This server includes private MRI and microscopy datasets, which have been curated and organized according to the BIDS convention.

git+ssh:// has a max size of ~1TB.

It hosts BIDS datasets, version-controlled using git-annex. It is locked behind a VPN because much of our data is under medical ethics protections, and needs to be kept off the general internet.

Initial setup#


  1. You must have a *nix OS with git-annex>=8 installed. See git-annex installation.

  2. Make sure you have an ssh key.

    • If not, run ssh-keygen -t ed25519 -C Your keys will be in the hidden folder ~/.ssh/.

Getting an account#

Send your ssh public key – that is, the contents of ~/.ssh/ or ~/.ssh/ (the .pub file) – to one of the server admins and ask them to create your account.

A pubkey should look like

ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDE+b5vj+WvS5l6j56NF/leMpC2xT7JUCMUWDAqvWoVmNZ7UR3dGXQeTPTlmPmxPGD2Hk9/zFzxO2kYOt9o4lHQ0QQSKLUmTyuieyJE26wL1ZiLilmTgvgMxxkxvInF/Vr78V5Ll72zAmXzUxVSvuDGY2GRjnLreYheiqg1F3xTuD68uWInX8ZwA7NDtKpoZ7Aat063vD79WBrtiCfvAMbM8QhC3294zxqAjjy9fxs+TMTqAxtKdaWCA/eCs7sx9uvtFcj2Q9jxCMB3br5HyPLotgJMoIMt+fywj+vQG907LODRcqm9J0+ih+38/3Y6aqECMkHA9WWIfFywwjeA7EGr


ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIJwsjlem+acuTOZGyNQKjyI7kJe9ULkhZo7N04QfC/tA

Current server admins are:







The admins should follow Admin Guide > Add Users to create your account.

Connecting to

Because this server contains private medical data, you need to be on campus, connected to the VPN, or working from a server on campus, like joplin or rosenberg to access it.

If connecting from off-campus, connect to polyvpn.

🏚️ Verify connectivity by running ping If you cannot ping then you need to double-check your VPN connection; make sure it is connected, make sure you can reach joplin, and if it still isn’t working ask the Poly network admins to unblock your account from this server.

Verify you can use the server by running ssh help. If it hangs, triple-check again your VPN. If it asks for's password, double-check that ls -la ~/.ssh shows permissions of drwx------ for the . folder, and that the files id_ed25519 and (or id_rsa and exist with exactly those names. A successful connection looks like:

$ ssh help
Enter passphrase for key '/home/kousu/.ssh/id_ed25519.neuropoly': 
hello yourusername, this is git@data running gitolite3 3.6.11-2 (Debian) on git 2.27.0

list of remote commands available:



During daily usage, you will need to be on the polyvpn network.

You should also make sure to configure git annex for the best performance.


To see what datasets you have available, use info, for example:

ssh info

And the output would look like this:

hello yourusername, this is git@data running gitolite3 3.6.11-2 (Debian) on git 2.27.0
 R      datasets/..*
 R      datasets/basel-mp2rage
 R W    datasets/bavaria-quebec-spine-ms

You are identified to the server by your ssh keys, but notice that this tells you the username you are known as.


To download an existing repository use git clone:

git clone # download folders and metadata
cd sct-testing-large
git annex get .                                                # download images

If you just want to explore, you can opt for a portion of the image files by specifying paths instead of the last step, for example:

git annex get sub-karo*                                        # download images under any of sub-karo*/*


If you have already cloned a repository and you would like to get its latest version, do:

git pull && git annex sync --no-content && git annex get .


Despite not being hosted on Github, we are still using a pull-request workflow. So, to make changes to a dataset, first ask an admin to grant you upload rights, then make a working branch for your changes. If your initials are xy and you are working on some-topic:

git checkout -b xy/some-topic
# Edit your files, add new ones, etc. 
# Add all modified files to be commited
git add .
# To add specific files, do: git add path/to/new/file
# Commit and write a useful commit message
git commit

The first time before uploading, verify you have access with info. You need “W” (for “Write”) permission, like this:

ssh info datasets/uk-biobank

The output would look like:

hello yourusername, this is git@data running gitolite3 3.6.11-2 (Debian) on git 2.27.0

 R W    datasets/uk-biobank

Once you have access you can:

git annex copy --to=origin
git annex sync --no-content --only-annex
git push

Finally, ask one of that dataset’s reviewers to look at your pull request by opening an issue on neuropoly/data-management.

Reviewing Pull Requests#

If someone asks you to review their changes on branch xy/some-topic:

git fetch
git checkout xy/some-topic
git annex get .

Then look at the branch to see if it looks right to you.

To investigate what changed:

git log --stat master..HEAD # to see filenames
git log -p master..HEAD     # to see content, commit-by-commit
git diff master..HEAD       # to see content, overall

Also, it’s a good idea to run:

git annex whereis

To check that all the annexed files have been uploaded.

🏚️ git-annex is not well-suited to a pull-request flow. It is mostly designed for a single person to share data among many computers, not for multiple people to share data between a few computers. We can make it work but it needs some patience. Have a cat to make it better: 🐈🌺

Commit Rights#

Each repo has its own OWNERS group attached. These are the people allowed to commit to master, and usually they should be the reviewers as well.

In order to join this group, someone already in it needs to grant you access:

ssh perms datasets/my-new-repo + OWNERS yourusername

You can check if you have commit rights to a dataset “my-new-repo” by seeing if you appear in the group:

ssh perms datasets/my-new-repo -l | grep OWNERS


Once a branch is finalized:

git checkout master
git merge --ff-only xy/some-topic # or use git pull --squash xy/some-topic
git push  # no need for git-annex sync here, no annex files have been moved

(Optional) Clean up the branch:

git branch -d xy/some-topic
git branch -d synced/xy/some-topic   # redundancy
git push origin :xy/some-topic
git push origin :synced/xy/some-topic

New repository#

To make a new repo, follow this recipe.

Then, to upload it, pick a name under datasets/, e.g. “my-new-repo”, and do

git remote add origin
git branch -M master
git push -u origin master                 # initialize remote and upload metadata
git annex sync --cleanup -a --no-content  # initialize remote annex
git annex copy --to origin                # upload images to remote annex
# verify your .nii.gz files were annexed and uploaded
git annex whereis


To make a release, use an annotated git tag. Use the tag name for the name of the release, and the annotation for the release notes. Our naming convention for datasets is “rYYYYMMDD”.

For example, if today is September 8th, 2019, then to create a release do:

git tag -a r20190908

To view available releases, first download a dataset, then run

git tag -l

To see the release notes for a specific release, use

git show r20190908

To use a specific release, either download the dataset and then

git checkout r20190908

or, for example in a reproducible processing script, you can use clone -b to download only that specific release:

git clone --depth 1 -b r20190908


You can grant others permissions to your repositories with perms.

ssh perms datasets/my-new-repo + WRITERS someone # grant someone upload rights
ssh perms datasets/my-new-repo - WRITERS someone # revoke someone's upload rights
ssh perms datasets/my-new-repo + OWNERS researcher2 # grant someone rights to add (and remove) others and to merge to master
ssh perms datasets/my-new-repo -l # view users
ssh perms datasets/my-new-repo -lr # view access rules


ssh perms -h

and see for full details.


There is no way for a user to rename a repo directly (bug report). You can ask an admin to do it.


If you created or own a repo and decide it is no longer necessary:

ssh D trash repo

The “trash” is cleaned out after a week. Except it’s not, yet:

Add extra devices#

Like with Github, you can authorize any number of secondary devices.

For example, to authorize yourself from server2, log in to server2 and make an ssh key if one doesn’t exist (ssh-keygen), copy it (~/.ssh/ to a device that is already authenticated (e.g. as ~/, then authorize yourself by:

cat ~/ | ssh keys add @server2

Test it by running, from server2

ssh info

Admin Guide#

We are using Gitolite with git-annex as our dataset server. It is compatible with datalad but to reduce the fragility we only support the basics.

Datasets are stored as git repositories on the server, with the bulk of their data also stored on the server in each repo’s “annex” folder. Using git-annex enables data on-demand – in our default configuration, only the data needed for the active branch is actually downloaded by a user, and it is also possible for the user to choose specific folders to focus on. Datasets are git-annex ssh remotes.

gitolite manages users and their permissions. The repositories containing datasets are under*, and the server also contains a few admin-only repositories outside of datasets/*.

The VM is monitored here (requires VPN to connect to the dashboard monitor).

List users#

ssh keys list

Add users#

To grant access to a lab member, as above, ask the lab member to generate an ssh key using ssh-keygen and have them send you the public key. Save it to a file and add them with

cat | ssh keys add firstnamelastname

You can also paste the key in, followed by ctrl-d; this looks like:

ssh keys add firstnamelastname

The output looks like:

Enter passphrase for key '/home/kousu/.ssh/id_rsa.github': 
please supply the new key on STDIN (e.g. cat | ssh keys add @laptop).
ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAID11N3hQpJP4Okivd5xO3N0CuO24ioMwXYv+l/1PM/+z
Added SHA256:hwil2tmaw/prgIBX5odO8vOAj2i38gPrUGjGZnnkVvo :

You should use the person’s full name as their username, in the form firstnamelastname, with no spaces or periods or anything. It’s essentially an arbitrary string that the user doesn’t really need to know, since everyone is authenticated using just their public/private keys without supplying a username. The only time users see them is when they run info or use perms. We would like to use the format, but there is a bug, so just use firstnamelastname. Once someone is registered they can add and remove their own keys without having to know their username.


As admin, you can add or revoke any permissions to any repo using perms.

There is unfortunately no way to view permissions as another user so you will need to rely on people sending you screenshots if they are having problems but you can at least inspect the active sets of permissions on a repo with

ssh perms <repo> -l

If you need to add new namespaces or finer grained permissions, first, reconsider if the extra complexity and the risk of locking yourself out is worth it. Everything you should need to manage the lab should be doable via ssh help. If you are sure, then review gitolite’s permissions model and official docs for this use case, then:

git clone
cd gitolite-admin
vi conf/gitolite.conf  # optional: investigate/change the repo definitions
ls -R keydir/          # optional: investigate/change who has access; this *should* be unnecessary, use `keys` as above instead.
git add -u . && git push


As an admin, you can rename a repo by connecting to the server directly:

sudo -u git -i
cd repositories/datasets/
mv $dataset.git $new_name.git


You can also delete any repo using D.

You can also get rid of a dataset immediately by:

ssh D unlock datasets/<dataset>
ssh D rm datasets/<dataset>


Backups are automatically made to MIC-UNF’s servers.

except they’re not, yet:

You can access these if you need to recover by:



If you are having a problem, please open an issue here. Please don’t be shy, if you don’t report the issue, we won’t know about it and it will never be solved 😉

If the server is doing something strange, contact someone with sysadmin-access to the server.

These people can investigate by following the gitolote guide in the sysadmin docs.


  • Patel, Hiren - Wildrepos in Gitolite – detailing how a research lab manages their code and publications collaboratively through gitolite