• Choose a category
• All
• Classic-Fiction

A number of parameters are stored in the kernel image. Among these parameters is the name of the device to use as the root filesystem once the kernel boots. Another parameter is the text mode to use for the system console. All these parameters may be modified using the rdev command, which we discuss later in this section.

After the kernel has started, it attempts to mount a filesystem on the root device hardcoded in the kernel image itself. This will serve as the root filesystem—that is, the filesystem on /. "Managing Filesystems" in Chapter 10 discusses filesystems in more detail; all that you need to know for now is that the kernel image must contain the name of your root filesystem device. If the kernel can't mount a filesystem on this device, it gives up, issuing a kernel "panic" message. (Essentially, a kernel panic is a fatal error signaled by the kernel itself. A panic will occur whenever the kernel is terminally confused and can't continue with execution. For example, if there is a bug in the kernel itself, a panic might occur when it attempts to access memory that doesn't exist. We'll talk about kernel panics more in the section "What to Do in an Emergency" in Chapter 27.)

The root device stored in the kernel image is that of your root filesystem on the hard drive. This means that once the kernel boots, it mounts a hard drive partition as the root filesystem, and all control transfers to the hard drive. Once the kernel is loaded into memory, it stays there—the boot floppy need not be accessed again (until you reboot the system, of course).

Given a reasonably small kernel image, you can create your own boot floppy. On many Linux systems, the kernel itself is stored in the file /boot/vmlinuz.[*] This is not a universal convention, however; other Linux systems store the kernel in /vmlinuz or /vmlinux, and still others in a file such as /Image. (If you have multiple kernel images, you can use GRUB to select which one to boot. See the next section.) Note that newly installed Linux systems may not have a kernel image on the hard drive if a boot floppy was created for you. In any case, you can build your own kernel. It's often a good idea to do this anyway: you can customize the kernel to include only those drivers for your particular hardware. See "Building the Kernel" in Chapter 18 for details.

All right. Let's say that you have a kernel image in the file /boot/vmlinuz. To create a boot floppy, the first step is to use rdev to set the root device to that of your Linux root filesystem. (If you built the kernel yourself, this should be already set to the correct value, but it can't hurt to check with rdev.) We discussed how to create the root device in "Editing /etc/fstab" in Chapter 2.

As root, use rdev -h to print a usage message. As you will see, there are many supported options, allowing you to specify the root device (our task here), the swap device, ramdisk size, and so on. For the most part, you needn't concern yourself with these options now.

If we use the command rdev /boot/vmlinuz, the root device encoded in the kernel found in /boot/vmlinuz will be printed:

courgette:/# rdev /boot/vmlinuz

Root device /dev/hda1

If this is incorrect, and the Linux root filesystem is actually on /dev/hda3, we should use the following command:

courgette:/# rdev /boot/vmlinuz /dev/hda3

courgette:/#

rdev is the strong, silent type; nothing is printed when you set the root device, so run rdev /boot/vmlinuz again to check that it is set correctly.

Now you're ready to create the boot floppy. For best results, use a brand-new, formatted floppy. You can format the floppy under Windows or using fdformat under Linux; this will lay down the sector and track information so that the system can autodetect the size of the floppy. (See the section "Managing Filesystems" in Chapter 10 for more on using floppies.)

To create the boot floppy, use dd to copy the kernel image to it, as in the following example:

courgette:/# dd