Git not-fast-forward errors after git commit --amend

Question

I used git commit --amend to amend the previous commit. After that when I push my changes, I was rejected because of 'not -fast-forward' Errors. I have search for answers. Unfortunately, commands such as, git pull --rebase, git fetech origin don't work. If there is no conflict in my local repo, why my push failed.

Answer 1

NEVER AMEND OR REBASE A COMMIT YOU'VE ALREADY PUBLISHED!

If you publish a commit and somebody else fetches it, the commit is there to stay. When you amend or rebase, you create a new commit and forget the old one. But when somebody else already has the old commit, it will not get updated for them. So when they later merge, the two versions of the commit will merge causing havoc.

With this error, git is preventing you from pushing amended version of commits you've already published by mistake.

There are exceptions to the rule. If you are pushing to a backup that nobody works off, you can push new history there (it's called rewinding). And if there is a branch that is announced as being rewound (for example git's own "pu" branch and all topics not yet in "next"), it's obviously fine to rewind.

If you are certain you won't cause problems by this, you can tell git to go ahead and rewind by using

git push -f

It is also default for remotes configured as mirrors.

Note that some repositories can be configured with hook to prohibit rewinding or prohibit rewinding some branches anyway.

Answer 2

This happens because the commit was already in the remote repo, so you will have to rewrite history.

This means you have to do a force push:

git push -f

Be careful though, if you are collaborating with others they run into trouble since rewriting history is not a good thing.