Mullion Support

Mullion uses a 27-inch 5K iMac from late 2015 as a display for another Mac. It has two apps: Mullion Display on the Mac you work on, and Mullion Receiver on the iMac. Mullion is in development; this page describes the current build.

Requirements

• Mullion Display: macOS 14 or later on an Apple silicon Mac
• Mullion Receiver: macOS 12 or later, on the iMac
• Tested with iMac (Retina 5K, 27-inch, Late 2015) running macOS 12.7.6
• Both Macs on the same local network

Before you connect

1. Put Mullion Receiver in /Applications on the iMac. macOS relocates an app opened from Downloads, and launch-at-login then stops working.
2. Open Mullion Receiver on the iMac and leave it open. Mullion Display waits up to 30 seconds for it.
3. Grant permissions: Screen Recording to Mullion Display on the Mac you work on, Accessibility to both apps, and Post Events to Mullion Receiver on the iMac.

Mullion Display shows which permission is still missing.

Common questions

How do I pair the two Macs? Open Mullion Receiver on the iMac and choose to pair a new Mac. It shows a six-digit code, valid for five minutes. Enter the code in Mullion Display on your other Mac. You pair once; after that the two Macs connect on their own, over an encrypted connection.

Connect does nothing, or the other Mac's screen never appears. Mullion Display needs Screen Recording. Open System Settings › Privacy & Security › Screen Recording and turn Mullion Display on. macOS asks you to reopen the app; quit it, open it again, and connect again.

The iMac's keyboard or clicks don't reach my other Mac. On the Mac you work on, give Mullion Display Accessibility in System Settings › Privacy & Security. On the iMac, give Mullion Receiver Accessibility and Post Events; on macOS 12 these are in System Preferences › Security & Privacy › Privacy. Then start the stream again.

How do I stop streaming from the iMac? Press Control-Option-Command-S on the iMac. Streaming stops and your windows return to your other Mac's screen.

Ethernet or Wi-Fi? Both work. Mullion uses Ethernet when a cable is connected and switches to Wi-Fi when you unplug it, without restarting the stream.

Contact

Write to support@i4xstudio.com. Include both Macs' macOS versions, the iMac model, and whether you use Ethernet or Wi-Fi.

Privacy: see the Mullion privacy policy.