Sometimes it may happen that you have multiple git-annex repositories with the same UUID. This is usually because you did something special, like copying a repository with cp -a or dd instead of cloning it, or you just replaced a drive with a fresh one. In my case, the latter happened: I ran out of space on my media drive and replaced it with a larger drive. Since it had multiple git-annex repositories (and data not managed by git-annex), I simply used rsync to copy the drive over, which created duplicate git-annex repositories with the same UUIDs.

It may still be useful to reuse those repositories as distinct entities, and it is therefore important to assign new UUIDs to those cloned repositories so that content tracking works properly and you do not lose data.

In this case, you actually do not want to specify an existing UUID when you run reinit: you want git-annex to generate a new one for you. So, in that context, I've always wondered why git-annex-reinit absolutely requires an argument. I understand there may be other use cases where you may want to reinit a repository to an existing UUID, but that seems like a much less common use case, and one that may bring more trouble than is worth.

So I believe there should be an easy way to assign a fresh new UUID to a repository. reinit should allow doing that when no arguments are given: it should show the old and new UUID and maybe a warning message indicating that tracking information may be wrong now if the old UUID is not in use anymore.

As shown below, I also wonder if reinit should recommend the user perform a fsck to make sure the location logs reflect the change...

Workaround

It is obviously possible to assign a new UUID with the current command, by generating one by hand.

Git-annex doesn't have a user-visible way of generating a new UUID, so we'll have to improvise something. It uses the Data.UUID Haskell module, in V4 mode, which is the standard, random way of generating UUIDs. I believe that the uuidgen command, when ran in --random mode, will produce similarly unique UUIDs that are good enough for our purpose. So I have used this to reassign new UUIDs to cloned copies of repositories:

git annex reinit $(uuidgen)

The next step is to fix the location log so that the UUID change is reflected in the tracking information:

git annex fsck --fast

You may also want to set a new description for the new clone:

git annex describe here "bare 2TB Seagate barracuda HD"

Then, optionally, you will want to propagate that change to other repositories:

git annex sync

Thanks for any feedback or comments... -- anarcat