Re: Debug grub scripts without rebooting into grub shell.

[Glenn Washburn]

On Sat, 8 Jul 2023 19:58:29 +0800
Hongyi Zhao <hongyi.zhao@gmail.com> wrote:

> Hi here,
> 
> Are there some convenient methods to debug grub scripts without
> rebooting into grub shell?

I would recommend running the GRUB EFI application in QEMU, as it will act
more closely to when running on bare metal. Here's an example of a QEMU
command that I use when doing development:

qemu-system-x86_64 -name '[x86_64-efi] Test Grub' \
 -m 2048 -bios OVMF.fd --enable-kvm -boot once=c,menu=on \
 -nodefaults -rtc base=localtime -vga std -snapshot \
 -drive file=/home/grub-tester/bootloader/efidisk.img,format=raw \
 -device virtio-scsi-pci,id=scsi0,num_queues=4 \
 -device scsi-hd,drive=drive0,id=systema,bus=scsi0.0,scsi-id=0,lun=0,channel=0 
\ 
 -drive file=/dev/sdc,format=raw,if=none,id=drive0,readonly=on \
 -device scsi-hd,drive=drive1,id=systemb,bus=scsi0.0,scsi-id=0,lun=1,channel=0 \
 -drive file=/home/user/disk.img,format=raw,if=none,id=drive1,readonly=on

If you want to use a block device, then you'll need to run as root or
otherwise have correct permissions to read from the device. But you can have 
everything in a disk image file and not need to run as root.

Also You can add the options "--nographic -serial stdio" to have the interface
be via serial, which allows text selection. In this case GRUB will need to be
configured to output to serial.

Glenn