Ubuntu Manpage: borg-init - Initialize an empty repository

Provided by: borgbackup_1.1.15-1~ubuntu1.18.04.2_amd64

NAME

       borg-init - Initialize an empty repository

SYNOPSIS

       borg [common options] init [options] [REPOSITORY]

DESCRIPTION

This command initializes an empty repository. A repository is a filesystem directory containing the
deduplicated data from zero or more archives.

Encryption can be enabled at repository init time. It cannot be changed later.

It is not recommended to work without encryption. Repository encryption protects you e.g. against the
case that an attacker has access to your backup repository.

Borg relies on randomly generated key material and uses that for chunking, id generation, encryption and
authentication. The key material is encrypted using the passphrase you give before it is stored on-disk.

You need to be careful with the key / the passphrase:

If you want "passphrase-only" security, use one of the repokey modes. The key will be stored inside the
repository (in its "config" file). In above mentioned attack scenario, the attacker will have the key
(but not the passphrase).

If you want "passphrase and having-the-key" security, use one of the keyfile modes. The key will be
stored in your home directory (in .config/borg/keys). In the attack scenario, the attacker who has just
access to your repo won't have the key (and also not the passphrase).

Make a backup copy of the key file (keyfile mode) or repo config file (repokey mode) and keep it at a
safe place, so you still have the key in case it gets corrupted or lost. Also keep the passphrase at a
safe place. The backup that is encrypted with that key won't help you with that, of course.

Make sure you use a good passphrase. Not too short, not too simple. The real encryption / decryption key
is encrypted with / locked by your passphrase. If an attacker gets your key, he can't unlock and use it
without knowing the passphrase.

Be careful with special or non-ascii characters in your passphrase:

• Borg processes the passphrase as unicode (and encodes it as utf-8), so it does not have problems
dealing with even the strangest characters.

• BUT: that does not necessarily apply to your OS / VM / keyboard configuration.

So better use a long passphrase made from simple ascii chars than one that includes non-ascii stuff or
characters that are hard/impossible to enter on a different keyboard layout.

You can change your passphrase for existing repos at any time, it won't affect the encryption/decryption
key or other secrets.

Encryption modes
You can choose from the encryption modes seen in the table below on a per-repo basis. The mode determines
encryption algorithm, hash/MAC algorithm and also the key storage location.

Example: borg init --encryption repokey ...
┌──────────┬───────────────────────┬────────────────────────┬────────────────────────┐
│ Hash/MAC │ Not encrypted no auth │ Not encrypted, but │ Encrypted (AEAD w/ │
│ │ │ authenticated │ AES) and authenticated │
├──────────┼───────────────────────┼────────────────────────┼────────────────────────┤
│ SHA-256 │ none │ authenticated │ repokey keyfile │
├──────────┼───────────────────────┼────────────────────────┼────────────────────────┤
│ BLAKE2b │ n/a │ authenticated-blake2 │ repokey-blake2 │
│ │ │ │ keyfile-blake2 │
└──────────┴───────────────────────┴────────────────────────┴────────────────────────┘

Modes marked like this in the above table are new in Borg 1.1 and are not backwards-compatible with Borg
1.0.x.

On modern Intel/AMD CPUs (except very cheap ones), AES is usually hardware-accelerated. BLAKE2b is
faster than SHA256 on Intel/AMD 64-bit CPUs (except AMD Ryzen and future CPUs with SHA extensions), which
makes authenticated-blake2 faster than none and authenticated.

On modern ARM CPUs, NEON provides hardware acceleration for SHA256 making it faster than BLAKE2b-256
there. NEON accelerates AES as well.

Hardware acceleration is always used automatically when available.

repokey and keyfile use AES-CTR-256 for encryption and HMAC-SHA256 for authentication in an
encrypt-then-MAC (EtM) construction. The chunk ID hash is HMAC-SHA256 as well (with a separate key).
These modes are compatible with Borg 1.0.x.

repokey-blake2 and keyfile-blake2 are also authenticated encryption modes, but use BLAKE2b-256 instead of
HMAC-SHA256 for authentication. The chunk ID hash is a keyed BLAKE2b-256 hash. These modes are new and
not compatible with Borg 1.0.x.

authenticated mode uses no encryption, but authenticates repository contents through the same HMAC-SHA256
hash as the repokey and keyfile modes (it uses it as the chunk ID hash). The key is stored like repokey.
This mode is new and not compatible with Borg 1.0.x.

authenticated-blake2 is like authenticated, but uses the keyed BLAKE2b-256 hash from the other blake2
modes. This mode is new and not compatible with Borg 1.0.x.

none mode uses no encryption and no authentication. It uses SHA256 as chunk ID hash. This mode is not
recommended, you should rather consider using an authenticated or authenticated/encrypted mode. This mode
has possible denial-of-service issues when running borg create on contents controlled by an attacker.
Use it only for new repositories where no encryption is wanted and when compatibility with 1.0.x is
important. If compatibility with 1.0.x is not important, use authenticated-blake2 or authenticated
instead. This mode is compatible with Borg 1.0.x.

OPTIONS

       See borg-common(1) for common options of Borg commands.

   arguments
       REPOSITORY
              repository to create

   optional arguments
       -e MODE, --encryption MODE
              select encryption key mode (required)

       --append-only
              create an append-only mode repository

       --storage-quota QUOTA
              Set storage quota of the new repository (e.g. 5G, 1.5T). Default: no quota.

       --make-parent-dirs
              create the parent directories of the repository directory, if they are missing.

EXAMPLES

          # Local repository, repokey encryption, BLAKE2b (often faster, since Borg 1.1)
          $ borg init --encryption=repokey-blake2 /path/to/repo

          # Local repository (no encryption)
          $ borg init --encryption=none /path/to/repo

          # Remote repository (accesses a remote borg via ssh)
          # repokey: stores the (encrypted) key into <REPO_DIR>/config
          $ borg init --encryption=repokey-blake2 user@hostname:backup

          # Remote repository (accesses a remote borg via ssh)
          # keyfile: stores the (encrypted) key into ~/.config/borg/keys/
          $ borg init --encryption=keyfile user@hostname:backup

AUTHOR