Luca Boieru Luca Boieru - 3 months ago 17
Git Question

“tag already exists in the remote" error after recreating the git tag

I get the following error after I run the steps below:

To git@provider.com:username/repo-name.git
! [rejected] dev -> dev (already exists)
error: failed to push some refs to 'git@provider.com:username/repo-name.git'
hint: Updates were rejected because the tag already exists in the remote.



  1. Created the repository

  2. Cloned the repo on the local machine.

  3. Modified the README file, commited the changes and pushed the commit.

  4. Created tag
    dev
    :
    git tag dev

  5. Pushed tags:
    git push --tags

  6. Modified the README file, commited the changes and pushed the commit.

  7. Deleted tag
    dev
    , created it again and pushed tags:

    git tag -d dev
    git tag dev
    git push --tags



Why is this happening?

I am on Mac. My friends that use Linux (Ubuntu) don't have this problem. I know that I can use
git push --tags -f
to force the tag update, but this is dangerous (e.g. rewriting a commit made by mistake only in the tag, not in the branch).

Answer

When you ask to push tags, git push --tags sends (along with any commits and other objects needed and any other ref updates from the push settings) to the remote an update request of the form new-sha1 refs/tags/name. (Well, it sends however many: one of those for each tag.)

The update request is modified by the remote to add an old-sha1 (or again, one for each tag), then delivered to the pre-receive and/or update hooks (whichever hooks exist on the remote). Those hooks can decide whether to allow or reject the tag create/delete/update.

The old-sha1 value is the all-zeros "null" SHA-1 if the tag is being created. The new-sha1 is the null SHA-1 if the tag is being deleted. Otherwise both SHA-1 values are real, valid values.

Even with no hooks, there's a sort of "built-in hook" that is also run: the remote will refuse to move a tag unless you use the "force" flag (though the "built-in hook" is always OK with both "add" and "delete"). The rejection message you're seeing is coming from this built-in hook. (Incidentally, this same built-in hook also rejects branch updates that are not fast-forwards.)1

But—here's one of the keys to understanding what's going on—the git push step has no idea whether the remote has that tag now, and if so, what SHA-1 value it has. It only says "here's my complete list of tags, along with their SHA-1 values". The remote compares the values and if there are additions and/or changes, runs the hooks on those. (For tags that are the same, it does nothing at all. For tags you don't have that they do, it also does nothing!)

If you delete the tag locally, then push, your push simply does not transfer the tag. The remote assumes no change should be made.

If you delete the tag locally, then create it pointing to a new place, then push, your push transfers the tag, and the remote sees this as a tag-change and rejects the change, unless it's a force-push.

Thus, you have two options:

  • do a force-push, or
  • delete the tag on the remote.

The latter is possible via git push2 even though deleting the tag locally and pushing has no effect. Assuming the name of the remote is origin, and the tag you want it to delete is dev:

git push origin :refs/tags/dev

This asks the remote to delete the tag. The presence or absence of the tag dev in your local repository is irrelevant; this kind of push, with :remoteref as a refspec, is a pure-delete push.

The remote may or may not allow tag deletion (depending on any extra hooks added). If it allows the deletion, then the tag will be gone, and a second git push --tags, when you have a local dev tag pointing to some commit or annotated tag repo object, send your new dev tag. On the remote, dev will now be a newly created tag, so the remote will probably allow the push (again this depends on any extra hooks added).

The force-push is simpler. If you want to be sure not to update anything other than the tag, just tell git push to push only that one refspec:

git push --force origin refs/tags/dev:refs/tags/dev

(note: you don't need --tags if you're explicitly pushing just one tag ref-spec).


1Of course, the reason for this built-in hook is to help enforce the behavior that other users of that same remote-repo expect: that branches are not rewound, and tags do not move. If you force-push, you should let the other users know you are doing this, so that they can correct for it. Note that "tags don't move at all" is newly enforced by git 1.8.2; previous versions would allow the tag to "move forward" in the commit graph, much like branch names. See the git 1.8.2 release notes.

2It's trivial if you can log in on the remote. Just go to the git repository there and run git tag -d dev. Note that either way—deleting the tag on the remote, or using git push to delete it—there's a period of time when anyone who accesses the remote will find that the dev tag is missing.