Mixing versions in the nixos system profile

[ala...@dotmesh.com]

Hi there nixosers!

I've got user root's nixos channel set to https://nixos.org/channels/nixos-17.03 because I need to use ZFS 0.6 (for kernel API compatibility reasons, with zfs userland code that arrives in a docker image). I have my login user's nixos channel set to https://nixos.org/channels/nixos-18.03, rather than being totally stuck with old versions of everything.

However, I could now do with some of my system packages being a little newer - in particular, the version of docker I get (17.03.2-ce) lacks some features I now need.

What's the best way to mix different versions of packages in the nixos system itself? I've read about overriding things in configuration.nix at https://nixos.org/nixos/manual/index.html#sec-declarative-package-mgmt - could I copy-paste the ZFS packages from nixos-17.03 into my configuration.nix and have it override zfs in a more recent nixos version, creating a hybrid nixos (assuming there aren't incompatibilities between my downgraded ZFS packages and other packages, such as the kernel, of course...)?

Thanks,

Alaric

[Martí Serra]

Hi, Alaric, 

I've shared a gist with a setup that I've used for some time. 

I have a more complex setup now and I can share it if there is interest, but I believe that for what you are asking this is a really good option:

https://gist.github.com/xvapx/72cf377e6e9f64cb2ec3f141af7c0db5

xvapx

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