GRUB with disk images

One cool trick is to use GRUB and memdisk to boot floppy disk images. Using the memdisk kernel from the syslinux package, you can load disk images and execute them in a non-emulated environment. How might this be useful? Let’s say you have an organization with several different models of desktops and laptops. You could create a CD-R/W or a bootable USB flash memory key with all of the different BIOS upgrades or hardware tests. Rather than carry around a book of floppies, you can simply copy the floppy image and boot from the CD-R/W or USB flash memory key. Using this method, you can also add Memtest86+’s floppy image to your bootable CD-R/W or USB flash memory key and have it at your disposal. Here is an example of a menu.lst snippit using memdisk to boot into Memtest86+:

title MemTest86+ Ver 1.60
    kernel /boot/kernels/memdisk
    initrd /boot/images/memtestp.bin

There is nothing special about the filenames. The only important thing is that the path and name referenced matches with the actual files. Check out Sidebar 1 for more examples of disk images.

GRUB with DSLinux

Figure 3: DSLinux is a 50 MB fully-graphical live GNU/Linux distribution

So how can you boot a full GNU/Linux desktop off a USB flash memory key with GRUB? First, download the DSL ISO9660 image, and either burn it to a CD, or mount it via loopback:

# mkdir dsl-test
# mount -t iso9660 -o loop dsl-image.iso dsl-test

Next, copy the KNOPPIX file, kernel, and initial ramdisk:

# cp dsl-test/KNOPPIX/KNOPPIX /media/usb/boot/images/dsl
# cp dsl-test/boot/isolinux/linux24 /media/usb/boot/kernels/dsl-linux24
# cp dsl-test/boot/isolinux/minirt24.gz /media/usb/boot/images/dsl-minirt24.gz
# sync
# umount dsl-test && rmdir dsl-test

This assumes that your USB flash memory key is mounted at /media/usb. Next, edit the /media/usb/boot/grub/menu.lst file and make sure it looks like the entry in Sidebar 1. You might have noticed that the root line at the top of the menu.lst file says (hd0,0) even though we used (hd2,0) earlier. When you boot from the USB flash memory key, the key itself becomes hd0, even before the primary master hard drive. Once you have the menu.lst file edited, go ahead and reboot. Make sure that your BIOS is set to USB-HDD, USB-ZIP, or USB-FLOPPY. You might need to experiment to see which one works. Once you get to the menu, select the option for DSL. If you get a GRUB error and are unable to successfully boot into a kernel, press the ‘c’ key to open a GRUB prompt. You can try commands like find to help locate files to boot from.

GRUB splash images

Another cool function with GRUB is putting a splash image on the boot menu screen. By default, GRUB will make the menu screen a plain black-and-white menu. There are menu options to change the black and white colors, but why stop there? Grab your favorite picture, or head to one of the URLs listed below which have splash images created for you. If you are creating your own, it will need to be in XPM format, a maximum color palate of 14 colors, and 640x480 resolution size. The GIMP can help transform your graphic to these specifications. As an alternative, you can use the ImageMagick suite of programs. The application convert can help with this conversion process. You can run it as follows:

$ convert -resize 640x480 -colors 14 mycoolpicture.jpg mybootsplash.xpm
$ gzip mybootsplash.xpm

In this case, the file mycoolpicture.jpg will be resized to 640x480, reduced to 14 colors, and saved in the XPM graphical format. The second step compresses the XPM file using the gzip compression method. GRUB can display the gzipped-xpm splash images well.

If you don’t want to create your own splash image, check out some of the following web sites which have them available for download:

• GNU GRUB Public Splashimage Archive
• GRUB Splash
• Once you have the XPM or gzipped-xpm file, you need to add a line at the top of GRUB’s menu.lst to instruct GRUB to load the specified boot splash image. The line should read as follows:

splashimage=/boot/grub/debsplash.xpm.gz

In my case, I’m using the Debian boot splash image as my background.

GRUB on CD-R/W media

I’ve also mentioned several times about installing GRUB to use for a bootable CD-R/W disk. When generating the ISO image, you will use some special settings of mkisofs. The command to build a bootable GRUB CD-R/W looks like:

$ mkdir -p iso/boot/grub
$ cp stage2_eltorito iso/boot/grub
$ mkisofs -R -b boot/grub/stage2_eltorito -no-emul-boot \
    -boot-load-size 4 -boot-info-table -o grub.iso iso

The key is to copy the stage2_eltorito file into the /boot/grub directory of the CD image tree, and run mkisofs with the options specified above. As mentioned earlier, you can also burn a menu.lst file along with kernels and disk images and put them all on the CD. In the menu.lst, you will need to use (cd) as the device, rather than (hd0). Splash images work well, too.

Conclusion

Congratulations! Now you have a bootable USB flash memory key, with DSL and memtest86+, and even a nice boot splash image. You even have the knowledge to add extra images, like your favorite BIOS update disk image, and others. For more information, check out some of the links in the resources section below.

Resources

• Grub Homepage
• Grub Manual
• Memdisk
• Syslinux
• Memtest86+
• GNU GRUB Public Splashimage Archive
• GRUB Splash