Re: About my problem

From: Teilhard Knight (teilhk_at_Phreaker.net)
Date: 05/14/03

  • Next message: george donnelly: "FreeBSD Training in Spanish" 
    To: Matthew Seaman <m.seaman@infracaninophile.co.uk>, FreeBSD <freebsd-questions@freebsd.org>
Date: 14 May 2003 11:05:50 -0500

    On Wed, 2003-05-14 at 04:38, Matthew Seaman wrote:
    > On Wed, May 14, 2003 at 02:18:22AM -0500, Teilhard Knight wrote:
    > > For those who do not know what I am talking about, this is what is
    > > happening to me:
    > >
    > >
    > > I have compiled my kernel. Everything seems to be all right,
    > > except that on boot it cannot mount root.
    > >
    > > It displays: "mounting root from ufs:ad2s2a", and a failure message.
    > >
    > > Now, I am left at boot with an inquire for a manual root filesystem
    > > specification., like this:
    > >
    > > <fstype><device> mount <device> using filesystem <fstype>
    > >
    > > eg. ufs:/dev/da0s1a
    > >
    > > ? List valid disk boot devices
    > >
    > > <empty line> abort manual imput
    > >
    > > mountroot>
    > >
    > >
    > > The HD where FreeBSD is installed is ad2 in my previous kernel and in
    > > this new one it is ad1. I have now found out that this is the source of
    > > the problem. I checked the partition table, and the slices are called
    > > ad2s2a --> ad2s2g. If this is the case, no way I can mount root on a
    > > disk called ad1 with those slices.
    > >
    > > So, I'll pose a different question. Do you know of a possible way I can
    > > make my new kernel to spot my HD as ad2? To me this is the only solution
    > > possible.
    >
    > Hmmm... It's not impossible to recover from the situation you're in
    > without having to do anything unaesthetic, like re-installing. It is,
    > however, fairly tricky and requires use of some quite unfriendly
    > commands.
    >
    > Your aim is simply to edit /etc/fstab and change all references to ad2
    > over to ad1. Since the fstab is not correct for your current machine,
    > you can't boot to multiuser mode. You can, however, boot to single
    > user mode with the root partition you tell the kernel as above. After
    > power-on, interrupt the 10 second count down, and at the boot loader
    > prompt type:
    >
    > set root_disk_unit=1
    > boot /kernel -s
    >
    > This should get you to the single user prompt, but with the root
    > partition mounted read-only. In order to remount the root partition
    > read-write, you need to do two things. First, run fsck(8) to clean up
    > the file system and then run mount(8). Catch22 is that both of those
    > commands will use /etc/fstab as a database of filesystems to work on,
    > unless you take care to avoid that. Assuming that your root partition
    > is on /dev/ad1s1a, run:
    >
    > # fsck /dev/ad1s1a
    > # mount -u -o rw -t ufs /dev/ad1s1a /
    >
    > (Basically, you need to supply all required arguments to mount(8), to
    > stop it going to /etc/fstab to try and look them up.)
    >
    > Now you've got the root partition mounted read-write, you can edit the
    > /etc/fstab file. The tricky bit is that you only have the commands in
    > /bin available to do the editing with (assuming that you've used the
    > usual /, /usr partition layout). That means that you now have to get
    > down and dirty with ed(1) -- the Unix editor of last resort. This
    > command was originally designed for use on a teletype printer, so it
    > doesn't show you a listing of the whole file and let you navigate
    > around it in a natural way. The command syntax is a bit intimidating
    > to the uninitiated too. You can see the ed(1) man page at
    >
    > http://www.freebsd.org/cgi/man.cgi?query=ed&apropos=0&sektion=0&manpath=FreeBSD+4.7-stable&format=html
    >
    > Try this:
    >
    > Nb. You type the lines marked '<--' in the ed session.
    >
    > # cd /etc
    > # cp fstab fstab.bak
    > # ed fstab
    > 448 (--> ed outputs the size of the file here)
    > (<-- hit return, to get the ? prompt)
    > ? (--> ed output)
    > ,s/ad2/ad1/g (<-- substitute 'ad1' for 'ad2' everywhere)
    > ,w (<-- write out the changed file)
    > 448 (--> ed tells you the modified file size)
    > q (<-- quit ed)
    > # cat fstab
    >
    > Check the new contents of the fstab file for sanity. If you're happy,
    > then try and fsck and mount all your filesystems:
    >
    > # fsck -p
    > # mount -a
    >
    > If that works satisfactorily, you're done, and you can just type
    >
    > # reboot
    >
    > and the system *should* come up smoothly.

    Thank you, Matthew. I tried as you said, but I couldn't pass the first
    step. I got the message: "cannot boot /kernel, kernel module already
    loaded" Of course I tried "kernel" and other variants. If I typed
    "unload" and then what you said, I ended up with the prompt for the
    manual file system feed. But I could boot with a kernel back up I had
    and I made the modifications to the fstab file with a regular editor. My
    doubt was that the slices still were called ads2s2a, etc., but I
    supposed that that could change with the changes in the fstab file. I
    knew that if something went wrong, I could not boot anymore from my back
    up kernel, but I would get to the same request for a hand-input
    filesystem and I would only had to specify ad2s2a. Well, nothing worked.
    I cannot boot now. It seems to me that the utility to specify by hand
    the filesystem either doesn't work or that I have a deeper problem here.
    I am now tempted to get done with 4.8 and try 5.0. What do you think?

    By the way, I tried the repair console, and just the first feel of it
    made me step back.

    Teilhard Knight
    The Extraterrestrial

    Who ate my sandwich?

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