borg-check - Check repository consistency
borg [common options] check [options]
The check command verifies the consistency of a repository and the
corresponding archives.
check --repair is a potentially dangerous function and might lead
to data loss (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 this software with stress
testing software such as memory testers. Unreliable hardware can also lead
to data loss especially when this command is run in repair mode.
First, the underlying repository data files are checked:
- For all segments, the segment magic header is checked.
- For all objects stored in the segments, all metadata (e.g. CRC and size)
and all data is read. The read data is checked by size and CRC. Bit rot
and other types of accidental damage can be detected this way.
- In repair mode, if an integrity error is detected in a segment, try to
recover as many objects from the segment as possible.
- In repair mode, make sure that the index is consistent with the data
stored in the segments.
- If checking a remote repo via ssh:, the repo check is executed on
the server without causing significant network traffic.
- The repository check can be skipped using the --archives-only
option.
- A repository check can be time consuming. Partial checks are possible with
the --max-duration option.
Second, the consistency and correctness of the archive metadata is
verified:
- Is the repo manifest present? If not, it is rebuilt from archive metadata
chunks (this requires reading and decrypting of all metadata and
data).
- Check if archive metadata chunk is present; if not, remove archive from
manifest.
- For all files (items) in the archive, for all chunks referenced by these
files, check if chunk is present. In repair mode, if a chunk is not
present, replace it with a same-size replacement chunk of zeroes. If a
previously lost chunk reappears (e.g. via a later backup), in repair mode
the all-zero replacement chunk will be replaced by the correct chunk. This
requires reading of archive and file metadata, but not data.
- In repair mode, when all the archives were checked, orphaned chunks are
deleted from the repo. One cause of orphaned chunks are input file related
errors (like read errors) in the archive creation process.
- In verify-data mode, a complete cryptographic verification of the archive
data integrity is performed. This conflicts with --repository-only
as this mode only makes sense if the archive checks are enabled. The full
details of this mode are documented below.
- If checking a remote repo via ssh:, the archive check is executed
on the client machine because it requires decryption, and this is always
done client-side as key access is needed.
- The archive checks can be time consuming; they can be skipped using the
--repository-only option.
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 complete repository has
been checked. Example: Assuming a complete check took 7 hours, then running
a daily check with --max-duration=3600 (1 hour) resulted in one completed
check per week.
Attention: A partial --repository-only check can only do way less
checking than a full --repository-only check: only the non-cryptographic
checksum checks on segment file entries are done, while a full
--repository-only check would also do a repo index check. A partial check
cannot be combined with the --repair option. Partial checks may
therefore be useful only with very large repositories where a full check
would take too long. Doing a full repository check aborts a partial check;
the next partial check will restart from the beginning.
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. This is a cryptographic verification, which will detect
(accidental) corruption. For encrypted repositories it is tamper-resistant
as well, unless the attacker has access to the keys. It is also very
slow.
See borg-common(1) for common options of Borg commands.
- -a PATTERN, --match-archives PATTERN
- only consider archive names matching the pattern. see "borg help
match-archives".
- --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
- --oldest TIMESPAN
- consider archives between the oldest archive's timestamp and (oldest +
TIMESPAN), e.g. 7d or 12m.
- --newest TIMESPAN
- consider archives between the newest archive's timestamp and (newest -
TIMESPAN), e.g. 7d or 12m.
- --older TIMESPAN
- consider archives older than (now - TIMESPAN), e.g. 7d oder 12m.
- --newer TIMESPAN
- consider archives newer than (now - TIMESPAN), e.g. 7d or 12m.