Command Cheat Sheet

Command Cheat Sheet

Daily commands for developing, building, and operating Nix and NixOS.

Flakes and development

Command	Purpose
nix develop	Default project shell
nix develop .#backend	Named shell
nix flake init	Skeleton flake
nix flake check	Eval + checks.*
nix flake update	Refresh every input in flake.lock
nix flake update nixpkgs	Refresh one input
nix flake show	Outputs in this flake
nix flake metadata	Locked revisions
nix fmt	Formatter if formatter is set

Build, run, eval

Command	Purpose
nix build .#pkg	Build; symlink ./result
nix run .#app	Build and run
nix eval .#attr	Print a value
nix log ./result	Build log
nix repl .#	REPL on this flake

Inspect closures

Command	Purpose
nix path-info -Shr ./result	Closure size (the number that matters)
nix path-info ./result	Output path only
nix-store -q --references P	Direct runtime edges
nix-store -q --requisites P	Full runtime closure
nix-store -q --referrers P	Who points at P
nix-store -q --tree P	ASCII graph
nix why-depends A B	Why A’s closure contains B
nix-tree P	Interactive tree (nix run nixpkgs#nix-tree)
nom build .#pkg	nix build with a progress table

Fetchers

Command	Purpose
nix-prefetch-url URL	Hash a file (packed)
nix-prefetch-url --unpack URL	Hash an unpacked archive
nix hash convert --to sri HASH	Hex → SRI sha256-…

Copy and caches

Command	Purpose
nix copy --to file://$PWD/nar P	Directory cache
nix copy --to ssh://host P	Copy closure over SSH
cachix push desk-cache ./result	Upload to Cachix
nix show-config \| grep substituters	Which caches this daemon queries

Remote builders

Command	Purpose
nix build .#pkg --max-jobs 0 --builders 'ssh-ng://user@host system'	Realise only remotely
sudo ssh -i /root/.ssh/id_builder user@host nix-store --version	Daemon SSH must work without a password

NixOS

Command	Purpose
sudo nixos-rebuild switch --flake .#host	Build, activate, set boot default
sudo nixos-rebuild test --flake .#host	Activate without changing the boot default
sudo nixos-rebuild boot --flake .#host	Next reboot only
sudo nixos-rebuild dry-activate --flake .#host	Show unit changes, do nothing
sudo nixos-rebuild switch --rollback	Previous generation
sudo nix-env --list-generations --profile /nix/var/nix/profiles/system	Generation list
nixos-version	Running release

Home Manager

Command	Purpose
home-manager switch --flake .#user	Standalone user env
home-manager generations	User generations
home-manager switch --rollback	Previous user generation (standalone only)

GC and disk

Command	Purpose
nix-store --gc --print-roots	What is keeping paths alive
nix-collect-garbage	Delete unreferenced paths; keep generations
nix-collect-garbage --delete-older-than 14d	Drop old generations, then orphans
sudo nix-collect-garbage -d	All old generations (incident)
nix-store --optimise	Hard-link identical files
nix-store --verify --check-contents	Rehash after disk trouble
df -h /nix /boot	Store vs ESP — two different full-disk incidents

Backup (restic)

Command	Purpose
sudo systemctl start restic-backups-desk	Run the NixOS restic unit now
restic snapshots	List snapshots (needs -r and password file)
restic restore latest --target /tmp/drill	Restore drill