Why is "origin/HEAD" shown when running "git branch -r"?

The reason a bare repository can have a HEAD, is that because it determines which branch is initially checked out after a clone of the repository.

Normally, HEAD points to master, and that is the branch that is checked out when people clone the repository. Setting it to another branch (by editing HEAD in the bare repository) results in that branch being checked out on clone.

@robinst is correct.

In git, you can select which branch is checked out by default (i.e. when you clone). By default, origin/HEAD will point at that.

On GitHub, You can change this in the Admin settings for your GitHub repo. You can also do it from the command-line via

git remote set-head origin trunk

or delete it altogether via

git remote set-head origin -d

Example. Look at the 'Switch Branches' drop-down. trunk is checked, so origin/HEAD follows trunk.

I was under the impression that dedicated remote repos (like GitHub where no one will ssh in and work on that code, but only pull or push, etc) didn't and shouldn't have a HEAD because there was, basically, no working copy. Not so?

I had the exact same impression like you said.

And I even can not delete that origin/HEAD remote-tracking branch cloned from github by doing

git branch -d -r origin/HEAD

This had no effect.

Can some one tell me how I can delete that origin/HEAD remote-tracking branch?

update

Though I did not found why there is a origin/HEAD created when clone from github, I find a way to delete it.

The new version of git provide

git remote set-head <name> -d

to delete the useless HEAD pointer of remote-tracking branch.

And we can also change the dumb default name 'origin' to whatever we want by using

git remote rename origin <new_name>

Hope this can help. :)