We have a number of iMacs (models 14,1 to 16,2) running in a StorNext 5 environment as Distributed LAN Clients (DLC). These machines have Apple USB Ethernet adaptors attached to provide a secondary Ethernet interface for the StorNext Metadata network. We have updated three machines (one 14,1 model, and two 16,2 models) with the most recent Security Update (not the latest 10.12.3 update).

All three machines fail to reboot until the Apple USB Ethernet adaptor is temporarily removed. All three machines stay on a black screen indefinitely until the Apple USB Ethernet adaptor is removed. Once the Apple USB Ethernet adaptor is unplugged the Apple logo appears and the machines boot up as normal.

This behaviour is consistent across all three machines since the update. Machine #1 is a 14,1 model running El Capitan 10.11.6. Machines #2 and #3 are 16,2 models running Sierra 10.12.2. All three machines rebooted perfectly before the latest Security Update was installed.

Though we are able to re-insert the Apple USB Ethernet adaptor during boot time (and therefore get our SAN volume mounted) this is not an ideal situation. All three of these machines are managed remotely, and if they are rebooted while unattended they will not come back online.

We have had some success making the USB Ethernet inactive in System Preferences/Network before applying the update, but this does not work every time.

TL;DR, the most recent Security Update for El Cap and Sierra breaks our iMacs with Apple USB Ethernet adaptors attached.

Anybody else encountered this?

  • I have a separate lap network for testing and use the Thunderbolt to Ethernet Adapter and I have not had any problems. I also have a generic USB to Ethernet adapter and I didn't find any issue with booting. I would first try a different adapter to rule out "Apple" issues.
    – Allan
    Jan 23, 2017 at 21:09
  • Thanks for your comment. We have found the Thunderbolt adapters work perfectly well in our tests, too, but we do not have any third-party USB Ethernet adapters to test with. We were hoping not to have replace the entire collection of USB Ethernet adaptors with Thunderbolt ones as this creates a few other headaches besides the cost - we have a few machines running outboard A/V hardware and drives via Thunderbolt as well as external displays, which means we have to daisychain devices.
    – Peeet
    Jan 23, 2017 at 21:55

1 Answer 1


It seems the latest update (10.12.3) for Sierra clients has fixed this problem, I was able to start one of the affected Macs from cold and restart without it sticking on the black screen.

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