Ubuntu – Recovering GRUB after installing Windows 7?


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How can I repair GRUB? (How to get Ubuntu back after installing Windows?)

I installed Windows 7 after it crashed, and now I am unable to boot Ubuntu. Ubuntu partitions are still there. I tried using Boot-Repair, but it didn't work!

Best Answer

  • You can re-install grub in the Master Boot Record using the LiveCD for you distribution version,

    It goes like this:

    • Boot from LiveCD ⋯ please try to use a LiveCD that has the same version of Grub2 as the installed version

    • Mount the root of the installed Ubuntu at /mnt

    • Change root

    • Update grub

    • Install grub

    • Reboot

    The above steps are from near the bottom of the Ubuntu Community Documentation of Grub2

    After booting from the liveCD ( select "Try Ubuntu" on the opening screen)

    Then start up a terminal (dash, type-in terminal, … )…

    • It may be easier to open this web page while running LiveCD. Firefox should allow you to do this.

    Type in the terminal sudo fdisk -l - and enter your password if asked. That's a lower case L. Find the installed Ubuntu partitions, (from mine with other disks snipped ― here):

    me@mycomputer:~$sudo fdisk -l
    Disk /dev/sde: 300.1 GB, 300089646592 bytes
    255 heads, 63 sectors/track, 36483 cylinders, total 586112591 sectors
    Units = sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disk identifier: 0xc3f5ebeb
    Device    Boot      Start         End      Blocks   Id  System
    /dev/sde2       138464296   586110975   223823340    5  Extended
    /dev/sde3   *        2048   138463231    69230592   83  Linux
    /dev/sde5       138464298   313460279    87497991    7  HPFS/NTFS/exFAT
    /dev/sde6       313460736   317650943     2095104   82  Linux swap / Solaris
    /dev/sde7       317652992   581922815   132134912   83  Linux
    /dev/sde8       581924864   586110975     2093056   82  Linux swap / Solaris
    Partition table entries are not in disk order

    Find your Linux installation (Id=83, System=Linux0 then type in

    sudo mount /dev/sde3 /mnt

    but use your partition instead of /dev/sde3(my root partition is sde3, sde7 is my home partition).

    This is assuming that you do not have a separate /boot partition. If you do, you will need to also mount it by typing

    sudo mount /dev/sd·· /mnt/boot

    where sd·· is the partition where you installed the separate boot directory.

    ls /mnt - just checking to see if I got it right:

    me@mycomputer:~$ sudo mount /dev/sde3 /mnt
    me@mycomputer:~$ ls /mnt
    bin   cdrom  etc   initrd.img      lib         media  opt   root  sbin     srv  tmp  var      vmlinuz.old
    boot  dev    home  initrd.img.old  lost+found  mnt    proc  run   selinux  sys  usr  vmlinuz

    You should test to see if the boot directory is properly installed. Type in ls /mnt/boot and if it is empty, the boot directory is not installed. It should look something like this:

    me@mycomputer:~$ ls /boot
    abi-2.6.35-30-generic     initrd.img-2.6.35-30-generic  System.map-2.6.35-31-generic
    abi-2.6.35-31-generic     initrd.img-2.6.35-31-generic  vmcoreinfo-2.6.35-30-generic
    config-2.6.35-30-generic  memtest86+.bin                vmcoreinfo-2.6.35-31-generic
    config-2.6.35-31-generic  memtest86+_multiboot.bin      vmlinuz-2.6.35-30-generic
    grub                      System.map-2.6.35-30-generic  vmlinuz-2.6.35-31-generic


    for i in /dev /dev/pts /proc /sys; do sudo mount -B $i /mnt$i; done
    sudo chroot /mnt #change the root
    sudo update-grub # now update grub


    me@mycomputer:~$ sudo for i in /dev /dev/pts /proc /sys; do sudo mount -B $i /mnt$i; done
    me@mycomputer:~$ sudo chroot /mnt
    me@mycomputer:~$ sudo update-grub
    Generating grub.cfg ...
    Found linux image: /boot/vmlinuz-3.0.0-13-generic
    Found initrd image: /boot/initrd.img-3.0.0-13-generic
    Found linux image: /boot/vmlinuz-3.0.0-12-generic
    Found initrd image: /boot/initrd.img-3.0.0-12-generic
    Found memtest86+ image: /boot/memtest86+.bin
    Found Microsoft Windows XP Professional on /dev/sdc1

    Now to re-install grub in the MBR. You will need to know which disk your system boots from, and find it in the fdisk -l listing you have already done. Then type in sudo grub-install /dev/sd replacing sd· with the disk you will boot from.

    me@mycomputer:~$ sudo grub-install /dev/sd·

    Then type in Crtl-D to exit chroot.

    Then type in sudo for i in /sys /proc /dev/pts /dev; do sudo umount /mnt$i; done - as one line

    me@mycomputer:~$ sudo for i in /sys /proc /dev/pts /dev; do sudo umount /mnt$i; done

    If you mounted a separate /boot partition, type in sudo umount /mnt/boot

    me@mycomputer:~$ sudo umount /mnt/boot

    Then type in sudo umount /mnt

    me@mycomputer:~$ sudo umount /mnt

    Then type in sudo reboot to restart he system (remember to remove the LiveCD).

    me@mycomputer:~$ sudo reboot

    Hopefully, grub will be installed.

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