[syslinux] Extlinux no longer bootable, how to fix?

[Ady Ady]

> 
> - its menu shows up fine but can’t boot /vmlinuz
> - after sellecting the menu, it shows “Loading /vmlinuz...” then
> flashed “failed”, and go back to the menu again.
> 
> Here is my extlinux menu:
> 
> LABEL LU18R1
>         MENU LABEL LUbuntu ^Bionic
>         MENU DEFAULT
>         KERNEL /vmlinuz
>         APPEND initrd=/initrd.img
> root=UUID=ad26a5d8-a4ee-42d3-96aa-1f6f0eaa3968 ro net.ifnames=0 --
> 
> - the same extlinux config works from the original mirroring source. -
> I've made sure the UUID is updated, thought I think it is irrelevant as
> it is the loading of /vmlinuz failed. - I.e., the real problem is
> loading the /vmlinuz from extlinux
> 
> To confirm the situation, I've duplicate my linux system to at least
> three HD partitions, and none of them works. However, using the exactly
> same steps, when duplicate to my USB key, the system boots up
> beautifully. That's why I'm saying that it is a strange problem.
 
 
There are several things to try. Let's start for the simplest.

In your EXTLINUX config file, instead of using:

KERNEL /vmlinuz

try changing it to:

LINUX /vmlinuz

Then, when you get to the boot menu, exit the menu and get to the boot 
prompt instead (by pressing [Esc], more than once if needed).

Then, from the boot prompt, type in:

LU18R1

which is the label you are using. Press [Enter].

With this minimal changes, are you seeing the same exact behavior as 
before? Are the resulting messages the same as before? Any additional 
clue?

If this is not enough, I would suggest carefully reading the 
"Filesystem" wiki page in the Syslinux wiki. This is just a "hunch" 
(based on some "clues" in your email, although you have not explicitly 
mentioned the filesystems that you are using for the bootloader in your 
HDD nor for the USB device).

If the wiki page doesn't give you any clues either, we'll see how to 
proceed then, depending on your report(s). There are several more 
things to troubleshoot, if required.

Regards,
Ady.