I mostly use git to track changes (very useful to check on what I’ve been up to when it’s late in the night!) but occasionally I need to use it to roll back to a previous commit. This is the command I always forget, and today it took me more than one minute to find the answer (or formulate the right question) on google.
The answer, unsurprisingly on stackoverflow: in your [git tracked] working directory enter this terminal command:
git reset --hard <tag/branch/commit id>
Where you replace the gubbins inside the angle brackets with the SHA ID of your commit. Find this easily using GitX.