# 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.

## 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_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: It always chunks all my files, even unchanged ones! 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_FUSE_IMPL Choose the lowlevel FUSE implementation borg shall use for borg mount. This is a comma-separated list of implementation names, they are tried in the given order, e.g.: • pyfuse3,llfuse: default, first try to load pyfuse3, then try to load llfuse. • llfuse,pyfuse3: first try to load llfuse, then try to load pyfuse3. • pyfuse3: only try to load pyfuse3 • llfuse: only try to load llfuse • none: do not try to load an implementation 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). retry_erofs Retry opening a file without O_NOATIME if opening a file with O_NOATIME caused EROFS. You will need this to make archives from volume shadow copies in WSL1 (Windows Subsystem for Linux 1). 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: Do I need to take security precautions regarding the cache? 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 $XDG_CONFIG_HOME/borg is being used instead. This directory contains all borg configuration directories, see the FAQ for a security advisory about the data in this directory: How important is the$HOME/.config/borg directory?
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
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)

• 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)
• rename(2) / MoveFile(Ex) should work as specified, i.e. on the same file system it should be a move (not a copy) operation, and in case of a directory it should fail if the destination exists and is not an empty directory, since this 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).

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):