Creating a Boot Disk

When you are logged in as root, you might want to take a few minutes to create a fresh boot disk or copy the boot disk you already have.

There are a number of reasons you should make a boot disk. It can help you recover from a system failure, it can help you test a new kernel you have downloaded and compiled, and it can help you share your computer with more than one operating system.

You were given the opportunity to make a boot disk when you installed Red Hat Linux. If you chose not to make a boot disk at installation, here is your chance to start from scratch.

To create a boot disk:

Go to a shell prompt and make sure you are logged in as root. At the shell prompt, if you see something like [newuser@localhost newuser]$, for example, type:

[newuser@localhost newuser]$ su -
Password: yourrootpassword
[root@localhost newuser]# 

Put a standard diskette in the floppy drive.

TipNaming The Floppy Drive

In Linux, the floppy drive is referred to as /dev/fd0.

If you have previously used the diskette, remember that you will lose everything on the diskette!

At the prompt, type:

uname -r

Your kernel version will be displayed. The kernel is the heart of any Linux system. Your kernel version will be something similar to:


There will be several numbers after 2.4, for example: 2.4.1).

Now that you have found the kernel version, you can tell the mkbootdisk command which kernel to copy to your diskette.

Type the following command:

mkbootdisk --device /dev/fd0 2.4.x-yy

If you do not tell mkbootdisk where to copy the kernel, it will default to copying to the diskette in /dev/fd0.

Press [Enter]. When the light on your floppy drive goes off, remove and label the disk.

TipClearing The Screen

If your screen becomes crowded, you can always start with a clean slate by typing clear at the prompt.

TipThe su and su - Commands

The command su means substitute users, and it lets you temporarily log in as another user. When you type su all by itself and press [Enter], you become root (also called the superuser) while still inside your login shell. Typing su - makes you become root with root's login shell — that is, it is as if you had logged in as root. What is the difference? There are some commands which can be performed only if you have logged in as root; so typing su - allows you to perform these commands without logging out and logging back in.