Provided by: borgbackup_1.2.6-2_amd64 
NAME
borg-check - Check repository consistency
SYNOPSIS
borg [common options] check [options] [REPOSITORY_OR_ARCHIVE]
DESCRIPTION
The check command verifies the consistency of a repository and its archives. It consists
of two major steps:
1. Checking the consistency of the repository itself. This includes checking the segment
magic headers, and both the metadata and data of all objects in the segments. The read
data is checked by size and CRC. Bit rot and other types of accidental damage can be
detected this way. Running the repository check can be split into multiple partial
checks using --max-duration. When checking a remote repository, please note that the
checks run on the server and do not cause significant network traffic.
2. Checking consistency and correctness of the archive metadata and optionally archive
data (requires --verify-data). This includes ensuring that the repository manifest
exists, the archive metadata chunk is present, and that all chunks referencing files
(items) in the archive exist. This requires reading archive and file metadata, but not
data. To cryptographically verify the file (content) data integrity pass --verify-data,
but keep in mind that this requires reading all data and is hence very time consuming.
When checking archives of a remote repository, archive checks run on the client machine
because they require decrypting data and therefore the encryption key.
Both steps can also be run independently. Pass --repository-only to run the repository
checks only, or pass --archives-only to run the archive checks only.
The --max-duration option can be used to split a long-running repository check into
multiple partial checks. After the given number of seconds the check is interrupted. The
next partial check will continue where the previous one stopped, until the full repository
has been checked. Assuming a complete check would take 7 hours, then running a daily check
with --max-duration=3600 (1 hour) would result in one full repository check per week.
Doing a full repository check aborts any previous partial check; the next partial check
will restart from the beginning. With partial repository checks you can run neither
archive checks, nor enable repair mode. Consequently, if you want to use --max-duration
you must also pass --repository-only, and must not pass --archives-only, nor --repair.
Warning: Please note that partial repository checks (i.e. running it with --max-duration)
can only perform non-cryptographic checksum checks on the segment files. A full repository
check (i.e. without --max-duration) can also do a repository index check. Enabling partial
repository checks excepts archive checks for the same reason. Therefore partial checks may
be useful with very large repositories only where a full check would take too long.
The --verify-data option will perform a full integrity verification (as opposed to
checking the CRC32 of the segment) of data, which means reading the data from the
repository, decrypting and decompressing it. It is a complete cryptographic verification
and hence very time consuming, but will detect any accidental and malicious corruption.
Tamper-resistance is only guaranteed for encrypted repositories against attackers without
access to the keys. You can not use --verify-data with --repository-only.
About repair mode
The check command is a readonly task by default. If any corruption is found, Borg will
report the issue and proceed with checking. To actually repair the issues found, pass
--repair.
NOTE:
--repair is a POTENTIALLY DANGEROUS FEATURE and might lead to data loss! This does not
just include data that was previously lost anyway, but might include more data for
kinds of corruption it is not capable of dealing with. BE VERY CAREFUL!
Pursuant to the previous warning it is also highly recommended to test the reliability of
the hardware running Borg with stress testing software. This especially includes storage
and memory testers. Unreliable hardware might lead to additional data loss.
It is highly recommended to create a backup of your repository before running in repair
mode (i.e. running it with --repair).
Repair mode will attempt to fix any corruptions found. Fixing corruptions does not mean
recovering lost data: Borg can not magically restore data lost due to e.g. a hardware
failure. Repairing a repository means sacrificing some data for the sake of the repository
as a whole and the remaining data. Hence it is, by definition, a potentially lossy task.
In practice, repair mode hooks into both the repository and archive checks:
1. When checking the repository's consistency, repair mode will try to recover as many
objects from segments with integrity errors as possible, and ensure that the index is
consistent with the data stored in the segments.
2. When checking the consistency and correctness of archives, repair mode might remove
whole archives from the manifest if their archive metadata chunk is corrupt or lost. On
a chunk level (i.e. the contents of files), repair mode will replace corrupt or lost
chunks with a same-size replacement chunk of zeroes. If a previously zeroed chunk
reappears, repair mode will restore this lost chunk using the new chunk. Lastly, repair
mode will also delete orphaned chunks (e.g. caused by read errors while creating the
archive).
Most steps taken by repair mode have a one-time effect on the repository, like removing a
lost archive from the repository. However, replacing a corrupt or lost chunk with an
all-zero replacement will have an ongoing effect on the repository: When attempting to
extract a file referencing an all-zero chunk, the extract command will distinctly warn
about it. The FUSE filesystem created by the mount command will reject reading such a
"zero-patched" file unless a special mount option is given.
As mentioned earlier, Borg might be able to "heal" a "zero-patched" file in repair mode,
if all its previously lost chunks reappear (e.g. via a later backup). This is achieved by
Borg not only keeping track of the all-zero replacement chunks, but also by keeping
metadata about the lost chunks. In repair mode Borg will check whether a previously lost
chunk reappeared and will replace the all-zero replacement chunk by the reappeared chunk.
If all lost chunks of a "zero-patched" file reappear, this effectively "heals" the file.
Consequently, if lost chunks were repaired earlier, it is advised to run --repair a second
time after creating some new backups.
OPTIONS
See borg-common(1) for common options of Borg commands.
arguments
REPOSITORY_OR_ARCHIVE
repository or archive to check consistency of
options
--repository-only
only perform repository checks
--archives-only
only perform archives checks
--verify-data
perform cryptographic archive data integrity verification (conflicts with
--repository-only)
--repair
attempt to repair any inconsistencies found
--save-space
work slower, but using less space
--max-duration SECONDS
do only a partial repo check for max. SECONDS seconds (Default: unlimited)
Archive filters
-P PREFIX, --prefix PREFIX
only consider archive names starting with this prefix. (deprecated)
-a GLOB, --glob-archives GLOB
only consider archive names matching the glob. sh: rules apply, see "borg help
patterns".
--sort-by KEYS
Comma-separated list of sorting keys; valid keys are: timestamp, name, id; default
is: timestamp
--first N
consider first N archives after other filters were applied
--last N
consider last N archives after other filters were applied
SEE ALSO
borg-common(1)
AUTHOR
The Borg Collective
2023-08-30 BORG-CHECK(1)