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

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.

Answer 2

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.

Answer 3

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 would 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

Answer 4

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.

Answer 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.

Answer 6

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