Boot with GRUB

Using the GRUB command line is cool, but after a few thousand system starts, you will probably get a little tired of entering the same commands at the GRUB prompt and long for something a little more automated. Good news from the GRUB gang: you get a fully configurable menu interface at no extra charge! The GRUB boot menu gives you point-and-shoot boot selection, unattended default boot after a configurable timeout, any number of fallback boots if previous boots fail, toggle between command-line and menu modes, and interactive editing of menu selections and password protection. These features give GRUB an ease of use to match its tremendous functionality.

When GRUB boots, it automatically looks for the /boot/grub/menu.lst file on its boot device (the last three letters are “ELL ess tee” and not “one ess tee”). If the file is found, GRUB automatically enters its menu mode and presents the user with a stunning interface, as shown in Figure 2.

Figure 2. GRUB's Boot Menu Interface

Listing 1 [found at LJ's web site] shows the configuration file responsible for this demonstration menu. As you can see, it is a simple text file typical of many UNIX configuration files, where lines starting with hashes (#) and blank lines are ignored.

The first set of commands sets general configuration variables. The timeout command sets the time in seconds to wait for the user to make a selection before proceeding automatically to the default boot. The default command sets which of the following boot stanzas GRUB should attempt to boot automatically. Boot stanzas are numbered implicitly, starting from zero, according to their order of appearance in the configuration file. This order is also how they will be listed in the menu.

The fallback command specifies which of the boot stanzas to load if the default should fail. It is possible to set more than one fallback, as is shown in the example.

The color command lets you breathe a bit of life into the text-mode menu screen. The syntax for the color command is

color  foreground/background  [ hilite-fg/hilite-bg ]

where each of the foreground/background colors is specified with a name from the set of black, blue, green, cyan, red, magenta, brown and light-gray; dark-gray, light-blue, light-green, light-cyan, light-cyan, light-red, light-magenta, yellow and white. Among these colors, only the first eight are used for the background. The optional highlight color pair, if specified, will be used to show the current menu selection. When not specified, GRUB will use the inverse of the normal colors.

The rest of the configuration file consists of the boot stanzas for our demonstration system. The title command marks the beginning of a new boot stanza, and its argument is the label that will be displayed for its entry in the menu, from the first non-white-space character to the end of the line. The remaining commands in each stanza are identical to those used when working from the GRUB command line. The exception here is that we no longer need to give a boot command; GRUB does this job without asking.

This example configuration gives only a sample of the many flexible uses of the GRUB boot loader. Besides multiple OSes, you can use GRUB to set up menu selections for test kernels, rescue kernels, different kernel options and so on.

All in all, the GRUB configuration file will be very similar to your /etc/lilo.conf. And after working with the GRUB command line and these examples, it should be a simple matter of firing up your favorite text editor and creating a menu configuration file suitable for your own system and preferences. Don't worry if it's not perfect the first time; you will see that you can make changes interactively, and the GRUB command line is always available as a fallback.

Once you've got your configuration file, mount your GRUB floppy again, and copy the file (say it has been saved as mygrub.conf) into the magic location:

cp  mygrub.conf /floppy/boot/grub/menu.lst

Now when you boot with your GRUB floppy—presto!—you will be greeted with a lovely boot menu like the one in Figure 2. If you like, just stare at it for the few seconds it needs to count down from the timeout setting, and then it will automatically boot into your default OS. Or, use the arrow keys to highlight the OS you want to load and press return. Or, type c to go to the now-familiar GRUB command prompt. From the command prompt, press ESC to go back to the boot menu again.

It is also possible to edit the entries displayed in the menu. Typing e will open a simple vi-like editor interface for the highlighted entry. This allows you to adjust or add any settings to the configuration before booting. Any changes made here will then remain in effect for the duration of the GRUB session. To make permanent changes, you will later need to edit the configuration file on the boot disk, saving the changes with your text editor.

Play with your GRUB floppy configuration until you have it set up the way you like. After just a few system boots, you'll be slinging through GRUB like hashbrowns in a diner.