MacBook Pro 2018 not booting from external drive for recovery

[haralds]

My MacBook Pro 2018 just arrived and got bricked during App Migration. After much pain I ended up formatting and doing a SLOOOOOW internet setup.

I was able to get into the recovery partition and disable the T2 external boot prevention prior format. You are totally hosed, if you do not have a system password.

But I was unable to boot from two High Sierra 10.13.6 drives, one freshly installed. I was also unable to start from an installer setup on Flash stick using the tools included in the Apple installer.

I have NEVER run into this.

 

[chscag]

There has been lots of discussion in these forums regarding the 2018 MacBook Pros and problems arising from the T2. You may be better off (if possible) taking the machine to your nearest Apple store to swap it out for a new one or contact Apple support to do the same.

 

[patwithamac]

My MacBook Pro 2018 just arrived and got bricked during App Migration. After much pain I ended up formatting and doing a SLOOOOOW internet setup.

I was able to get into the recovery partition and disable the T2 external boot prevention prior format. You are totally hosed, if you do not have a system password.

But I was unable to boot from two High Sierra 10.13.6 drives, one freshly installed. I was also unable to start from an installer setup on Flash stick using the tools included in the Apple installer.

I have NEVER run into this.

Ya, I noticed the same behavior too.
Soon after receiving my new 15" 2018, I needed to reformat the SSD (with APFS case-sensitive).
Using the procedure outlined here I disabled secure boot, and enabled booting from external media.
I have a bootable USB stick with the High Sierra installer on it, and the 2018 would not boot from it. It would only do an Internet boot. Upon holding the Option key after power-on, I see the option to select the Installer on the USB stick, and I select it. But, the selection is ignored and it proceeds directly to Internet boot.

I can boot from that same USB stick just fine on my late 2011 MBP.

It took a little while, but it eventually finished Internet booting, and I was eventually able to fully reformat the SSD. I'm back up a running with an SSD formatted APFS case-sensitive now.

Still... I would like to know why it wouldn't boot from the USB stick.

 

[ssn637]

Damn! I'm having the same problem with my newly-arrived MacBook Pro 13" i7 model! I first updated macOS High Sierra using the supplemental update I'd previously downloaded to ensure the CPU throttling problem would be taken care of via the firmware update. I then booted via CMD + R, entered the Startup Security Utility, disabled secure boot and selected the option to allow booting from external media.

I had a macOS Mojave developer beta 5 image prepared on a USB-C Flash Disk and wanted to perform a clean installation after erasing the internal SSD to APFS (Encrypted), but when I restarted using the Option key, even though the Mojave installer was visible, I was told the system needed a software update in order to boot from the external drive. So I connected to the internet while still in recovery mode, allowed the update to download and install, and tried again. Same error message!

I then restarted in macOS High Sierra, entered System Utilities and tried to select the Mojave installer as my start up disk. But this time I was told the computer was unable to boot from the flash disk because of an error with the "Bless Tool". What the heck is that?

If anyone has any luck performing a clean installation of macOS Mojave Beta 5 from a USB Flash Drive on these new models, I'd be eternally grateful if he or she could post the solution here!

Cheers

Edit:
OK, I was finally able to boot from the USB-C Flash Drive by first installing macOS Mojave Beta 5 from the application within the internal SSD and then rebooting into the USB-C Drive startup disk and performing the installation a second time after erasing the internal SSD. Apparently, the original system's macOS High Sierra was unable to boot from the external media, but after "upgrading" to Mojave Beta 5 the external disk was recognized and I could proceed.

 

[patwithamac]

I am able to boot from a USB stick created with a process just posted by @TriBruin here