If you are one of the millions of developers who use Git, you may have come across the “detached HEAD state”. It is a strange phrase, but it’s not as alarming as it might sound. Here’s what it means. In Git, HEAD refers to the currently checked-out branch’s latest commit. However, in a detached HEAD state, the HEAD does not point to any branch, but instead points to a specific commit or the remote repository. If you want to keep the changes you made while in the detached HEAD state, you can solve this problem with three simple steps:
- Creating a new branch
- Committing the changes
- Merging the changes
Git is fast, scalable, and has more commands and flexibility than older version control systems (VCS). But learning Git is more complicated than it was with older systems. Complex commands and a less intuitive user interface can sometimes lead to unwanted states, including the detached HEAD state. In this article, we will explore what the Git detached HEAD state is and some situations that cause it. Then, we will demonstrate how to save or discard changes in a detached head so you can quickly recover from the situation.
What is a normal HEAD state
Below is a diagram of the Git HEAD in a normal state, pointing to the latest commit in the main branch.
In this image, the HEAD points to the latest commit and current checked-out branch on every commit in the current branch.
HEAD is also a common state when working with multiple branches.
In this situation, you have two branches, the main branch and a feature branch. Since you are checked out to the feature branch, HEAD points there. You can create this scenario with the following Git commands:
git branch feature
git checkout feature
git commit -m “checked out to feature”
git checkout Main
git commit
git commit -m “Latest commit”
git checkout feature
What does detached HEAD mean?
In Git, the detached HEAD state occurs when the HEAD does not point to a branch, but instead points to a specific commit or the remote repository.
In both of the diagrams in the previous section, HEAD points to the most recent commit in the currently checked out branch, which is its normal state. In Git, you can also check out a particular commit, which results in the detached HEAD state. Continuing from the previous scenario, if you check out to the first commit on the main branch, you will see that HEAD is now detached.
In this case, HEAD does not point to any branch—it references a commit.
Scenarios that can cause a detached HEAD state
You can find yourself in a detached HEAD state primarily through two scenarios:
- Checking out a specific Secure Hash Algorithm 1 (SHA-1) commit hash
- Checking out to a remote branch without fetching it first
We already demonstrated that if you check out the SHA-1 commit hash, you will be in the detached HEAD state. Another situation that causes a detached HEAD is checking out the remote branch. If you check out to the origin (main) branch, which is read-only, you will be in the detached HEAD state.
Some other scenarios can cause a detached HEAD as well. For example, checking out to a specific tag name or adding ^0 on any given branch causes the detached HEAD state.
How to save changes in a detached HEAD
If you find yourself a detached HEAD state and realize it quickly, you can quickly recover by checking out the previous branch. But what if you are in the detached HEAD state by mistake then perform commits over commits? If you are committing in the detached HEAD state, does that mean your changes are not saved?
Not at all. It just means you are not currently attached to any branch, and as a result, your HEAD is detached. To keep the changes made while in the detached HEAD state, use these three steps:
- Create a new branch
- Commit the changes
- Merge the changes
Create a new branch
To save changes committed in a detached HEAD state, you first need to create a new branch.
Continuing from the scenario described above, you create a new branch called temp-branch. As soon as you make the branch and check out to it, the HEAD is no longer detached.
Commit the changes
After checking out to the new branch, you can commit the changes, which Git will preserve.
Merge the changes
Now, you check out to the branch where you want the changes. In this case, you want to merge the changes to the main branch. So, you first need to check out the main branch, then merge the changes from temp-branch and add the final commit message.
With these simple steps, you have successfully preserved your changes and recovered from the Git detached HEAD state.
How to discard changes in a detached HEAD
If you want to discard the changes in the detached HEAD state, you only need to check out to the existing or previous branch. The commits on the detached HEAD state will not affect your existing branch, and Git will archive them.
The diagram below shows a situation in which, after going into the detached HEAD state, you make two commits that you do not want to keep. Then, you check out to the main branch. The dotted circles indicate that these commits are no longer part of any branch, and Git will delete them.
Note that once Git prunes your detached HEAD state commits, there is no way to get them back. However, if they have not been deleted, you can check out to that SHA-1 commit hash, create a branch, and merge it to the desired branch to preserve the changes.
Conclusion
Git is a valuable developer tool and more popular than older versioning tools such as CVS and Subversion. That said, it can be more complex and challenging to master, and can sometimes lead to confusing situations such as the detached HEAD state.
If you find yourself in the detached HEAD state, remember that you can always preserve your changes by creating and checking out to a new branch, then committing and merging the changes in the desired branch. If you do not want to save the changes, you can simply check out to any branch, and Git removes those commits.
Also, Git 2.23 has a new command, git switch. This is not a new feature but an alternative command to git checkout so you can switch between the branches and create a new branch. To change from one branch to another, use git switch branchName to create a new branch, then switch to it using the git switch -c branchName command.
Although finding your code in the detached HEAD state is not ideal, you can use these methods to move or remove your commits and quickly get your project back on track.
