I'm relatively new to unRAID and I have had unraid running for about 20 days.  I had unraid set-up with and I was making some adjustments to my case (tying down wires, ...)  I went to restart and the system would not boot.  I get the message "Reboot and Select proper boot device or insert Boot Media in selected Boot device and press a key.   I have read the USB drive in another system and it appears readable with no errors.  I have tried several USB ports directly on the motherboard and that does not resolve it either.

It makes it to what appears to be a grub screen.   I tried all the options on the boot window. (Safe Mode, ....) but it will not boot.  It does start to boot unraid but fails.  I capture this with my camera.
Loading /bzimage...OK
Loading /bzroot...OK

Loading /bzroot-gui...OK

EFI stub: ERROR: exit_boot() failed!
EFI stub: ERROR: efi_stub_entry() failed!   

 

These last two error messages are almost not visible as they are cleared so quickly.
Then it moves to the Unbootable media message.

I think my usb is corrupted somehow but not sure if there is any way to recover it.

The config folder from flash (or better, a current flash backup), is all you need to get all of your configuration going again on a new install.

So I get a new USB stick, create a unRaid boot drive, and then copy the config folder from the old drive?  Does that sound correct?

Thanks for your help.
Ron

See if you can get the same USB drive to work so you won't have to transfer the license.

 

Just copy the config folder somewhere, then try to make a new install on the same USB drive.

 

If that will boot, then you can copy the config folder back to it to get your configuration back.

I just got this same error today after rebooting the server, but I restarted it a second time and it booted correctly.

I did the steps above (built a new USB Stick) and it is the same problem.  Similar to you it booted eventually but took more than one try.  The motherboard also has an LED status code.  When it was not booting, it was reading various 40's values which I'm assuming was CPU temperature (normal behavior).  It has booted now and it is reading FF while it is up and running.  I believe FF is suppose to be a failed boot.  Seems backwards to me so this is why I'm wondering if it  could be a bad bios that I upgraded recently.  I think this is unlikley

 

Also more likely is a bad VRM or PSU.  I unplugged everything from the motherboard and remove the drives from the psu to lighten the load on the PSU but the boot problems still persisted. I'm going to do some additional hardware testing, removing case plugs (usb mostly) from the motherboard since that could be causing a problem.  I'm currently thinking it is going to be a new motherboard, CPU and memory (as my motherboard is old).

Still thinking it through as it is up and running right now.