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I am learning git and am following the excellent tutorials at http://gitimmersion.com.

In those tutorials, there is a blurb that tries to explain detached HEADs, and that states:

A “detached HEAD” message in git just means that HEAD (the part of git that tracks what your current working directory should match) is pointing directly to a commit rather than a branch. Any changes that are committed in this state are only remembered as long as you don’t switch to a different branch. As soon as you checkout a new branch or tag, the detached commits will be “lost” (because HEAD has moved). If you want to save commits done in a detached state, you need to create a branch to remember the commits.

A few questions on this:

  1. What exactly is a detached HEAD, and what conditions create it?
  2. Why is a detached HEAD pointing to a specific commit and not a branch?
  3. When you have a detached HEAD, do you always need to create a new branch to be able to commit/push the changes in it? Why/why not?

Thanks in advance!

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If you are working in your repo and do git checkout <SHA> you will be in a "detached HEAD". You are not on a branch (the commit is likely to be on multiple branches). You are checked out to a specific instance in the history.

A detached head can also occur when you are rebasing. You are checked out to a specific commit.

You would need to create a branch in order to commit/push changes because you would be creating commits that would be "in limbo" with no way to identify them other than the SHA. Git will remove the commit during its garbage collection because of it not being on a branch.

Checkout the "Detached Head" Section on this page for more in depth information: http://git-scm.com/docs/git-checkout

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