Universal Control between Mac and iPad: a working setup, and the diagnostic commands when it stops

Universal Control is one of the more genuinely magical things macOS does — slide your cursor off the right edge of your Mac and it appears on your iPad, you keep typing without changing keyboards, you drag a file across both screens. When it works, it feels like the way computers were always supposed to work. When it doesn’t, the only advice you’ll find online is “turn both devices off and on again.” That sometimes works. More often it doesn’t. Here’s a working setup, and the actual diagnostic commands to run when it stops connecting.

The setup that reliably works

Before troubleshooting, get the prerequisites right. Universal Control is fussier about preconditions than Apple’s marketing implies:

Both devices on the same Apple ID with two-factor authentication enabled. Family-sharing accounts don’t count — both must be the same primary Apple ID.
Both on Wi-Fi and Bluetooth, both turned on, both visible to each other. Universal Control discovers the peer over Bluetooth and then transports the input over Wi-Fi. Either being off kills it.
Handoff enabled on both devices. System Settings → General → AirDrop & Handoff (Mac); Settings → General → AirPlay & Handoff (iPad). Universal Control piggybacks on the same plumbing.
Same network — really the same. If your Mac is on a 5 GHz SSID and your iPad is on a 2.4 GHz guest network, even if both have the same name, Universal Control’s mDNS discovery won’t see across them. Put both on the exact same SSID.
Within ~10 meters of each other. Bluetooth Low Energy range. The discovery beacon doesn’t reach across a wall reliably.
Universal Control toggle on (Mac): System Settings → Displays → Advanced. The toggle was buried in Sidecar settings in older macOS releases; in Sequoia / Tahoe / 27 it’s a top-level “Universal Control” item under Displays.

If all of those are true, drag the cursor off the screen edge toward the iPad. The first time, give it 10–15 seconds — first-pair takes longer than re-pair.

When it stops working: don’t just reboot

Universal Control fails in a small set of consistent ways. The “reboot both devices” advice works because rebooting clears all of them at once. With targeted diagnostics, you can usually identify which one and fix only that.

1. Check that the Continuity daemon is healthy on the Mac

ps -ef | grep -i continuity | grep -v grep
launchctl list | grep -i continuity

You should see com.apple.continuityd active and not in a crash-restart loop. If it’s restarting repeatedly:

log show --predicate 'subsystem CONTAINS "continuity"' --last 30m \
  --style compact 2>/dev/null | head -50

Look for repeated errors. The most common one is “Could not establish IDS session” — that means iMessage / FaceTime infrastructure on the Mac thinks it’s signed out, even though you’re signed in in System Settings. Fix: sign out of iCloud entirely, sign back in. Yes, that’s heavy. It’s also the only thing that reliably fixes the IDS-session loop.

2. Confirm Bluetooth Low Energy is actually advertising

system_profiler SPBluetoothDataType | grep -A3 "State:"
# Should show: State: On

# Check for IOBluetooth crashes
log show --predicate 'process == "bluetoothd"' --last 1h \
  --style compact 2>/dev/null | grep -iE "crash|panic|stuck"

If bluetoothd has been bouncing or panicking, Universal Control won’t see the iPad even when it’s right there. Restart Bluetooth without rebooting:

sudo pkill bluetoothd
# It auto-relaunches. Within 10 seconds your devices reconnect.

That alone fixes ~40% of “Universal Control disappeared today” cases for me.

3. Verify mDNS discovery sees the iPad

# Browse for Apple's continuity service on the local network
dns-sd -B _companion-link._tcp local.

# Should list at least one entry per Apple device on the LAN.
# If you don't see your iPad, the LAN-side discovery is broken — usually router/SSID.

If dns-sd doesn’t show the iPad, check:

Are both devices on the same SSID? Run networksetup -getairportnetwork en0 on the Mac and compare to the iPad’s network name.
Does your router have “client isolation” / “AP isolation” enabled? It blocks devices from seeing each other on the LAN. Disable it.
Does your router have a “guest network” the iPad accidentally joined? Same SSID names but different VLANs is the worst case.

4. The reset that works without a reboot

If everything looks healthy individually but Universal Control still won’t engage, the cleanest reset:

sudo killall -KILL identityservicesd
sudo killall -KILL imagent
sudo killall -KILL ContinuitySupport       # if running
sudo pkill -KILL bluetoothd

All of those auto-restart. The combined effect is: re-establish the IDS session, re-pair Bluetooth, re-discover the iPad. On the iPad side, just toggle Bluetooth off and on, then toggle Wi-Fi off and on. That’s the iPad equivalent of the same kill-restart sequence.

When Universal Control just isn’t right for the moment

If you need a working “two screens / one keyboard” arrangement right now and Universal Control is being stubborn, fall back to Sidecar (which uses the same Continuity stack but is more robust because it streams the Mac’s display rather than coordinating between two independent OSes). Same prerequisites, different feature, and it almost always connects when Universal Control won’t.

Universal Control is great when it works. The above commands turn “it doesn’t work, must reboot” into “I know which subsystem is unhappy and how to nudge it” — which, on a Mac you actually use for work, is the difference between losing five minutes and losing forty.