borg-environment(1)

Name
borg-environment - Details regarding environment

DESCRIPTION

Borg uses some environment variables for automation:

General:

BORG_REPO
    When set, use the value to give the default repository location. Use this so you do not need to type --repo /path/to/my/repo all the time.

BORG_OTHER_REPO
    Similar to BORG_REPO, but gives the default for --other-repo.

BORG_PASSPHRASE (and BORG_OTHER_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 (and BORG_OTHER_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 (and BORG_OTHER_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 use case for this is to fully automate borg key 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_DEBUG_PASSPHRASE
    When set to YES, display debugging information that includes passphrases used and passphrase related env vars set.

BORG_EXIT_CODES
    When set to "modern", the borg process will return more specific exit codes (rc). When set to "legacy", the borg process will return rc 2 for all errors, 1 for all warnings, 0 for success. Default is "modern".

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 an all-zero MAC address or other reasons to better control the host id externally, 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_HOSTNAME
    When set, use this value as the hostname (instead of the auto-detected one), e.g. to run borg on one host, but impersonate another host. This affects the hostname stored in newly created archives as well as the {hostname} placeholder.

BORG_USERNAME
    When set, use this value as the username (instead of the auto-detected one), e.g. to run borg as one user, but impersonate another user. This affects the username stored in newly created archives as well as the {user} placeholder.

BORG_LOCK_WAIT
    You can set the default value for the --lock-wait option with this, so you do not need to give it as a command line option.

BORG_LOGGING_CONF
    When set, use the given filename as INI-style logging configuration (see <https://docs.python.org/3/library/logging.config.html#configuration-file-format>). 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. This is the replacement for the removed --rsh CMD command line option. borg also gives this to borgstore as BORGSTORE_RSH, except if that is already set.

BORG_REMOTE_PATH
    When set, use the given path as borg executable on the remote (defaults to "borg" if unset). This is the replacement for the removed --remote-path PATH command line option.

BORG_UNITS
    Determines how borg formats sizes in its human-readable output:

•   si (default): decimal units, e.g. 1.23 MB (1kB = 1000B)

•   iec: binary units, e.g. 1.18 MiB (1KiB = 1024B)

•   raw: exact byte counts, e.g. 1234567 B

    Use raw if you want to parse sizes with scripts (e.g. for monitoring), so you do not have to deal with scaled values and different units. Alternatively, use a command's --json output or, for the commands supporting --format, the size related format keys - sizes are given as byte counts there anyway.

    BORG_UNITS=iec is the replacement for the removed BORG_IEC environment variable (and for the --iec command line option removed before that).

BORG_PROGRESS_FPS
    How often the --progress output is updated at most, in updates per second (default: 5). Fractional values are allowed, e.g. BORG_PROGRESS_FPS=0.1 limits it to one update every 10 seconds. Lower values are useful when the output goes into a logfile rather than to an interactive terminal.

BORG_SPINNER
    Controls the spinner borg animates on a terminal while doing work of unknown duration:

•   unset (default): animate, using Unicode frames if the terminal can display them

•   ascii: animate, but only use ASCII frames (|/-\)

•   off: do not animate, only output the messages next to the spinner

    The spinner is animated only on an interactive terminal anyway (and never with --log-json), and its colour follows the usual NO_COLOR and COLORTERM conventions. See also BORG_PROGRESS_FPS: it also gives the spinner its frame rate.

BORG_DEBUG_PROFILE
    When set to a filename, write an execution profile in Borg format into that file (see debugging). If the filename ends with .pyprof, a Python-compatible profile is written instead. This is the replacement for the removed --debug-profile command line option. Note: every borg invocation writes the profile, so unset it again when you are done.

BORG_REPO_PERMISSIONS
    Set repository permissions, see also: borg_serve

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: 2). The files cache is used to determine quickly whether a file is unchanged.

BORG_ASSERT_ID
    Comma-separated list of the places where borg shall verify that a chunk's content matches its chunk id (chunkid == id_hash(content)) after decrypting and decompressing it. Verifying costs a full hash pass over everything that is read at such a place.

    Default (variable not set):

        BORG_ASSERT_ID=repair,transfer,rechunk

    These are the place names that can be listed:

read
    Every read that decompresses a chunk: borg extract, borg mount, borg export-tar, borg diff, ... This is by far the most data borg reads, so this place is not in the default, see the explanation below.

repair
    borg check --repair. It rebuilds archives from the item metadata stream it reads, re-packing it into new chunks with freshly computed ids, and it recreates manifest and archives directory entries from what it reads.

transfer
    borg transfer, for everything it reads from the source repository. Transferring re-anchors the content in another repository, which is a trust boundary.

rechunk
    borg recreate --chunker-params ..., i.e. re-chunking reads. Re-chunking computes new chunk ids from the content it reads, so a violation would not be noticeable any more afterwards. (Re-chunking in borg transfer is covered by transfer.)

    An unknown place name is an error. An empty value (BORG_ASSERT_ID=) verifies at none of these places, but still where borg always verifies (see below).

    Why read is not in the default: for encrypted repositories (all the AEAD ciphersuites), the chunk id is part of the AEAD additional authenticated data, so a successful decryption already proves that a holder of the repository key deliberately stored exactly this ciphertext for exactly this chunk id. A malicious or buggy repository can therefore not swap, splice or substitute objects, whether the id is verified on read or not. What the id check adds is the detection of chunks whose content does not match their id, which only a malicious or compromised borg client that had your borg key could have written (e.g. to poison future deduplication). If that is in your threat model - e.g. because some machines writing into the repository are not fully trusted - add read to the list:

        BORG_ASSERT_ID=read,repair,transfer,rechunk

    Otherwise, running borg check --verify-data periodically is recommended: it is the audit that re-certifies the invariant for all chunks in the background, instead of on every read.

    Independent of this variable, borg always verifies the chunk id:

•   in borg check --verify-data. That audit is what makes not verifying elsewhere defensible, so it is not configurable (there is no verify_data place name).

•   for authenticated and none mode repositories: there is no AEAD there, so the id check is the read path's integrity check and switching it off would remove it completely. Same for reading borg 1.x repositories (borg transfer).

BORG_BLAKE3_MT_THRESHOLD
    When set to a numeric value, chunks of at least that many KiB get their id computed by multi-threaded BLAKE3, smaller ones single-threaded (default: 256, i.e. 256KiB). Only relevant for repositories using --id-hash blake3. Multi-threading only pays off for big enough chunks and the break-even point depends on the machine's core count, so the default is deliberately conservative. Run scripts/blake3-optimize-mt-threshold.py to measure the best value for your machine - it sweeps input sizes, prints the recommended threshold and the command to set it, and can optionally show a chart of the measurements in your browser (--html --open). 0 means "always multi-threaded", a very large value effectively disables multi-threading.

BORG_ZSTD_MT_WORKERS
    When set to a numeric value, use that many threads to zstd-compress a single chunk (default: the cpu count, but at most 4). 0 or 1 means single-threaded compression. Only relevant when compressing with zstd. Chunks below 768KiB are always compressed single-threaded: libzstd will not use a compression job smaller than 512KiB, so a small chunk gets split very unevenly and multi-threading it would be slower than not doing it at all. The default is capped at 4 because a chunk of the size the default chunker aims at (2MiB) splits into just 4 such jobs: threads beyond that get (nearly) no work, but the whole thread pool is created again for every chunk. Measured on a 12-core machine, 4 threads beat 12 on every test corpus at the default zstd,-4 (+13% .. +37%). Raising the value only pays off if you configured the chunker for much bigger chunks. borg export-tar compresses one long stream instead of separate chunks and always defaults to the cpu count. Multi-threading trades a little compression ratio for speed (measured at zstd,3: +0.05% archive size for 1MiB chunks, +0.64% for 8MiB ones, more at higher levels), and it uses more cpu time in total to reduce the wallclock time. Set it to 1 if you would rather have the smaller archive, or if borg has to share the cpu with other work. Single-threaded can even be faster on data zstd races through anyway, e.g. already-compressed/incompressible data or long-repeat data like VM images.

BORG_FASTCDC_KERNEL / BORG_BUZHASH64_KERNEL
    Select the scan kernel the fastcdc / buzhash64 chunker uses. Accepted values are avx512, avx2, neon, blockwise and scalar. The default is whichever benchmarked fastest for the architecture: neon on aarch64, and scalar (the plain sequential loop) on x86-64, where the compiler folds the rolling hash update into a single instruction and thereby beats the vector kernels. Other architectures get blockwise, the portable multi-lane C kernel. All kernels chunk identically - same cut points, same chunk ids - and differ only in speed, so this is safe to change at any time, also for an existing repository. Which kernel is fastest is not predictable from the instruction set: it depends on the cpu and on the compiler that built borg, and the sequential loop wins on some machines. Measure on your own hardware with borg benchmark cpu --chunking before overriding the default. avx512 and avx2 exist only on x86-64, neon only on aarch64, and only if the compiler that built borg supported them; scalar and blockwise are portable C and always available. Requesting a kernel that this build or this cpu cannot run is an error rather than a silent fallback, so a benchmark can not accidentally measure a different kernel. borg create --debug logs the chunker and the kernel it was created with.

BORG_AES_CHUNKER_KERNEL
    Select the scan kernel used by the AES based chunkers - one variable for all three of toeplitz-aes, rabin-aes and goldilocks-aes. Accepted values are vaes, aes-ni, aes-arm64 and evp. Unlike the chunker kernels above, wider is simply faster here, so the default is the best path this build and cpu offer: vaes, else aes-ni on x86-64, aes-arm64 on aarch64, and evp (the portable OpenSSL path) where there is no AES hardware path. As with the chunker kernels above, all of them chunk identically and differ only in speed, and a kernel that can not run here is an error rather than a silent fallback. vaes and aes-ni exist only on x86-64, aes-arm64 only on aarch64. vaes additionally needs a compiler that knows it (gcc >= 11 / clang >= 14), so a cpu supporting VAES is not by itself enough to have that kernel available.

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_MSGPACK_VERSION_CHECK
    Controls whether Borg checks the msgpack version. The default is yes (strict check). Set to no to disable the version check and allow any installed msgpack version. Use this at your own risk; malfunctioning or incompatible msgpack versions may cause subtle bugs or repository data corruption.

BORG_FUSE_IMPL
    Choose the low-level 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.:

•   mfusepy,pyfuse3,llfuse: default, first try to load mfusepy, then pyfuse3, then llfuse.

•   llfuse,pyfuse3: first try to load llfuse, then try to load pyfuse3.

•   mfusepy: only try to load mfusepy

•   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 built-in 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 self-tests 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 behavior (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).

authenticated_no_key
    Work around a lost passphrase or key for an authenticated-* mode repository (these are only authenticated, but not encrypted). If the key is missing in the repository config, add key = anything there.

    Without the key, borg can not verify anything that needs it: neither the authentication tag of the repository objects nor the chunk ids. It therefore reads the repository unverified - a corrupted or tampered repository will not be detected. (This only concerns the authenticated-* modes; the none-* modes need no key and keep verifying their checksums.)

    This workaround is only for emergencies and only to extract data from an affected repository (read-only access):

        BORG_WORKAROUNDS=authenticated_no_key borg extract --repo repo archive

    After you have extracted all data you need, you MUST delete the repository:

        BORG_WORKAROUNDS=authenticated_no_key borg delete repo

    Now you can init a fresh repo. Make sure you do not use the workaround any more.

Output formatting:

BORG_CHECK_FORMAT
    Giving the default value for borg check --format=X.

BORG_FIND_FORMAT
    Giving the default value for borg find --format=X.

BORG_LIST_FORMAT
    Giving the default value for borg list --format=X.

BORG_REPO_LIST_FORMAT
    Giving the default value for borg repo-list --format=X.

BORG_PRUNE_FORMAT
    Giving the default value for borg prune --format=X.

BORG_MOUNT_ARCHIVE_DIR_FORMAT
    Giving the format of the archive directory names when borg mount or borg webdav show a whole repository, default: {name}. The placeholders are the ones of borg repo-list --format; names that are not unique get -{id:.8} appended. See borg mount --help.

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 DELETE the repository completely 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 2 uses the platformdirs library (<https://pypi.org/project/platformdirs/>) to determine default directory locations. This means that default paths are platform-specific:

•   Linux: XDG Base Directory Specification paths are used (e.g. ~/.config/borg, ~/.cache/borg, ~/.local/share/borg). XDG_* environment variables are honoured (see <https://specifications.freedesktop.org/basedir-spec/0.6/ar01s03.html>).

•   macOS: native macOS directories are used by default (e.g. ~/Library/Application Support/borg, ~/Library/Caches/borg). XDG_* environment variables are honoured if set.

•   Windows: Windows AppData directories are used (e.g. C:\Users\<user>\AppData\Roaming\borg, C:\Users\<user>\AppData\Local\borg). XDG_* environment variables are not honoured.

    On all platforms, you can override each directory individually using the specific environment variables described below. You can also set BORG_BASE_DIR to force borg to use BORG_BASE_DIR/.config/borg, BORG_BASE_DIR/.cache/borg, etc., regardless of the platform.

    Default directory locations by platform (when no BORG_* environment variables are set):

        Directory  Linux                 macOS                                 Windows
        Config     ~/.config/borg        ~/Library/Application Support/borg    %APPDATA%\borg
        Cache      ~/.cache/borg         ~/Library/Caches/borg                 %LOCALAPPDATA%\borg\Cache
        Data       ~/.local/share/borg   ~/Library/Application Support/borg    %LOCALAPPDATA%\borg
        Runtime    /run/user/<uid>/borg  ~/Library/Caches/TemporaryItems/borg  %TEMP%\borg
        Keys       <config_dir>/keys     <config_dir>/keys                     <config_dir>\keys
        Security   <data_dir>/security   <data_dir>/security                   <data_dir>\security

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 the platform-specific cache directory (see table above). If BORG_BASE_DIR is set, defaults to $BORG_BASE_DIR/.cache/borg. On Linux and macOS, XDG_CACHE_HOME is also honoured if BORG_BASE_DIR is not set. 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 the platform-specific config directory (see table above). If BORG_BASE_DIR is set, defaults to $BORG_BASE_DIR/.config/borg. On Linux and macOS, XDG_CONFIG_HOME is also honoured if BORG_BASE_DIR is not set. This directory contains all borg configuration directories, see the FAQ for a security advisory about the data in this directory: home_config_borg

BORG_DATA_DIR
    Defaults to the platform-specific data directory (see table above). If BORG_BASE_DIR is set, defaults to $BORG_BASE_DIR/.local/share/borg. On Linux and macOS, XDG_DATA_HOME is also honoured if BORG_BASE_DIR is not set. This directory contains all borg data directories, see the FAQ for a security advisory about the data in this directory: home_data_borg

BORG_RUNTIME_DIR
    Defaults to the platform-specific runtime directory (see table above). If BORG_BASE_DIR is set, defaults to $BORG_BASE_DIR/.cache/borg. On Linux and macOS, XDG_RUNTIME_DIR is also honoured if BORG_BASE_DIR is not set. This directory contains borg runtime files, like e.g. the socket file.

BORG_SECURITY_DIR
    Defaults to $BORG_DATA_DIR/security. This directory contains 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 path as repository key file. Please note that this is only for rather special applications that externally fully manage the key files:

•   this setting only applies to the keyfile modes (not to the repokey modes).

•   using a full, absolute path to the key file is recommended.

•   all directories in the given path must exist.

•   this setting forces borg to use the key file at the given location.

•   the key file must either exist (for most commands) or will be created (borg repo-create).

•   you need to give a different path for different repositories.

•   you need to point to the correct key file matching the repository the command will operate on.

TMPDIR
    This is where temporary files are stored (might need a lot of temporary space for some operations), see <https://docs.python.org/3/library/tempfile.html#tempfile.gettempdir> for details.

Building:

BORG_OPENSSL_NAME
    Defines the subdirectory name for OpenSSL (setup.py).

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

BORG_LIBACL_PREFIX
    Adds given prefix directory to the default locations. If an 'include/acl/libacl.h' is found Borg will be linked against the system libacl instead of a bundled implementation. (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)

Automatic option environment variables:
    Borg uses jsonargparse (<https://jsonargparse.readthedocs.io/>) with default_env=True, which means that every command-line option can also be set via an environment variable.

    The environment variable name is derived from the program name (borg), the subcommand (if any), and the option name, all converted to uppercase with dashes replaced by underscores.

    For top-level options (not specific to a subcommand), the pattern is:

        BORG_<OPTION>

    For example, --lock-wait can be set via BORG_LOCK_WAIT.

    For subcommand options, the subcommand and option are separated by a double underscore:

        BORG_<SUBCOMMAND>__<OPTION>

    For example, borg create --comment can be set via BORG_CREATE__COMMENT.

    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).

Author
The Borg Collective