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I have a git repository with two branches: master and live. I work on master. Once I deem my changes ready for production, I merge them into live, which is checked out in the production system. I work on the project alone.

With this setup, live always used to simply be a few commits behind master. So when I did a git merge master on live, the merge would be performed via fast-forward.

As of recently, doing git merge master while on live results in a merge performed by the recursive strategy. I don't know if the reason for this is that I once accidentally committed a change first on live, and only afterwards merged it onto master.

git diff master live yields no output, ie. the two branches have the same file contents.

What can I do to get my git repository into a "clean" state so it again uses the fast-forward strategy by default?

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  • Have you tried explicitly asking for fast-forward merges with git merge --ff-only master? Commented Feb 26, 2015 at 18:25
  • Instead of using git diff, try git cherry -v master live (and live master). This will tell you what commits are the latter branch that aren't on the former. If you made a commit on live and then later merged it to master, it could have ended up with a different commit hash (even though your file contents are the same)... so maybe things started to skew from there? Commented Feb 26, 2015 at 21:18
  • Thank you for your replies. @dg99: git merge --ff-only master gives fatal: Not possible to fast-forward, aborting.. @hinerm: git cherry -v master live (and live master) both give no result. So strange! Commented Feb 27, 2015 at 16:14

1 Answer 1

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I think the problem was caused because:

  1. I accidentally committed something (let's call it A) on live instead of master.
  2. I then committed something else (B say) on master.
  3. I realised I made the mistake 1. and merged live onto master.
  4. I still needed to merge B onto live, so I merged master onto live.

I think this created a "crossing" of commit paths that makes it impossible for git merge to fast-forward.

The solution was to first ensure that the two branches really did have the same contents:

git diff master..live git cherry -v master live git cherry -v live master

all yielded no result. Then I changed live to point at exactly the same commit as master:

git branch -f live ae5e70... # Hash of the commit pointed to by master git push --force origin live:live

Now I can fast-forward again. Note that this can be dangerous and should probably not be done when the repository is shared.

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