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deucalion verify

Checks that the backup on the drive is complete and undamaged.

$ deucalion verify --help
usage: deucalion verify [-h] [--full] [--target NAME]

check the backup on the drive is complete and undamaged

options:
  -h, --help     show this help message and exit
  --full         also re-read every file and compare checksums
  --target NAME  which registered drive to use
Mode What it checks How long
deucalion verify (quick) Every file in the backup is on the drive, with the right size. Seconds to minutes.
deucalion verify --full The same, and it reads every file and compares its checksum (SHA-256) with the one recorded at backup time. Finds files damaged on the drive. As long as reading the whole backup from the drive: for example, at 120 MB per second (a typical USB hard disk), about 15 minutes per 100 GB. 
$ deucalion verify --full
Verified 648 files, 157.0 MB — full (checksums)
The backup is intact.

When something is wrong, it lists what, and marks those files so the next backup copies them again:

$ 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.
Problem Meaning
Missing on drive The file isn't on the drive any more.
Wrong size The file on the drive has a different size than recorded.
Damaged (checksum mismatch) (--full) The content changed: the drive may be failing, or the file was changed outside Deucalion.

Then run deucalion backup: the files are copied again from your computer (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

If problems come back

Damaged files that keep appearing mean the drive itself is failing. Copy your backup to another drive soon (see Move your backups to a bigger drive).

Option What it does
--full Also read every file and compare checksums.
--target NAME Which backup drive.

Ctrl+C stops it ("Stopped before the end."). Problems found until then are still marked.

Exit codes

0 the backup is intact; 1 problems found (or the drive isn't available); 130 stopped.