git-annex/ special remotes/ git-lfs

git-annex has a special remote that lets it store content in git-lfs repositories.

See storing data in git-lfs for some examples of how to use this.

## configuration

These parameters can be passed to `git annex initremote` to configure the git-lfs special remote:

- `url` - Required. The url to the git-lfs repository to use. Can be either a ssh url (scp-style is also accepted) or a https url.

- `encryption` - One of "none", "hybrid", "shared", or "pubkey". Required. See encryption. Also see the encryption notes below.

- `keyid` - Specifies the gpg key to use for encryption of both the files git-annex stores in the repository, as well as to encrypt the git repository itself when using gcrypt.

- `apiurl` - Optional. The url to the LFS API endpoint. This can be a https or a http url. When this is not specified, or is not set to an url, the API endpoint url is guessed based on the url parameter.

## efficiency note

Since git-lfs uses SHA256 checksums, git-annex needs to keep track of the SHA256 of content stored in it, in order to be able to retrieve that content. When a git-annex key uses a backend of SHA256 or SHA256E, that's easy. But, if a git-annex key uses some other backend, git-annex has to additionally store the SHA256 checksum into the git-annex branch when storing content in git-lfs. That adds a small bit of size overhead to using this remote.

When encrypting data sent to the git-lfs remote, git-annex always has to store its SHA256 checksum in the git-annex branch.

## encryption notes

To encrypt a git-lfs repository, there are two separate things that have to be encrypted: the data git-annex stores there, and the content of the git repository itself. After all, a git-lfs remote is a git remote and git push doesn't encrypt data by default.

To encrypt your git pushes, you can use git-remote-gcrypt and prefix the repository url with "gcrypt::"

To make git-annex encrypt the data it stores, you can use the encryption= configuration.

An example of combining the two:

    git annex initremote lfstest type=git-lfs url=gcrypt::git@github.com:username/somerepo.git encryption=shared

In that example, the git-annex shared encryption key is stored in git, but that's ok because git push will encrypt it, along with all the other git data, using your gpg key. You could instead use "encryption=shared keyid=" to make git-annex and gcrypt both encrypt to a specified gpg key.

git-annex will detect if one part of the repository is encrypted, but you forgot to encrypt the other part, and will refuse to set up such an insecure half-encrypted repository.

If you use encryption=hybrid, you can later add more gpg keys that can access the files git-annex stored in the git-lfs repository. However, due to the way git-remote-gcrypt encrypts the git repository, you will need to somehow force it to re-push everything again, so that the encrypted repository can be decrypted by the added keys. Probably this can be done by setting `GCRYPT_FULL_REPACK` and doing a forced push of branches.

git-annex will set `remote.<name>`gcrypt-publish-participants` when setting up a repository that uses gcrypt. This is done to avoid unnecessary gpg passphrase prompts, but it does publish the gpg keyids that can decrypt the repository. Unset it if you need to obscure that.

## limitations

The git-lfs protocol does not support deleting content, so git-annex cannot delete anything from a git-lfs special remote.

The git-lfs protocol does not support resuming uploads, and so an interrupted upload will have to restart from the beginning. Interrupted downloads will resume.

git-lfs has a concept of git ref based access control, so a user may only be able to send content associated with a particular git ref. git-annex does not currently provide any git ref, so won't work with a git-lfs server that uses that.

git-annex only supports the "basic" git-lfs transfer adapter, but that's the one used by most git-lfs servers.

The git-lfs protocol is designed around batching of transfers, but git-annex doesn't do batching. This may cause it to fall afoul of rate limiting of git-lfs servers when transferring a lot of files.

Comments on this page are closed.