Re: Debug grub scripts without rebooting into grub shell.

[Glenn Washburn]

On Thu, 13 Jul 2023 08:40:07 +0800
Hongyi Zhao <hongyi.zhao@gmail.com> wrote:

> On Thu, Jul 13, 2023 at 8:33 AM Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
> >
> > On Thu, Jul 13, 2023 at 1:19 AM Glenn Washburn
> > <development@efficientek.com> wrote:
> > >
> > > On Wed, 12 Jul 2023 15:26:18 +0800
> > > Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
> > >
> > > > On Wed, Jul 12, 2023 at 2:15 PM Glenn Washburn
> > > > <development@efficientek.com> wrote:
> > > > >
> > > > > On Wed, 12 Jul 2023 09:25:15 +0800
> > > > > Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
> > > > >
> > > > > > On Wed, Jul 12, 2023 at 5:26 AM Glenn Washburn
> > > > > > <development@efficientek.com> wrote:
> > > > > > >
> > > > > > > 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.
> > > > > >
> > > > > > I tried to adapt your approach to my case, but it didn't work:
> > > > > >
> > > > > > werner@X10DAi:/media/werner/a5d0e46f-aea7-43f0-9a3e-cfb6d517d214/EFI/grub-mkstandalone$
> > > > > > sudo 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=./grubx64.efi,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
> > > > > > format=raw,if=none,id=drive1,readonly=on
> > > > > > qemu-system-x86_64: -drive
> > > > > > file=/dev/sdc,format=raw,if=none,id=drive0,readonly=on: Could not 
> > > > > > open
> > > > > > '/dev/sdc': No such file or directory
> > > > >
> > > > > The above arguments emulate two disks. One coming from grubx64.efi and
> > > > > one /dev/sdc. I think for your use case, you only need one drive. But
> > > > > it needs to be an EFI bootable disk image. The file grubx64.efi is 
> > > > > just
> > > > > the EFI application, not the disk image, which contains grubx64.efi.
> > > > > Remember, the disk image file will show up as a scsi hard drive, so it
> > > > > needs to look like a bootable drive (ie has a GPT label and EFI System
> > > > > Partition correctly setup). This link[1] shows how to do it on a block
> > > > > device, but you can create everything in a file too (though you might
> > > > > need to learn how to use losetup).
> > > > >
> > > > > Glenn
> > > > >
> > > > > [1]
> > > > > https://old.nixaid.com/creating-uefi-bootable-usb-flash-drive-with-several-linux-distributions/
> > > >
> > > > I noticed the following description on the above Tech blog, which is
> > > > used to construct the linux & initrd lines based on the corresponding
> > > > grub configurations on the iso files:
> > > >
> > > > To construct linux & initrd lines I have used the contents of
> > > > isolinux/menu.cfg file (in some cases it is different, but easy to
> > > > find using grep) that can be accessed if you simply mount/open the
> > > > .iso file
> > > >
> > > >
> > > > But I want to know whether this can be used as a general method to
> > > > construct the linux & initrd lines to boot the isos using grub.
> > >
> > > No, it won't work in general, but it might work for most of your isos
> > > depending on which ones you use. Checkout supergrubdisk[1] as Andrei
> > > mentioned. Also here are a couple other links that might be
> > > helpful[2][3].
> > >
> > > Glenn
> > >
> > > [1]
> > > https://github.com/supergrub/supergrub/blob/master/menus/sgd/autoiso.cfg
> > > [2] https://github.com/jim945/autoiso-multiboot
> > > [3] https://www.supergrubdisk.org/wiki/Loopback.cfg
> >
> > Thank you very much again for these wonderful tips and tricks.
> >
> > Basically, there are two main types of methods mentioned here used to
> > boot the iso without burning it:
> >
> > 1. isolinux (linux & initrd) based method.
> > 2. Loopback.cfg based method.

Lots of confusion here. isolinux is a cdrom bootloader, which may load
kernel + initrd, but is not the same thing. And loopback.cfg is just a
grub script to do create a menuentry for (usually) loading the kernel +
initrd with the proper options so the initrd can find the iso. This is
in the lookpack.cfg link I sent, please read it again.

> > So, I want to know which method is more robust or advisable when
> > installing an operating system directly using an iso image?

This question doesn't really make sense. Once you're booted into the
installer iso image, you can install as you normally would. It doesn't
matter how you booted the iso.

Glenn

> 
> See https://github.com/jim945/autoiso-multiboot/issues/1 for the
> related discussion.
> 
> > > >
> > > > Best,
> > > > Zhao
> > > >
> > > > >
> > > > > >
> > > > > > > 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
> > > > > >
> > > > > > Zhao