The GRand Unified Boot loader, or GRUB, has all but replaced the default boot loader on many GNU/Linux distributions. It includes some conveniences over LILO, the LInux LOader. One advantage is not having to remember to run /sbin/lilo every time you make a configuration change. It also can function as a boot loader for removable media such as floppies, CD-R/W and USB flash memory keys. It is short-sighted to view GRUB only as a boot loader to be installed on a hard drive of a GNU/Linux system. Combined with a few other utilities, GRUB can be a powerful and good-looking tool for your home, organization or workplace.

Introduction

First, what exactly is GRUB? GRUB is a boot loader, which means it passes control of the boot process from the Power-On Self Test (POST) to the kernel of your GNU/Linux distribution. GRUB works in a modular, layered fashion so that any unneeded modules are not loaded. Not only does this reduce execution time, but it saves valuable resources when running from removable media. GRUB optionally loads its configuration file at run/boot time, so you don’t have to type in commands manually each time. However, the command-line option is still available in case there is an error in your configuration file. So why use GRUB when there are other options out there? The beauty of free software is that you have choices. Alternatives to GRUB include LILO, syslinux and isolinux. The benefit of GRUB is that it will work in many different types of boot devices, but you only need to learn one set of menu commands. In addition, GRUB can work on other forms of bootable storage, such as CD-R/W, USB flash memory keys, floppy disks, and even via a TFTP server with PXE ROM booting.

Installing GRUB on a USB flash memory key

Figure 1: you can run GRUB on a USB flash memory key!

I got the inspiration for this article after trying DSLinux (or DSL), which is a fully graphical Linux distribution weighing in around 50 MB. After seeing an advertisement on their website for a USB flash memory drive with DSL installed, I figured I could probably learn how to set DSL up myself on my Lexar 256 MB JumpDrive. The DSL documentation pointed towards installing via syslinux and reconfiguring the cylinder/head/sector information of my JumpDrive, but I didn’t have any luck trying to get my USB flash memory key to boot successfully. Finally, I tried using GRUB and I was up and running with DSL in no time!

First, I recommend creating a directory structure to organize your boot-related files, and keep them separate from any other files you’d like to keep on the USB flash memory key. You could create two partitions, but I couldn’t get both partitions to load correctly when I inserted the key back into Windows. On my USB flash memory key, I created a root folder named boot to hold all the data necessary for USB booting (see figure 2). Under the boot folder, I created a directory named grub for GRUB-related files, images which are initial ramdisk (initrd), floppy, or disk images, and finally kernels to hold all the kernels. You may want to organize your boot folder differently, but make sure that you change the corresponding paths and directory names in GRUB’s menu.lst file. The menu.lst file that I use can be found in Sidebar 1.

Figure 2: this is the file structure on my USB Memory Key

Next, you’ll need to copy some of GRUB’s stage files, including stage1, stage2, and fat_stage1_5, and put them into the boot/grub directory on the USB flash memory key. These will allow GRUB to boot into GNU/Linux and other operating systems. After the files are copied over, it’s time to install GRUB to the Master Boot Record (MBR) of the USB flash memory key.

Luckily, it’s the same process as installing to a hard drive:

# grub
grub> find /boot/grub/stage1
 (hd0,1)
 (hd2,0)

On my system, hd0 is /dev/hda and hd2 happens to be /dev/sda. Just to make sure, we can use a bash-like tab completion to look through a filesystem:

grub> find (hd2,0)/boot/im<TAB>
grub> find (hd2,0)/boot/images/

Since the /boot directory on /dev/hda doesn’t have an images directory, I know that (hd2) is the hard drive that I want to install GRUB on:

grub> root (hd2,0)
 Filesystem is type fat, partition type 0xb
grub> setup (hd2)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/fat_stage1_5" exists... yes
 Running "embed /boot/grub/fat_stage1_5 (hd2)"...  15 sectors are embedded.
succeeded
 Running "install /boot/grub/stage1 (hd2) (hd2)1+15 p (hd2,0)/boot/grub/stage2
/boot/grub/menu.lst"... succeeded
Done.
grub> quit

Great! Now we have GRUB in the USB flash memory key’s MBR. Now, we have to put some files on the memory key to boot into and create a menu.lst file!