disk /nix full : doc needed

[ymettier]

When I toolbox update, I will need more and more disk space.

I know that nix-collect-garbage -d is the solution to my problem. But if you don't know it, you cannot invent it.

Suggestion : when you toolbox update, at the end, you could print some message like this :

If you want to free some disk space you can run this command : 
  nix-collect-garbage -d

Example :

$ toolbox update
[toolbox]: Updating toolbox ...
[toolbox]: Running "nix-channel --update toolbox"

unpacking channels...
[toolbox]: Running "nix-env -f '<toolbox>' -u -b"

unpacking 'https://github.com/NixOS/nixpkgs-channels/archive/029a5de08390bb03c3f44230b064fd1850c6658a.tar.gz'...
unpacking 'https://github.com/nix-community/pypi2nix-overrides/archive/100c15ec7dfe7d241402ecfb1e796328d0eaf1ec.tar.gz'...
unpacking 'https://github.com/Caascad/os/archive/1.1.0.tar.gz'...
unpacking 'https://github.com/NixOS/nixpkgs-channels/archive/2efedf8fc74e8056f81bd18899276b085becf6dc.tar.gz'...
unpacking 'https://github.com/Caascad/tf/archive/1.6.3.tar.gz'...

If you want to free some disk space you can run this command : 
  nix-collect-garbage -d

[Benjile]

I am not sure that using nix-collect-garbage -d is a real solution. A big part of /nix is populated by our use_nix directive in .envrc. It would be wiped by the garbage collector and then any cd command would repopulate /nix ending probably by a disk full again.

I think the real solution here is to increase the disk space reserved for /nix.

Displaying such a message would lead some of use to put this command in crontab, and you really do not want that.

Maybe a paragraph in README should be enough.