The man page for
tmutil mentions that Time Machine records checksums of files, and lists a
verifychecksums command. The man page is sparse on details, and does not otherwise mention checksums. I was wondering whether Time Machine ever automatically verifies these checksums (or if these are only verified when you run
verifychecksums manually)? The page also says checksums are not retroactively computed, so how can I list the files in my latest backup for which no checksum is available? Also, is it known what checksumming algorithm is used?
verifychecksums path ... Compute a checksum of data contained within a backup and verify the result(s) against checksum information computed at the time of backup. No output is generated for matching checksums. Issues are reported using the following legend: ! The file's current checksum does not match the expected recorded checksum. ? The file's recorded checksum is invalid. Beginning in OS X 10.11, Time Machine records checksums of files copied into snapshots. Checksums are not retroactively computed for files that were copied by earlier releases of OS X.
The above is from the
tmutil man page in OS X 10.11.6, maybe the one in macOS Sierra has more details.