Pain of the LVM and Fix

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Mar 052007
 

    Problem domain:

    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:

    1. Having required kernel features loaded from modules.
    2. Having those disk devices created holding the lvm volumes to boot on
    3. 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.

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      • undefined

        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.

      • phoenixlpr

        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. :( .

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