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docs/bootable floppies.txt
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docs/bootable floppies.txt
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From: Ron Smits (ron@draconia.hacktic.nl)
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Subject: Re: Creating root disk
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Newsgroups: comp.os.linux.admin
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View this article only
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Date: 1994-03-23 00:35:41 PST
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Laurent Chavey (chavey@ori.cis.udel.edu) wrote:
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: How does one create a root floppy from linux.
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: thank you.
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--
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Included is a BOOTFLOP-HOWTO that I wrote a few months ago
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Ron Smits
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ron@draconia.hacktic.nl
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Ron.Smits@Netherlands.NCR.COM
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/*-( My opinions are my opinions, My boss's opinions are his opinions )-*/
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/*-( They might not be the same -*/
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The Making of a bootable floppy
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February 1, 1994
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Ron Smits
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(ron@draconia.hacktic.nl)
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Every now and then the question arises on the net on how to make a
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bootable disk. There are several reasons for people to make a bootable
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disk. They want to have an emergency disk, they want to roll their on
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distribution set or they just want to know how it is done.
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This document will be an attempt to describe all the necessary steps
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that will lead to a bootable floppy. At the end of the document you
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will know how to make bootable floppy that will load itself into a
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ramdisk and how to make one that's just bootable. It's basically the
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same.
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Any comments on how to improve this document, please let me know on
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the above mail address. All comments and suggestions are welcome.
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----------------------------------------------------------------------
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Right let's get on with it. I will describe the way I usually follow
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when making a bootable disk. (I do this so every now and then to keep
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kernels uptotdate and to pass among my friends and collegues to let
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them experience the 'Linux' feel).
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1. The kernel
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Create a kernel with root device set to /dev/fd0. You can accomplish
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this in two ways:
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1. Edit Makefile in /usr/src/linux and set the variable `ROOT_DEV' to
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/dev/fd0 or keep it empty. If you keep it empty, the default of
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FLOPPY will be used by build. Personnaly I like to fill it in,
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keeps you from guessing and remembering what the default was.
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2. take an exsisting kernel and patch it with `rdev' like this
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# rdev -r zImage /dev/fd0
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this will patch the kernel named zImage to use the floppy as
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rootdevice.
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----
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2. the files
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Create a subdirectory somewhere on your system as root. Call it for
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example /tmp/bootflop. In this directory create the following
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directories:
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bin
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etc
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etc/lilo
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lib
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dev
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You must populate these directories with some esential files in order
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to have a working system:
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bin:
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cp, df, fsck, fsck.ext2, fsck.minix, ls, rm, sh, vi, mount
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All these commands, except vi, can --normally-- be found in /bin. vi
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is usually in /usr/bin.
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etc:
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zImage, fstab
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Fstab is needed for df to work properly, plus you can populate it to
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have your harddisks mounted on several mnt mountpoints. zImage is the
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kernel you made in step 1.
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etc/lilo:
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any_d.b, boot.b, chain.b, floppy, disktab, lilo, map, mkck,
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os2_d.b.
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These files are needed to make the floppy bootable.(We'll come back to
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one of them later). The file floppy is the lilo configuration file see
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point 3.
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lib:
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libc.so.4
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This is the shared library. The other commands need it! Forget it and
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be amazed when you start from the disk (come on try it :-))
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----
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3. Lilo configuration
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I always use Lilo to make floppies (and my harddisk) bootable. Here
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is a copy of the config file I use for floppies, it's named floppy:
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#
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# lilo configuration for floppy boot
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install = /mnt/etc/lilo/boot.b
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map = /mnt/etc/lilo/map
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backup = /mnt/etc/lilo/junk
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compact
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vga = normal
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root = /dev/fd0
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boot = /dev/fd0
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image = /mnt/etc/zImage
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label = zLinux
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As you can see, I presume that the floppy is mounted as /mnt when we
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are making it. it is _*VERY*_ important that the keywords `install'
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and `map' point to files on the floppy, so in the /mnt/etc/lilo
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directory. Otherwise the machine will not boot. The backup may point
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to something else.
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----
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4. The floppy
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Be smart, use a new one!
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format it:
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# fdformat /dev/fd0H1440
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Make a filesystem on it:
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# mkfs -t minix /dev/fd0 1440
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mount it:
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# mount -t minix /dev/fd0 /mnt
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The reason I use a minix filesystem is twofold, first of all, the
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minix filesystem has less overhead than the more advanced filesystems
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like extfs and ext2fs. And secondly, the kernel demands a minix
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filesystem, if you want to copy it to a ramdisk
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Now copy the tree structure that we made to it:
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# cd /tmp/bootflop
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# find . -print | cpio -pvdum /mnt
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After having populated these directories, go to /mnt/dev and make the
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device nodes:
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# cd /mnt/dev
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# /dev/MAKEDEV generic
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(Note: I know MAKEDEV is somewhere in a package, but I haven't the
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faintest idea where. If you need it and can't find it, drop me a line,
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I'll mail it to you)
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----
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5. Making it bootable (finally)
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We now have a filesytem with the bare minimum on it to make it run as
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a standalone system. with the tools we placed on it, we can even do
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some repairing, so the last thing to do is to make it bootable. If you
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made a lilo configuration file as described in point 3, you can do the
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following:
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# cd /mnt/etc/lilo
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# ./lilo -v -C config
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You should expect the following as output from lilo:
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LILO version 0.10
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Written 1992,1993 by Werner Almesberger
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Reading boot sector from /dev/fd0
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Merging with /etc/lilo/boot.b
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Boot image: /mnt/etc/zImage
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Added zLinux
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/etc/lilo/junk exists - no backup copy made.
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Writing boot sector.
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That's it! you've made a bootable floppy, unmount it and try it out!
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----
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6. bootable floppy with a ramdisk.
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The last thing I want to explain is how to create a ramdisk. The
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purpose of having a ramdisk is to have your floppy drive free to be
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able to mount another floppy with even more tools and rescue material
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on it. (I personally never do it, but have a bootflop with ramdisk any
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because it's faster then the floppydrive).
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Actually it's extremely easy and can be done with a one line
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modification. The kernel provides all the hooks needed. Add the
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following line to /mnt/etc/lilo/floppy
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ramdisk = 1440
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perform the actions in point 5 again and presto, You have a bootable
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floppy that copies itself into a ramdisk, leaving your floppydrive
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free for other more important stuff.
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----
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7. the End?
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The steps described above have been extensively tested by over a
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longer periode of time. It has proven it's worth! And it made me
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paranoide, I always make sure that I have at least 2 of them. Murphy
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lurks in the corner!.
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This HOWTO is far from perfect, so all remarks and suggestions are
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welcome. If the interest is ther. I will keep maintaining it.
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february 4, 1994
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Ron Smits
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ron@draconia.hacktic.nl
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