docker: make sure nix config check works

[drupol]

Motivation

This current PR addresses a small issue I encountered during the making of #13354.

When running nix config check inside the official Nix Docker image, the following failure was raised:

bash-5.2# nix config check
[PASS] PATH contains only one nix version.
[FAIL] Found profiles outside of /nix/var/nix/profiles.
The generation this profile points to might not have a gcroot and could be
garbage collected, resulting in broken symlinks.

  "/root/.nix-profile/bin"

[PASS] Client protocol matches store protocol.
[INFO] You are trusted by store uri: local

This PR proposes a fix for that issue. I would appreciate any feedback on the approach, and I am happy to adjust the implementation if needed.

Context

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[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/nix-official-docker-image-with-custom-ssl-certificate/65527/3

[drupol]

Thanks!

[h0nIg]

@drupol i dont know why you removed this line, however i can say that it is causing a loss of all installed profiles. with 2.29 the profile list is not empty, with 2.30 it is empty causing other side effects

$ docker run -ti nixos/nix:2.30.2
bash-5.2# ls -lsa /root/
total 16
4 drwxr-xr-x 3 root root 4096 Jan  1  1980 .
4 drwxr-xr-x 1 root root 4096 Aug  6 18:26 ..
4 lrwxrwxrwx 1 root root   74 Jan  1  1980 .nix-channels -> /nix/store/wb9abgrwawwmdpdkj8jx9j4cnpp93b7h-base-system/root/.nix-channels
4 drwxr-xr-x 2 root root 4096 Jan  1  1980 .nix-defexpr
bash-5.2#
bash-5.2# nix profile list --extra-experimental-features nix-command
bash-5.2#

$ docker run -ti nixos/nix:2.29.1
bash-5.2# ls -lsa /root/
total 16
4 drwxr-xr-x 3 root root 4096 Jan  1  1980 .
4 drwxr-xr-x 1 root root 4096 Aug  6 18:31 ..
4 lrwxrwxrwx 1 root root   74 Jan  1  1980 .nix-channels -> /nix/store/gmkw6bw21s67hf01c93k39wf0dsp9gy7-base-system/root/.nix-channels
4 drwxr-xr-x 2 root root 4096 Jan  1  1980 .nix-defexpr
0 lrwxrwxrwx 1 root root   29 Jan  1  1980 .nix-profile -> /nix/var/nix/profiles/default

bash-5.2# nix profile list --extra-experimental-features nix-command
Name:               bash-interactive
Store paths:        /nix/store/41pi0jiyvlhxgpfhxzvb44w1skc8yp4z-bash-interactive-5.2p37

Name:               coreutils-full
Store paths:        /nix/store/9rf6b6s2cs8r62srk00arcydf8xd59jy-coreutils-full-9.7

.....