undo-installation.md

Undo installation

Nix supports atomic rollback of your packages to a previous state. Rollback is the same as undoing your last action (or actions). Each new set of packages is called a generation.

We can inspect changes to our packages with --list-generations:

$ nix-env --list-generations
 1     2015-09-21 23:05:34
 2     2015-09-22 17:10:56
 3     2015-09-24 10:49:51   (current)

Let's undo our last change (e.g. the installation of hello):

$ nix-env --rollback
switching from generation 3 to 2

Checking with --list-generations we can see that we're now on the previous install (2). Note that generation 3 is still around.

$ nix-env --list-generations
 1     2015-09-21 23:05:34
 2     2015-09-22 17:10:56   (current)
 3     2015-09-24 10:49:51

With generation 3 still around, we can switch back to it like so:

$ nix-env --switch-generation 3

With --switch-generation we can in fact switch to any generation, e.g. your install from 4 weeks ago.