Why did my Git repo enter a detached HEAD state?

Question

I ended up with a detached head today, the same problem as described in: git push says everything up-to-date even though I have local changes

As far as I know I didn't do anything out of the ordinary, just commits and pushes from my local repo.

So how did I end up with a detached HEAD?

Answer 1

Any checkout of a commit that is not the name of one of your branches will get you a detached HEAD. A SHA1 which represents the tip of a branch still gives a detached HEAD. Only a checkout of a local branch name avoids that mode.

See committing with a detached HEAD

When HEAD is detached, commits work like normal, except no named branch gets updated. (You can think of this as an anonymous branch.)

For example, if you checkout a "remote branch" without tracking it first, you can end up with a detached HEAD.

See git: switch branch without detaching head

Meaning: git checkout origin/main (or origin/master in the old days) would result in:

Note: switching to 'origin/main'.  You are in 'detached HEAD' state. You can look around, make experimental changes and commit them, and you can discard any commits you make in this state without impacting any branches by switching back to a branch.  If you want to create a new branch to retain commits you create, you may do so (now or later) by using -c with the switch command. Example:    git switch -c <new-branch-name>  Or undo this operation with:    git switch -  Turn off this advice by setting config variable advice.detachedHead to false  HEAD is now at a1b2c3d My commit message 

That is why you should not use git checkout anymore, but the new git switch command.

With git switch, the same attempt to "checkout" (switch to) a remote branch would fail immediately:

git switch origin/main fatal: a branch is expected, got remote branch 'origin/main' 

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To add more on git switch:

With Git 2.23 (August 2019), you don't have to use the confusing git checkout command anymore.

git switch can also checkout a branch, and get a detach HEAD, except:

• it has an explicit --detach option

To check out commit HEAD~3 for temporary inspection or experiment without creating a new branch:

git switch --detach HEAD~3 HEAD is now at 9fc9555312 Merge branch 'cc/shared-index-permbits' 

• it cannot detached by mistake a remote tracking branch

See:

C:\Users\vonc\arepo>git checkout origin/master Note: switching to 'origin/master'.  You are in 'detached HEAD' state. You can look around, make experimental changes and commit them, and you can discard any commits you make in this state without impacting any branches by switching back to a branch. 

Vs. using the new git switch command:

C:\Users\vonc\arepo>git switch origin/master fatal: a branch is expected, got remote branch 'origin/master' 

If you wanted to create a new local branch tracking a remote branch:

git switch <branch>  

If <branch> is not found but there does exist a tracking branch in exactly one remote (call it <remote>) with a matching name, treat as equivalent to

git switch -c <branch> --track <remote>/<branch> 

No more mistake!
No more unwanted detached HEAD!

Answer 2

I reproduced this just now by accident:

1. lists the remote branches

   git branch -r       origin/Feature/f1234       origin/master 

2. I want to checkout one locally, so I cut paste:

   git checkout origin/Feature/f1234 

3. Presto! Detached HEAD state

   You are in 'detached HEAD' state. [...]) 

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Solution #1:

Do not include origin/ at the front of my branch spec when checking it out:

git checkout Feature/f1234 

Solution #2:

Add -b parameter which creates a local branch from the remote

git checkout -b origin/Feature/f1234 or

git checkout -b Feature/f1234 it will fall back to origin automatically