borg-check - Check repository consistency
borg [common options] check [options] [REPOSITORY_OR_ARCHIVE]
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!
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.
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.
- 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 --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.
- -P PREFIX, --prefix PREFIX
- only consider archive names starting with this prefix.
- -a GLOB, --glob-archives GLOB
- only consider archive names matching the glob. sh: rules apply, see
"borg help patterns". --prefix and --glob-archives
are mutually exclusive.
- --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