Running Linux, 5th Edition - Matthias Kalle Dalheimer [332]
We are going to look at a sample grub.conf file. You can use this file as a base for your own grub.conf and edit it for your own system.
It should be said at this point that GRUB is very flexible and can actually drop you into a shell that lets you enter GRUB commands interactively during the boot process. However, most users would find this both tedious and error-prone, which is why we describe another use here, which will provide you with a convenient menu that you can select from (for example, in order to boot different kernels or even different operating systems). With this setup, the grub.conf file can be quite concise. Here is an example:
root (hd0,0)
install --stage2=/boot/grub/stage2 /grub/stage1 (hd0) /grub/stage2 0x8000
(hd0,0)/grub/menu.lst
quit
The first line specifies the drive to boot from. In this case, it is the first partition on the first hard disk--hd is for hard disk, the first zero is for the first hard disk in the system, and the second zero for the first partition on that particular hard disk (GRUB always starts counting at zero!). It is quite common among Linux users to reserve a small partition (often mounted as /boot) for the kernel image and booting-related files. Because there have been limits in the past regarding the parts of the disk from which bootloaders could load kernel images, it has become customary to make this partition the very first one. Although these limits are mostly gone with modern hardware, modern BIOSes, and modern bootloaders, this tradition prevails, and it definitely does not hurt to keep it.
A few more examples: (fd0) would mean to boot from the first floppy disk in the system, and (hd3,4) would mean the fifth partition on the fourth hard drive (of one lucky Linux user who apparently can afford lots of hardware). There is also the special name (nd) which is used for booting the kernel image from the network, something that is beyond the scope of this book.
The second line is fairly complex. It would go too far to dissect the complete booting process, but we can at least say that GRUB uses a two-stage booting process, and this command specifies where to get the instructions for the two stages from, at which address to load them into the computer's memory, and what to do then. The "what to do then" part is the most interesting for us; in the example configuration file, it is the (hd0,0)/grub/menu.lst part at the end. Where should this file be located so that GRUB can find it? If you try:
pooh:~ # ls /grub/menu.lst
/bin/ls: /grub/menu.lst: No such file or directory
you will not find it. But remember that GRUB uses the parentheses to denote a device, in our case a hard disk partition, the first partition on the first hard drive. This could be anywhere, of course, but if you remember that most systems create a small partition that does not contain much except the kernel image and the bootloader files, and that it is often mounted as /boot, you can try:
pooh:~ # ls /boot/grub/menu.lst
/boot/grub/menu.lst
Aha! Of course, if you are installing GRUB from scratch on your system and, unlike us, do not have a preinstalled configuration that you are just fiddling around with, then you will not get a result here either. Rest assured, however, that this is where GRUB will search for the menu file.
What would such a menu file look like? Here is an example of a version that loads two different Linux configurations and MS-Windows, all presented in a convenient menu:
default 0
timeout 10
title Linux
kernel (hd0,5)/boot/vmlinuz root=/dev/hda6 vga=0x314
title Linux Failsafe
kernel (hd0,5)/boot/vmlinuz root=/dev/hda6 ide=nodma apm=off acpi=off vga=normal noresume
barrier=off nosmp noapic maxcpus=0 3
title Windows
root (hd0,0)
chainloader +1
The first two lines together mean that when the boot menu is presented by GRUB, the user has 10