preseed/early_command doesn't work from kernel command line

[Andrew Kanaber]

Using the Ubuntu netboot installer as obtained from http://archive.ubuntu.com/ubuntu/dists/bionic-updates/main/installer-amd64/current/images/netboot/ubuntu-installer/amd64/ the installer fails to run a preseed/early_command set from the kernel command line (added to the menu entry in grub.cfg).

A precisely equivalent config does cause the command to run in Debian 10 and 9, so this appears to be a difference between Debian's version of debian-installer and the one in Ubuntu. The preseeded command can be made to work in Ubuntu if instead placed in a preseed.cfg inserted into the initrd, so the issue appears to be specific to setting preseed/early_command from the kernel commandline.

For example, setting only the following grub config options: (this is on a Xen system)

    set root=(xen/xvdd,msdos1)
    linux /installer-ubuntu/18.04/linux "preseed/early_command=logger wibble"
    initrd /installer-ubuntu/18.04/initrd.gz

and the interrupting the install, starting a shell and running 'grep wibble /var/log/syslog' shows only the kernel commandline, whereas on Debian 10 with the following grub config

    set root=(xen/xvdd,msdos1)
    linux /installer-debian/10/vmlinuz "preseed/early_command=logger wibble"
    initrd /installer-debian/10/initrd.gz

and again interrupting the install and running 'grep wibble /var/log/syslog' from the shell produces:
Sep 24 17:09:57 kernel: [ 0.000000] Command line: "preseed/early_command=logger wibble"
Sep 24 17:09:57 kernel: [ 0.412794] Kernel command line: "preseed/early_command=logger wibble"
Sep 24 17:09:57 preseed: running preseed command preseed/early_command: logger wibble
Sep 24 17:09:57 root: wibble

adding DEBCONF_DEBUG=5 to the kernel command line on Ubuntu and running
'egrep early_command\|wibble /var/log/syslog' produces:
Sep 24 17:19:13 kernel: [ 0.000000] Command line: "preseed/early_command=logger wibble" DEBCONF_DEBUG=5
Sep 24 17:19:13 kernel: [ 0.000000] Kernel command line: "preseed/early_command=logger wibble" DEBCONF_DEBUG=5
Sep 24 17:19:14 frontend: --> GET preseed/early_command
Sep 24 17:19:14 frontend: --> SET preseed/early_command logger wibble
Sep 24 17:19:14 frontend: --> METAGET preseed/early_command type
Sep 24 17:19:14 frontend: --> FSET preseed/early_command seen true

So the preseed value does get picked up by debconf, it's just that the installer never actually runs the command.

Thanks for your help,