I regularly use my iMac as an external display for my macbook using target display mode (TDM). Since upgrading my iMac to Sierra, the screen locking behavior has changed in a disturbing way. I'm hoping there's a configuration flag I can set to revert to the old behavior. Here's the situation:
- I unlock the iMac. (log in to my account)
- Connect the two macs with thunderbolt.
- Hit command-f2 to enable TDM. iMac is now an external monitor for macbook.
- Use the macbook for a while. Lock the screen, walk away. Wait a long time.
- Unplug the thunderbolt cable.
- The iMac is logged in and unlocked. (!!)
Previously (before Sierra) on step 6, the iMac would have its account locked, which is of course what I want my mac to do if I haven't been using it in a long time.
How can I get my iMac to lock its account when it's being used as an external monitor in TDM mode? Right now, it seems using TDM is a major security hole for the iMac.