I have a set of systems that needs a custom Linux kernel image to support the hardware. With previous releases I was able to copy the working vmlinuz and update the initrd files for that kernel in the casper directory on the install ISO and recreate the ISO image and it would boot and work fine.
The 24.04 release has changed to use compressed modules instead of a compressed initrd. I am building kernel debian packages using the Canonical process (fakeroot debian/rules binary) and they all seem to work fine on a running system.
I have analysed the contents of the initrd file (see below) and the one created while installing my built kernel packages seems to match. However when I use the vmlinuz and initrd images produced for ISO image when I try to boot I get:
Begin: Running /scripts/init-premount ... done.
Begin: Mounting root file system ... Begin: Running /scripts/local-top ... done.
Begin: Running /scripts/local-premount ... [ 1.781241] Btrfs loaded, zoned=yes, fsverity=yes
Scanning for Btrfs filesystems
done.
No root device specified. Boot arguments must include a root= parameter.
I have compared the contents of the original initrd and my initrd images. My initrd has the same file list execpt the particular directory name in /usr/lib/modules matches the version of my kernel. The directory structure and the particular *.ko.zst files all the have the same names and the "file" command shows then are the same type (.kernel/fs/nls/nls_ucs2_utils.ko.zst: Zstandard compressed data (v0.8+), Dictionary ID: None).
In the 22.04 ISO I had to recreate the initrd image because it included a number of other directories besides /usr/lib/{modules, firmware}. It was more than just the modules and included the bin, etc, lib, sbin, etc. directories to make it a boot to ramdisk type image I expected was needed for a live image system.
Something basic has changed between 22.04 and 24.04. Please let me know the process needed to update the /casper/vmlinuz and /casper/initrd files for the 24.04 ISO.
Thanks in advance for any help.
Johnnie
