How to undoing a git rebase?

When using Git for version control, git rebase is a commonly used command to reorganize the commit history. However, if errors occur during the rebase or you realize the rebase operation is not what you intended, you may need to undo this rebase.

To undo a completed rebase, several methods are available:

1. Using git reflog and git reset

Git's reflog records all changes to the HEAD in your repository, including commits, rebases, and merges. Using reflog, you can locate the HEAD position prior to the rebase operation and use the reset command to revert to that state.

For example:

bash
# View reflog to find the state to revert to
 git reflog

# Assuming the commit before rebase is HEAD@{5}
 git reset --hard HEAD@{5}

This will undo the rebase and reset your branch to its previous state.

2. Using a Backup Branch

Creating a backup branch before performing the rebase is a safe practice. This allows you to easily switch to the backup branch if the rebase does not meet your expectations.

For example:

bash
# Create a backup branch before rebase
 git branch backup-branch

# To revert the rebase, switch to the backup branch
 git checkout backup-branch
# If you decide to use the backup branch's content, do:
 git branch -f main backup-branch
 git checkout main

This enables you to restore to the state before the rebase while retaining a copy of the branch unaffected by the rebase.

Summary

Using git reflog and git reset is the most straightforward method to undo a rebase, as it enables you to directly revert to any previous state. However, using a backup branch adds an extra layer of safety, particularly when dealing with complex rebases or working on public branches.

In my practical experience, I encountered a situation where, after rebasing a feature branch onto the main branch, I discovered that several files had incorrect merge outcomes, which directly impacted the project's functionality. At that time, I used git reflog to examine the history and git reset --hard to revert to the state prior to the rebase. I then reviewed and performed the rebase step by step, ensuring that each step's changes were accurate. This experience taught me to develop the habit of checking reflog and using backup branches before performing complex Git operations.

Resetting the branch to its old commit is the best solution because it restores the previous state without any effort.

However, if you accidentally lost these commits (for example, due to garbage collection on the repository or it being a new clone), you can always rebase the branch again.

The key is the --onto option.

Assume you have a topic branch named topic that you created from the master branch. At some point on the branch, you performed the rebase. Now you want to undo this operation. Here's how: git rebase master

git rebase --onto 0deadbeef master topic

This will fetch all commits not yet included in master and apply them to 0deadbeef.

With --onto, you can rearrange your history into almost any shape.