All about JSON: How to develop frontends

Borg does not have a public API on the Python level. That does not keep you from writing import borg, but does mean that there are no release-to-release guarantees on what you might find in that package, not even for point releases (2.0.x), and there is no documentation beyond the code and the internals documents.

Borg does on the other hand provide an API on a command-line level. In other words, a frontend should (for example) create a backup archive by invoking :ref:`borg_create`, provide command-line parameters/options as needed, and parse JSON output from Borg.

Important: JSON output is expected to be UTF-8, but currently borg depends on the locale being configured for that (must be a UTF-8 locale and not "C" or "ascii"), so that Python will choose to encode to UTF-8. The same applies to any inputs read by borg, they are expected to be UTF-8 encoded also.

On POSIX systems, you can usually set environment vars to choose a UTF-8 locale:

export LANG=en_US.UTF-8
export LC_CTYPE=en_US.UTF-8

Another way to get Python's stdin/stdout/stderr streams to use UTF-8 encoding (without having a UTF-8 locale / LANG / LC_CTYPE) is:

export PYTHONIOENCODING=utf-8

See :issue:`2273` for more details.

Dealing with non-unicode byte sequences and JSON limitations

Paths on POSIX systems can have arbitrary bytes in them (except 0x00 which is used as string terminator in C).

Nowadays, UTF-8 encoded paths (which decode to valid unicode) are the usual thing, but a lot of systems still have paths from the past, when other, non-unicode codings were used. Especially old Samba shares often have wild mixtures of misc. encodings, sometimes even very broken stuff.

borg deals with such non-unicode paths ("with funny/broken characters") by decoding such byte sequences using UTF-8 coding and "surrogateescape" error handling mode, which maps invalid bytes to special unicode code points (surrogate escapes). When encoding such a unicode string back to a byte sequence, the original byte sequence will be reproduced exactly.

JSON should only contain valid unicode text without any surrogate escapes, so we can't just directly have a surrogate-escaped path in JSON ("path" is only one example, this also affects other text-like content).

Borg deals with this situation like this (since borg 2.0):

For a valid unicode path (no surrogate escapes), the JSON will only have "path": path.

For a non-unicode path (with surrogate escapes), the JSON will have 2 entries:

"path": path_approximation (pure valid unicode, all invalid bytes will show up as "?")
"path_b64": path_bytes_base64_encoded (if you decode the base64, you get the original path byte string)

JSON users need to pick whatever suits their needs best. The suggested procedure (shown for "path") is:

check if there is a "path_b64" key.
if it is there, you will know that the original bytes path did not cleanly UTF-8-decode into unicode (has some invalid bytes) and that the string given by the "path" key is only an approximation, but not the precise path. if you need precision, you must base64-decode the value of "path_b64" and deal with the arbitrary byte string you'll get. if an approximation is fine, use the value of the "path" key.
if it is not there, the value of the "path" key is all you need (the original bytes path is its UTF-8 encoding).

Logging

Especially for graphical frontends it is important to be able to convey and reformat progress information in meaningful ways. The --log-json option turns the stderr stream of Borg into a stream of JSON lines, where each line is a JSON object. The type key of the object determines its other contents.

Warning

JSON logging requires successful argument parsing. Even with --log-json specified, a parsing error will be printed in plain text, because logging set-up happens after all arguments are parsed.

The following types are in use. Progress information is governed by the usual rules for progress information, it is not produced unless --progress is specified.

archive_progress

Output during operations creating archives (:ref:`borg_create`, :ref:`borg_import-tar`, :ref:`borg_recreate` and :ref:`borg_transfer`). The following keys exist, each represents the current progress.

original_size: Original size of the data processed so far (before compression and deduplication)
deduplicated_size: Deduplicated size of the data processed so far (before compression): the size of the chunks that were new to the repository
nfiles: Number of (regular) files processed so far
hashing_time: Seconds spent hashing file contents so far (float)
chunking_time: Seconds spent chunking file contents so far (float)
files_stats: Object mapping the single-character file status (as used by --list) to the number of files that got that status so far, e.g. {"A": 3, "d": 3}
store_stats: Object with the storage backend statistics. It is empty here, it is only filled in for the final :ref:`borg_create` --json output on stdout, see Archive formats.
path: Current path (absent if there is no current item)
time: Unix timestamp (float)
finished: boolean indicating whether the operation has finished, only the last object for an operation can have this property set to true. That last object has no keys besides time, type and finished.

progress_message

A message-based progress information with no concrete progress information, just a message saying what is currently being worked on.

operation: unique, opaque integer ID of the operation
:ref:`msgid <msgid>`: Message ID of the operation (may be null)
finished: boolean indicating whether the operation has finished, only the last object for an operation can have this property set to true.
message: current progress message (empty string for finished == true)
time: Unix timestamp (float)

progress_percent

Absolute progress information with defined end/total and current value.

operation: unique, opaque integer ID of the operation
:ref:`msgid <msgid>`: Message ID of the operation (may be null)
finished: boolean indicating whether the operation has finished, only the last object for an operation can have this property set to true.
message: A formatted progress message, this will include the percentage and perhaps other information (empty string for finished == true)
current: Current value (usually less-or-equal to total, absent for finished == true)
info: Array that describes the current item, may be null, contents depend on msgid (absent for finished == true)
total: Total value (absent for finished == true)
time: Unix timestamp (float)

file_status

This is only output by :ref:`borg_create`, :ref:`borg_import-tar` and :ref:`borg_recreate` if --list is specified. The usual rules for the file listing applies, including the --filter option.

status: Single-character status as for regular list output
path: Path of the file system object

log_message

Any regular log output invokes this type. Regular log options and filtering applies to these as well.

time: Unix timestamp (float)
levelname: Upper-case log level name (also called severity). Defined levels are: DEBUG, INFO, WARNING, ERROR, CRITICAL
name: Name of the emitting entity
message: Formatted log message
:ref:`msgid <msgid>`: Message ID, may be null or absent

See Prompts for the types used by prompts.

Examples (reformatted, each object would be on exactly one line)

:ref:`borg_extract` progress:

{"message": " 20.0% Extracting: src/linux/baz/file3", "current": 50012, "total": 250012,
 "info": ["src/linux/baz/file3"], "operation": 1, "msgid": "extract",
 "type": "progress_percent", "finished": false, "time": 1787900399.5558112}
{"message": " 20.0% Extracting: src/linux/file1", "current": 250012, "total": 250012,
 "info": ["src/linux/file1"], "operation": 1, "msgid": "extract",
 "type": "progress_percent", "finished": false, "time": 1787900399.5561972}
{"message": "", "operation": 1, "msgid": "extract", "type": "progress_percent",
 "finished": true, "time": 1787900399.556339}

:ref:`borg_create` file listing with progress:

{"original_size": 0, "deduplicated_size": 0, "nfiles": 0, "hashing_time": 0.0, "chunking_time": 0.0,
 "files_stats": {}, "store_stats": {}, "path": "src", "time": 1787900398.684961, "type": "archive_progress",
 "finished": false}
{"type": "file_status", "status": "A", "path": "src/linux/baz/file2"}
{"type": "file_status", "status": "A", "path": "src/linux/baz/file3"}
{"type": "file_status", "status": "d", "path": "src/linux/baz"}
{"type": "file_status", "status": "A", "path": "src/linux/file1"}
{"type": "file_status", "status": "d", "path": "src/linux"}
{"type": "file_status", "status": "d", "path": "src"}
{"time": 1787900398.686938, "type": "archive_progress", "finished": true}

Saving the local cache at the end of :ref:`borg_create`:

{"message": "Saving files cache", "operation": 1, "msgid": "cache.close", "type": "progress_message", "finished": false, "time": 1787900398.719723}
{"message": "Saving index", "operation": 1, "msgid": "cache.close", "type": "progress_message", "finished": false, "time": 1787900398.728792}
{"message": "Saving cache config", "operation": 1, "msgid": "cache.close", "type": "progress_message", "finished": false, "time": 1787900398.7294679}
{"message": "", "operation": 1, "msgid": "cache.close", "type": "progress_message", "finished": true, "time": 1787900398.739775}

A debug log message:

{"type": "log_message", "time": 1787900399.0667, "message": "19 self-tests completed in 0.02 seconds",
 "levelname": "DEBUG", "name": "borg.archiver"}

An error log message, carrying a msgid:

{"type": "log_message", "time": 1787900383.5105972,
 "message": "Repository proto='file', ... does not exist.",
 "levelname": "ERROR", "name": "borg.archiver", "msgid": "Repository.DoesNotExist"}

Prompts

Borg asks a few yes/no questions interactively; the "Prompts" list at the end of Message IDs enumerates them. Answers are read verbatim from stdin. The questions and the messages about their processing are written to stderr: as plain text by default, or as JSON objects (one per line, like log messages) when --log-json is given.

Prompts use the question_prompt and question_prompt_retry types for the prompt itself, and question_invalid_answer, question_accepted_default, question_accepted_true, question_accepted_false and question_env_answer types for information about prompt processing.

The message property contains the same string displayed regularly in the same situation, while the msgid property contains a msgid, the name of the environment variable that can be used to override the prompt. It is the same for all JSON messages pertaining to the same prompt. question_env_answer messages additionally have an env_var property with the name of the environment variable the answer was taken from.

A frontend should not try to answer these prompts interactively. Every prompt has an environment variable that overrides it (the variable name is the prompt's msgid): if it is set, its value is used as if it had been typed in, and borg never waits for input. For example, with BORG_CHECK_I_KNOW_WHAT_I_AM_DOING=NO in the environment, borg check --repair prints the question, answers it with NO and fails with the CancelledByUser msgid (rc 3).

Examples (reformatted, each object would be on exactly one line)

Providing an invalid answer:

{"type": "question_prompt", "msgid": "BORG_CHECK_I_KNOW_WHAT_I_AM_DOING",
 "message": "This is a potentially dangerous function.\n... Type 'YES' if you understand this and want to continue: "}
incorrect answer  # input on stdin
{"type": "question_invalid_answer", "msgid": "BORG_CHECK_I_KNOW_WHAT_I_AM_DOING",
 "message": "Invalid answer, aborting."}

Providing a false (negative) answer via the environment variable:

{"type": "question_prompt", "msgid": "BORG_CHECK_I_KNOW_WHAT_I_AM_DOING",
 "message": "This is a potentially dangerous function.\n... Type 'YES' if you understand this and want to continue: "}
{"env_var": "BORG_CHECK_I_KNOW_WHAT_I_AM_DOING", "type": "question_env_answer",
 "msgid": "BORG_CHECK_I_KNOW_WHAT_I_AM_DOING",
 "message": "NO (from BORG_CHECK_I_KNOW_WHAT_I_AM_DOING)"}
{"type": "question_accepted_false", "msgid": "BORG_CHECK_I_KNOW_WHAT_I_AM_DOING",
 "message": "Aborting."}

Providing a true (affirmative) answer:

{"type": "question_prompt", "msgid": "BORG_CHECK_I_KNOW_WHAT_I_AM_DOING",
 "message": "This is a potentially dangerous function.\n... Type 'YES' if you understand this and want to continue: "}
YES  # input on stdin
# no further output, just like the prompt without --log-json

Passphrase prompts

Passphrase prompts should be handled differently. Use the environment variables BORG_PASSPHRASE and BORG_NEW_PASSPHRASE (see :ref:`env_vars` for reference) to pass passphrases to Borg, don't use the interactive passphrase prompts.

When setting a new passphrase (:ref:`borg_repo-create`, :ref:`borg_key_change-passphrase`) normally Borg prompts whether it should display the passphrase. This can be suppressed by setting the environment variable BORG_DISPLAY_PASSPHRASE to no.

When "confronted" with an unknown repository, where the application does not know whether the repository is encrypted, the following algorithm can be followed to detect encryption:

Set BORG_PASSPHRASE to gibberish (for example a freshly generated UUID4, which cannot possibly be the passphrase)
Invoke borg repo-list -r repository ...
If this fails, due the repository being encrypted and the passphrase obviously being wrong, you'll get an error with the PassphraseWrong msgid.

The repository is encrypted, for further access the application will need the passphrase.
If this does not fail, then the repository is not encrypted.

Standard output

stdout is different and more command-dependent than logging. Commands like :ref:`borg_repo-info`, :ref:`borg_repo-list`, :ref:`borg_info`, :ref:`borg_create` and :ref:`borg_analyze` implement a --json option which turns their regular output into a single JSON object.

Some commands, like :ref:`borg_list` and :ref:`borg_diff`, can produce a lot of JSON. Since many JSON implementations don't support a streaming mode of operation, which is pretty much required to deal with this amount of JSON, these commands implement a --json-lines option which generates output in the JSON lines format, which is simply a number of JSON objects separated by new lines.

Dates are formatted according to ISO 8601 in the local time zone of the borg client, including the UTC offset, e.g. 2026-08-28T08:59:56.761172+02:00. Repository and archive timestamps and the item timestamps of :ref:`borg_list` have microsecond precision (6 fraction digits). The item timestamps of :ref:`borg_diff` have nanosecond precision (9 fraction digits), because that is how borg stores them.

The root object of '--json' output will contain at least a repository key with an object containing:

id: The ID of the repository, normally 64 hex characters
location: Canonicalized repository path, thus this may be different from what is specified on the command line
last_modified: Date when the repository was last modified by the Borg client

The encryption key, if present, contains:

encryption: Textual cipher / AE algorithm name (same as :ref:`borg_repo-create` --encryption names)
id_hash: Textual id hash function name (same as :ref:`borg_repo-create` --id-hash names)
keyfile: Path to the local key file used for access. Depending on the key location this may be absent.

The cache key, if present, contains:

path: Path to the local repository cache

:ref:`borg_repo-info` additionally emits a security_dir key with the path of the local security directory of the repository.

Example borg repo-info --json output:

{
    "cache": {
        "path": "/home/user/.cache/borg/65d7898e2142485f44506fb11c0fcd6d7dfd0341716385246068584a62632a94"
    },
    "encryption": {
        "encryption": "aes256-ocb",
        "id_hash": "sha256"
    },
    "repository": {
        "id": "65d7898e2142485f44506fb11c0fcd6d7dfd0341716385246068584a62632a94",
        "last_modified": "2026-08-28T08:59:55.908686+02:00",
        "location": "/home/user/repository"
    },
    "security_dir": "/home/user/.local/share/borg/security/65d7898e2142485f44506fb11c0fcd6d7dfd0341716385246068584a62632a94"
}

Archive formats

:ref:`borg_info` uses an extended format for archives, which is more expensive to retrieve, while :ref:`borg_repo-list` uses a simpler format that is faster to retrieve. Either return archives in an array under the archives key, while :ref:`borg_create` and :ref:`borg_import-tar` return a single archive object under the archive key.

:ref:`borg_create` with --dry-run does not create an archive, so there is no archive key. Instead, it returns dry_run (true) and a reduced stats object with nfiles and original_size, both computed from file system metadata without reading the file contents.

Both formats always contain a name key with the archive name, the id key with the hexadecimal archive ID and the time key with the nominal archive timestamp. The borg repo-list format additionally always has an archive key, an alias of name.

borg info, borg create and borg import-tar further have:

start

Start timestamp of the archive creation

end

End timestamp of the archive creation

duration

Duration in seconds between start and end (float)

command_line

The command line that created the archive, as one shell-quoted string.

The note about paths from above applies here as well.

stats

Archive statistics:

original_size: Size of the file contents and the metadata in this archive, before compression and deduplication
deduplicated_size: Size of the file contents and the metadata in this archive that were new to the repository when the archive was created (this archive's deduplicated size, before compression). Only given by borg create and borg import-tar, see below.
nfiles: Number of regular files in the archive
hashing_time: Seconds spent hashing file contents (float)
chunking_time: Seconds spent chunking file contents (float)
files_stats: Object mapping the single-character file status to the number of files with that status
store_stats: Object with the statistics of the storage backend (call counts, transferred volumes, times, cache hits/misses, ...)

borg create and borg import-tar fill all of these in for the archive they have just created. borg info only reads original_size and nfiles from the archive metadata; hashing_time, chunking_time, files_stats and store_stats are 0 or empty there and deduplicated_size is absent: computing the deduplicated size of an existing archive is expensive, so it is only known while the archive is being created.

Compressed sizes are not given at all. Use :ref:`borg_analyze` for the deduplicated size of a set of archives and borg compact --stats for the repository-wide numbers.

:ref:`borg_info` further has:

hostname: Hostname of the creating host
username: Name of the creating user
cwd: Working directory the archive was created in
comment: Archive comment, if any
tags: Array of the archive's tags
chunker_params: The chunker parameters the archive has been created with.

Some keys/values are more expensive to compute than others (e.g. because it requires opening the archive, not just the archives directory). To optimize for speed, borg repo-list does not determine these values except when they are requested. The --format option is used for that (for normal mode as well as for --json mode), so, to have the comment included in the json output, you will need:

borg repo-list --format "{name}{comment}" --json

Note that the default --format of borg repo-list already requests tags, username, hostname and comment, so these show up unless you give a --format without them.

Example of a simple archive listing (borg repo-list --format "{name}{comment}" --json):

{
    "archives": [
        {
            "archive": "src-2026-08-28",
            "comment": "",
            "id": "b0f88c1245506d1f8ba283908c2d7d42d50bb7c7e4120134eafe16c5f0cde192",
            "name": "src-2026-08-28",
            "time": "2026-08-28T08:59:56.761172+02:00"
        }
    ],
    "encryption": {
        "encryption": "aes256-ocb",
        "id_hash": "sha256"
    },
    "repository": {
        "id": "65d7898e2142485f44506fb11c0fcd6d7dfd0341716385246068584a62632a94",
        "last_modified": "2026-08-28T08:59:56.764587+02:00",
        "location": "/home/user/repository"
    }
}

The same archive with more information (borg info --last 1 --json):

{
    "archives": [
        {
            "chunker_params": [
                "fastcdc",
                19,
                23,
                21,
                2
            ],
            "command_line": "/home/user/.local/bin/borg create --json src-2026-08-28 src",
            "comment": "",
            "cwd": "/home/user",
            "duration": 0.002238,
            "end": "2026-08-28T08:59:56.763410+02:00",
            "hostname": "host",
            "id": "b0f88c1245506d1f8ba283908c2d7d42d50bb7c7e4120134eafe16c5f0cde192",
            "name": "src-2026-08-28",
            "start": "2026-08-28T08:59:56.761172+02:00",
            "stats": {
                "chunking_time": 0.0,
                "files_stats": {},
                "hashing_time": 0.0,
                "nfiles": 3,
                "original_size": 250047,
                "store_stats": {}
            },
            "tags": [],
            "time": "2026-08-28T08:59:56.761172+02:00",
            "username": "user"
        }
    ],
    "cache": {
        "path": "/home/user/.cache/borg/65d7898e2142485f44506fb11c0fcd6d7dfd0341716385246068584a62632a94"
    },
    "encryption": {
        "encryption": "aes256-ocb",
        "id_hash": "sha256"
    },
    "repository": {
        "id": "65d7898e2142485f44506fb11c0fcd6d7dfd0341716385246068584a62632a94",
        "last_modified": "2026-08-28T08:59:56.764587+02:00",
        "location": "/home/user/repository"
    }
}

The archive :ref:`borg_create` has just created (borg create --json), with the statistics it collected while running:

{
    "archive": {
        "command_line": "/home/user/.local/bin/borg create --json src-2026-08-28 src",
        "duration": 0.002238,
        "end": "2026-08-28T08:59:56.763410+02:00",
        "id": "b0f88c1245506d1f8ba283908c2d7d42d50bb7c7e4120134eafe16c5f0cde192",
        "name": "src-2026-08-28",
        "start": "2026-08-28T08:59:56.761172+02:00",
        "stats": {
            "chunking_time": 7.81649723649025e-05,
            "deduplicated_size": 250510,
            "files_stats": {
                "A": 3,
                "d": 3
            },
            "hashing_time": 0.00010525097604840994,
            "nfiles": 3,
            "original_size": 250510,
            "store_stats": {
                "backend_load_calls": 8,
                "backend_load_volume": 2298,
                "backend_store_calls": 6,
                "backend_store_volume": 253555,
                "load_calls": 8,
                "load_throughput": 8997087.104958186,
                "load_time": 0.000255416,
                "load_volume": 2298,
                "store_calls": 6,
                "store_throughput": 120882023.28345428,
                "store_time": 0.002097541,
                "store_volume": 253555
            }
        },
        "time": "2026-08-28T08:59:56.761172+02:00"
    },
    "cache": {
        "path": "/home/user/.cache/borg/65d7898e2142485f44506fb11c0fcd6d7dfd0341716385246068584a62632a94"
    },
    "encryption": {
        "encryption": "aes256-ocb",
        "id_hash": "sha256"
    },
    "repository": {
        "id": "65d7898e2142485f44506fb11c0fcd6d7dfd0341716385246068584a62632a94",
        "last_modified": "2026-08-28T08:59:56.764587+02:00",
        "location": "/home/user/repository"
    }
}

The store_stats object above is shortened; borg reports more keys there, e.g. the counters and times of the other storage operations and of the pack cache.

File listings

Each archive item (file, directory, ...) is described by one object in the :ref:`borg_list` output. Refer to the borg list documentation for the available keys and their meaning.

The keys path, target, hlid, type, mode, uid, gid, user, group, flags and inode are always present; flags and inode are null if the source file system did not provide them. The keys used in --format are added to that; the default format contributes size and mtime.

Example (excerpt) of borg list --json-lines:

{"flags": 0, "gid": 0, "group": "wheel", "hlid": "", "inode": 714338381, "mode": "drwxr-xr-x", "mtime": "2026-08-28T08:59:55.543471+02:00", "path": "src/linux/baz", "size": 0, "target": "", "type": "d", "uid": 501, "user": "user"}
{"flags": 0, "gid": 0, "group": "wheel", "hlid": "", "inode": 714338384, "mode": "-rw-r--r--", "mtime": "2026-08-28T08:59:55.543551+02:00", "path": "src/linux/baz/file3", "size": 12, "target": "", "type": "-", "uid": 501, "user": "user"}

Archive Differencing

Each item that :ref:`borg_diff` reports as different between the two archives (in its file contents, in its metadata like mode, owner or timestamps, or because it only exists in one of the archives) is represented by an ItemDiff object. The properties of an ItemDiff object are:

path:: The filename/path of the Item (file, directory, symlink).
changes:: A list of Change objects describing the changes made to the item in the two archives. For example, a file whose contents were modified usually has three changes: the content change itself and the resulting mtime and ctime changes (see the example below).

The Change object can contain a number of properties depending on the type of change that occurred. If a 'property' is not required for the type of change, it is not output. The possible properties of a Change object are:

type:

The type property is always present. It identifies the type of change and will be one of these values:

modified - the file contents changed.
added - the file was added.
removed - the file was removed.
added directory / removed directory - the directory was added / removed.
added link / removed link - the symlink was added / removed.
changed link - the symlink target was changed.
added blkdev / removed blkdev - the block device was added / removed.
added chrdev / removed chrdev - the character device was added / removed.
added fifo / removed fifo - the fifo was added / removed.
changed mode - the mode (file type and permission bits) was changed.
changed type - the file type was changed, e.g. a file was replaced by a directory of the same name. This always comes together with a changed mode change.
changed owner - user and/or group ownership changed.
changed user - user ownership changed. Only emitted together with changed owner.
changed group - group ownership changed. Only emitted together with changed owner.
ctime - the ctime of the item changed.
mtime - the mtime of the item changed.

added:

If type is 'modified', 'added' or 'removed', added and removed give the amount of data (in bytes) added and removed. For 'added', removed is 0; for 'removed', added is 0. For 'modified', added / removed is the total size of the chunks only present in the ARCHIVE2 / ARCHIVE1 version of the file, so both are 0 for a file whose chunks were merely reordered or duplicated. If the chunk ids can not be compared (the archives were created with different --chunker-params), a 'modified' change has neither property and the only information available is that the file contents were modified.

removed:

See added property.

item1:

The value in ARCHIVE1. It is present for 'changed mode', 'changed type', 'changed owner', 'changed user', 'changed group', 'ctime' and 'mtime':

for 'changed mode' the mode string as ls -l prints it,
for 'changed type' the first character of that mode string,
for 'changed owner' a two-element array of user and group,
for 'changed user' / 'changed group' the user / the group,
for 'ctime' / 'mtime' an ISO 8601 timestamp.

User and group are given by name; with --numeric-ids, the numeric uid and gid are given instead (as JSON numbers instead of strings).

item2:

The corresponding value in ARCHIVE2, see item1.

--content-only suppresses the metadata changes, i.e. the changed mode, changed type, changed owner, changed user, changed group, ctime and mtime changes. Items that have only such changes are then not printed at all.

With --stats, a final line of the shape {"stats": {...}} follows the per-path lines. It has no path and no changes property, so it is easy to tell apart. The stats object has these properties (all of them JSON numbers):

added_items:: The number of items that only exist in ARCHIVE2.
removed_items:: The number of items that only exist in ARCHIVE1.
changed_items:: The number of items that exist in both archives, but differ.
size_added:: The total amount of file content (in bytes) added by all of these items, i.e. the sum of the added properties of their content changes (see above).
size_removed:: The total amount of file content (in bytes) removed by all of these items, i.e. the sum of the removed properties of their content changes (see above).
unknown_size_items:: The number of items whose content was modified by an unknown amount (see added above). They are counted in changed_items, but contribute nothing to size_added / size_removed.

--content-only narrows these counts the same way it narrows the per-path output.

Example of borg diff --json-lines --sort-by path ARCHIVE1 ARCHIVE2:

{"changes": [{"item1": "2026-08-28T09:00:12.822775921+02:00", "item2": "2026-08-28T09:00:14.334539472+02:00", "type": "ctime"}, {"item1": "2026-08-28T09:00:12.822775921+02:00", "item2": "2026-08-28T09:00:14.334539472+02:00", "type": "mtime"}], "path": "data"}
{"changes": [{"type": "removed directory"}], "path": "data/dir1"}
{"changes": [{"type": "added directory"}], "path": "data/dir2"}
{"changes": [{"type": "removed fifo"}], "path": "data/fifo1"}
{"changes": [{"item1": ["user", "staff"], "item2": ["user", "admin"], "type": "changed owner"}, {"item1": "staff", "item2": "admin", "type": "changed group"}, {"item1": "-rwxr-xr-x", "item2": "-rw-r--r--", "type": "changed mode"}, {"item1": "2026-08-28T09:00:12.829163282+02:00", "item2": "2026-08-28T09:00:14.321948295+02:00", "type": "ctime"}], "path": "data/file1"}
{"changes": [{"added": 0, "removed": 4, "type": "removed"}], "path": "data/file2"}
{"changes": [{"added": 8, "removed": 0, "type": "added"}], "path": "data/file3"}
{"changes": [{"added": 8, "removed": 4, "type": "modified"}, {"item1": "2026-08-28T09:00:12.816498270+02:00", "item2": "2026-08-28T09:00:14.334788977+02:00", "type": "ctime"}, {"item1": "2026-08-28T09:00:12.816498270+02:00", "item2": "2026-08-28T09:00:14.334788977+02:00", "type": "mtime"}], "path": "data/file5"}
{"changes": [{"type": "changed link"}, {"item1": "2026-08-28T09:00:12.820243127+02:00", "item2": "2026-08-28T09:00:14.332850526+02:00", "type": "ctime"}, {"item1": "2026-08-28T09:00:12.820210210+02:00", "item2": "2026-08-28T09:00:14.332821942+02:00", "type": "mtime"}], "path": "data/link1"}

With --stats, the same command additionally ends with:

{"stats": {"added_items": 2, "changed_items": 4, "removed_items": 3, "size_added": 16, "size_removed": 8, "unknown_size_items": 0}}

Archive Analysis

:ref:`borg_analyze` --json emits the numbers of its text report as one object. All sizes are byte values; the compression factor the text report shows is stored_size / source_size.

Without --group-by, the dedup_size and hotspots keys are present.

dedup_size describes the considered set of archives:

considered_archives: Number of archives matching the archive filters
total_archives: Number of non-deleted archives in the repository
whole_repository: True if no archive was left over by the filters, so the considered set is the whole repository. Every referenced chunk is then trivially exclusive to the set, and the exclusive key is absent.
deduplicated: Object with source_size and stored_size: the summed size of the union of chunks the considered archives reference, chunks shared within the set counted once
exclusive: Object with source_size and stored_size: the chunks referenced only by the considered set, i.e. what deleting the whole set would free. Absent if whole_repository is true.
unreferenced: Object with stored_size and chunks: the chunks no non-deleted archive references, which borg compact could free. Their source size is not known, as it is only recorded in the archives referencing a chunk.
total_chunks: Number of chunks in the repository chunk index
missing_chunks: Number of chunks referenced by an archive but absent from the repository chunk index

hotspots is a list of objects with path (directory path) and size (bytes of chunks added or removed in that directory between consecutive archives), busiest directory first. It is null if fewer than two archives matched, as hot spots need at least two archives to compare.

With --group-by, the by_group key is present instead, decomposing the whole repository:

archives: Number of non-deleted archives in the repository
group_by: List of the archive attributes the archives were grouped by, as given to --group-by
groups: List of objects with group, archives (number of archives in that group), source_size and stored_size. group is an object mapping each group_by attribute to this group's value for it, e.g. {"name": "home", "host": "host1"}. The sizes are what is exclusive to that group: no archive of another group references those chunks. Biggest stored_size first.
shared: Object with source_size and stored_size: the chunks referenced by two or more groups
unreferenced: As above
total: Object with archives, source_size and stored_size. Each chunk is counted in exactly one of groups, shared and unreferenced, so the groups and shared sizes add up to total.
total_chunks, missing_chunks: As above

Example of borg analyze -a 'sh:userA-*' --json:

{
    "dedup_size": {
        "considered_archives": 2,
        "deduplicated": {"source_size": 3000, "stored_size": 3536},
        "exclusive": {"source_size": 2000, "stored_size": 3338},
        "missing_chunks": 0,
        "total_archives": 3,
        "total_chunks": 13,
        "unreferenced": {"chunks": 0, "stored_size": 0},
        "whole_repository": false
    },
    "encryption": {"encryption": "aes256-ocb", "id_hash": "sha256"},
    "hotspots": [{"path": "home/user/src", "size": 1000}],
    "repository": {
        "id": "06e4027d32f8eae8333f8fe06b1c2c46bf12f22ad10bd4d04a0f30751a26d77b",
        "last_modified": "2026-08-01T22:46:05.886533",
        "location": "/home/user/repository"
    }
}

Message IDs

Message IDs are strings that essentially give a log message or operation a name, without actually using the full text, since texts change more frequently. Message IDs are unambiguous and reduce the need to parse log messages.

Assigned message IDs and related error RCs (exit codes) are:

Errors

Error rc: 2 traceback: no: Error: {}
ErrorWithTraceback rc: 2 traceback: yes: Error: {}
Buffer.MemoryLimitExceeded rc: 2 traceback: no: Requested buffer size {} is above the limit of {}.
EfficientCollectionQueue.SizeUnderflow rc: 2 traceback: no: Could not pop the first {} elements; collection only has {} elements.
RTError rc: 2 traceback: no: Runtime error: {}
CancelledByUser rc: 3 traceback: no: Cancelled by user.
CommandError rc: 4 traceback: no: Command error: {}
PlaceholderError rc: 5 traceback: no: Formatting Error: "{}".format({}): {}({})
InvalidPlaceholder rc: 6 traceback: no: Invalid placeholder "{}" in string: {}
Repository.AlreadyExists rc: 10 traceback: no: A repository already exists at {}.
Repository.CheckNeeded rc: 12 traceback: yes: Inconsistency detected. Please run "borg check {}".
Repository.DoesNotExist rc: 13 traceback: no: Repository {} does not exist.
Repository.InsufficientFreeSpaceError rc: 14 traceback: no: Insufficient free space to complete the transaction (required: {}, available: {}).
Repository.InvalidRepository rc: 15 traceback: no: {} is not a valid repository. Check the repository config.
Repository.InvalidRepositoryConfig rc: 16 traceback: no: {} does not have a valid config. Check the repository config [{}].
Repository.ObjectNotFound rc: 17 traceback: yes: Object with key {} not found in repository {}.
Repository.ParentPathDoesNotExist rc: 18 traceback: no: The parent path of the repository directory [{}] does not exist.
Repository.PathAlreadyExists rc: 19 traceback: no: There is already something at {}.
Repository.PathPermissionDenied rc: 21 traceback: no: Permission denied to {}.
Repository.PackLocationUnknown rc: 22 traceback: yes: Object with key {} is indexed but its pack location is unresolved in repository {}.
Repository.PackNotFound rc: 23 traceback: yes: Object with key {} is indexed to pack {}, but that whole pack is missing from repository {}.
Repository.PermissionDenied rc: 24 traceback: no: Repository permission denied: {}
MandatoryFeatureUnsupported rc: 25 traceback: no: Unsupported repository feature(s) {}. A newer version of Borg is required to access this repository.
NoManifestError rc: 26 traceback: no: Repository has no manifest.
UnsupportedManifestError rc: 27 traceback: no: Unsupported manifest envelope. A newer version is required to access this repository.
Archive.AlreadyExists rc: 30 traceback: no: Archive {} already exists
Archive.DoesNotExist rc: 31 traceback: no: Archive {} does not exist
Archive.IncompatibleFilesystemEncodingError rc: 32 traceback: no: Failed to encode filename "{}" into file system encoding "{}". Consider configuring the LANG environment variable.
KeyfileInvalidError rc: 40 traceback: no: Invalid key data for repository {} found in {}.
KeyfileMismatchError rc: 41 traceback: no: Mismatch between repository {} and key file {}.
KeyfileNotFoundError rc: 42 traceback: no: No key file for repository {} found in {}.
NotABorgKeyFile rc: 43 traceback: no: This file is not a Borg key backup, aborting.
RepoKeyNotFoundError rc: 44 traceback: no: No key found in repository {}.
RepoIdMismatch rc: 45 traceback: no: This key backup seems to be for a different backup repository, aborting.
UnencryptedRepo rc: 46 traceback: no: Key management not available for unencrypted repositories.
UnknownKeyType rc: 47 traceback: no: Key type {0} is unknown.
UnsupportedPayloadError rc: 48 traceback: no: Unsupported payload type {}. A newer version is required to access this repository.
UnsupportedKeyFormatError rc: 49 traceback: no: Your Borg key is stored in an unsupported format. Try using a newer version of Borg.
NoPassphraseFailure rc: 50 traceback: no: Cannot acquire a passphrase: {}.
PasscommandFailure rc: 51 traceback: no: Passcommand supplied in BORG_PASSCOMMAND failed: {}.
PassphraseWrong rc: 52 traceback: no: Passphrase supplied in BORG_PASSPHRASE, by BORG_PASSCOMMAND, or via BORG_PASSPHRASE_FD is incorrect.
PasswordRetriesExceeded rc: 53 traceback: no: Exceeded the maximum password retries.
CacheInitAbortedError rc: 60 traceback: no: Cache initialization aborted
EncryptionMethodMismatch rc: 61 traceback: no: Repository encryption method changed since last access, refusing to continue
RepositoryAccessAborted rc: 62 traceback: no: Repository access aborted
RepositoryIDNotUnique rc: 63 traceback: no: Cache is newer than repository - do you have multiple, independently updated repos with same ID?
RepositoryReplay rc: 64 traceback: no: Cache, or information obtained from the security directory is newer than repository - this is either an attack or unsafe (multiple repos with same ID)
LockError rc: 70 traceback: no: Failed to acquire the lock {}.
LockErrorT rc: 71 traceback: yes: Failed to acquire the lock {}.
LockFailed rc: 72 traceback: yes: Failed to create/acquire the lock {} ({}).
LockTimeout rc: 73 traceback: no: Failed to create/acquire the lock {} (timeout). {}
NotLocked rc: 74 traceback: yes: Failed to release the lock {} (was not locked).
NotMyLock rc: 75 traceback: yes: Failed to release the lock {} (was/is locked, but not by me).

These six msgids are shared by the repository lock (storelocking) and the filesystem lock (fslocking), which only the legacy borg 1.x repository code uses (e.g. during borg transfer --from-borg1). The messages are the same except for LockTimeout, which the fslocking variant emits without the trailing hint.

ConnectionClosed rc: 80 traceback: no: Connection closed by remote host.
ConnectionClosedWithHint rc: 81 traceback: no: Connection closed by remote host. {}
InvalidRPCMethod rc: 82 traceback: no: RPC method {} is not valid.
PathNotAllowed rc: 83 traceback: no: Repository path not allowed: {}.
LegacyRemoteRepository.RPCServerOutdated rc: 84 traceback: no: Borg server is too old for {}. Required version {}
UnexpectedRPCDataFormatFromClient rc: 85 traceback: no: Borg {}: Got unexpected RPC data format from client.
UnexpectedRPCDataFormatFromServer rc: 86 traceback: no: Got unexpected RPC data format from server: {}
ConnectionBrokenWithHint rc: 87 traceback: no: Connection to remote host is broken. {}
IntegrityError rc: 90 traceback: yes: Data integrity error: {}
FileIntegrityError rc: 91 traceback: yes: File failed integrity check: {}
DecompressionError rc: 92 traceback: yes: Decompression error: {}
CorruptPack rc: 93 traceback: no: {}. Run "borg check --repair" to recover the objects that are still readable.

Reading a legacy borg 1.x repository (e.g. borg transfer --from-borg1) raises the LegacyRepository.* and LegacyRemoteRepository.* variants of the repository and RPC errors above. They use the same RCs as their non-legacy counterparts.

Warnings

BorgWarning rc: 1: Warning: {}
BackupWarning rc: 1: {}: {}
FileChangedWarning rc: 100: {}: file changed while we backed it up.
IncludePatternNeverMatchedWarning rc: 101: Include pattern '{}' never matched.
BackupError rc: 102: {}: backup error
BackupRaceConditionError rc: 103: {}: file type or inode changed while we backed it up (race condition, skipped file)
BackupOSError rc: 104: {}: {}
BackupPermissionError rc: 105: {}: {}
BackupIOError rc: 106: {}: {}
BackupFileNotFoundError rc: 107: {}: {}
BackupSymlinkParentError rc: 108: {}: not extracted, a parent directory is a symlink (malicious or corrupted archive)
BackupPathTraversalError rc: 109: {}: not extracted, path contains "../" (malicious or corrupted archive)
BackupHardlinkSourceError rc: 110: {}: not extracted, hardlink source path is unsafe (malicious or corrupted archive)
BackupTimeoutError rc: 111: {}: {}
BackupBrokenSymlinkError rc: 112: {}: {}
BackupDamagedChunksError rc: 113: {}: {}

Operations

cache.close

Saving the local cache (files cache, chunks index, cache config) at the end of a command.
cache.build_chunkindex_from_repo

Rebuilding the chunk index by reading all pack file headers from the repository, e.g. when it cannot be built from the stored index fragments or when borg check --repair rebuilds a corrupt index.
check.index
check.packs
check.verify_data
check.rebuild_archives
check.rebuild_archives_directory
repository.merge_packs
compact.analyze_archives
compact.compact_packs
repo_compress.recompress
analyze.dedup_size
analyze.analyze_archives
extract

Used by :ref:`borg_extract` and :ref:`borg_export-tar`. info is one string element, the name of the path currently extracted.
extract.permissions
prune

Prompts

BORG_UNKNOWN_UNENCRYPTED_REPO_ACCESS_IS_OK: For "Warning: Attempting to access a previously unknown unencrypted repository!"
BORG_RELOCATED_REPO_ACCESS_IS_OK: For "Warning: The repository at location ... was previously located at ..."
BORG_CHECK_I_KNOW_WHAT_I_AM_DOING: For "This is a potentially dangerous function..." (check --repair)
BORG_DELETE_I_KNOW_WHAT_I_AM_DOING: For "You requested to DELETE the following repository completely including ... archives it contains:" (repo-delete)
BORG_DISPLAY_PASSPHRASE: For "Do you want your passphrase to be displayed for verification? [yN]:" (interactive entry of a new passphrase)

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