Why did my Git repo enter a detached HEAD state?

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.)

https://i.stack.imgur.com/YwJDh.png

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 is not found but there does exist a tracking branch in exactly one remote (call it ) with a matching name, treat as equivalent to git switch -c --track /

No more mistake! No more unwanted detached HEAD!

And if you git switch <tag> instead of git switch --detach <tag>, Git 2.36 will help you to remember the missing --detach option.

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I reproduced this just now by accident:

lists the remote branches git branch -r origin/Feature/f1234 origin/master I want to checkout one locally, so I cut paste: git checkout origin/Feature/f1234 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

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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.

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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.

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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.

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If git was to rename detached HEAD I would have it named as a HEAD that isn’t identified by a branch and will soon be forgotten.

We as people can easily remember branch names. We do git checkout new-button-feature / git checkout main. main and new-button-feature are easy to remember. And we can just do git branch and get a list of all branches. But to do the same with just commits you'd have to do git reflog which is very tedious. Because you have thousands of commits but only very few branches.

A detached commit’s identifier is just its SHA. So suppose you checked out a commit (not a branch) i.e. you did git checkout d747dd10e450871928a56c9cb7c6577cf61fdf31 you'll get:

Note: checking out 'd747dd10e450871928a56c9cb7c6577cf61fdf31'. You are in 'detached HEAD' state. ...

Then if you made some changes and made a commit, you're still NOT on a branch.

Do you think you'd remember the commit SHA? You won't!

git doesn't want this to happen. Hence it's informing your HEAD is not associated to a branch so you're more inclined to checkout a new branch. As a result below that message it also says:

If you want to create a new branch to retain commits you create, you may do so (now or later) by using -b with the checkout command again. Example: git checkout -b

To go a bit deeper a branch is built in a way that it's smart. It will update its HEAD as you make commits. Tags on the other hand are not meant to be like that. If you checkout a tag, then you're again on a detached HEAD. The main reason is that if you make a new commit from that tag then given that that commit is not referenced by anything (not any branch or tag) then still its considered a detached HEAD.

Attached HEADs can only happen when you're on a branch.

For more see here

HEAD is a pointer, and it points — directly or indirectly — to a particular commit: Attached HEAD means that it is attached to some branch (i.e. it points to a branch). Detached HEAD means that it is not attached to any branch, i.e. it points directly to some commit.

To look at from another angle, if you're on a branch and do cat .git/HEAD you'd get:

ref: refs/heads/Your-current-branch-name

Then if you do cat refs/heads/Your-current-branch-name then you'd also see the SHA of the commit that your branch is pointing/referencing to.

However if you were on a detached HEAD you and cat .git/HEAD you'd just get the SHA of the commit and nothing more:

639ce5dd952a645b7c3fcbe89e88e3dd081a9912

By nothing more I mean the head isn't pointing to any branch. It's just directly pointing to a commit.

As a result of all this, anytime you checkout a commit (without using the branch name to checkout), even if that commit was the latest commit of your main branch, you're still in a detached HEAD because your HEAD is not pointing to any of your local branches. Hence even checking out a tag will put you in a detached HEAD. To add onto that, even checking out a remote branch that you have fetched into your computer would result in a detached head ie git checkout origin main would also end up as a detached head...

Summary

All of the following will cause detached head:

checkout any commit

checkout any tag

checkout any remote branch

You're only on an attached head, if you've checked out a local branch

Special thanks to Josh Caswell & Saagar Jha in helping me figure this out.

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It can easily happen if you try to undo changes you've made by re-checking-out files and not quite getting the syntax right.

You can look at the output of git log - you could paste the tail of the log here since the last successful commit, and we could all see what you did. Or you could paste-bin it and ask nicely in #git on freenode IRC.

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A simple accidental way is to do a git checkout head as a typo of HEAD.

Try this:

git init
touch Readme.md
git add Readme.md
git commit
git checkout head

which gives

Note: checking out 'head'.

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 performing another checkout.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:

  git checkout -b <new-branch-name>

HEAD is now at 9354043... Readme

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The other way to get in a git detached head state is to try to commit to a remote branch. Something like:

git fetch
git checkout origin/foo
vi bar
git commit -a -m 'changed bar'

Note that if you do this, any further attempt to checkout origin/foo will drop you back into a detached head state!

The solution is to create your own local foo branch that tracks origin/foo, then optionally push.

This probably has nothing to do with your original problem, but this page is high on the google hits for "git detached head" and this scenario is severely under-documented.

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When you checkout to a commit git checkout <commit-hash> or to a remote branch your HEAD will get detached and try to create a new commit on it.

Commits that are not reachable by any branch or tag will be garbage collected and removed from the repository after 30 days.

Another way to solve this is by creating a new branch for the newly created commit and checkout to it. git checkout -b <branch-name> <commit-hash>

This article illustrates how you can get to detached HEAD state.

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Following VonC's comment, here is the short version of how I resolved this same 'detached HEAD' issue.

Created a branch in my remote; origin/feature/dev In my local run git fetch, so now my local will be aware of this new remote branch Now run git switch feature/dev, and we are done!

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Detached HEAD

HEAD is a pointer to the currently checked out branch or commit, it answers the question: Where am I right now in the repository? HEAD can be in either of two states, attached (default) or detached, depending on if you've checked out a local branch or not.

OP: How did I end up with a detached HEAD?

Operations than leave HEAD in detached state

Ending up in detached HEAD state can be due to various reasons, below are 5 common cases (perhaps did you do any of the following):

Checking out a particular commit using its hash, i.e. $ git checkout 14ko3

Explicitly checking out a remote branch, i.e. $ git checkout origin/master

Switching to a branch using the detached flag (Git 2.23), i.e. $ git switch master --detached

Checking out a tag, i.e. $ git checkout v1.0.1

Performing an interactive rebase (or a regular rebase containing conflicting changes), i.e. $ git rebase master feature-1 --interactive

In detached state experimental changes can be made without impacting any existing branch. See infographic below illustrating the difference between committing in attached vs detached state.

https://i.stack.imgur.com/1iPL0.png

A common misconception is that the message You are in 'detached HEAD' state is of erroneous tone, when in fact it just describes how HEAD is referencing the current snapshot.

Moving from detached to attached state

To move from detached to attached state, you can either create a new branch from where you're at, or switch back to an existing branch.

Note: any commits created in detached state will eventually (post garbage collection) be discarded if you switch to another existing branch, without first persisting your changes in a new branch.

Source: Above excerpt is taken from this full length post on the subject: What is HEAD in Git?

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For my case it happens this way:

Create a new branch (feb_debugging).

Run git fetch

I see new branch (feb_debugging) pulled

Now, I use git checkout origin/feb_debugging

Here it gets me to HEAD is now at....

For fixing I just need another checkout

git checkout feb_debugging

Now git says that I am at feb_debugging branch.

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