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The manifest

Most backup drives are formatted as exFAT (or NTFS), so that Windows and macOS can read them. These filesystems can't store some details that Linux keeps for every file:

  • permissions: who may read, change or run a file (for example, your SSH keys must be readable only by you);
  • owner and group;
  • symbolic links (shortcuts that point to another file or folder);
  • some characters in names and the difference between Notes.txt and notes.txt.

Deucalion keeps all of this in a small database on the drive, the manifest: Deucalion-Backup/.deucalion/manifest.sqlite. For every file and folder in the backup it records:

  • its original name and folder;
  • where it is stored on the drive (which may be a slightly different name, see File names on exFAT);
  • its permissions, owner, group, size and modification time;
  • the target of a link;
  • a checksum (a fingerprint of its content, SHA-256) that verify --full uses to find damaged files.

When you restore, Deucalion reads the manifest and puts every detail back. For example, ~/.ssh comes back with its strict permissions, and links are recreated as links.

The manifest also records the history of your backups (shown on the Overview page and by deucalion status).

A copy is kept

After every completed backup, Deucalion saves a copy of the manifest as manifest.sqlite.bak next to it. The manifest is written with the safest settings (every change is written to the drive before the next one), so it survives a drive that is unplugged or a computer that loses power in the middle of a backup.

You don't need it to read your files

The files in the backup are normal files. You can open and copy them without Deucalion and without the manifest (see Open your backup without Deucalion). The manifest is only needed to put back the Linux details exactly.