General

Borg consists of a number of commands. Each command accepts a number of arguments and options and interprets various environment variables. The following sections will describe each command in detail.

Commands, options, parameters, paths and such are set in fixed-width. Option values are underlined. Borg has few options accepting a fixed set of values (e.g. --encryption of borg init).

Experimental features are marked with red stripes on the sides, like this paragraph.

Experimental features are not stable, which means that they may be changed in incompatible ways or even removed entirely without prior notice in following releases.

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.

Type of log output

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. If BORG_PASSPHRASE is also set, it takes precedence. See also BORG_NEW_PASSPHRASE.
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_LOGGING_CONF
When set, use the given filename as INI-style logging configuration.
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.
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_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: It always chunks all my files, even unchanged ones!
TMPDIR
where temporary files are stored (might need a lot of temporary space for some operations)
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 “Warning: ‘check –repair’ is an experimental feature that might result in data loss.”
BORG_DELETE_I_KNOW_WHAT_I_AM_DOING=NO (or =YES)
For “You requested to completely DELETE the repository including all archives it contains:”
BORG_RECREATE_I_KNOW_WHAT_I_AM_DOING=NO (or =YES)
For “recreate is an experimental feature.”

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_KEYS_DIR
Default to ‘~/.config/borg/keys’. This directory contains keys for encrypted repositories.
BORG_KEY_FILE
When set, use the given filename as repository key file.
BORG_SECURITY_DIR
Default to ‘~/.config/borg/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_CACHE_DIR
Default to ‘~/.cache/borg’. This directory contains the local cache and might need a lot of space for dealing with big repositories).
BORG_CONFIG_DIR
Default to ‘~/.config/borg’. This directory contains the whole config directories.
Building:
BORG_OPENSSL_PREFIX
Adds given OpenSSL header file directory to the default locations (setup.py).
BORG_LZ4_PREFIX
Adds given LZ4 header file directory to the default locations (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)

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

  • 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 --inplace

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):
None.
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
  • 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
OpenBSD n/a n/a
NetBSD n/a No [2]
Solaris 11 No [3] n/a
OpenIndiana
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](1, 2) 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 degress 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.

In case you are interested in more details (like formulas), please see Internals. For details on the available JSON output, refer to All about JSON: How to develop frontends.

Common options

All Borg commands share these options:

-h, --help show this help message and exit
--critical work on log level CRITICAL
--error work on log level ERROR
--warning work on log level WARNING (default)
--info, -v, --verbose work on log level INFO
--debug enable debug output, work on log level DEBUG
--debug-topic TOPIC enable TOPIC debugging (can be specified multiple times). The logger path is borg.debug.<TOPIC> if TOPIC is not fully qualified.
-p, --progress show progress information
--log-json Output one JSON object per log line instead of formatted text.
--lock-wait SECONDS wait at most SECONDS for acquiring a repository/cache lock (default: 1).
--show-version show/log the borg version
--show-rc show/log the return code (rc)
--no-files-cache do not load/update the file metadata cache used to detect unchanged files
--umask M set umask to M (local and remote, default: 0077)
--remote-path PATH use PATH as borg executable on the remote (default: “borg”)
--remote-ratelimit RATE set remote network upload rate limit in kiByte/s (default: 0=unlimited)
--consider-part-files treat part files like normal files (e.g. to list/extract them)
--debug-profile FILE Write execution profile in Borg format into FILE. For local use a Python-compatible file can be generated by suffixing FILE with ”.pyprof”.

Examples

# Create an archive and log: borg version, files list, return code
$ borg create --show-version --list --show-rc /path/to/repo::my-files files