Reinstalling GRUB (from ArchWiki)

* 1 Introduction
* 2 Booting the Install CD
    o 2.1 Mounting Your Current Installation
    o 2.2 Reinstalling GRUB
    o 2.3 Errors

***Introduction***

This guide will show you how reinstall GRUB with an Arch Installation CD if you lose GRUB somehow.

In this guide, I'll be using hda1 as my root udev type references. If you are using a pre-0.7.1 installation CD, you will have to substitute udev references with devfs references.

Also, be aware that this guide is aimed at people using IDE drives, not SCSI or SATA drives, so subsitute SCSI and SATA names where applicable if you are attempting this with non-IDE hardware. 

***Booting the Install CD***

The first thing you will need is an Install CD. Any install CD should work, however, using the latest CD will be easier than using an older CD.

Boot the CD as if you were doing an installation (*DO NOT* use the root= option) and move on to the next step.

**Mounting Your Current Installation**

Now, you need to mount your current installation. The general process for this is as follows. You need to know what the proper partitions and filesystem types are for your disks, as well as ensuring you mount all necessary drives and other various system filesystems.

The directions below are EXAMPLES; do not follow them character for character unless your setup is identical.

--For an IDE setup with seperate boot partition, ext3 filesystem:
 cd /
 mount -t ext3 /dev/hda3 /mnt #With a pre-0.7.1 CD, hda1 will be /dev/discs/disc0/part1
 mount -t ext3 /dev/hda1 /boot
 mount -o bind /dev /mnt/dev
 mount -t proc none /mnt/proc
 mount -t sysfs none /mnt/sys
 chroot /mnt /bin/bash

--For a SCSI setup, ext3 filesystem:
 cd /
 mount -t ext3 /dev/sda1 /mnt
 mount -o bind /dev /mnt/dev
 mount -t proc none /mnt/proc
 mount -t sysfs none /mnt/sys
 chroot /mnt /bin/bash

Now you should be logged in as root, and into your current installation as if you had just booted it and logged in as root. Move on to the next step!

**Reinstalling GRUB**

Edit /boot/grub/menu.lst and make sure that everything is in order. Once you are completely sure that menu.lst is correct, run the following command (assuming /dev/hda or /dev/sda is your boot device):

 grub-install /dev/hda
   or
 grub-install /dev/sda

This command should complete sucessfully if you have followed all the steps. (If not, take a look at the notes below.) That's it, you're done! Exit the chroot and reboot:

 cd /
 umount -a
 exit
 cd /
 umount -a
 reboot

**Errors**

If you get an error that says "The file /boot/grub/stage1 was not read correctly", it probably means that your fstab/mtab is incorrect for some reason and needs to be fixed up. These files are /etc/mtab and /etc/fstab. Edit them and make sure they point to the correct partitions, then re-run grub-install.

If you get an error that says sed: can't read /boot/grub/device.map: No such file or directory, it means that you need to use the --recheck option with grub-install.

 grub-install --recheck /dev/hda

Hopefully that covers all the issues you should encounter. If you get any other errors, reboot and do the guide step by step again.

Hope this guide was helpful!

(This guide is based off an article on ArchWiki located at http://wiki.archlinux.org/index.php/Reinstalling_GRUB.)