I have a machine that currently has linux mint 16.04 on it.
I would like to install debian 10 on it, but the installer really wants access to a cd drive, and one just isn't available.
However, the linux mint 16.04 system does have grub2 on it.
So it is possible for me to boot from an iso image stored in the filesystem just like a regular file. It's just a matter of writing a menu entry in /etc/grub/40_custom.
I know this works because i've booted into a live cd image of linux mint 20.1 (using the filesystem, not a cdrom), and started an installation process. I backed out of it, because i would like to install debian 10, not just a later version of mint.
When i do the same thing with debian, it starts off ok, doing some simple things like setting the language and the keyboard layout, but then it complains that it cannot find a cd rom. This is true with both the netinst image, as well as with a jigdo xfce image which i think should have everything necessary and not need a cd rom. For reference, my debian menu entry is
menuentry "debian-10-iso" {
set isofile="/USER/iso/debian-10.7.0-amd64-xfce-CD-1.iso"
loopback loop (hd0,gptNN)$isofile
linux (loop)/install.amd/vmlinuz boot=install.amd iso-scan/filename=$isofile noprompt noeject
initrd (loop)/install.amd/initrd.gz
}
Here, USER is the user name in whose account the iso image is, and gptNN stands for the particular partition where home is mounted for the user USER.
So my first question is whether there's a better iso image i can use, or if i can fix this up by giving more arguments to the linux invocation line or something else in the menu entry.
The second question is whether there's a way, from grub (grub2, actually), of dropping down to the bios. I imagine this is quite impossible, but if i'm wrong, please let me know. The reason i would like to do this is that it is very hard for me to interrupt the boot process fast enough to get to the bios, and i've only managed to do it once or twice after many tries. If i were in the bios, i might be able to figure out if it could boot from usb, and i could set the boot order to do this, and make a bootable usb version of netinst (perhaps).
Or perhaps there's some other way to approach the problem? For example, i've already created a partition to hold the debian system i want to put on the machine. Is there some way of hand-populating it? I do have a running debian 10 system on another machine, and i suppose i could tar it up and unpack it into the new partition on the mint machine. But i'm not sure if there's something outside the filesystem but inside the partition which is necessary for it to be bootable.
Thanks in advance for any advice!
dan