I think I sorted out part of my problem.
For those who I made them lost, a summary of what I'm trying to do.
I'm trying to boot Debian 10 via Grub's loopback device, in order to
make a multiboot USB with several Linux distros by copying just the
ISOs.
I already read Debian installer CD has an initrd with no iso-scan
package, so won't work out of the box and must use hd-media initrd and
vmlinuz to make it work.
So I downloaded, renamed, and placed them in same directory as Debian
installer ISO, in the USB partition. Then created grub.cfg config in
USB:
iso_path=/boot/iso/debian-10.2.0-amd64-xfce-CD-1.iso
export iso_path
search --set=root --file "$iso_path"
loopback loop "$iso_path"
menuentry "Graphical install" {
bootoptions="iso-scan/filename=$iso_path desktop=xfce vga=788 ---
quiet"
linux /boot/iso/DebianVmlinuz $bootoptions
initrd /boot/iso/debianGtkInitrd.gz
}
Then tested booting from USB, and the graphical installer does start,
but after selecting language, locale and keyboard, I got this message:
"The quick scan for installer ISO images, which looks only in common
places, did not find an installer ISO image. It's possible that a more
thorough search will find the ISO image, but it may take a long time. Do
you wish to do a full scan?"
Now, my recent problem was that even by answering yes, it didn't find
the installer ISO which is right there in the USB.
How sorted? It turned people here were right: I needed to update both
initrd and installer ISO, since version 10.2 was released just 5 days
ago...
Having done this I retried. Still get the above message, but now
thorough search is able to find and use the installer ISO.
Now, my last issue is: quick scan always fails, looking only in "common
places". So perhaps the location in the USB sdb3/boot/isos is not
considered a "common place" and thus only full search can find it here.
Can this behavior be changed?
Maybe somehow telling quick scan to search in custom directories in
grub.cfg?
For this matter, why isn't iso-scan/filename actually working?
Thanks.
