kernel panic:VFS: cannot mount root fs

sunils at compucomtech.co.in sunils at compucomtech.co.in
Fri Feb 18 01:59:51 PST 2005


Hello,
Thanx for ur lfs-5.1.1 book.Now I 'm successfully runnin' my lfs on my
machine.Now I 'm makin' a bootable/live cd of it.For this I 'm followin'
ur algo "HOW TO MAKE A LFS LINUX BOOTABLE CD" n another algo which is
attached with this letter.
  I 'm workin' on a PIII machine n usin' FC1(kernel-2.4.22). Actually I
created a bootable floppy and lfs is successfully bootin' from this
floppy.Then I made a image of this floppy and write it on the cd with the
whole filesystem as mentioned in the algo attached.My system started
bootin' but after few steps it stopped with the followin' msg:

kernal panic: VFS cannot mount root fs

I also tried with ur algo but the same msg appeared.I 'm using GRUB as the
bootloader and my meenu.lst in the floppy is as follows:

default 0
timeout 10
root (fd0)
kernel /boot/lfskernel root=/dev/ram0 init=/linuxrc
initrd /boot/initrd.gz

Sir I 've already wasted 7-8 cds' due to this process.I am bein' very much
frustated for last one month....Anyway you plz tell me exactly what should
be the entries of the menu.lst and where should I put my linuxrc script.

Thanx and bye
---sunsom------


-------------- next part --------------
TITLE:          Boot-CD
LFS VERSION:    All
AUTHOR:	        Nicholas Dille <webmaster at rakshas.de>

SYNOPSIS:
	How to create a bootcd from a working LFS system

HINT:
ver 1.4
25/07/2001

Contents
--------

    0. Preface
    1. Why create a boot cd
    2. Kernel customization
    3. LFS system preparation
        3.1 Introduction
        3.2 Linking /tmp and /var to harddisk
             3.2.1 Handling of /tmp
             3.2.2 Handling of /var
        3.3 Linking /tmp and /var to ramdisk
             3.3.1 Handling of /tmp
             3.3.2 Handling of /var
        3.4 Boot script(s)
    4. Installation script
    5. Creating a boot disk
    6. Burning
    7. Listings
        7.1  /
        7.2  /etc/init.d
        7.3  /etc/rc0.d
        7.4  /etc/rc1.d
        7.5  /etc/rc2.d
        7.6  /etc/rc3.d
        7.7  /etc/rc4.d
        7.8  /etc/rc5.d
        7.9  /etc/rc6.d
        7.10 /etc/rcS.d
        7.11 /etc/inittab
    8. History


1. Why create a boot cd
   ---------------------

    Although I'm not that long with LFS I already read several threads on lfs-
    discuss about people having problems compiling certain parts of an LFS sys-
    tem due to beta version of gcc or other important packages shipped with
    their favorite distribution.
    In addition I don't like the idea of installing a "commercial" distribution
    in order to install a customized LFS system. That ain't right ;-)

    So I figured that we should be able to create a bootable cd with some kind
    of linux system on it which will provide a proper environment for the in-
    stallation.

    And what fits better than LFS itself? (I'll leave that one to you ...)

    It also gives some clues about automatically starting the installation
    which then is left to you to hack/figure out. But we should probably start
    using alfs (to give them testers?).

    So that's what it's all about.


2. Kernel customization
   ---------------------

    Since we are about to boot from a cd and use the cd image as root partition
    we certainly need ISO9660 support compiled in. This part is absolutly vi-
    tal!
    When trying to mount the root partition the kernel does not have access to
    any kind of modules (since they are on the root partition which is to be
    mounted) so it has to rely on compiled-in support.

    After the system has booted up we also want to partition our harddrive.
    Therefore you should include any filesystems you might need during instal-
    lation.

    [So far I have not tested including those additional filesystems as module
     but I guess that should work just fine]


3. LFS system preparation
   -----------------------

3.1 Introduction
    -------------

    The major problem which arises when having a read-only root partition is
    that some part of the system may be relying on writable access in certain
    directories.

    Let us have a quick look at the content of $LFS of a typical system:

        drwxr-xr-x   2 root     root         1603 Oct 15 22:16 bin
        drwxr-xr-x   4 root     root         4096 Dec  5 00:12 boot
        drwxr-xr-x   8 root     root        44096 Feb 11 10:02 dev
        drwxr-xr-x  45 root     root         5334 Feb 11 11:02 etc
        drwxr-xr-x  13 root     root          250 Jan  9 00:39 home
        drwxr-xr-x   5 root     root         1869 Jan  4 23:58 lib
        drwxr-xr-x   5 root     root           95 Aug 27 22:12 mnt
        dr-xr-xr-x  54 root     root            0 Feb 11 11:02 proc
        drwx--x--x  20 root     root          679 Jan 30 17:27 root
        drwxr-xr-x   5 root     root         5068 Jan  4 23:58 sbin
        drwxrwxrwt   5 root     root          200 Feb 11 10:03 tmp
        drwxr-xr-x  27 root     root          663 Dec 13 17:34 usr
        drwxr-xr-x  26 root     root          541 Sep  5 23:53 var

    The following directories should not cause any problems:
        bin, boot, etc, lib, root, sbin, usr
    [Need explanation why no problem?]
    The content of those directories should be static and seldomly changed.

    Mount points for other filesystems won't cause a problem because you can
    mount a filesystem with writable access on a mount point in a read-only
    filesystem. I guess the kernel keeps those mappings in memory and not in
    the inodes.
    That means we can cancel out problems caused by: dev, home, mnt, proc.

    This leaves us with tmp and var.


3.2 Linking /tmp and /var to harddisk
    ----------------------------------

    So far I've always preferred this version since I intend to build a boot cd
    that will be usable on almost every system including those with very little
    ram.


3.2.1 Handling of /tmp
      -----------------

    As implied by the name /tmp is used for storing temporary data. Unfortuna-
    tely this is not under our control whether this directory is used and,
    therefore, needs some special handling.

    Since there is no standardized structure for this place we can simply link
    it to the tmp directory on the partition which we will use for instal-
    lation.

    For example, if you intend to compile you system in /lfs (which will then
    be $LFS during the installation) you need to include a symlink for /tmp on
    the CD pointing to /lfs/tmp.
    If you decide for the symlink version of handling /tmp you will need to de-
    cide which directory you will install in before burning the CD!


3.2.2 Handling of /var
      -----------------

    /var usually contains runtime or state stuff and may also be changed [is
    that right? clumsily expressed?].

    Since /var may contain mail spool directories, pid files and has a prede-
    fined directory structure, we can't just link it onto our install partition
    since that could be causing collisions with programs run in our chroot en-
    vironment or perhaps even earlier.

    Therefore we should tar /var and put it in / which you will do by executing
    the following command in your CD root directory:

        tar cfz var/ var.tar.gz

    After bootup after we mounted our installation partition (let's say in
    /lfs), we create a directory "whatever" and untar /var in "whatever".

    The original /var should be a symlink to this directory, eg
        var -> /lfs/whatever/var


3.3 Linking /tmp and /var to ramdisk
    ---------------------------------

    First of all we need to create the ramdisk which I did with the following
    commands:

        dd if=/dev/zero of=/dev/rd/0 bs=1k count=4096
        mke2fs -m 0 /dev/rd/0
        mount /dev/rd/0 /rd

    Please feel reminded that you need to change the device name to the proper
    name on your system. This was created using devfs!

    The next two sub-chapters have hardly changed since /tmp and /var are
    simply linked to /rd/tmp and /rd/var


3.3.1 Handling of /tmp
      -----------------

    Create a link in your root directory to point /tmp to /rd/tmp/.

    During bootup you need to create the directory /rd/tmp/ for the link /tmp
    to not point to nirvana.


3.3.2 Handling of /var
      -----------------

    Create a link in your root directory to point /var to /rd/var/.
    You'll also need to create a tarball of your original /var and place it in
    / which I described in 3.2.2.

    During bootup you will need to unpack the tarball of /var in /rd.


3.4 Boot scripts
    -------------

    I stripped /etc/init.d and /etc/rc?.d off everything that is not absolutly
    vital.
    The only task left is loading a keymap.

    Please refer to the directory listing (chapter 5) at the end of the docu-
    ment.


4. Installation script
   --------------------

    This part is certainly up to you. You might want to include aLFS or some
    compilation system which you have written yourself. Perhaps you will even
    leave out this part and manually install the packages.
    But anyway you will have to put the packages on the CD to have them handy
    when you need them.

    To give you an idea what my CD does: I put a script in /etc/init.d/install
    which will be started from inittab during boot. This will ask the user some
    important stuff, i.e. which partition to install on.
    It will then startup the compilation.

    You might even want to boot to a bash and leave out any kind of automatic
    installation. This will happen if you pass an additional kernel parameter
    from the bootloader "init=/bin/bash".


5. Creating a boot floppy
   -----------------------

    Although some of you might be tempted to ask whether I will now describe
    the process to create a boot disk using grub I will not start an argument
    about this. This is a question of belief ;-)

    First you need to get grub from http://www.gnu.org and install it on your
    system with the following commands:

            ./configure --prefix=/usr &&
            make &&
            make install

        a) You then create an ext2 filesystem on a disk.
            (Please use an empty disk or be sure that you understand that you
            will loose all your data on this disk. So much for the disclaimer)

        b) Mount this disk to your favorite disk-mount-directory
            (lets call it $FLOPPY)

        c) Create /boot and /boot/grub on your floppy:

                mkdir -p $FLOPPY/boot/grub

        d) Copy the grub boot loader onto the disk:

                cp /usr/share/grub/i386-pc/stage* $FLOPPY/boot/grub

        e) Put your kernel in $FLOPPY/boot and call it "linux"

        f) Start the grub shell by executing "grub"

        g) Install grub on your boot disk (still in the grub shell):

                install (fd0)/boot/grub/stage1 (fd0) (fd0)/boot/grub/stage2

        h) Now you need to create the file $FLOPPY/boot/grub/menu.lst with the
            following content:

                default 0
                timeout 2

                title        template
                root (fd0)
                kernel (fd0)/boot/linux devfs=mount root=/dev/cdroms/cdrom0

            If you do not use devfs, please remove "devfs=mount" from the last
            line in menu.lst and replace "/dev/cdroms/cdrom0" with the name of
            your cdrom device.

    If you want to keep the resulting bootable cd as generic as possible you
    do not need to worry about the cdrom device name since you will be able to
    edit the menu entries of grub at boot time to reflect the underlying
    system.

    You are now ready to burn your LFS installation onto a CD which will be
    able to boot using the cdrom.


6. Burning
   --------

    After creating a proper boot floppy with your custom kernel (see 2) put the
    image in /boot.
    To do this execute the following command in the root directory of your lfs
    system:

        dd if=/dev/floppy/0 of=boot/image bs=1024

    The guys of you who are not using devfs will need to substitute
    /dev/floppy/0 with /dev/fd0.

    To burn the whole stuff on cd I used the following command:

        mkisofs -rlDJLV "LFS" /lfscd -b boot/image -c boot/catalog \
            | cdrecord -v -eject dev=/dev/cdroms/cdrom0 speed=4 -data -

    Things to check:

        a) Don't use -f. It causes symlinks to be ignored.

        b) substitute dev=... with your cdrom device


7. Listing
   --------

7.1  /
     --

        drwxr-xr-x   2 root  root    35 Feb  9 21:10 alfs
        drwxr-xr-x   2 root  root  1250 Feb  9 20:10 bin
        drwxr-xr-x   3 root  root   295 Feb 10 14:05 boot
        drwxr-xr-x   3 root  root    54 Feb  9 17:33 dev
        drwxr-xr-x  12 root  root   795 Feb 12 13:48 etc
        drwxr-xr-x   2 root  root    35 Feb  9 17:33 home
        drwxr-xr-x   3 root  root  2494 Feb  9 20:52 lib
        drwxr-xr-x   2 root  root    35 Feb  9 17:33 mnt
        drwxr-xr-x   2 root  root    35 Feb  9 17:33 proc
        drwxr-x---   2 root  root    64 Feb  9 18:13 root
        drwxr-xr-x   2 root  root  1272 Feb  9 20:10 sbin
        lrwxrwxrwx   1 root  root     8 Feb 10 21:57 tmp -> alfs/tmp
        drwxr-xr-x  14 root  root   346 Feb  9 20:10 usr
        lrwxrwxrwx   1 root  root    14 Feb 10 21:57 var -> alfs/00-rw/var
        -rw-r--r--   1 root  root  1043 Feb 10 21:56 var.tar.gz


7.2  /etc/init.d
     ------------

    This directory contains a new script "install" which goes through the in-
    stallation procedure and should be specific for your setup.

        -rwxr-xr--   1 root  root  1734 Jan 26 02:05 checkfs
        -rwxr-xr--   1 root  root  1118 Jan 26 02:05 ethnet
        -rwxr-xr--   1 root  root   867 Feb  2 02:46 fcron
        -rwxr-xr--   1 root  root  4940 Jan 26 02:05 functions
        -rwxr-xr--   1 root  root    83 Jan 26 02:05 halt
        -rwxr-xr-x   1 root  root   988 Feb 12 13:51 install
        -rwxr-xr--   1 root  root   200 Jan 26 02:05 loadkeys
        -rwxr-xr--   1 root  root   725 Jan 26 02:05 localnet
        -rwxr-xr--   1 root  root   355 Jan 26 02:05 mountfs
        -rwxr-xr--   1 root  root  4219 Jan 26 02:05 rc
        -rwxr-xr--   1 root  root   235 Jan 26 02:05 rcS
        -rwxr-xr--   1 root  root   123 Jan 26 02:05 reboot
        -rwxr-xr--   1 root  root   276 Jan 26 02:05 sendsignals
        -rwxr-xr--   1 root  root   338 Jan 26 02:05 setclock
        -rwxr-xr--   1 root  root  1062 Jan 26 02:05 sysklogd
        -rwxr-xr--   1 root  root   696 Jan 26 02:05 template
        -rwxr-xr--   1 root  root   234 Jan 26 02:05 umountfs


7.3  /etc/rc0.d
     -----------

        lrwxrwxrwx   1 root  root  21 Feb 12 13:44 S80sendsignals
                                                    -> ../init.d/sendsignals
        lrwxrwxrwx   1 root  root  14 Feb 12 13:44 S99halt -> ../init.d/halt


7.4  /etc/rc1.d
     -----------

    [empty]


7.5  /etc/rc2.d
     -----------

    [empty]


7.6  /etc/rc3.d
     -----------

    [empty]


7.7  /etc/rc4.d
     -----------

    [empty]


7.8  /etc/rc5.d
     -----------

    [empty]


7.9  /etc/rc6.d
     -----------

        lrwxrwxrwx 1 root  root   21 Feb 12 13:44 S80sendsignals
                                                   -> ../init.d/sendsignals
        lrwxrwxrwx 1 root  root   16 Feb 12 13:44 S99reboot -> ../init.d/reboot

7.10 /etc/rcS.d
     -----------

        lrwxrwxrwx 1 root  root   18 Jan 26 02:11 S30loadkeys
                                                   -> ../init.d/loadkeys


7.11 /etc/inittab
     -------------

    Please note that I replaced the definition for an agetty on vc/1 with the
    install script /etc/init.d/install which will only be run once (keyword
    "once").
    I also removed 4 of the 5 remaining agetty definitions since this installa-
    tion will run automatically.

        # Begin /etc/inittab

        id:3:initdefault:

        si::sysinit:/etc/init.d/rcS

        l0:0:wait:/etc/init.d/rc 0
        l1:S1:wait:/etc/init.d/rc 1
        l2:2:wait:/etc/init.d/rc 2
        l3:3:wait:/etc/init.d/rc 3
        l4:4:wait:/etc/init.d/rc 4
        l5:5:wait:/etc/init.d/rc 5
        l6:6:wait:/etc/init.d/rc 6

        ft:06:respawn:/sbin/sulogin

        ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now

        su:S1:respawn:/sbin/sulogin
        1:2345:respawn:/sbin/agetty vc/1 9600
        2:2345:respawn:/sbin/agetty vc/2 9600

        # End /etc/inittab


8. History
   --------

    2001-07-25  released version 1.4:
                According to Gerard's suggestion I added a few lines describing
                how to get the boot image off the floppy and place it in the
                lfs tree for the boot cd.
                Corrections: - The most important was a fix to the instruction
                               of creating a boot disk where i misspelled the
                               command to install grub on the floppy.
                             - I deleted/changed some instructions leftover
                               from my original CD in 4 and 7.11
                Additions: - Added some further description to 3.2.1, 3.2.2

    2001-06-22  released version 1.3:
                I added instructions to create a grub based boot disk.

    2001-03-10  released version 1.2:
                After I got several mail from people asking for a new version
                of this howto with some hints how to create the cd with ram-
                disk support.

    2001-02-12  released version 1.0


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