git: rename local branch failed

I don't know why my attempt of renaming local branch failed. I basically cloned the project, then I also have a submodule within the project, and I downloaded the submodule code as well. However, when I use git branch within the submodule, I have:

* (no branch)
  master

The code looks like I'm on another branch but the output shows that it doesn't have a name. Then I searched online to find how to rename local branch and I got this:

git branch -m <newname>

After I run this command git gave me this error:

error: refname refs/heads/HEAD not found
fatal: Branch rename failed

Anybody know why this happens? Thanks.

I get into this issue too. The reason is that I didn't have any commit on this git repository.

When I run the command git branch -M main. I get the following error message.

error: refname refs/heads/master not found
fatal: Branch rename failed

After I add my first commit by the following command, all things work.

git add .
git commit -m 'Init'

You are currently in detached head state. You must checkout a new branch to associate it with the current commit:

git checkout -b new_branch

I thought it was a conflict of "git init" creating master branch and github's (new) "main".

After:

git add .
git commit -m "first commit" 

I was able to git branch -M main

You can change the name from master to main in few steps, locally before you even make a commit.

1. Navigate to the directory where your project sits.
2. In it, show hidden file since by default, .git would be hidden.
3. Inside .git, there is a file, HEAD, open it in a text editor. You'd see, ref: refs/heads/master.
4. Simple enough, change, master to main.

We just renamed the master branch as main. Verify this merely by entering, git branch from the terminal.

My guess is that you're not on a branch named "(no branch)", but rather not on a branch.

If you first checkout master:

git checkout master

and then create a new branch:

git checkout -b new_branch

that would make it look like you'd expect.