What is backed up

• Valheim: the world folder (.db2, .fwl2, .ok, .chunks and .chunk files), or the .db + .fwl pair for older worlds.
• Project Zomboid: the world save, the player database and the server's settings files.

Automatic backups

• A server run becomes eligible for a backup once at least one player connects.
• If the server starts and nobody connects, no backup is made.
• The backup is taken when that run ends: the server is stopped by hand or by auto stop, restarted, or recreated after a settings change. Deleting a server also backs up an eligible run first.
• Backups are taken after the server has stopped, so they hold the world as it was saved on shutdown.

Manual backups

• Made every time you use Download in a server's Manage panel: the zip you download is also saved here.
• While the server is running this is its last autosave (Valheim saves about every 30 minutes). Stop the server first for an up-to-the-minute copy.

Retention

• The newest 5 automatic and newest 5 manual backups are kept for each server. Older ones are deleted when a new backup is made.
• Backups are stored on the VPS in /srv/gameservers/backups/<game>/<auto|manual>/, outside the server's own folder, so they are kept even if the server and its world files are deleted.