This sections shows how to provide repository storage securely for users. Optionally, each user can have a storage quota.
Repositories are accessed through SSH. Each user of the service should have her own login which is only able to access the user’s files. Technically it would be possible to have multiple users share one login, however, separating them is better. Separate logins increase isolation and are thus an additional layer of security and safety for both the provider and the users.
For example, if a user manages to breach
borg serve then she can
only damage her own data (assuming that the system does not have further
Use the standard directory structure of the operating system. Each user is assigned a home directory and repositories of the user reside in her home directory.
~user/.ssh/authorized_keys file is the most important
piece for a correct deployment. It allows the user to log in via
their public key (which must be provided by the user), and restricts
SSH access to safe operations only.
command="borg serve --restrict-to-repository /home/<user>/repository",restrict
<key type> <key> <key host>
The text shown above needs to be written on a single line!
If this file should be automatically updated (e.g. by a web console), pay utmost attention to sanitizing user input. Strip all whitespace around the user-supplied key, ensure that it only contains ASCII with no control characters and that it consists of three parts separated by a single space. Ensure that no newlines are contained within the key.
restrict keyword enables all restrictions, i.e. disables port, agent
and X11 forwarding, as well as disabling PTY allocation and execution of ~/.ssh/rc.
If any future restriction capabilities are added to authorized_keys
files they will be included in this set.
command keyword forces execution of the specified command line
upon login. This must be
borg serve. The
option permits access to exactly one repository. It can be given
multiple times to permit access to more than one repository.
The repository may not exist yet; it can be initialized by the user, which allows for encryption.
Storage quotas can be enabled by adding the
borg serve command line:
restrict,command="borg serve --storage-quota 20G ..." ...
The storage quotas of repositories are completely independent. If a client is able to access multiple repositories, each repository can be filled to the specified quota.
If storage quotas are used, ensure that all deployed Borg releases support storage quotas.
Refer to Storage quotas for more details on storage quotas.
Specificities: Append-only repositories
borg init via a
borg serve --append-only server will not
create a repository that is configured to be append-only by its repository
--append-only arguments in
authorized_keys will override the
repository config, therefore append-only mode can be enabled on a key by key