Boot error when trying to boot on Mac

[jkugler]

I download the image (version on Linux, unzipped it, and created the USB drive this way:

dd if=memtest86-usb.img of=/dev/sdd

It reported as writing it out. I ran sync, took the drive out, and put it in the Mac system. Booted, held down Option (Alt) and got boot disk screen. Select "Windows" and hit enter. It waits a little while, and then I get a black screen, white text, and it just says "Boot error." How may I go about debugging this?

[David (PassMark)]

What version number of MemTest86?
Are you sure /dev/sdd was the correct device for your USB drive?
Do the contents of the USB drive look OK (it isn't empty for example)?

On newer Macs, from 2018, with the Apple T2 Security Chip, you may need to change the SecureBoot settings
for MemTest86 to boot. Please see the following page for instructions:
https://support.apple.com/en-us/HT208330

[jkugler]

This was the latest version eight image pulled down from web site.

Yes, /dev/sdd was the device that was created when I inserted the USB key.

fdisk reports two partitions.

Device Start End Sectors Size Type
/dev/sdd1 2048 512000 509953 249M Microsoft basic data
/dev/sdd2 514048 1023966 509919 249M EFI System

This is a 2013 iMac. It does show empty when I open it up on the Mac, oddly enough, so I don't know what's going on.

[jkugler]

Despite what fdisk says, this is that Linux tells me, so I'm not sure what's going on

8 48 7816704 sdd
8 49 7816672 sdd1

[David (PassMark)]

I can't remember exactly what file systems these old Macs support. Can you look at the content of the USB drive on a Windows machine. (or just make a new USB drive on a windows machine),

[jkugler]

Well, I figured it out. Somehow a file got created at /dev/sdd, and some things were referencing the actual file, and some were referencing the device.

I apologize for all the noise.

[David (PassMark)]

Glad you sorted it out.