Add command that output system information like nix-info

[davidak]

nix-info is kind of an official tool since its used in nixpkgs issues, but it has some issues.

For example:

1. It fails when the channel hasn't been populated. (for examples in iso images made by nixos-generators)

[root@targets-host:~]# nix run nixpkgs.nix-info -c nix-info -m
warning: Nix search path entry '/nix/var/nix/profiles/per-user/root/channels/nixos' does not exist, ignoring
warning: Nix search path entry '/nix/var/nix/profiles/per-user/root/channels' does not exist, ignoring
error: file 'nixpkgs' was not found in the Nix search path (add it using $NIX_PATH or -I)

[root@targets-host:~]# nix-channel --list
nixos https://nixos.org/channels/nixos-19.03

2. It doesn't report the nixpkgs version that was used to build the current system. Which is what we are interested in for nixos bug reports.

3. nix run nixpkgs.*** don't work when you use a channel but have no internet connection.

Including an official command in Nix would solve 1 and 3. An output for 2 can be added.

I think it shouldn't be part of nix doctor to only output problems there, but add another command, maybe nix info or nix system?

Initially reported at nix-community/nixos-generators#37

[stale]

I marked this as stale due to inactivity. → More info

[stale]

I closed this issue due to inactivity. → More info

[srid]

I'd also suggest adding a flag to output this information as JSON. So nix info --json can be run and parsed by other programs to extract the relevant information.