git push: refs/heads/my/subbranch exists, cannot create

It's not a folder that exists, it's a branch. (Well, there may be a folder/directory involved somewhere—or maybe not, as references get "packed" and stop existing as files within directories.)

• If branch b exists, no branch named b/anything can be created.
• Likewise, if branch dev/b exists, dev/b/c cannot be created.

This is a git internal limitation. In this particular case, remote origin has a branch named dev/sub (regardless of whether you have it or not, the important thing is whether the remote has it). In order to create, on origin, a branch named dev/sub/master, you must first delete the branch named dev/sub on origin:

git push origin :dev/sub

(Of course, deleting this branch may delete something important over there, so be sure you know what you are doing. Generally, you might want to git fetch origin first, capturing their dev/sub as your origin/dev/sub. You can then make a local branch named dev/renamed-sub pointing to the same commit, create dev/renamed-sub on the remote, delete the remote dev/sub, and then create dev/sub/master on the remote.)

If you can log in on the remote (the system that origin is hosted on), you can go into the repository over there and simply rename the local dev/sub branch. (Based on comments below, I suspect that there's a broken auto-deploy script over there as well, which probably should be fixed to only deploy "deployable" branches, rather than everything that gets pushed. But I am just guessing here.)

I was in a state when I couldn't even fetch because my repo had info about non-existing remote branches I didn't even had checked out. I solved it by running combination (thanks @torek) of:

• git branch -r list local copies of remote branches
• git ls-remote list remote branches
• git fetch --prune origin update local copies of remote branches (this actually didn't help me)
• git remote prune origin remove info about removed remote branches (this did)

For me -->

Error =

fatal: cannot lock ref 'refs/heads/release/wl/2.3': 'refs/heads/release/wl' 
exists; cannot create 'refs/heads/release/wl/2.3'

Solution =

$~ git update-ref -d refs/heads/release/wl
$~ git checkout release/wl/2.3

The currently accepted answer didn't help me because I didn't have a ref on the remote repo to delete - it was purely on my local! So if you're in that situation, here's what to do:

This is the issue I was facing:

$ git fetch origin
error: cannot lock ref 'refs/remotes/origin/fix/sub-branch': 
'refs/remotes/origin/fix' exists; cannot create 
'refs/remotes/origin/fix/sub-branch'
From <repo URL>
 ! [new branch]      fix/sub-branch          -> origin/fix/sub-branch
 (unable to update local ref)

I tried the accepted answer's suggestion but got this:

$ git push origin :fix
error: unable to delete 'fix': remote ref does not exist
error: failed to push some refs to <repo URL>

So the ref didn't even exist on origin - it was clearly just hanging around somewhere on my local repo. So I ran $ git remote show me, which produced:

Remote branches:
...
refs/remotes/origin/fix             stale (use 'git remote prune' to remove)
...

Which then made the solution clear:

$ git remote prune origin
Pruning origin
URL: <redacted>
 * [pruned] origin/fix

With this, the problem disappeared:

$ git fetch origin
remote: Counting objects: 5, done.
remote: Total 5 (delta 2), reused 2 (delta 2), pack-reused 3
Unpacking objects: 100% (5/5), done.
From <repo URL>
 * [new branch]      fix/sub-branch          -> origin/fix/sub-branch

Try this command to fix it:

git gc

to run a number of housekeeping tasks within the current repository and remove unreachable objects (by invoking git prune and git fsck --unreachable).

Read more: git help gc and git help prune