Distribute `nixos-rebuild` with non-nixos nix distribution

[mkaito]

I'm currently working on a web app project that is deployed to a NixOS server. Our deployment consists of running nixos-rebuild --target-host to push things to the server.

The problem is, nixos-rebuild is only available on NixOS proper, not on the standalone nix distribution. I had to deal with some grumpy people when I explained that they needed to get themselves a NixOS VM in order to run deployments.

I don't think there's anything preventing at least the --target-host part of nix-rebuild being available as part of the standard nix distribution.

[lukateras]

I think that at the very least we should expose it at top-level.

[mkaito]

I expect these to come up as counter arguments:

Just use nixops you dimwit

I tried, but I couldn't get it to work. And nixos-rebuild is super easy to use. Just point at a configuration.nix and it even builds everything remotely, which my peers with laptops appreciate.

CI/CD pipeline

Does such a thing even exist for NixOS?

[srhb]

If it's interesting to you, nixos was recently exposed as a top level attribute, so you could do

nix-build -E 'let pkgs = import <nixpkgs> {}; in (pkgs.nixos {}).nixos-rebuild'

[Mic92]

nix-shell version:

$ nix-shell -E 'with import <nixpkgs> {}; stdenv.mkDerivation { name = "foo"; buildInputs = [ (nixos {}).nixos-rebuild ]; }'

or:

$ nix-shell -E 'with import <nixpkgs> {}; stdenv.mkDerivation { name = "foo"; buildInputs = [ (nixos {}).nixos-rebuild ]; }' --command "nixos-rebuild dry-build"

[mkaito]

This does the job:

#!/usr/bin/env bash

nix-shell -E 'with import <nixpkgs> {}; stdenv.mkDerivation { name = "foo"; buildInputs = [ (nixos {}).nixos-rebuild ]; }' --run "nixos-rebuild $*"

Drop it in a file nixos-rebuild, put on path, done. Thanks @Mic92 !

[Mic92]

It can be even simplified:

$ nix-shell -p '(nixos{}).nixos-rebuild'

[mkaito]

Nice! Can we put this in the Nix distribution?

[Mic92]

I backported d9f1e37ec72f0b4d55ef8d8f24aa4fc499fe878c:

Now you can do:

$ nix-shell -p 'nixos-rebuild'

This will be part of the upcoming release 18.09.

[matthewbauer]

@Mic92 That was reverted by @edolstra due to evaluation concerns (every nix-env -qa has to evaluate a full nixos).

I think the best solution for this would be to move nixos-rebuild to all-packages.nix & rework NixOS to use that.

[Mic92]

Makes sense. I was not aware of that. I also backported the revert: 51b62e6a8c9

However:

nix-shell -p '(nixos{}).nixos-rebuild'

should be easy enough.

[adrian-gierakowski]

@mkaito @Mic92 is this still working for you?

when I run:

env NIXOS_CONFIG=$(pwd)/configuration.nix nix-shell -p '(nixos{}).nixos-rebuild' --run 'nixos-rebuild switch --target-host $MY_HOST'

I get the following error:

/nix/store/17843hfbsnyqxkjx6v7sdrln855npyll-nixos-rebuild/bin/nixos-rebuild: line 268: systemctl: command not found
building Nix...
unix_listener: path "/var/folders/dm/3dxc156d67l5241z0y2tt8h80000gn/T/nixos-rebuild.FS9L0q/ssh-130.211.114.86.iLXNmuqNiJwgmhy5" too long for Unix domain socket
/nix/store/17843hfbsnyqxkjx6v7sdrln855npyll-nixos-rebuild/bin/nixos-rebuild: line 343: /var/folders/dm/3dxc156d67l5241z0y2tt8h80000gn/T/nixos-rebuild.FS9L0q/nix/bin/nix-instantiate: cannot execute binary file: Exec format error
building the system configuration...
/nix/store/17843hfbsnyqxkjx6v7sdrln855npyll-nixos-rebuild/bin/nixos-rebuild: line 181: /var/folders/dm/3dxc156d67l5241z0y2tt8h80000gn/T/nixos-rebuild.FS9L0q/nix/bin/nix-instantiate: cannot execute binary file: Exec format error

looks to me like it might be similar to: https://github.com/NixOS/hydra/pull/641

[mkaito]

Currently using this:

nix-shell -E "with import <nixpkgs> {}; mkShell { buildInputs = [ (nixos {}).nixos-rebuild ]; }" --run "nixos-rebuild $*"

And yes, it works.

[Mic92]

@mkaito @Mic92 is this still working for you?

when I run:

env NIXOS_CONFIG=$(pwd)/configuration.nix nix-shell -p '(nixos{}).nixos-rebuild' --run 'nixos-rebuild switch --target-host $MY_HOST'

I get the following error:

/nix/store/17843hfbsnyqxkjx6v7sdrln855npyll-nixos-rebuild/bin/nixos-rebuild: line 268: systemctl: command not found
building Nix...
unix_listener: path "/var/folders/dm/3dxc156d67l5241z0y2tt8h80000gn/T/nixos-rebuild.FS9L0q/ssh-130.211.114.86.iLXNmuqNiJwgmhy5" too long for Unix domain socket
/nix/store/17843hfbsnyqxkjx6v7sdrln855npyll-nixos-rebuild/bin/nixos-rebuild: line 343: /var/folders/dm/3dxc156d67l5241z0y2tt8h80000gn/T/nixos-rebuild.FS9L0q/nix/bin/nix-instantiate: cannot execute binary file: Exec format error
building the system configuration...
/nix/store/17843hfbsnyqxkjx6v7sdrln855npyll-nixos-rebuild/bin/nixos-rebuild: line 181: /var/folders/dm/3dxc156d67l5241z0y2tt8h80000gn/T/nixos-rebuild.FS9L0q/nix/bin/nix-instantiate: cannot execute binary file: Exec format error

looks to me like it might be similar to: NixOS/hydra#641

I never tested this on non-Linux targets. This might require some other flags. Adding --no-build-nix might help.

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[Mic92]

I think we gave enough work-arounds on how to achieve this.

[mkaito]

Well, that's a shame, but such is life.

[Mic92]

Sorry but apparently bringing nixos modules into all-packages scope apparently makes nix evaluation a lot slower. There are people who want to use nix on machines with little RAM. I don't think its too much to ask to use one of one-liners posted above. If you are interested in improving the situation consider making them more visible by adding them to the manual or the nixos wiki.

[kevincox]

It seems like bringing nixos into scope was a side effect of how it was implemented. Wouldn't it be possible to move nixos-rebuild into a regular nixpkgs package and reference that from nixos?

(~On another note does anyone know how to install it using nix-env instead of nix-shell? I can't get it to work~ nix-env -i -E 'e: ((e.nixpkgs {}).nixos{}).nixos-rebuild')

[Mic92]

It seems like bringing nixos into scope was a side effect of how it was implemented. Wouldn't it be possible to move nixos-rebuild into a regular nixpkgs package and reference that from nixos?

(~On another note does anyone know how to install it using nix-env instead of nix-shell? I can't get it to work~ nix-env -i -E 'e: ((e.nixpkgs {}).nixos{}).nixos-rebuild')

Yes. nix-env also works.