Using GRUB to load Windows XP

Using GRUB to load Windows XP located on a second hard disk
Written by James McDonald on 01-Sept-03.

Please read this warning BEFORE you start.

Because my trusty old Pentium III died I moved two hard disks onto my Athlon 1GHz machine and made my Redhat 9.0 Linux install the Primary or first hard disk . The windows XP install which I use occassionally I inserted as the slave drive on the same IDE0 Channel. This is my setup as follows.

IDE0
Channel 0 = GNU/Linux Redhat 9.0 20GB

IDE0 Channel 1 = Windows XP SP1 30GB

IDE1 Channel 0 = DVD/CD ROM/CDRW

The out put from fdisk for my harddisks was this

[root@p3
james]# /sbin/fdisk -l

Disk /dev/hda: 20.4 GB, 20485785600 bytes
255 heads, 63 sectors/track, 2490 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot   
Start       End   
Blocks   Id  System

/dev/hda1  
*        
1        13   
104391   83  Linux

/dev/hda2           
14      2360  18852277+  83 
Linux

/dev/hda3         
2361      2490   1044225  
82  Linux swap

Disk /dev/hdb: 30.0 GB, 30020272128 bytes
255 heads, 63 sectors/track, 3649 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot   
Start       End   
Blocks   Id  System

/dev/hdb1  
*        
1      1020   8193118+  
7  HPFS/NTFS

/dev/hdb2         
1021      3649  21117442+  
7  HPFS/NTFS

I still wanted to be able to boot my XP install but I didn't want to go the way of installing the Windows XP boot loader (this is the booting Linux from Windows way of doing it - Not the booting Windows from Linux which is what I wanted)

I tried lilo but found the options confusing (and googling didn't give an obvious solution), but GRUB had a good bit of information on running DOS/Windows.

I found the info by running:

info
grub

# Look for
booting another OS and then find the Windows section

I didn't have GRUB installed I was running lilo so I installed GRUB to the MBR (master boot record) of the first hard disk by running the following command

/sbin/grub-install /dev/hda

# because the second hard disk wasn't present when grub was originally
installed

# it had to be added to the /boot/grub/device.map file

vi

/boot/grub/device.map

# this device map was generated by anaconda

(fd0)     /dev/fd0

(hd0)     /dev/hda

(hd1)   /dev/hdb

# added this line

Contents of /etc/grub.conf

#
grub.conf generated by anaconda

#

# Note that you do not have to rerun grub after making changes to this
file

# NOTICE: You have a /boot partition. This means that

# all kernel and initrd paths are relative to /boot/, eg.

# root (hd0,0)

# kernel /vmlinuz-version ro root=/dev/hda2

# initrd /initrd-version.img

#boot=/dev/hda

default=0

timeout=10

splashimage=(hd0,0)/grub/splash.xpm.gz

title Red Hat Linux (2.4.20-8)

    root (hd0,0)

    kernel /vmlinuz-2.4.20-8 ro root=LABEL=/ hdc=ide-scsi

    initrd /initrd-2.4.20-8.img

title Windows XP

    # as far as I can understand it the Windows
XP hard disk hd1 

    # needs to think it is the first disk on the IDE bus
in order to boot

    # so do a swap and add the following two commands to
change it

    map (hd0)
(hd1)

    map (hd1) (hd0)

    # you then need to tell grub which hard disk
and which partition to read the booting information from

    # although you have done a swap using the above
commands the disks don't change their labelling

    # so use hd1,0 as the root device (in grub all
numbering starts at zero)

    # the telltale to knowing which partition to add to
the rootnoverify option 

    # is the output of fdisk -l the `*' on /dev/hdb1
showing it's the active or boot partition

    rootnoverify
(hd1,0)

    # now tell grub that you are going to be
doing an indirect boot using an external chainloader

    # i.e it's going to grab the Windows boot code and
run it instead 

    # of directly loading the linux kernel like it
usually does.

   
chainloader +1

    # not sure exactly what makeactive does 

    # I'm assuming it is marking the root partition you
specified

    # with the rootnoverify command as the active or
boot partition 

    # if it isn't already marked as the `*' or boot
partition

    makeactive

nb: Make sure you back up your data and configuration before playing with your hard disk configuration it can really suck to lose important information.