booting from btrfs with extlinux not working

mps_ul · 07-31-2016, 11:16 AM

Hi there!
I have a fresh 14.2 installation with / on a btrfs partition and try to get extlinux to work. I have done something similar in the past but I am not shure what I am doing wrong this time...

Some facts about the system and what I have done so far:

old BIOS system, nothing special here
/dev/sdb1 is used as /, no seperate partition for /boot/
/dev/sdb1 was created with plain mkfs.btrfs with no options
mbr.bin from the syslinux directory was dd'ed to /dev/sdb
I created a directory /boot/syslinux
I ran
Code:
```
extlinux -i /boot/syslinux
```
which didn't complain and just replied something like /boot/syslinux is on /dev/sdb. It did not put any files there, though. I m not shure if this is the intended behaviour.
/dev/sdb1 is marked as boot partition in fdisk
I have copied all *.c32 files into /boot/syslinux as some tutorials suggest

I have created a file named extlinux.conf in /boot/syslinux it reads like this:

Code:

TIMEOUT 1000
UI menu.c32

MENU TITLE Slackboot

LABEL slack_huge_1
	MENU LABEL Slack Huge 1
	LINUX /boot/vmlinuz-huge

LABEL slack_huge_2
	MENU LABEL Slack Huge 2
	LINUX /boot/vmlinuz-huge

This configuration might or might not work, but I am not even getting to the menu. When I am trying to boot the system, I am greeted with the line

Code:

SYSLINUX 4.07 EDD 2013-07-25 [...copyright notice...]

and nothing more happens. No prompt, no menu, no reaction on any keyboard input.
Now I am looking for a way to debug this and to understand where extlijnux is stuck and why.

Thanks in advance,
mps

STDOUBT · 07-31-2016, 05:32 PM

Welcome to LQ!
I'm not clear on what is your goal here.
Why can you not simply do a normal installation and boot from your btrfs / using lilo?
There should be no need to use syslinux, and besides:

Quote:

man extlinux

...extlinux - install the SYSLINUX bootloader on a ext2/ext3 filesystem...

bassmadrigal · 07-31-2016, 06:09 PM

Quote:

Originally Posted by STDOUBT

Why can you not simply do a normal installation and boot from your btrfs / using lilo?

I don't believe lilo supports booting from btrfs. If you want btrfs as the root partition, you'll want to use an ext partition for /boot/.

mps_ul · 08-03-2016, 07:52 AM

Hi!

Quote:

Originally Posted by STDOUBT

Why can you not simply do a normal installation and boot from your btrfs / using lilo?

To be honest: I did not check if LILO supports BTRFS before installing because I remembered that extlinux was the only sane option the last time I installed on BTRFS. After some googling now, it doesn't seem like this has changed.

The man-page for extlinux is not precise in this case, it is in fact meant to be used for BTRFS (so says the project homepage and also slackdocs)

I am quite confident about the general idea, I am just not shure what I did wrong and how to analyze it.

mps

atelszewski · 08-03-2016, 09:24 AM

Hi,

I've been recently struggling with extlinux, but I finally managed to have it working.
I can't spot possible errors in your installation procedure, but I'll detail you mine, that works for me.

Please note that I'm not using menus, just text prompt.
Also, instead of installing under /boot/syslinux I install under /boot.
In my example, I'm using /dev/sda, so make sure to adjust for it.

Code:

$ extlinux --install /boot
$ dd count=1 bs=440 conv=notrunc if=/usr/share/syslinux/mbr.bin of=/dev/sda

I believe that upon successful installation, you should have the following file in your install dir:

Code:

$ ls -l /boot/ldlinux.sys 
-r--r--r-- 1 root root 37888 Dec 14  2015 /boot/ldlinux.sys

And then config reads like that:

Code:

$ cat /boot/syslinux.cfg 
PROMPT  1
TIMEOUT 5
DEFAULT vmlinuz-generic

LABEL vmlinuz-huge
  KERNEL vmlinuz-huge
  APPEND ro root=/dev/sda2

LABEL vmlinuz-generic
  KERNEL vmlinuz-generic
  APPEND ro
  INITRD initrd.gz

Please note that I didn't specify the full path to the kernel and initrd. This is really important when your rootfs is using unsupported (by extlinux) file system. The path to the kernel has to be relative to where the syslinux.cfg is placed. So, for simplicity reasons, I install everything under /boot. I have removed lilo/grub packages from my system, to the /boot directory looks clean ;-) :

Code:

$ ls -l /boot
total 26588
lrwxrwxrwx 1 root root      37 Jun 21 10:24 README.initrd -> /usr/doc/mkinitrd-1.4.8/README.initrd
lrwxrwxrwx 1 root root      22 Jun 25 10:22 System.map -> System.map-huge-4.4.14
-rw-r--r-- 1 root root 2725240 Jun 24 20:31 System.map-generic-4.4.14
-rw-r--r-- 1 root root 3958084 Jun 24 20:38 System.map-huge-4.4.14
lrwxrwxrwx 1 root root      18 Jun 25 10:22 config -> config-huge-4.4.14
-rw-r--r-- 1 root root  159775 Jun 24 20:31 config-generic-4.4.14
-rw-r--r-- 1 root root  159775 Jun 24 20:38 config-huge-4.4.14
-rw-r--r-- 1 root root 7208762 Jul 30 18:10 initrd.gz
-rw-r--r-- 1 root root  946176 Jul  7 00:28 intel-ucode.cpio
-r--r--r-- 1 root root   37888 Dec 14  2015 ldlinux.sys
-rw-r--r-- 1 root root     319 Jul 31 03:44 syslinux.cfg
lrwxrwxrwx 1 root root      19 Jun 25 10:22 vmlinuz -> vmlinuz-huge-4.4.14
lrwxrwxrwx 1 root root      22 Jun 25 10:22 vmlinuz-generic -> vmlinuz-generic-4.4.14
-rw-r--r-- 1 root root 4377248 Jun 24 20:31 vmlinuz-generic-4.4.14
lrwxrwxrwx 1 root root      19 Jun 25 10:22 vmlinuz-huge -> vmlinuz-huge-4.4.14
-rw-r--r-- 1 root root 7630144 Jun 24 20:38 vmlinuz-huge-4.4.14

EDIT:

It's important to flag the boot partition bootable. I'm writing this for the record, because you said you've marked yours bootable.

--
Best regards,
Andrzej Telszewski