Using binary cache with custom kernel?

Help
1

Hi,
I have 2 nixos machines, both with the same pinned kernel thanks to this block: Linux kernel - NixOS Wiki.

I’d like to have one machine building it and the other machine installing it from cachix. I can see the 2nd machine is downloading the .drv of this custom kernel from cachix but it’s still building the kernel… any idea why?
I have other custom packages pushed in cachix and I can see that the 2nd machine isn’t re-building but only using the binary cache. I’m thinking this block from the wiki just doesn’t work with binary cache?

Any ideas?

Thanks in advance :slight_smile:

2

Are all the other inputs the same as well? Eg. Are both machines pinned to the same channel “commit”?

3

Yes, I even copied over the content of /etc/nixos and just updated minor things like IP and hostname. As I said it works with other custom packages but not the kernel.

4

Are you using channels? Do you pin them? If not are you really sure both are using the same?

Alternatively, have you tried building somewhere else and then nix copy-store?

5

What I ended doing was something like this:
NIXOS_CONFIG=$PWD/configuration.nix nixos-rebuild switch --target-host computer2 --use-remote-sudo from computer1 to computer2 and it worked. But when I copy the configuration.nix and all files from computer1 to computer2:/etc/nixos, it still wants to rebuild the kernel and other custom packages. I’m a bit lost on how to debug further.

6

Might be that you need a kernel module which needs the linux.dev output at build-time. On the builder, that exists of course but it won’t be pushed to cachix.