When I reboot a headless Mac Mini server running macOS Mojave with sudo reboot, it becomes non-ssh-able. The same happens if a "fake monitor" HDMI display emulator is plugged in. This happens consistently with multiple Mac Mini machines. Interestingly, a "hard reboot" (holding the power button until the machine switches off, and then turning it on again) allows the host to come back online, even without plugging in a monitor.

Also, this issue does not happen if a real monitor is plugged in -- in this case the machine reboots fine and comes back online.


The obvious thing to check is if you have FileVault enabled and attach a display simulator dongle. In the FileVault case, the machine does not restart to the OS but to a firmware / limited log in screen, but having a display connected won’t enable/disable FileVault.

You will want to have a remote KVM or someone that can log in for unexpected power failures. See this thread for a lot more options like power, display and management options for headless Macs.

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