ERROR: Could not connect to lockdownd: Invalid HostID (-21) when this Mac’s pairing record for the phone is missing or no longer matches.
Why it happens
The phone forgot this Mac, or this Mac holds an old pairing.Fix
- Unplug the iPhone and plug it back in.
- Unlock it and tap Trust, then enter your passcode.
- Choose Check again in Mobster for Mac, or run
mobster doctor.
Check it worked
idevice_id -l prints the phone’s UDID, and mobster doctor prints no not trusted line for it.
Checked 26 Oct 2026 against Mobster 0.4.0. Back to Troubleshooting.