What is the ‘fatal: refusing to merge unrelated histories’ error?

Git refusing to merge unrelated histories It appears when a developer tries to merge two unrelated projects into a single branch When performing a git rebase, if you get the error message "fatal: refusing to merge unrelated histories", it means that the branch you are trying to rebase onto has no commits in common with the branch you are currently on. This can occur when you are trying to rebase a branch onto a completely different branch that was created independently and has no relation to the branch you are currently on.

To resolve this issue, you can use the "--allow-unrelated-histories" flag when running the rebase command, like so:

git rebase --allow-unrelated-histories <upstream>

This flag tells git to allow the rebase to proceed even though the histories are unrelated. But be aware that by doing this, you may lose some of the commits or changes in your branch.

Alternatively, you can merge the branches using git merge command which will create a new merge commit and will keep both histories.

git merge <branch>

Another option is to use git pull with the --rebase flag.

git pull --rebase <remote> <branch>

This command will fetch the latest changes from the remote and rebase your local changes on top of them.

Why does ‘fatal: refusing to merge unrelated histories’ happen?

The error message "fatal: refusing to merge unrelated histories" occurs when Git is trying to perform a rebase operation, but the branch you are currently on has no commits in common with the branch you are trying to rebase onto. This means that the two branches were created independently and have no history in common, making it difficult for Git to determine how to merge the changes.

This can happen in a few different scenarios:

• You are trying to rebase a branch that was created from an entirely different repository or from a completely different starting point.
• You are trying to rebase a branch that was created a long time ago and has since diverged significantly from the branch you are currently on.
• You are trying to rebase a branch that was forked from a completely different branch, and has no commits in common with the branch you are currently on.

By default, Git is designed to be conservative and prevent such operations, as it may cause confusion and/or data loss. Git requires explicit instructions to proceed such as --allow-unrelated-histories flag or merge command which will preserve the history of both branches.