When working on a shared Git repository, you may sometimes see the "fatal: Not possible to fast-forward, aborting" error. This happens when your local branch and the remote branch have split, meaning the remote branch has new commits that are not in your local branch. In this article, we'll look at the steps to fix this error and talk about some good habits to prevent it in the future.
Resolving the "fatal: Not possible to fast-forward, aborting" Error
Step 1: Get the latest changes from the remote branch
To fix the "fatal: Not possible to fast-forward, aborting" error, use the git fetch command to get the latest changes from the remote repository. git fetch updates your local copy of the remote branch without merging the changes into your current branch. This lets you see the new commits on the remote branch without changing your local branch.
git fetch originThis command gets the latest changes from the remote repository named "origin".
Step 2: Check the difference between local and remote branches
After getting the latest changes, use git status to check the current status of your local branch. Compare the head of your local branch with the head of the remote branch. This will help you find any conflicting changes between the branches. If the remote branch has new commits that are not in your local branch, you'll need to add those changes.
git statusThe output will show you the current branch, its link with the remote branch, and any uncommitted changes.
Step 3: Pick a way to add remote changes
There are two common ways to add remote changes to your local branch: merging and rebasing.
git mergecombines the remote changes with your local changes, making a new merge commit.git rebaseputs your local commits on top of the remote changes, giving a linear history without a merge commit.
Pick the way that works best for your situation and development workflow.
| Method | Description | When to Use |
|---|---|---|
git merge |
Combines remote changes with local changes, making a merge commit | - Working on a shared branch - Keeping commit history |
git rebase |
Puts local commits on top of remote changes, giving a linear history | - Working on a feature branch - Keeping a clean commit history |
Step 4a: Merge remote changes using git merge
If you pick git merge, run the command git merge <remote-branch> to merge the remote changes into your local branch. If there are any conflicting changes, git will ask you to fix the merge conflicts manually. After fixing the conflicts, stage the changes and make a new commit to finish the merge process. This will make a merge commit in your branch's history.
git merge origin/mainThis command merges the changes from the remote branch "origin/main" into your current local branch.
Step 4b: Rebase local commits on top of remote changes using git rebase
If you like git rebase, run the command git pull --rebase to rebase your local commits on top of the remote changes. This will apply your local commits one by one on top of the remote branch's head. If there are any conflicting changes during the rebase process, git will pause and let you fix the conflicts for each commit. After fixing the conflicts, continue the rebase process until all commits are applied. Rebasing makes a linear history without a merge commit.
git pull --rebaseThis command gets the latest changes from the remote repository and rebases your local commits on top of them.
Step 5: Push the updated local branch to the remote repository
Once you have successfully merged or rebased the remote changes into your local branch, use the git push command to push the updated local branch to the remote repository. This will make your changes available to other developers working on the same branch. If you used git rebase, you may need to use git push --force to overwrite the remote branch with your rebased local branch.
git push origin mainThis command pushes the changes from your local branch to the remote branch named "main" on the "origin" repository.
Cause
What causes this git error?
The "fatal: Not possible to fast-forward, aborting" error happens when your local branch and the remote branch have diverged. This means the remote branch has new commits that are not in your local branch. When this happens, git cannot do a fast-forward merge.
A fast-forward merge is only possible when your local branch is directly behind the remote branch in terms of commit history. If your local branch has commits that the remote branch does not have, or if the remote branch has commits that your local branch does not have, git cannot do a fast-forward merge.
In this example, the remote branch has commits 1, 2, and 3, while the local branch has commits 1 and 4. Since the branches have diverged, a fast-forward merge is not possible.
What is a fast-forward merge in git?
A fast-forward merge is a type of merge that happens when your current branch is an ancestor of the branch you are trying to merge. In other words, the branch you are merging into has not diverged from your current branch.
In a fast-forward merge, git simply moves the pointer of your current branch forward to the latest commit of the branch you are merging. This is possible because there are no conflicting changes between the branches.
In this case, Branch B can be fast-forwarded to the latest commit of Branch A (Commit 3) because Branch B is directly behind Branch A in terms of commit history.
Fast-forward merging is not possible when the branches have diverged, meaning both branches have unique commits that the other branch does not have.
Why does git abort the merge process?
Git aborts the merge process to prevent the loss of commit history. If git allowed the merge to continue despite the branches having diverged, it could lead to the loss of commits from one of the branches.
By aborting the merge, git is maintaining the integrity of your repository's commit history. It prevents the creation of a merge commit that could lose important changes made in either branch.
Instead of automatically merging the diverged branches, git requires you to integrate the remote changes into your local branch using either git merge or git rebase. This way, you have control over how the changes are added and can resolve any conflicts that may arise during the process.
Here's a table summarizing the reasons for git aborting the merge process:
| Reason | Explanation |
|---|---|
| Prevent loss of commit history | Aborting the merge prevents the loss of commits from either branch |
| Maintain repository integrity | Avoids creating a merge commit that could lose important changes |
| Require explicit integration | Allows user control over adding changes and resolving conflicts |
By aborting the merge and requiring explicit integration, git makes sure that you are aware of the diverged branches and can make decisions on how to proceed with merging the changes.
Best Practices
Keep your local branch up to date with the remote branch
To avoid the "fatal: Not possible to fast-forward, aborting" error, it's important to keep your local branch up to date with the remote branch. Here are some steps you can follow:
-
Fetch the latest changes from the remote branch:
git fetch -
Merge or rebase the changes into your local branch:
- Using merge:
git merge origin/main - Using rebase:
git pull --rebase
- Using merge:
Consider running these commands frequently, especially before starting new work or pushing your changes to the remote repository. By keeping your local branch in sync with the remote branch, you minimize the risk of encountering the "fatal: Not possible to fast-forward, aborting" error.
Example workflow
Use branching and pull requests for collaborative development
To make collaborative development better and reduce conflicts, use a branching strategy and pull requests:
- Make separate branches for different features, bug fixes, or experiments
- Work on the feature branch and commit changes locally
- Push the feature branch to the remote repository
- Make a pull request to merge the changes into the main branch
- Review, discuss, and test the changes during the pull request process
- Fix any conflicts or issues before merging
- Merge the pull request into the main branch
