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Note that you need to use such boot options only if the kernel doesn't detect your hardware at boot time, which is unlikely unless you have very old or very uncommon hardware. You should already know if this is necessary, based on your experiences with installing Linux; in general, you should have to specify kernel parameters in the kernel lines in the GRUB menu file only if you had to specify these boot options when first booting the Linux installation media.

There are a number of other boot-time options. Most of them deal with hardware detection, which has already been discussed in Chapter 2. However, the following additional options may also be useful to you:

single

Boot the system in single-user mode; skip all the system configuration and start a root shell on the console. See "What to Do in an Emergency" in Chapter 27 for hints on using this.

root= partition

Mounts the named partition as the Linux root filesystem.

ro

Mounts the root filesystem as read-only. This is usually done in order to run fsck; see "Checking and Repairing Filesystems" in Chapter 10.

ramdisk= size

Specifies a size, in bytes, for the ramdisk device. Most users need not worry about using the ramdisk; it's useful primarily for installation.

vga= mode

Sets the VGA display mode. Valid modes are normal, extended, ask, or an integer.

mem= size

Tells the kernel how much RAM you have. If you have 64 MB or less, the kernel can get this information from the BIOS, but if you use an older kernel and you have more, you will have to tell the kernel the exact amount, or it will use only the first 64 MB. For example, if you have 128 MB, specify mem=128m. Fortunately, this is no longer necessary with newer kernels.

Any of these options can be entered by hand at the GRUB boot prompt or specified in the kernel line in the GRUB configuration file.

Removing GRUB

If you have GRUB installed on your MBR, the easiest way to remove it on Windows 95/98/ME is to use Windows FDISK. The command:

FDISK /MBR

runs FDISK and overwrites the MBR with a valid Windows boot record. On Windows NT/2000/XP, the procedure is a lot more involved.

* * *

[*] A Linux boot floppy may instead contain a GRUB boot record, which causes the system to boot a kernel from the hard drive. We discuss this in the next section, when we talk more about GRUB.

[*] Why the silly filename? On many Unix systems, the kernel is stored in a file named /vmunix where vm stands for "virtual memory." Naturally, Linux has to be different and names its kernel images vmlinux, and places them in the directory /boot to get them out of the root directory. The name vmlinuz was adopted to differentiate compressed kernel images from uncompressed images. Actually, the name and location of the kernel don't matter a bit, as long as you either have a boot floppy containing a kernel, or GRUB knows how to find the kernel image.

System Startup and Initialization

In this section, we talk about exactly what happens when the system boots. Understanding this process and the files involved is important for performing various kinds of system configuration.

Kernel Boot Messages

The first step is booting the kernel. As described in the previous section, this can be done from floppy or hard drive. As the kernel loads into memory, it will print messages to the system console, but usually also saves them in the system logfiles as well. As root, you can always check the file /var/log/messages (which contains kernel messages emitted during runtime as well). The command dmesg prints out the last lines of the kernel message ring buffer; directly after booting, naturally, you will get the boot messages .

The following few paragraphs go through a couple of the more interesting messages and explain what they mean. These messages are all printed by the kernel itself, as each device driver is initialized. The exact messages printed depend on what drivers are compiled into your kernel and