NixOS Cheatsheet

If you’ve ever felt overwhelmed by NixOS commands, flakes, or the dreaded garbage collection panic, this guide is for you. It’s not just a cheatsheet—it’s a practical survival kit for running NixOS with flakes, keeping your system clean, and always having a rollback strategy when things go sideways.

🖥️ NixOS Essentials

Task	Command
Show version	`nixos-version`
Edit config (classic)	`sudo nano /etc/nixos/configuration.nix`
Rebuild + switch	`sudo nixos-rebuild switch`
Build only (no switch)	`sudo nixos-rebuild build`
Roll back last rebuild	`sudo nixos-rebuild switch --rollback`
List generations	`sudo nix-env --list-generations --profile /nix/var/nix/profiles/system`

⚡ Flakes Basics

Task	Command
Init flake	`nix flake init -t templates#nixos`
Show flake outputs	`nix flake show`
Update all inputs	`nix flake update --commit-lock-file`
Update one input	`nix flake lock --update-input nixpkgs --commit-lock-file`
Build system	`sudo nixos-rebuild build --flake .#<hostname>`
Switch system	`sudo nixos-rebuild switch --flake .#<hostname>`
Boot (safe)	`sudo nixos-rebuild boot --flake .#<hostname>`

🔄 Safe Updates & Rollbacks

Keeping your system updated is great… until it doesn’t boot. Here’s how to avoid disasters.

Scenario	Command / Action
Preview changes	`nix store diff-closures /nix/var/nix/profiles/system ./result`
Safe upgrade (boot next gen only after reboot)	`sudo nixos-rebuild boot --flake .#<host>`
Roll back after bad switch	`sudo nixos-rebuild switch --rollback`
Boot into old system	Select an older generation at bootloader
Revert to last good commit	`git checkout <commit>` + `sudo nixos-rebuild boot --flake .#<host>`

Quick Routine

nix flake update --commit-lock-file

sudo nixos-rebuild build --flake .#<host>

nix store diff-closures /nix/var/nix/profiles/system ./result

sudo nixos-rebuild boot --flake .#<host>

sudo reboot

🧹 Garbage Collection & Store Management

NixOS keeps everything by default—which is great for rollbacks but eats disk space fast.

Task	Command
Collect garbage	`sudo nix-collect-garbage`
Delete old gens + GC	`sudo nix-collect-garbage -d`
GC older than 14 days	`sudo nix-collect-garbage --delete-older-than 14d`
Optimize store (deduplication)	`sudo nix store optimise`
Check system size	`nix path-info -Sh /run/current-system`

Configure Automatic GC (NixOS module)

{
 boot.loader.systemd-boot.configurationLimit = 20;
 nix.gc = {
 automatic = true;
 dates = "weekly";
 options = "--delete-older-than 14d";
 };
}

🧭 Pro Tips

Always prefer boot over switch when testing major updates. Reboot to try it, rollback at bootloader if it fails.
Keep your lockfile in git. Rollbacks are trivial when you can checkout an old commit.
GC smartly. Don’t delete all history immediately—keep 14+ days for safety.
Use nix store diff-closures before switching, to see what really changed.

🚀 Final Thoughts

Running NixOS with flakes doesn’t have to feel like juggling chainsaws. With a solid update routine, rollback plan, and controlled garbage collection, you’ll have both cutting-edge packages and peace of mind.

This cheatsheet is meant to be your daily companion—bookmark it, print it, or stick it on your wall. Happy hacking!

Blogpost created with AI help

🖥️ NixOS Essentials#

⚡ Flakes Basics#