Boot MBP in Target Disk Mode with Broken Display and Encrypted

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Boot MBP in Target Disk Mode with Broken Display and Encrypted

My macbook pro 2018 (running latest 10.14.3) has a broken display and is encrypted. Before I send my computer with the broken display to Apple for repair, I want to backup using TimeMachine.

The easy solution is to plug an external monitor into the broken computer. I've already tried, and for some unclear reason it doesn't work. So my next option is to use another MBP to load the broken computer's drive using Target Disk mode.

So I put my broken computer in Target Disk mode by powering on and holding onto the key "T". I've connected the two computers using a Thunderbolt 3 to Thunderbolt 3 cable. Even though the display is broken, I know the target computer is in Target Disk mode because I can see the disk on my host computer. However, when I try to boot the host computer using the drive of the broken computer in Target Disk it doesn't work. My hypothesis is because my target computer is encrypted.

How do I boot my target computer onto my host computer? There is never an option to decrypt my target computer during the startup.

Edit:

I found this on the web: FileVault encryption: If the Mac you intend to use Target Disk Mode on is using FileVault to encrypt the internal drive, then Target Disk Mode will fail. To use Target Disk Mode, you need to turn off FileVault before booting the Mac in Target Disk Mode.

Based on that, I need to run off Filevault on my broken computer. Question is, how do I do that with a broken display?

Posted on Mar 5, 2019 2:47 PM

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Answer 1

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ifrog3c Author

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Mar 27, 2019 3:49 PM in response to ifrog3c

To close the loop on this issue ... the only solution I found was to connect my broken display computer to another working mbp via thunderbolt 3 cable by putting my broken display computer in target disk mode.

I then used Carbon Copy to make a clone/backup of my hard drive on my broken display computer. My broken display computer should be returned by Apple soon, total damage $680 not including tax. So if my computer returns with the hard drive wiped, I will use my carbon copy clone to restore.

Lesson learned. Be very careful when closing the clamshell by making sure nothing like a lightning cable is sandwiched in between. The tolerances of the clamshell are very close and your display will break.

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Answer 2

HWTech

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60,284 points

Mar 5, 2019 7:07 PM in response to ifrog3c

The 2018 Macs have a new T2 Security chip and by default Apple has the systems configured not to allow booting of external drives. The only way to allow booting of external devices is by booting into Recovery Mode and running the new security app to change the default settings.

If closing the laptop lid doesn't get video to the external display, then I'm not sure. Might be a dongle issue. I don't have any personal experience with the 2018 models yet. Do you have remote access enabled?

I thought with Target Disk Mode, at least you could make one more copy of your files. You could use Carbon Copy Cloner to make an image of your user folder or even of your whole drive. Here are a couple of articles about the new security features of the T2 chip:

https://support.apple.com/en-us/HT208198

https://blog.macsales.com/46677-all-about-the-apple-t2-security-chip-and-startup-security-utility

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Answer 3

HWTech

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Mar 5, 2019 3:13 PM in response to ifrog3c

I'm not sure if this is still valid with the T2 chip and Mojave, but launch Disk Utility and select the "Mount" option. On older systems this will prompt you for the FileVault password and unlock the drive.

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Answer 4

ifrog3c Author

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Mar 5, 2019 3:22 PM in response to HWTech

Nice suggestion. The mount option is still there ... so I was able to mount the drive in Target Disk mode after inputting my password. BUT ... still no obvious way to boot the host computer using the drive in Target Disk mode. After mounting the drive, I exited Disk Utility and selected the Target drive but it still booted with the host drive.

Is there something you were thinking I should do after mounting the Target drive?

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Answer 5

Mar 5, 2019 8:42 PM in response to ifrog3c

All you really seem to need is a display.

What did you connect, using what adapters, and what was the result?

Did you try Command+F1 shortcut to Mirror displays? (not sure if fn key is required as well)

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Answer 6

ifrog3c Author

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Mar 6, 2019 11:51 PM in response to HWTech

You are correct about changing the default settings for the boot security. I went into Recovery mode and changed the default settings so that I could boot other target disks on the host computer. Still no joy, and I'm 99% sure nothing will work unless I am able to turn off encryption on the broken computer, which seems impossible with no display.

I have tried connecting the broken computer to external monitors using thunderbolt, usb-c, and a usb-c to DP cable. Nothing works. I did a google search of this same problem and there is at least one other person who also broke their display on their 2018 macbook pro and inexplicably is unable to use an external display.

Good call on the carbon copy. I think this is my only option since I am able to access the broken computer's drive when it's in target disk mode, I just can't boot it.

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Answer 7

Mar 27, 2019 4:54 PM in response to ifrog3c

I think a second lesson is, "ALWAYS have a recent backup."

If you don't want to take the time to make one, that is what Time Machine is all about.

Time machine runs automatically at low priority in the background, so you keep working, and when you look up, its latest backup is less than an hour old, and you did not have to do anything to make it happen.

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Answer 8

ifrog3c Author

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Apr 3, 2019 3:50 AM in response to Grant Bennet-Alder

Yes, I completely agree.

For the full story, I do use TimeMachine, so I generally always have a backup. Recently, the TimeMachine volume on my NAS became full and I haven't been able to backup to it. So I need to increase my volume on the NAS. Normally TimeMachine will delete old backups to make room but the volume is quite small and I have more than one computer backing to the NAS.

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Boot MBP in Target Disk Mode with Broken Display and Encrypted

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