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 │ Not encrypted, but │ Encrypted (AEAD w/ │
│ │ auth │ 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