Pain of the LVM and Fix
Posted by elitelinux on March 5th, 2007
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I have started to use LVM(2) and converted my system on lvm2 devices. I have noticed that I need to use initrd in order to boot up because all of my partitions were using lvm except /boot. I had 2 versions of debian-netsint on CD. I could boot up with them and with some debian kernel (2.6.8-2)installed from deb, but not the kernel I have complied (2.6.20). I got a kernel panic: missing root device and init: dev/console was missing.
Path to solve:
I realized that I have to try to use udev. I tried to create my initrd with mkinitrd. It was quite flexible with transfering files to my initrd, but it turns to be a dead end.
I have realized that one of the cause was devfs have been removed from the kernel around version 2.6.13-17. Thanks Linus it was a great idea to drop it this point from the 2.6 tree. I have thought that the stable tree is not a playground.
I have switched to mkinitramfs. It looks a bit complicated for the first look. It took some time to hook on. My first advice is use the break option, so it will stop after init-premount level and execute a shell.
Needed things to boot from an LVM root:
- Having required kernel features loaded from modules.
- Having those disk devices created holding the lvm volumes to boot on
- Having and running vgchange -ay
My way:
/etc/initramfs-tools/initramfs.conf:
MODULES=list
BOOT=local
This is my hook script:
/etc/initramfs-tools/hooks/lvm:
#!/bin/sh -e
PREREQS=”"
prereqs() { echo “$PREREQS”; }
case “$1″ in
prereqs)
prereqs
exit 0
;;
esac. /usr/share/initramfs-tools/hook-functions
copy_exec /lib/lvm-default/lvm /sbin/
/etc/initramfs-tools/scripts/init-premount/my_lvm:
case $1 in
# get pre-requisites
prereqs)
prereqs
exit 0
;;
esac# Do the work here.
mkdir /dev/mapper
/bin/mknod /dev/hda1 b 3 1
/bin/mknod /dev/hda2 b 3 2
/sbin/lvm vgchange -ay# Handle an error:
Well, my hook script transfers the actual running lvm to initrd and the script: my_lvm makes the rest of the work.
Have fun! I hope I could save some headaches with this cookbook.
March 5th, 2007 at 4:27 pm
don’t know why the manual customization is necessary as i recently switched from yaird to mkinitramfs on a “root on lvm2 over software raid” 2.6.15 and 2.6.18 etch setup, but without any problems.
(i switched to mkinitramfs as it appears to be the most mature, the ubuntu/debian default, and the long(er)-term solution.)
the default works but i later customized the configuration to deactivate unnecessary scripts and modules that were being ran/loaded at boot, but that didn’t require anything more than editing config files and removing/renaming scripts.
i definitely didn’t have to create nor edit any scripts.
March 6th, 2007 at 7:53 am
I have updated my sid before. It was not working. I’ve put a 2.6.18-4-686 kernel up from deb(debian-testing-i386-netinst.iso) and it still was not working.
After all I have started to digg into the initrds. I prefer initramfs-tools, its more flexible.
I’ve installed from the same netinst disk(2.6.18-4-686) to my HP laptop. It was not booting again.
.