The main goal of Borg is to provide an efficient and secure way to backup data. The data deduplication technique used makes Borg suitable for daily backups since only changes are stored. The authenticated encryption technique makes it suitable for backups to not fully trusted targets.

Borg stores a set of files in an archive. A repository is a collection of archives. The format of repositories is Borg-specific. Borg does not distinguish archives from each other in any way other than their name, it does not matter when or where archives were created (e.g. different hosts).

EXAMPLES

A step-by-step example

Before a backup can be made a repository has to be initialized:
$ borg init --encryption=repokey /path/to/repo
Backup the ~/src and ~/Documents directories into an archive called Monday:
$ borg create /path/to/repo::Monday ~/src ~/Documents
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
------------------------------------------------------------------------------
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
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
...
Restore the Monday archive by extracting the files relative to the current directory:
$ borg extract /path/to/repo::Monday
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.

NOTES

Positional Arguments and Options: Order matters

Borg only supports taking options (-s and --progress in the example) to the left or right of all positional arguments (repo::archive and path in the example), but not in between them:

borg create -s --progress repo::archive path  # good and preferred
borg create repo::archive path -s --progress  # also works
borg create -s repo::archive path --progress  # works, but ugly
borg create repo::archive -s --progress path  # BAD

This is due to a problem in the argparse module: https://bugs.python.org/issue15112

Repository URLs

Local filesystem (or locally mounted network filesystem):

/path/to/repo - filesystem path to repo directory, absolute path

path/to/repo - filesystem path to repo directory, relative path

Also, stuff like ~/path/to/repo or ~other/path/to/repo works (this is expanded by your shell).

Note: you may also prepend a file:// to a filesystem path to get URL style.

Remote repositories accessed via ssh user@host:

user@host:/path/to/repo - remote repo, absolute path

ssh://user@host:port/path/to/repo - same, alternative syntax, port can be given

Remote repositories with relative paths can be given using this syntax:

user@host:path/to/repo - path relative to current directory

user@host:~/path/to/repo - path relative to user's home directory

user@host:~other/path/to/repo - path relative to other's home directory

Note: giving user@host:/./path/to/repo or user@host:/~/path/to/repo or user@host:/~other/path/to/repo is also supported, but not required here.

Remote repositories with relative paths, alternative syntax with port:

ssh://user@host:port/./path/to/repo - path relative to current directory

ssh://user@host:port/~/path/to/repo - path relative to user's home directory

ssh://user@host:port/~other/path/to/repo - path relative to other's home directory

If you frequently need the same repo URL, it is a good idea to set the BORG_REPO environment variable to set a default for the repo URL:

export BORG_REPO='ssh://user@host:port/path/to/repo'

Then just leave away the repo URL if only a repo URL is needed and you want to use the default - it will be read from BORG_REPO then.

Use :: syntax to give the repo URL when syntax requires giving a positional argument for the repo (e.g. borg mount :: /mnt).

Repository / Archive Locations

Many commands want either a repository (just give the repo URL, see above) or an archive location, which is a repo URL followed by ::archive_name.

Archive names must not contain the / (slash) character. For simplicity, maybe also avoid blanks or other characters that have special meaning on the shell or in a filesystem (borg mount will use the archive name as directory name).

If you have set BORG_REPO (see above) and an archive location is needed, use ::archive_name - the repo URL part is then read from BORG_REPO.

Logging

Borg writes all log output to stderr by default. But please note that something showing up on stderr does not indicate an error condition just because it is on stderr. Please check the log levels of the messages and the return code of borg for determining error, warning or success conditions.

If you want to capture the log output to a file, just redirect it:

borg create repo::archive myfiles 2>> logfile

Custom logging configurations can be implemented via BORG_LOGGING_CONF.

The log level of the builtin logging configuration defaults to WARNING. This is because we want Borg to be mostly silent and only output warnings, errors and critical messages, unless output has been requested by supplying an option that implies output (e.g. --list or --progress).

Log levels: DEBUG < INFO < WARNING < ERROR < CRITICAL

Use --debug to set DEBUG log level - to get debug, info, warning, error and critical level output.

Use --info (or -v or --verbose) to set INFO log level - to get info, warning, error and critical level output.

Use --warning (default) to set WARNING log level - to get warning, error and critical level output.

Use --error to set ERROR log level - to get error and critical level output.

Use --critical to set CRITICAL log level - to get critical level output.

While you can set misc. log levels, do not expect that every command will give different output on different log levels - it's just a possibility.

WARNING:

Options --critical and --error are provided for completeness, their usage is not recommended as you might miss important information.

Return codes

Borg can exit with the following return codes (rc):

_
Return code	Meaning
_
0	success (logged as INFO)
_
1	warning (operation reached its normal end, but there were warnings -- you should check the log, logged as WARNING)
_
2	error (like a fatal error, a local or remote exception, the operation did not reach its normal end, logged as ERROR)
_
128+N	killed by signal N (e.g. 137 == kill -9)
_

If you use --show-rc, the return code is also logged at the indicated level as the last log entry.

Environment Variables

Borg uses some environment variables for automation:

General:

BORG_REPO

When set, use the value to give the default repository location. If a command needs an archive parameter, you can abbreviate as ::archive. If a command needs a repository parameter, you can either leave it away or abbreviate as ::, if a positional parameter is required.

BORG_PASSPHRASE

When set, use the value to answer the passphrase question for encrypted repositories. It is used when a passphrase is needed to access an encrypted repo as well as when a new passphrase should be initially set when initializing an encrypted repo. See also BORG_NEW_PASSPHRASE.

BORG_PASSCOMMAND

When set, use the standard output of the command (trailing newlines are stripped) to answer the passphrase question for encrypted repositories. It is used when a passphrase is needed to access an encrypted repo as well as when a new passphrase should be initially set when initializing an encrypted repo. Note that the command is executed without a shell. So variables, like $HOME will work, but ~ won't. If BORG_PASSPHRASE is also set, it takes precedence. See also BORG_NEW_PASSPHRASE.

BORG_PASSPHRASE_FD

When set, specifies a file descriptor to read a passphrase from. Programs starting borg may choose to open an anonymous pipe and use it to pass a passphrase. This is safer than passing via BORG_PASSPHRASE, because on some systems (e.g. Linux) environment can be examined by other processes. If BORG_PASSPHRASE or BORG_PASSCOMMAND are also set, they take precedence.

BORG_NEW_PASSPHRASE

When set, use the value to answer the passphrase question when a new passphrase is asked for. This variable is checked first. If it is not set, BORG_PASSPHRASE and BORG_PASSCOMMAND will also be checked. Main usecase for this is to fully automate borg change-passphrase.

BORG_DISPLAY_PASSPHRASE

When set, use the value to answer the "display the passphrase for verification" question when defining a new passphrase for encrypted repositories.

BORG_HOSTNAME_IS_UNIQUE=no

Borg assumes that it can derive a unique hostname / identity (see borg debug info). If this is not the case or you do not want Borg to automatically remove stale locks, set this to no.

BORG_HOST_ID

Borg usually computes a host id from the FQDN plus the results of uuid.getnode() (which usually returns a unique id based on the MAC address of the network interface. Except if that MAC happens to be all-zero - in that case it returns a random value, which is not what we want (because it kills automatic stale lock removal). So, if you have a all-zero MAC address or other reasons to better externally control the host id, just set this environment variable to a unique value. If all your FQDNs are unique, you can just use the FQDN. If not, use fqdn@uniqueid.

BORG_LOGGING_CONF

When set, use the given filename as INI-style logging configuration. A basic example conf can be found at docs/misc/logging.conf.

BORG_RSH

When set, use this command instead of ssh. This can be used to specify ssh options, such as a custom identity file ssh -i /path/to/private/key. See man ssh for other options. Using the --rsh CMD commandline option overrides the environment variable.

BORG_REMOTE_PATH

When set, use the given path as borg executable on the remote (defaults to "borg" if unset). Using --remote-path PATH commandline option overrides the environment variable.

BORG_FILES_CACHE_SUFFIX

When set to a value at least one character long, instructs borg to use a specifically named (based on the suffix) alternative files cache. This can be used to avoid loading and saving cache entries for backup sources other than the current sources.

BORG_FILES_CACHE_TTL

When set to a numeric value, this determines the maximum "time to live" for the files cache entries (default: 20). The files cache is used to quickly determine whether a file is unchanged. The FAQ explains this more detailed in: always_chunking

BORG_SHOW_SYSINFO

When set to no (default: yes), system information (like OS, Python version, ...) in exceptions is not shown. Please only use for good reasons as it makes issues harder to analyze.

BORG_LIBC

borg uses ctypes.util.find_library to locate the 'c' library (aka libc). find_library needs a shell and will invoke some tools like ldconfig, gcc/cc or objdump. If a shell or these tools are not available, you can give the name of your libc via BORG_LIBC=libc.so.6 (for example) and borg will not try the find_library call.

BORG_SELFTEST

This can be used to influence borg's builtin self-tests. The default is to execute the tests at the beginning of each borg command invocation.

BORG_SELFTEST=disabled can be used to switch off the tests and rather save some time. Disabling is not recommended for normal borg users, but large scale borg storage providers can use this to optimize production servers after at least doing a one-time test borg (with selftests not disabled) when installing or upgrading machines / OS / borg.

BORG_WORKAROUNDS

A list of comma separated strings that trigger workarounds in borg, e.g. to work around bugs in other software.

Currently known strings are:

basesyncfile

Use the more simple BaseSyncFile code to avoid issues with sync_file_range. You might need this to run borg on WSL (Windows Subsystem for Linux) or in systemd.nspawn containers on some architectures (e.g. ARM). Using this does not affect data safety, but might result in a more bursty write to disk behaviour (not continuously streaming to disk).

Some automatic answerers (if set, they automatically answer confirmation questions):

BORG_UNKNOWN_UNENCRYPTED_REPO_ACCESS_IS_OK=no (or =yes)

For "Warning: Attempting to access a previously unknown unencrypted repository"

BORG_RELOCATED_REPO_ACCESS_IS_OK=no (or =yes)

For "Warning: The repository at location ... was previously located at ..."

BORG_CHECK_I_KNOW_WHAT_I_AM_DOING=NO (or =YES)

For "This is a potentially dangerous function..." (check --repair)

BORG_DELETE_I_KNOW_WHAT_I_AM_DOING=NO (or =YES)

For "You requested to completely DELETE the repository including all archives it contains:"

Note: answers are case sensitive. setting an invalid answer value might either give the default answer or ask you interactively, depending on whether retries are allowed (they by default are allowed). So please test your scripts interactively before making them a non-interactive script.

Directories and files:

BORG_BASE_DIR

Defaults to $HOME or ~$USER or ~ (in that order). If you want to move all borg-specific folders to a custom path at once, all you need to do is to modify BORG_BASE_DIR: the other paths for cache, config etc. will adapt accordingly (assuming you didn't set them to a different custom value).

BORG_CACHE_DIR

Defaults to $BORG_BASE_DIR/.cache/borg. If BORG_BASE_DIR is not explicitly set while XDG env var XDG_CACHE_HOME is set, then $XDG_CACHE_HOME/borg is being used instead. This directory contains the local cache and might need a lot of space for dealing with big repositories. Make sure you're aware of the associated security aspects of the cache location: cache_security

BORG_CONFIG_DIR

Defaults to $BORG_BASE_DIR/.config/borg. If BORG_BASE_DIR is not explicitly set while XDG env var XDG_CONFIG_HOME is set, then $XDG_CONFIG_HOME/borg is being used instead. This directory contains all borg configuration directories, see the FAQ for a security advisory about the data in this directory: home_config_borg

BORG_SECURITY_DIR

Defaults to $BORG_CONFIG_DIR/security. This directory contains information borg uses to track its usage of NONCES ("numbers used once" - usually in encryption context) and other security relevant data.

BORG_KEYS_DIR

Defaults to $BORG_CONFIG_DIR/keys. This directory contains keys for encrypted repositories.

BORG_KEY_FILE

When set, use the given filename as repository key file.

TMPDIR

This is where temporary files are stored (might need a lot of temporary space for some operations), see tempfile for details.

Building:

BORG_OPENSSL_PREFIX

Adds given OpenSSL header file directory to the default locations (setup.py).

BORG_LIBLZ4_PREFIX

Adds given prefix directory to the default locations. If a 'include/lz4.h' is found Borg will be linked against the system liblz4 instead of a bundled implementation. (setup.py)

BORG_LIBB2_PREFIX

Adds given prefix directory to the default locations. If a 'include/blake2.h' is found Borg will be linked against the system libb2 instead of a bundled implementation. (setup.py)

BORG_LIBZSTD_PREFIX

Adds given prefix directory to the default locations. If a 'include/zstd.h' is found Borg will be linked against the system libzstd instead of a bundled implementation. (setup.py)

Please note:

Be very careful when using the "yes" sayers, the warnings with prompt exist for your / your data's security/safety.

Also be very careful when putting your passphrase into a script, make sure it has appropriate file permissions (e.g. mode 600, root:root).

File systems

We strongly recommend against using Borg (or any other database-like software) on non-journaling file systems like FAT, since it is not possible to assume any consistency in case of power failures (or a sudden disconnect of an external drive or similar failures).

While Borg uses a data store that is resilient against these failures when used on journaling file systems, it is not possible to guarantee this with some hardware -- independent of the software used. We don't know a list of affected hardware.

If you are suspicious whether your Borg repository is still consistent and readable after one of the failures mentioned above occurred, run borg check --verify-data to make sure it is consistent. Requirements for Borg repository file systems.INDENT 0.0

Long file names
At least three directory levels with short names
Typically, file sizes up to a few hundred MB. Large repositories may require large files (>2 GB).
Up to 1000 files per directory (10000 for repositories initialized with Borg 1.0)
mkdir(2) should be atomic, since it is used for locking
Hardlinks are needed for borg_upgrade (if --inplace option is not used). Also hardlinks are used for more safe and secure file updating (e.g. of the repo config file), but the code tries to work also if hardlinks are not supported.

Units

To display quantities, Borg takes care of respecting the usual conventions of scale. Disk sizes are displayed in decimal, using powers of ten (so kB means 1000 bytes). For memory usage, binary prefixes are used, and are indicated using the IEC binary prefixes, using powers of two (so KiB means 1024 bytes).

Date and Time

We format date and time conforming to ISO-8601, that is: YYYY-MM-DD and HH:MM:SS (24h clock).

For more information about that, see: https://xkcd.com/1179/

Unless otherwise noted, we display local date and time. Internally, we store and process date and time as UTC.

Resource Usage

Borg might use a lot of resources depending on the size of the data set it is dealing with.

If one uses Borg in a client/server way (with a ssh: repository), the resource usage occurs in part on the client and in another part on the server.

If one uses Borg as a single process (with a filesystem repo), all the resource usage occurs in that one process, so just add up client + server to get the approximate resource usage.

CPU client:

borg create: does chunking, hashing, compression, crypto (high CPU usage)

chunks cache sync: quite heavy on CPU, doing lots of hashtable operations.

borg extract: crypto, decompression (medium to high CPU usage)

borg check: similar to extract, but depends on options given.

borg prune / borg delete archive: low to medium CPU usage

borg delete repo: done on the server

It won't go beyond 100% of 1 core as the code is currently single-threaded. Especially higher zlib and lzma compression levels use significant amounts of CPU cycles. Crypto might be cheap on the CPU (if hardware accelerated) or expensive (if not).

CPU server:

It usually doesn't need much CPU, it just deals with the key/value store (repository) and uses the repository index for that.

borg check: the repository check computes the checksums of all chunks (medium CPU usage) borg delete repo: low CPU usage

CPU (only for client/server operation):

When using borg in a client/server way with a ssh:-type repo, the ssh processes used for the transport layer will need some CPU on the client and on the server due to the crypto they are doing - esp. if you are pumping big amounts of data.

Memory (RAM) client:

The chunks index and the files index are read into memory for performance reasons. Might need big amounts of memory (see below). Compression, esp. lzma compression with high levels might need substantial amounts of memory.

Memory (RAM) server:

The server process will load the repository index into memory. Might need considerable amounts of memory, but less than on the client (see below).

Chunks index (client only):

Proportional to the amount of data chunks in your repo. Lots of chunks in your repo imply a big chunks index. It is possible to tweak the chunker params (see create options).

Files index (client only):

Proportional to the amount of files in your last backups. Can be switched off (see create options), but next backup might be much slower if you do. The speed benefit of using the files cache is proportional to file size.

Repository index (server only):

Proportional to the amount of data chunks in your repo. Lots of chunks in your repo imply a big repository index. It is possible to tweak the chunker params (see create options) to influence the amount of chunks being created.

Temporary files (client):

Reading data and metadata from a FUSE mounted repository will consume up to the size of all deduplicated, small chunks in the repository. Big chunks won't be locally cached.

Temporary files (server):

A non-trivial amount of data will be stored on the remote temp directory for each client that connects to it. For some remotes, this can fill the default temporary directory at /tmp. This can be remediated by ensuring the $TMPDIR, $TEMP, or $TMP environment variable is properly set for the sshd process. For some OSes, this can be done just by setting the correct value in the .bashrc (or equivalent login config file for other shells), however in other cases it may be necessary to first enable PermitUserEnvironment yes in your sshd_config file, then add environment="TMPDIR=/my/big/tmpdir" at the start of the public key to be used in the authorized_hosts file.

Cache files (client only):

Contains the chunks index and files index (plus a collection of single- archive chunk indexes which might need huge amounts of disk space, depending on archive count and size - see FAQ about how to reduce).

Network (only for client/server operation):

If your repository is remote, all deduplicated (and optionally compressed/ encrypted) data of course has to go over the connection (ssh:// repo url). If you use a locally mounted network filesystem, additionally some copy operations used for transaction support also go over the connection. If you backup multiple sources to one target repository, additional traffic happens for cache resynchronization.

Support for file metadata

Besides regular file and directory structures, Borg can preserve

symlinks (stored as symlink, the symlink is not followed)

special files:

character and block device files (restored via mknod)

FIFOs ("named pipes")

special file contents can be backed up in --read-special mode. By default the metadata to create them with mknod(2), mkfifo(2) etc. is stored.

hardlinked regular files, devices, FIFOs (considering all items in the same archive)

timestamps in nanosecond precision: mtime, atime, ctime

other timestamps: birthtime (on platforms supporting it)

permissions:

IDs of owning user and owning group

names of owning user and owning group (if the IDs can be resolved)

Unix Mode/Permissions (u/g/o permissions, suid, sgid, sticky)

On some platforms additional features are supported:

_
Platform	ACLs [5]	xattr [6]	Flags [7]
_
Linux	Yes	Yes	Yes [1]
_
Mac OS X	Yes	Yes	Yes (all)
_
FreeBSD	Yes	Yes	Yes (all)
_
OpenBSD	n/a	n/a	Yes (all)
_
NetBSD	n/a	No [2]	Yes (all)
_
Solaris and derivatives	No [3]	No [3]	n/a
_
Windows (cygwin)	No [4]	No	No
_

Other Unix-like operating systems may work as well, but have not been tested at all.

Note that most of the platform-dependent features also depend on the file system. For example, ntfs-3g on Linux isn't able to convey NTFS ACLs.

[1]: Only "nodump", "immutable", "compressed" and "append" are supported. Feature request #618 for more flags.
[2]: Feature request #1332
[3]: Feature request #1337
[4]: Cygwin tries to map NTFS ACLs to permissions with varying degrees of success.
[5]: The native access control list mechanism of the OS. This normally limits access to non-native ACLs. For example, NTFS ACLs aren't completely accessible on Linux with ntfs-3g.
[6]: extended attributes; key-value pairs attached to a file, mainly used by the OS. This includes resource forks on Mac OS X.
[7]: aka BSD flags. The Linux set of flags [1] is portable across platforms. The BSDs define additional flags.

AUTHOR

The Borg Collective