Quick Start

This chapter will get you started with Borg and covers various use cases.

A step by step example

  1. Before a backup can be made a repository has to be initialized:

    $ borg init --encryption=repokey /path/to/repo
    
  2. Backup the ~/src and ~/Documents directories into an archive called Monday:

    $ borg create /path/to/repo::Monday ~/src ~/Documents
    
  3. The next day create a new archive called Tuesday:

    $ borg create --stats /path/to/repo::Tuesday ~/src ~/Documents
    

    This backup will be a lot quicker and a lot smaller since only new never before seen data is stored. The --stats option causes Borg to output statistics about the newly created archive such as the amount of unique data (not shared with other archives):

    ------------------------------------------------------------------------------
    Archive name: Tuesday
    Archive fingerprint: bd31004d58f51ea06ff735d2e5ac49376901b21d58035f8fb05dbf866566e3c2
    Time (start): Tue, 2016-02-16 18:15:11
    Time (end):   Tue, 2016-02-16 18:15:11
    
    Duration: 0.19 seconds
    Number of files: 127
    ------------------------------------------------------------------------------
                          Original size      Compressed size    Deduplicated size
    This archive:                4.16 MB              4.17 MB             26.78 kB
    All archives:                8.33 MB              8.34 MB              4.19 MB
    
                          Unique chunks         Total chunks
    Chunk index:                     132                  261
    ------------------------------------------------------------------------------
    
  4. List all archives in the repository:

    $ borg list /path/to/repo
    Monday                               Mon, 2016-02-15 19:14:44
    Tuesday                              Tue, 2016-02-16 19:15:11
    
  5. List the contents of the Monday archive:

    $ borg list /path/to/repo::Monday
    drwxr-xr-x user   group          0 Mon, 2016-02-15 18:22:30 home/user/Documents
    -rw-r--r-- user   group       7961 Mon, 2016-02-15 18:22:30 home/user/Documents/Important.doc
    ...
    
  6. Restore the Monday archive by extracting the files relative to the current directory:

    $ borg extract /path/to/repo::Monday
    
  7. Recover disk space by manually deleting the Monday archive:

    $ borg delete /path/to/repo::Monday
    

Note

Borg is quiet by default (it works on WARNING log level). You can use options like --progress or --list to get specific reports during command execution. You can also add the -v (or --verbose or --info) option to adjust the log level to INFO to get other informational messages.

Important note about free space

Before you start creating backups, please make sure that there is always a good amount of free space on the filesystem that has your backup repository (and also on ~/.cache). A few GB should suffice for most hard-drive sized repositories. See also Indexes / Caches memory usage.

Borg doesn’t use space reserved for root on repository disks (even when run as root), on file systems which do not support this mechanism (e.g. XFS) we recommend to reserve some space in Borg itself just to be safe by adjusting the additional_free_space setting (a good starting point is 2G):

borg config /path/to/repo additional_free_space 2G

If Borg runs out of disk space, it tries to free as much space as it can while aborting the current operation safely, which allows the user to free more space by deleting/pruning archives. This mechanism is not bullet-proof in some circumstances [1].

If you really run out of disk space, it can be hard or impossible to free space, because Borg needs free space to operate - even to delete backup archives.

You can use some monitoring process or just include the free space information in your backup log files (you check them regularly anyway, right?).

Also helpful:

  • create a big file as a “space reserve”, that you can delete to free space
  • if you use LVM: use a LV + a filesystem that you can resize later and have some unallocated PEs you can add to the LV.
  • consider using quotas
  • use prune regularly
[1]

This failsafe can fail in these circumstances:

  • The underlying file system doesn’t support statvfs(2), or returns incorrect data, or the repository doesn’t reside on a single file system
  • Other tasks fill the disk simultaneously
  • Hard quotas (which may not be reflected in statvfs(2))

Automating backups

The following example script is meant to be run daily by the root user on different local machines. It backs up a machine’s important files (but not the complete operating system) to a repository ~/backup/main on a remote server. Some files which aren’t necessarily needed in this backup are excluded. See borg help patterns on how to add more exclude options.

After the backup this script also uses the borg prune subcommand to keep only a certain number of old archives and deletes the others in order to preserve disk space.

Before running, make sure that the repository is initialized as documented in Remote repositories and that the script has the correct permissions to be executable by the root user, but not executable or readable by anyone else, i.e. root:root 0700.

You can use this script as a starting point and modify it where it’s necessary to fit your setup.

Do not forget to test your created backups to make sure everything you need is being backed up and that the prune command is keeping and deleting the correct backups.

#!/bin/sh

# Setting this, so the repo does not need to be given on the commandline:
export BORG_REPO=ssh://username@example.com:2022/~/backup/main

# Setting this, so you won't be asked for your repository passphrase:
export BORG_PASSPHRASE='XYZl0ngandsecurepa_55_phrasea&&123'
# or this to ask an external program to supply the passphrase:
export BORG_PASSCOMMAND='pass show backup'

# some helpers and error handling:
info() { printf "\n%s %s\n\n" "$( date )" "$*" >&2; }
trap 'echo $( date ) Backup interrupted >&2; exit 2' INT TERM

info "Starting backup"

# Backup the most important directories into an archive named after
# the machine this script is currently running on:

borg create                         \
    --verbose                       \
    --filter AME                    \
    --list                          \
    --stats                         \
    --show-rc                       \
    --compression lz4               \
    --exclude-caches                \
    --exclude '/home/*/.cache/*'    \
    --exclude '/var/cache/*'        \
    --exclude '/var/tmp/*'          \
                                    \
    ::'{hostname}-{now}'            \
    /etc                            \
    /home                           \
    /root                           \
    /var                            \

backup_exit=$?

info "Pruning repository"

# Use the `prune` subcommand to maintain 7 daily, 4 weekly and 6 monthly
# archives of THIS machine. The '{hostname}-' prefix is very important to
# limit prune's operation to this machine's archives and not apply to
# other machines' archives also:

borg prune                          \
    --list                          \
    --prefix '{hostname}-'          \
    --show-rc                       \
    --keep-daily    7               \
    --keep-weekly   4               \
    --keep-monthly  6               \

prune_exit=$?

# use highest exit code as global exit code
global_exit=$(( backup_exit > prune_exit ? backup_exit : prune_exit ))

if [ ${global_exit} -eq 1 ];
then
    info "Backup and/or Prune finished with a warning"
fi

if [ ${global_exit} -gt 1 ];
then
    info "Backup and/or Prune finished with an error"
fi

exit ${global_exit}

Pitfalls with shell variables and environment variables

This applies to all environment variables you want Borg to see, not just BORG_PASSPHRASE. The short explanation is: always export your variable, and use single quotes if you’re unsure of the details of your shell’s expansion behavior. E.g.:

export BORG_PASSPHRASE='complicated & long'

This is because export exposes variables to subprocesses, which Borg may be one of. More on export can be found in the “ENVIRONMENT” section of the bash(1) man page.

Beware of how sudo interacts with environment variables. For example, you may be surprised that the following export has no effect on your command:

export BORG_PASSPHRASE='complicated & long'
sudo ./yourborgwrapper.sh  # still prompts for password

For more information, refer to the sudo(8) man page and env_keep in the sudoers(5) man page.

Tip

To debug what your borg process is actually seeing, find its PID (ps aux|grep borg) and then look into /proc/<PID>/environ.

Backup compression

The default is lz4 (very fast, but low compression ratio), but other methods are supported for different situations.

If you have a fast repo storage and you want minimum CPU usage, no compression:

$ borg create --compression none /path/to/repo::arch ~

If you have a less fast repo storage and you want a bit more compression (N=0..9, 0 means no compression, 9 means high compression):

$ borg create --compression zlib,N /path/to/repo::arch ~

If you have a very slow repo storage and you want high compression (N=0..9, 0 means low compression, 9 means high compression):

$ borg create --compression lzma,N /path/to/repo::arch ~

You’ll need to experiment a bit to find the best compression for your use case. Keep an eye on CPU load and throughput.

Repository encryption

Repository encryption can be enabled or disabled at repository creation time (the default is enabled, with repokey method):

$ borg init --encryption=none|repokey|keyfile PATH

When repository encryption is enabled all data is encrypted using 256-bit AES encryption and the integrity and authenticity is verified using HMAC-SHA256.

All data is encrypted on the client before being written to the repository. This means that an attacker who manages to compromise the host containing an encrypted archive will not be able to access any of the data, even while the backup is being made.

Borg supports different methods to store the AES and HMAC keys.

repokey mode
The key is stored inside the repository (in its “config” file). Use this mode if you trust in your good passphrase giving you enough protection. The repository server never sees the plaintext key.
keyfile mode
The key is stored on your local disk (in ~/.config/borg/keys/). Use this mode if you want “passphrase and having-the-key” security.

In both modes, the key is stored in encrypted form and can be only decrypted by providing the correct passphrase.

For automated backups the passphrase can be specified using the BORG_PASSPHRASE environment variable.

Note

Be careful about how you set that environment, see this note about password environments for more information.

Warning

The repository data is totally inaccessible without the key and the key 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 your passphrase at a safe place.

You can make backups using borg key export subcommand.

If you want to print a backup of your key to paper use the --paper option of this command and print the result, or this print template if you need a version with QR-Code.

A backup inside of the backup that is encrypted with that key/passphrase won’t help you with that, of course.

Remote repositories

Borg can initialize and access repositories on remote hosts if the host is accessible using SSH. This is fastest and easiest when Borg is installed on the remote host, in which case the following syntax is used:

$ borg init user@hostname:/path/to/repo

Note: please see the usage chapter for a full documentation of repo URLs.

Remote operations over SSH can be automated with SSH keys. You can restrict the use of the SSH keypair by prepending a forced command to the SSH public key in the remote server’s authorized_keys file. This example will start Borg in server mode and limit it to a specific filesystem path:

command="borg serve --restrict-to-path /path/to/repo",restrict ssh-rsa AAAAB3[...]

If it is not possible to install Borg on the remote host, it is still possible to use the remote host to store a repository by mounting the remote filesystem, for example, using sshfs:

$ sshfs user@hostname:/path/to /path/to
$ borg init /path/to/repo
$ fusermount -u /path/to

You can also use other remote filesystems in a similar way. Just be careful, not all filesystems out there are really stable and working good enough to be acceptable for backup usage.