git refname 'origin/master' is ambiguous

I have a git repository that is tracking several remote branches:

$ git branch -a
* master
  remotes/git-svn
  remotes/origin/master
  remotes/trunk

When I try to setup a default one I get the following error:

$ git branch --set-upstream-to=origin/master master
warning: refname 'origin/master' is ambiguous.
fatal: Ambiguous object name: 'origin/master'.

I would like to kremove some of the remote master branches but the master references are still there. How can I remove them to be able to set the default upstream branch to origin/master?

$ git show-ref master
cba97a58c99743c355b569bbf35636c8823c2d96 refs/heads/master
6726b4985107e2ddc7539f95e1a6aba536d35bc6 refs/origin/master
d83f025cd3800ed7acd76b2e52ae296e33f1cd07 refs/original/refs/heads/master
cba97a58c99743c355b569bbf35636c8823c2d96 refs/remotes/origin/master

The output of git branch -a shows that you have a remote-tracking branch called origin/master. Perfectly normal.

However, the output of git show-ref master contains

6726b4985107e2ddc7539f95e1a6aba536d35bc6 refs/origin/master

which indicates that you most likely ran something like the following low-level command:

git update-ref refs/origin/master master

This command creates a branch (pointing at the same commit as master) called origin/master, but living directly under refs/, i.e. outside the refs/heads/ namespace, where local branches normally live. Quite suspicious... Did you mean to do that?

Such a branch won't get listed by git branch -a. Git is getting confused, though, because it sees two branches whose refnames end with origin/master:

• refs/remotes/origin/master, your remote-tracking branch, and
• refs/origin/master, the local branch that you created (by accident) outside refs/heads/.

Solution

If you did not mean to create refs/origin/master

Simply delete it:

git update-ref -d refs/origin/master

Then, there won't be any ambiguity, and Git will comply when you try to set master's upstream.

If you did mean to create refs/origin/master

To avoid ambiguity, simply specify the full refname of the branch you wish to set as master's upstream:

git branch --set-upstream-to=refs/remotes/origin/master master

---

To fix ideas, here is some code that reproduces the situation in one of my GitHub repos:

$ cd ~/Desktop
$ git clone https://github.com/Jubobs/gitdags && cd gitdags

$ git update-ref refs/origin/master

$ git branch -a
* master
  remotes/origin/HEAD -> origin/master
  remotes/origin/master

$ git show-ref master
15b28ec22dfb072ff4369b35ef18df51bb55e900 refs/heads/master
15b28ec22dfb072ff4369b35ef18df51bb55e900 refs/origin/master
15b28ec22dfb072ff4369b35ef18df51bb55e900 refs/remotes/origin/HEAD
15b28ec22dfb072ff4369b35ef18df51bb55e900 refs/remotes/origin/master

$ git branch --set-upstream-to=origin/master master
warning: refname 'origin/master' is ambiguous.
fatal: Ambiguous object name: 'origin/master'.

$ git update-ref -d refs/origin/master
$ git branch --set-upstream-to=origin/master master
Branch master set up to track remote branch master from origin.

You probably accidentally created a local ref called 'origin/master'

for instance, if you did this

git branch origin/master

It would lead to this problem. This one looks suspect "refs/origin/master". "refs/heads/master" is your local master, "refs/remotes/origin/master" is your remote branch reference, and "refs/origin/master" is probably a mistake that is screwing you up.

You just need to delete that reference (git update-ref -d ) and things will start working again.

I faced the same problem few days back where there were multiple references created of the same branch.

Things i tried:

> git show-ref (will give you the list of references, from the
> references list you can check if there are multiple references created
> for the branch you are working on or not.)

If there are multiple references created then simply remove it

rm .git/refs/heads/master

After removing the references you can take the checkout of the branch from remote origin only if you have pushed something in it, otherwise you have to redo everything which you did in the branch

git fetch origin
git checkout origin/branchName

This solution worked out for me in case of ambiguous branches.

I had a very similar problem due to an accidental tag named "master", showing in git show-ref master as refs/tags/master. The fix in this case was:

git tag -d master

Check your .git/config file. You may run into this problem if you have more than one remote repo configured with the same:

fetch = +refs/heads/*:refs/remotes/origin/*.

The other remote server should have a different name, eg.:

fetch = +refs/heads/*:refs/remotes/another_repo/*

If the .git directory itself contains a ref called master, i.e. .git/master, you will see the same error message. The nasty issue here is that you won't get this ref reported by commands like git branch -a nor git show-ref master. (git version 2.30.0.windows.2)