How can I rollback a git repository to a specific commit?

To undo the most recent commit I do this:

First:

git log

get the very latest SHA id to undo.

git revert SHA

That will create a new commit that does the exact opposite of your commit. Then you can push this new commit to bring your app to the state it was before, and your git history will show these changes accordingly.

This is good for an immediate redo of something you just committed, which I find is more often the case for me.

As Mike metioned, you can also do this:

git revert HEAD

git reset --hard <old-commit-id>
git push -f <remote-name> <branch-name>

Note: As written in comments below, Using this is dangerous in a collaborative environment: you're rewriting history