How to Fix Automatic Hostname Changes (iMac 2 to iMac 3) on macOS Sequoia

guide Hostname iMac2015 macOSSequoia Networking OpenCoreLegacyPatcher
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macOS sequoia

How to Resolve Network Hostname Conflicts on macOS Sequoia

iMac 2015 users running macOS Sequoia via OpenCore Legacy Patcher may experience an issue where the computer\'s network hostname changes automatically (e.g. appending a number like iMac (4) or iMac (5)). This behaviour is caused by network routing loops or DNS conflicts (often associated with Tailscale or Bonjour sleep proxy), rather than OCLP hardware spoofing.

1. Prerequisites

  • Target Hardware: iMac 2015 models running macOS Sequoia.
  • Required Tools: macOS Terminal.

2. Compatibility Snapshot

  • Scope: Universal macOS networking bug; not related to OCLP serial number modifications.

3. Installation Preparation

  1. Open Terminal: Launch the Terminal application on your Mac.

4. EFI and config.plist Review

  1. This does not apply to this case as the configurations are managed inside the macOS network subsystem.

5. Post-Installation

  1. Set Static Hostname: Run the following commands in Terminal to force macOS to use a static, immutable hostname: sudo scutil --set ComputerName "MyiMac", sudo scutil --set HostName "MyiMac.local", and sudo scutil --set LocalHostName "MyiMac".
  2. Restart Bonjour: Reload the network responder daemon: sudo killall -HUP mDNSResponder.

6. Troubleshooting

Reported Issue: Hostname continues to increment
  1. Tailscale conflict: If using Tailscale, disable "MagicDNS" in your Tailscale admin console, as it can conflict with local mDNS configurations.
  2. Router cache: Reboot your local Wi-Fi router to clear stale DHCP reservations linked to your Mac\'s MAC address.

7. Dual Boot and Advanced Configuration

  • This does not apply to this case as network hostnames are operating system-specific.

8. Verification, Maintenance and Rollback

  • Verify Fix: Go to System Settings -> General -> About and verify that the Computer Name remains unchanged after a system reboot.

9. References and Glossary

  • mDNSResponder: The system daemon responsible for managing multicast DNS requests for Bonjour services.

Original Question: "How is this happening?"

How is this happening?

Every so often, the only iMac on my network (2015 4K, OCLP Patched, latest Sequoia update) reports that its hostname was already taken and has been automatically changed.

It just went from iMac 4 to iMac 5 :')

Could this have something to do with running some sort of spoofing in OCLP? (to enable sidecar functions on this particular model). Or maybe because of Tailscale?

submitted by /u/pieterv1
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on 4:37:00 PM

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