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Check that a backup is intact

What you'll do: check that every file in the backup is on the drive and undamaged.
What you need: your backup drive; a terminal (this check is only on the command line).
How long it takes: the quick check takes seconds; the full check reads the whole backup (for example about 15 minutes per 100 GB on a USB hard disk).

Drives can fail slowly. Checking now and then (for example every few months, and before you move to a new computer) tells you while you can still fix it.

The app has no Verify button. Use the command line for this check (open a terminal with Ctrl+Alt+T and follow the other tab).

  1. The quick check, that every file is there with the right size:

    $ deucalion verify
Verified 648 files, 157.0 MB — quick (sizes)
The backup is intact.

  2. The full check, that every file's content is exactly what was backed up:

    $ deucalion verify --full
Verified 648 files, 157.0 MB — full (checksums)
The backup is intact.

If it finds problems

It lists them and marks those files, so the next backup copies them again from your computer:

$ deucalion verify --full
Verified 648 files, 157.0 MB — full (checksums)
  Damaged (checksum mismatch):
    home/Documents/CV - Alex.pdf
Problems found. The next backup will copy these files again.

  1. Run a backup (in the app or with deucalion backup). The damaged file counts as changed and is copied again; the damaged copy goes to Removed Files.

    $ deucalion backup
Backing up to Alex Backup  /media/alex/Alex Backup/Deucalion-Backup
Saving the system recipe (packages, settings, services) — you may be asked for your administrator password…
Backup plan (full: everything)
  New files:              11   21.4 MB
  Changed files:           1   177.7 KB (previous versions go to _removed/)
  Gone/excluded:           0   0 B (moved to _removed/)
  Unchanged:             647   156.8 MB
Backup finished in 0s: copied 12 files (21.6 MB), moved 0 items to _removed/.
Log: /media/alex/Alex Backup/Deucalion-Backup/.deucalion/logs/2026-10-12_091155-backup.log

  2. Check again with deucalion verify --full:

    $ deucalion verify --full
Verified 659 files, 178.4 MB — full (checksums)
The backup is intact.

If the file is no longer on your computer

Then the backup was the only copy, and the damaged copy can't be repaired. It may still be partly readable in Removed Files. If problems keep coming back, the drive is failing: move your backup to another drive (see Move your backups to a bigger drive).

What you have now: confidence that your backup can be restored.

Next steps: deucalion verify for all options.