Boot camp

Get back to where you once booted

When you install an operating system on your PC's hard disk, the process usually puts a small program called a boot loader in a reserved hard disk location called the master boot record. When the PC powers up, it launches the boot loader program stored in the master boot record (MBR), which in turn loads the operating system or offers a menu of operating system choices.

After you install Linux on your Windows system, the Linux boot loader (these days, most distributions use GRUB, the GNU GRand Unix Bootloader) replaces the Windows NTLDR boot loader. (There is a way to add your Linux installation to NTLDR using a free utility called bootpart - www.winimage.com/bootpart.htm - but I can't think of a good reason to go through the hassle).

However, if you reinstall Windows (because you're upgrading, or recovering from an incurable spyware infestation, for example), it'll overwrite the Linux bootloader with NTLDR, removing the option to boot to Linux. To restore the Linux boot loader, boot the PC with a Linux installation disc and select its rescue mode. There, you can use the command-line version of the GRUB boot loader to detect the Linux partition and restore GRUB to the hard disk's master boot record, where it will be located in most dual-boot configurations.

If yours is located elsewhere, you're probably already a GRUB expert. To become one, which is not a bad idea for someone who dual-boots Windows and Linux, start with the official GRUB Manual - you'll find it at www.gnu.org/software/grub/manual.

Grubbing About

One of the problems that people sometimes experience when using GRUB to try Linux out on a dual-booted Windows XP PC isn't the difficulty of setting up a dual-boot system, it's actually getting things back to the way they were if you change your mind afterwards.Say for example, you were thinking of giving Ubuntu a spin, and used the installer's built-in partition manager to create a separate Linux partition on your Windows system. The installer will replace your master boot record with GRUB, allowing you to choose which OS you want to boot into.If you decide that this isn't for you, and use Windows to delete the Linux partition, you'll find that the next boot will fail, because GRUB is looking for an OS that's no longer visible.If you find yourself in this lamentable condition, you'll need to dig out your Windows XP disc, boot from CD and select the Recovery Console (press "R" at the Setup menu prompt).When you get to the prompt, type fixmbr and follow the prompts to replace GRUB with a functional master boot record, click here to view a screenshot. If you don't have your original disc to hand, you might want to try Mbrfix from www.sysint.no/en/index.aspx. This will also work with earlier versions of Windows.