix/NixOS so I'd rather give it a go before the PR is merged.
  
  Sorry, missed a character, try again
  
  I'm so deep in the weeds. I don't know what questions to ask.
  
  Okay, I've actually figured simplifying it out, it's not that bad. Let me share my config:
  
  First, since the PR isn't in nixos-unstable yet, I'm adding the fork as a flake input
  
  inputs = { nixpkgs-lemmy.url = "github:CobaltCause/nixpkgs/lemmy-module-improvements"; };
  
  then, in my system configuration, I add this:
  
  # Not sure if this is required, maybe caddy auto-allows it networking.firewall.interfaces.eth0.allowedTCPPorts = [443 80]; # Override the lemmy module with the one from the PR disabledModules = ["services/web-apps/lemmy.nix"]; imports = [ "${inputs.nixpkgs-lemmy}/nixos/modules/services/web-apps/lemmy.nix" ]; services.lemmy = { database.createLocally = true; database.uri = "postgres:///lemmy?host=/run/postgresql&user=lemmy"; enable = true; settings = { hostname = "<YOUR_HOSTNAME>"; }; caddy.enable = true; };
  
  and, that's it!
  However, I'm not sure if it will cleanly deploy, as you might get an error while starting.
  If so, please check postgresql logs sudo journalctl -fu postgresql. The error will most likely be something like this:
  [...] [10289] ERROR: permission denied: "RI_ConstraintTrigger_a_16639" is a system trigger [...]
  
  If that happens, you need to manually run the migration until the fix is merged into Lemmy. Here's how I did it:
  
  sudo su - postgres
  
  psql -v ON_ERROR_STOP=1 lemmy postgres
  
  (in psql) SET ROLE lemmy;
  
  Paste the SQL code from here: https://github.com/LemmyNet/lemmy/issues/2784#issuecomment-1578337686
  
  After that's done, you can exit the postgres CLI by typing \q, exit the postgres user and just simply sudo systemctl restart lemmy which should start properly now, and be accessible to the outside network.
  Open it and it will give you the initial setup screen. Good luck!
  
  Note that the PR got merged into nixpkgs now, but hasn't made it's way forward (see https://nixpk.gs/pr-tracker.html?pr=236295), so that's why you need to do the override for now Also, a fix for the issue with the migrations (if still occuring) has been merged yesterday, but it's not in any release yet, and especially not in nixpkgs. You could most likely get around it by using overrideAttrs to change the source to make it build from a newer commit.
  
  Is this sort of lag the nature of package managers that will inherently be part of NixOS and nixpk?
  
  Nixpkgs is by nature fully reproducible and declarative - that means you can't write a nix package to just build from master branch. You also have to specify the sha256 hash to absolutely make sure the source is the same for everyone.
  With flakes, it's a bit easier, because if the package you're trying to build has a flake, you can just update it in your own lockfile and it will be rebuilt from the latest version.
  If using something from nixpkgs, you have to wait (or PR yourself) for someone to PR the update, or you can also use overrideAttrs to do a "private" fix.
  For example, I'm using the wlsunset program, but wanted to build from a different branch, so I did this:
  
  (wlsunset.overrideAttrs (old: { src = fetchFromSourcehut { owner = "~kennylevinsen"; repo = old.pname; rev = "81cfb0b4f8e44db9e5ecb36222a24d53a953e6aa"; sha256 = "sha256-Lxuhsk4/5EHuKPkBbaRtCCQ/LFvIxyc+VQYEoaVT484="; }; }))
  
  This just changes the source attribute to another commit and another sha hash, and it works fine.
  
  In the end, the lag is just caused by the fact that it has to work. You never want to get some broken version that you want to avoid, so nix packages are always tested with the new versions, because it may turn out they may need some patching for that version, or they have some new dependencies.
  
  While we were talking I updated lemmy-server using overrideAttrs for my own use. It's honestly not that hard. You change the commit, specify some random incorrect hashes, build it, nix screams at you that the hash is incorrect (and generously provides the correct one), put the correct hash, and build again. Done.
  
  That kinda defeats the purpose of the hash.
  
  The hash isn't there for security, it's to make sure the code you're building against doesn't randomly change which could make the derivation fail to compile. For example, for the source, you can specify a literal HTTP download from a URL, and that file could be changed by the host at any given time, so it's there as a safeguard.
  
  Thanks for all of this information. Reading through documentation gives information on how to do things when everything is working perfectly. It's a large leap for a newcomer to handle the imperfect case.

26 comments