Apple doesn’t let you use a shared folder as a time machine destination in regular OSX (you can buy server and get that functionality), only a full volume or Time Capsule.
But you can use this command line trick:
- This assumes your Folder exported is called TimeMachine
- AFP mount your TimeMachine share via Command-K on the Mac you want to back up.
- Try this. It will probably fail with an error about locking:
sudo tmutil setdestination /Volumes/TimeMachine
- On the server you want to back up to, run
defaults write /private/var/db/dslocal/nodes/Default/sharepoints/TimeMachine.plist \ "timeMachineBackup" '(1)'
- Rerun
sudo tmutil setdestination /Volumes/TimeMachine
- Validate you can start your backup with:
tmutil startbackup