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What Is GRUB

• GRUB is a bootloader, it is the first thing that loads when the computer starts. It allows you to have different operating systems, and versions of them, on the same hard drive. For example you may have Windows and Linux on a computer, GRUB would load before either of these and give you a choice. You can also create a boot floppy with GRUB to use in case of emergency.

Increasing the GRUB timeout

• If you need to get into the grub menu you need to press ESC just after it starts. By default you have to press ESC very quickly. To increase this time edit /boot/grub/menu.lst, increasing the seconds in the TIMEOUT part. Alternatively you could have the menu always come up at boot time. To do this, comment out 'hiddenmenu' by inserting a # at the beginning of the line. Once you have changed menu.lst you must run:

    sudo update-grub

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• If the Ubuntu installer detected other operating systems on the disk during the installation, then the grub menu will be displayed by default and the timeout will be increased, so the step above will be unnecessary.

Setting kernel parameters

• In /boot/grub/menu.lst, you will find a line like this:

    # kopt=root=/dev/sda1 ro

  It is a comment, but do not remove the '# ' at the beginning. THIS IS IMPORTANT.

  If you require additional kernel parameters (for example, if someone has asked you to test booting with certain parameters in order to troubleshoot a problem), add them to the end of the line, for example to add noapic:

    # kopt=root=/dev/sda1 ro noapic

  After editing the file, run:

    sudo update-grub

If /boot is on another partition

• If /boot is mounted on another partition and you use update-grub, then you may run into problems. One fix is to use grub-install, which is a distribution-agnostic way to install grub.

    sudo grub-install --root-directory=/boot /dev/sda

  This is probably less desirable because update-grub is very good at setting things up properly, therefore it should be used instead.

  Another fix is to create a symlink in /boot to itself:

    cd /boot
    sudo ln -s . boot

  The reasoning behind this is when grub boots, it looks at whatever partition it is installed on. update-grub (and grub-install) assumes that everything is in /boot. When /boot is on the same partition as /, then all is OK, as menu.lst will be in /boot/grub. If /boot is on a separate partition, then grub sees /boot as / (hence the '--root-directory' above). By adding a symlink, when it looks for /boot/grub, it will be there. By creating the symlink, you have put a loop in the file system, which may cause problems when using certain options of cp, mv, etc.

Bootsplash

• Grub allows an image to be displayed behind the menu. You can obtain a set of images with the package "grub-splashimages", or you can make your own. The images must be 640x480 pixels, contain no more than 16 colors (but a smaller number like 12 works better to allow some different colors for the menu text), and be in gzipped xpm format. The GIMP can be used to resize (Image -> Scale Image...), reduce colors (Image -> Mode -> Indexed...), and can save to .xpm.gz files. After creating a splash image, add a line like

    splashimage=(hd0,4)/grub/splash.xpm.gz

  to your menu.lst file. A useful trick is to make a symlink to the actual image named splash.xpm.gz.

    cd /boot/grub
    sudo ln -s my_image.xpm.gz splash.xpm.gz 

  Grub loads the image from the disk upon boot; it is not stored in the MBR. If you use a symlink, you will not have to edit menu.lst and reinstall grub to change the image, you just have to change the symlink. Here is an image of the GNU by Peter Gerwinski: attachment:gnu-head.xpm.gz

Splash Image with update-grub

• The command update-grub will automatically pick up /boot/grub/splash.xpm.gz and configure the menu.lst file for you. It will take care of the correct hdX and partition number [no need to type in (hd0,4)].

    sudo apt-get install grub-splashimages
    sudo ln -s /boot/grub/splashimages/my_image.xpm.gz /boot/grub/splash.xpm.gz
    sudo update-grub

  Note: replace the my_image.xpm.gz with the one that you want.

Creating a boot floppy

• You can use grub to create a boot floppy. See ["/BootFloppy"]

Change the default operating system

• By default, Grub in Ubuntu boots Ubuntu by default. If you wish to change this to another operating system, see ["/ChangeDefaultOS"]

Network booting

• If you use LTSP or Edubuntu, you may want to boot from your network card.

  Specific network cards need a specifc rom to boot from. To find which one you need, run lsmod and then search for your floppy. Then go to www.rom-o-matic.com and get the appropriate rom.

  Edit /boot/grub/menu.lst and add the following before ### BEGIN AUTOMAGIC KERNELS LIST or after ### END DEBIAN AUTOMAGIC KERNELS LIST, otherwise your changes will be wiped out by security updates, etc.

    title LTSP
    root (hd0,2)
    kernel /boot/(rom you get from rom-o-matic)

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