Rewrite grub after messing it up

Have you ever messed up your grub boot loader? Maybe by installing windows och osx86? Try this.

Using the cd/usb boot up with grub

Boot up the cd/usb,press c in grub menu.Type:

grub>find /boot/grub/core.img
grub>root (hdx,y)   (previous command will output the x,y)
grub>kernel /boot/grub/core.img
grub>boot

After the boot command,you’ll go into grub2 menu.Select to boot up ubuntu,and run this command to restore grub:

sudo grub-install /dev/sda

Or.... do this:

Boot from livecd. Locate partitions using fdisk -l

sudo -i
mount /dev/sda7 /mnt
mount /dev/sda6 /mnt/boot  #skip this one if not have a separate /boot partition
grub-install --root-directory=/mnt/ /dev/sda

Please observe.

Once you have successfully booted linux from the harddrive it is always a good idea to run:

sudo update-grub