GNU GRUB
FAQ
How do I remove older generations from the bootloader?
First, collect garbages in your system, then rebuild. The scripts will collect leftover files.
The first command, in the example below, removes everything older than 14 days.
$ sudo nix-collect-garbage --delete-older-than 14d
$ sudo nixos-rebuild boot
How do I use GRUB in text mode?
Sometimes you need to access GRUB in text mode (e.g. when using out of band management systems like HP ILO in "textcons" mode). To enable text mode you have to disable the GRUB splash screen:
boot.loader.grub.splashImage = null;