PXE netboot to load OS from /dev/sda1

[John Naggets <hostingnuggets@gmail.com>]

Hi,

I have installed Debian 9 onto an old laptop with an SSD disk.
Unfortunately the BIOS does not support booting from that SSD disk so
I would like to "abuse" of PXE in order to boot my installed Linux
from /dev/sda1.

For that purpose I setup a PXE server on another machine on the same
LAN using the netboot.tar.gz file from Debian 9 and slightly adapted
the pxelinux.cfg/default file to add the following entry:

LABEL netboot
        KERNEL debian-installer/amd64/linux
        APPEND initrd=debian-installer/amd64/initrd.gz root=/dev/sda1

Unfortunately it still boots the Debian installer and somehow does not
boot from /dev/sda1. I thought having "root=/dev/sda1" should make it
boot from /dev/sda1 and hence skip the installer part. At least I
think it used to work in the past.

Does anyone see what I am missing here?

Best,
John