Issue
I was following this instruction to try to shrink my virtual nixos. It says,
You can’t actually use zerofree on your / partition while you’re booted into the standard Linux environment. Instead, you’ll want to boot into a special recovery mode where your normal root partition isn’t mounted.
But I can't find a place to boot into recovery mode in nixos. Question: How to boot into some mode where my root partiion isn't mounted in nixos? Or how do I do zerofree in nixos?
Solution
NixOS does not have a recovery mode that uses an alternative root filesystem. You can do it yourself by adding extra entries to your bootloader by adding boot.loader.grub.extraEntries to your configuration.nix.
This way, you can boot into an another partition. You will need to prepare an extra installation on that partition. But considering that it's a VM there's probably a better option:
You may be able to attach the root filesystem of your stopped VM to a VM that has its own rootfs with zerofree on it. This way, you won't have to muck about with extra partitions.
Answered By - Robert Hensing Answer Checked By - Candace Johnson (WPSolving Volunteer)