Git: warning: refname 'master' is ambiguous

I saw a few people asking the same question on here but it seems none of their advice is applicable to me. I'm getting the warning that is in the title of this but I don't have any tags named "master". This is the result of git branch -a:

* master
  remotes/origin/HEAD -> origin/master
  remotes/origin/master

Any idea what could be going wrong here? I've only been using git for a few months now, so it mostly just worries me that this ambiguity might mess with the repo in the future.

For me I tracked down the source of this warning to much earlier when I incorrectly issued an "update-ref" command. If you forget to specify the full refs/heads/mybranchname path in the first arg, then a file .git/mybranchname gets created, which later leads to this warning when you try to switch to that branch.

It is solved by simply deleting the .git/mybranchname, eg:

rm .git/master

And for reference, the correct form for the update-ref command is:

git update-ref refs/heads/mybranchname mytargetbranch

Don't forget the "refs/heads" part!

Also, my most common use-case for update-ref is simply manually moving a branch to point to another commit, which I've found a simpler syntax to do:

git branch -f myBranchToMove destinationBranchOrHash

This syntax is easier for me because it doesn't require that error-prone refs/heads path qualifier.

As detailed in "Git: refname 'master' is ambiguous", that means that, beside heads/master, you have another master in one of the following namespace within the git repo:

refs/<refname> 
refs/tags/<refname>
refs/heads/<refname>
refs/remotes/<refname>
refs/remotes/<refname>/HEAD

Or even ./<refname>, as mentioned in Magnus's answer.

For future reference, I had the same issue and what ended up to work for me was the solution described here. Basically, when you get Git: warning: refname 'xxx' is ambiguous warning, you can use: git show-ref xxx to check the references to xxx branch and validate which ones are having conflict.

In my scenario, it was a tag named xxx and branch name with the same name. The tag had been made by mistake and was removed from server so all I needed to do was to update my local tag to match the server: git fetch -p -P. This command is explained in details here

I had a similar problem (not master) when I created a branch with the same name as a tag.

This helped me remove the tag https://stackoverflow.com/a/5480292/150953

git push --delete origin tagname

git fetch --prune

git pull origin branch-name

should fix your problem.

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/*