Extlinux on Debian Jessie (Shallow Thoughts)

Extlinux on Debian Jessie

Debian "Sid" (unstable) stopped working on my Thinkpad X201 as of the last upgrade -- it's dropping mouse and keyboard events. With any luck that'll get straightened out soon -- I hear I'm not the only one having USB problems with recent Sid updates. But meanwhile, fortunately, I keep a couple of spare root partitions so I can try out different Linux distros. So I decided to switch to the current Debian stable version, "Jessie".

The mouse and keyboard worked fine there. Except it turned out I had never fully upgraded that partition to the "Jessie"; it was still on "Wheezy". So, with much trepidation, I attempted an apt-get update; apt-get dist-upgrade

After an interminable wait for everything to download, though, I was faced with a blue screen asking this:

No bootloader integration code anymore.
The extlinux package does not ship bootloader integration anymore.
If you are upgrading to this version of EXTLINUX your system will not boot any longer if EXTLINUX was the only configured bootloader.
Please install GRUB.
<Ok>

No -- it's not okay! I have good reasons for not using grub2 -- besides which, extlinux on exact machine has been working fine for years under Debian Sid. If it worked on Wheezy and works on Sid, why wouldn't it work on the version in between, Jessie?

And what does it mean not to ship "bootloader integration", anyway? That term is completely unclear, and googling was no help. There have been various Debian bugs filed but of course, no explanation from the developers for exactly what does and doesn't work.

My best guess is that what Debian means by "bootloader integration" is that there's a script that looks at /boot/extlinux/extlinux.conf, figures out which stanza corresponds to the current system, figures out whether there's a new kernel being installed that's different from the one in extlinux.conf, and updates the appropriate kernel and initrd lines to point to the new kernel.

If so, that's something I can do myself easily enough. But what if there's more to it? What would actually happen if I upgraded the extlinux package?

Of course, there's zero documentation on this. I found plenty of questions from people who had hit this warning, but most were from newbies who had no idea what extlinux was or why their systems were using it, and they were advised to install grub. I only found one hit from someone who was intentionally using extlinux. That person aborted the install, held back the package so the potentially nonbooting new version of extlinux wouldn't be installed, then updated extlinux.conf by hand, and apparently that worked fine.

It sounded like a reasonable bet. So here's what I did (as root, of course):

• Open another terminal window and run ps aux | grep apt to find the apt-get dist-upgrade process and kill it. (sudo pkill apt-get is probably an easier approach.) Ensure that apt has exited and there's a shell prompt in the window where the scary blue extlinux warning was.
• echo "extlinux hold" | dpkg --set-selections
• apt-get dist-upgrade and wait forever for all the packages to install
• aptitude search linux-image | grep '^i' to find out what kernel versions are installed. Pick one. I picked 3.14-2-686-pae because that happened to be the same kernel I was already running, from Sid.
• ls -l /boot and make sure that kernel is there, along with an initrd.img of the same version.
• Edit /boot/extlinux/extlinux.conf and find the stanza for the Jessie boot. Edit the kernel and append initrd lines to use the right kernel version.

It worked fine. I booted into jessie with the kernel I had specified. And hooray -- my keyboard and mouse work, so I can continue to use my system until Sid becomes usable again.