1.6 Nix garbage collection: cleaning up the store

Everything Nix ever downloaded is still on your disk, which is why removed packages reappear instantly, and why /nix/store grows into many gigabytes. This lesson shows how Nix garbage collection works, why the first nix-collect-garbage run frees less space than you expect, and which flag makes it thorough.

In this video

• A look inside /nix/store: measuring its size and understanding why removed packages are still there
• Running nix-collect-garbage and reading its output, and the reason a big chunk of the store survives the first run
• The extra flag that also deletes old profile generations, and exactly what you give up by using it
• When not to collect garbage: the flight and train rule
• How often cleanup makes sense in practice, with real store sizes from production machines, and a pointer to automatic garbage collection with limits

After this lesson

You know why your disk fills up, and you can free space deliberately without destroying the rollbacks you still want.