USB i386 VGA Build Key GPT Error

[gamerfreek]

I am trying to turn an old Mac into an opnsense firewall. I tried to create the opnsense USB key with rufus,win32DiskImager, and balenaEtcher with all of the same result. I try to use the opnsense i386 VGA version to write the bootable image to the USB device. After it finishes, I check to see if the USB drive is GPT and it changes it back to MBR. The mac isn't able to boot to it. Any help is greatly appreciated.

[Sparks Capone]

I ran into the same exact problem this weekend.

Here's the thread that describes the real issue:
https://forum.opnsense.org/index.php?topic=5121.msg21207#msg21207

Thanks to FlakStapper's post, I was able to repair my USB image using HxD Hex Editor. I found that if I opened the USB drive and the Image file side by side, Sector #2 on the thumb drive had been changed by Windows. All I did to "repair" my USB thumb drive was to copy Sector 2 from the image, and overwrite Sector #2 on my USB thumb drive.

After that, the thumb drive booted right up without the dreaded error message:
"gptboot: primary GPT table checksum mismatch"

Hopefully Franco or one of the other devs can fix this issue in the 32 bit images like they did for the 64 bit ones.

[franco]

If I remember correctly, Windows "corrects" GPT tables in images plugged into it, but actually breaks them if they do not have an even number of partitions.

That's unfortunate, but an easy workaround is to create a USB key with a Linux / BSD somewhere else.

amd64 was fixed in this way, but i386 is on its way to retirement so there will be no further image.

As long as you don't plug it into a Windows PC it will be fine. ;)


Cheers,
Franco

[gamerfreek]

Thanks so much for the help everyone. Things have been busy and will update when I attempt this again.

[gamerfreek]

Thanks for the assistance in recommending Linux to create the build key. I am pretty sure it was working. Not entirely sure. The mac mini still is not able to read the VGA or Nano versions of the i386 image. I am almost positive macs require GPT. I am going to attempt to virtualize it on Linux instead. Thanks!