CC @name-snrl to testing.

Works for me. But I'm not sure if this problem should be solved in this way. I see 3 possible solutions:

1. Current, where --upgrade respects --sudo. But in cases when user will run nixos-rebuild without --sudo and not as root, it will silently upgrade nixos user channel. And This behavior is not obvious to the user, because, as I mentioned in issue, the manual says: Update the root user's channel named ‘nixos’ before rebuilding the system.
2. Deprecate --upgrade(-all) options.
3. When user pass --upgrade(-all) flag we check whether the user is root or the command is run with --sudo flag. If neither is true, we throw an error, like: If you pass the --upgrade or --upgrade-all flag, you must also pass --sudo or run the command as root (e.g., with sudo).

wdyt @thiagokokada ?

it will silently upgrade nixos user channel

Oh, no, it doesn't. I see, it only loops over /nix/var/nix/profiles/per-user/root/channels/

edit: another "oh". I thought /nix/var/nix/profiles/per-user/root/channels/ isn't world-readable, but it's just symlinks on /nix/store:

> ls -la /nix/var/nix/profiles/per-user/root/channels
lrwxrwxrwx - root root  1 Jan  1970 nixos -> /nix/store/7wfpz53k2lsa62wg42dg54li0rzkjwrw-nixos/nixos
lrwxrwxrwx - root root  1 Jan  1970 manifest.nix -> /nix/store/2m8whkhdd2y2lgjkxkhvwz207b46bd0w-env-manifest.nix

So, yes, is it correct: in cases when nixos-rebuild is run without --sudo and not as root - it would look at /nix/var/nix/profiles/per-user/root/channels/, but updates user's channels

@name-snrl Ok, I added a check for --sudo/root. Can you review/test?

Works for me. But I'm not sure if this problem should be solved in this way. I see 3 possible solutions:

1. Current, where `--upgrade` respects `--sudo`. But in cases when user will run `nixos-rebuild` without `--sudo` and not as root, it will silently upgrade `nixos` user channel. And This behavior is not obvious to the user, because, as I mentioned in issue, the manual says: _Update the root user's channel named ‘nixos’ before rebuilding the system_.

2. Deprecate `--upgrade(-all)` options.

3. When user pass `--upgrade(-all)` flag we check whether the user is root or the command is run with `--sudo` flag. If neither is true, we throw an error, like: _If you pass the `--upgrade` or `--upgrade-all` flag, you must also pass `--sudo` or run the command as root (e.g., with sudo)._

Let me expand this a little. I think the current channel upgrade code is messy and maybe it shouldn't exist, so I would like to actually do 2, but I also think deprecating this option will cause headaches for channel users, so 3 is probably the quickest solution, this is why I decided to implement it.

Looks like a good change. Since flakes vs channels is a forever limbo discussion, I don't think there's a need to outright deprecate this feature just yet. This is definitely a good way to handle it without any weird silent behaviors.

Successfully created backport PR for release-25.05:

• [Backport release-25.05] nixos-rebuild-ng: run upgrade_channels with sudo #424887