Why did my Git repo enter a detached HEAD state?

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?

Solution 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'

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!

Solution 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. [...])
   

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

Solution 3:

try

git reflog 

this gives you a history of how your HEAD and branch pointers where moved in the past.

e.g. :

88ea06b HEAD@{0}: checkout: moving from DEVELOPMENT to remotes/origin/SomeNiceFeature e47bf80 HEAD@{1}: pull origin DEVELOPMENT: Fast-forward

the top of this list is one reasone one might encounter a DETACHED HEAD state ... checking out a remote tracking branch.

Solution 4:

Detached HEAD means that what's currently checked out is not a local branch.

Some scenarios that will result in a Detached HEAD state:

• If you checkout a remote branch, say origin/master. This is a read-only branch. Thus, when creating a commit from origin/master it will be free-floating, i.e. not connected to any branch.

• If you checkout a specific tag or commit. When doing a new commit from here, it will again be free-floating, i.e. not connected to any branch. Note that when a branch is checked out, new commits always gets automatically placed at the tip.

  When you want to go back and checkout a specific commit or tag to start working from there, you could create a new branch originating from that commit and switch to it by git checkout -b new_branch_name. This will prevent the Detached HEAD state as you now have a branch checked out and not a commit.

Solution 5:

It can happen if you have a tag named same as a branch.

Example: if "release/0.1" is tag name, then

git checkout release/0.1

produces detached HEAD at "release/0.1". If you expect release/0.1 to be a branch name, then you get confused.