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Thread: [Solved] Reinstalling grub2 MBR from Live-CD

  1. #1
    Join Date
    May 2008
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    119

    [Solved] Reinstalling grub2 MBR from Live-CD

    Got a nice little netbook, Samsung N150, alas with W7 taking all four primary partitions, removed the fourth without a hitch, made an extended one, and put UNR 10.04 into it after shrinking the 3rd.
    Ask me if you need details.

    After reboot, I get the Ubuntu menu entries in grub, as well as two W7 (Vista, héhé!) loaders. After some days, I made a mistake, and instead of the one with the real W7, I started the one with the W7 recovery. No way to stop it at loading, so I waited for the welcome screen, where I clicked "no, I don't want to recover W7". Nevermind. Windows is Windows and overwrote the MBR. So at reboot, just a blinking cursor.

    Question: How to write the MBR back? Without reinstalling?
    https://help.ubuntu.com/community/Re...tallingWindows
    isn't a bad start, but my partitioning is more complex:
    sda5 is boot
    sda6 is swap
    sda7 is root
    sda8 is home
    I am not sure I can do what is written there, since the mount will not mount boot and root. And if I mount both, oh well, maybe it works? I am not confident.

    So what I did, I booted to the UNR thumb drive (Live-CD), and opened a console.
    $ cd /mnt
    sudo mkdir oldroot
    sudo mkdir oldboot
    sudo mount /dev/sda7 oldroot
    sudo mount /dev/sda5 oldboot
    (ls -l oldroot and ls -l oldboot showed I mounted the right partitions)
    sudo -o bind oldboot oldroot/boot
    (ls -l oldroot/boot showed the correct vmlinuz, initrd, etc.)
    sudo chroot oldroot
    I might need these:
    # mount proc
    # mount dev
    # grub-install /dev/sda
    (no error shown)
    # exit
    $ exit
    Shutdown and rebooted, and everything was working again.

    I really, really, don't know why the UNR Live-CD doesn't contain a recovery for grub. I wonder, if it was written cleverly enough, to just put back the MBR if I selected the correct partitions during an install, without formatting them? I don't think so.
    Maybe I should file this as a RFE, that after partitioning, the user has a choice to just write back the MBR?

    Thanks for a really great Lucid Lynx for netbooks (if you never tried, you wouldn't notice how much faster Ubuntu boots and reacts, compared to the included W7 home edition!)

    Uwe

  2. #2
    Join Date
    Sep 2007
    Beans
    20
    Distro
    Ubuntu 10.04 Lucid Lynx

    Re: [Solved] Reinstalling grub2 MBR from Live-CD

    Hello udippel,

    Thank you for sharing this in the forum. I was looking how to fix the same issue for someone I know. I'll give a try to your way and let you know.

    RamsesII

  3. #3
    Join Date
    May 2005
    Location
    Dayton, OH
    Beans
    14
    Distro
    Ubuntu 10.04 Lucid Lynx

    Re: [Solved] Reinstalling grub2 MBR from Live-CD

    I have a similar problem.

    Samsung N110 with

    recovery partition on sda1
    WinXP on sda2
    extended partition on sda3
    Ubuntu 10.04 netbook remix on sda5 (ext4)
    swap on sda6
    /home on sda7 (ext4)

    Somehow the mbr or grub has gotten corrupted (possibly a winxp update).

    I've tried all the methods for redoing the mbr and grub2 but nothing has worked.

    When booting from a usb stick with the ubuntu netbook remix - the chroot process fails when trying to run chroot

    "chroot: cannot run command 'bin/bash': No such file or directory"

    In searching the net it would seem the problem might be that the usb stick is formatted fat32 and not ext2, 3, or 4. But I don't know how to make a usb stick bootable when formatted ext2, 3, or 4.

    Any thoughts?

  4. #4
    Join Date
    May 2008
    Beans
    119

    Re: [Solved] Reinstalling grub2 MBR from Live-CD

    Quote Originally Posted by EricBaenen View Post
    I have a similar problem.

    Samsung N110 with

    When booting from a usb stick with the ubuntu netbook remix - the chroot process fails when trying to run chroot

    "chroot: cannot run command 'bin/bash': No such file or directory"


    Nothing to do with file systems. Your stick isn't okay. Try to recreate your USB-stick with the "Startup Disk Creator".

    Good luck!

  5. #5
    Join Date
    May 2005
    Location
    Dayton, OH
    Beans
    14
    Distro
    Ubuntu 10.04 Lucid Lynx

    Re: [Solved] Reinstalling grub2 MBR from Live-CD

    Have recreated the usb stick with two different sticks, three different times - same result every time.

  6. #6
    Join Date
    May 2008
    Beans
    119

    Re: [Solved] Reinstalling grub2 MBR from Live-CD

    Never mind how often you did it. Something seems missing.
    Take one of your sticks, open a terminal (console), and give us the output of items like:

    which bash

    ls -l /bin/b*

    ls -l /

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