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This document desribes the require steps to create your own Linux mini-distribution that fit to a floppy disk. I assume that you have a Linux system running (based on kernel 2.2.x), understand the basics of Linux and have an experience of compiling the kernel.
To create a mini-distribution, you must have:
The last file is in this document.
Login first as root.
Make sure you have your Linux kernel source. You can verify this by the following command:
# ls /usr/src/linux
If this directory doesn't exist, you must install kernel source first. Please refer to the KERNEL-HOWTO
Ensure that your kernel has support for ramdisk. Otherwise, configure the kernel and recompiler it. (Refer to the Kernel-HOWTO).
Install the loopback device as necessary. You might have already this, check for losetup.
You must create a custom kernel which is basically a stripped-down version of Linux. To do this, copy the example .config file to your /usr/src/linux, and then:
# cd /usr/src/linux # make menuconfig
Customize your kernel as necessary. Only checkmark ('Y') the required options as you have to pack the kernel as small as possible. After finishing this process, you can build the kernel by the following commands:
# make deps # make zImage
If an error occurs because the image file is too large, do this:
# make bzImage
NOTE: If the same error still happens, it means that your kernel is too large. You must do make menuconfig again and disable support for many unnessary things.
If you add support for loadable module for the kernel, you must also perform this:
# make modules
Now, switch to your home directory and create a sub-directory named 'flop' (this is only an example, use whatever name you like):
# cd ~ # mkdir flop
Copy the newly created kernel to this directory:
# cp /usr/src/linux/arch/i386/boot/zImage .
NOTE: If you did make bzImage, copy the /usr/src/linux/arch/i386/zImage file then.
Copy install script file to your home directory.
Create a sub-directory named 'tree'.
# mkdir tree
Under this directory, create another directory tree which resembles a normal Linux partition. Therefore you need at least the following directories:
/bin /dev /etc /etc/rc.d /lib /lib/modules /mnt /proc /sbin /tmp /usr /usr/bin /var
Now we need some libraries, mostly glibc2. To do this, copy the following libraries for your main Linux system to ~/flop/tree/lib :
ld-2.1.2.so ld-linux.so.1.9.9 libtermcap.so.2.0.8
(The names may vary depend on your kernel version).
Since those files are too large to fit on a floppy (even in a compressed), you must strip debugging information from the file when copying those libraries. To do this, using the following command
# objcopy --strip-debug from target
Subsitute from and target to the above libraries (e.g: /lib/ld-2.1.2.so and ~/flop/tree/lib/ld-2.1.2.so).
If you add support for modules for your kernel, also copy the modules to ~/flop/tree/lib/modules.
Under ~/flop/tree/lib, make sure you have the following symbolic links:
ld-linux.so -> ld-linux.so.1 ld-linux.so.1 -> ld-linux.so.1.9.9 ld-linux.so.2 -> ld-2.1.2.so libc.so.6 -> libc-2.1.2.so libtermcap.so.2 -> libtermcap.so.2.0.8
You also need standard devices (node) in your ~/flop/tree/dev. The easiest way to do this is to copy those devices from your main Linux system and then strip down any unnecessary ones.
If later you want to mount a floppy drive or hard disks, create the mount point in ~/flop/tree/mnt. Again, the simple way is to copy from your system.
Directory ~/flop/tree/etc requires some file. Copy the following files from your system and then customize them as necessary:
fstab host.conf inittab profile rc.d services group hosts issue passwd protocols securetty termcap
Create ~/flop/tree/etc/rc.d/rc.reboot as follow:
PATH=/sbin:/bin:/usr/bin:/usr/sbin
[ "${BASH+bash}" = bash ] && enable kill
halt -w
echo "Turning off swap and accounting"
swapoff -a
echo "Unmounting file systems"
umount -a
mount -n -o remount,ro /
echo -n "Rebooting..."
/sbin/reboot -d -f -i
Also, create ~/flop/tree/etc/rc.d/rc.sysinit as follow:
mount -a echo "flop" > /proc/sys/kernel/hostname /sbin/ifconfig lo 127.0.0.1 netmask 255.0.0.0 /sbin/route add 127.0.0.1 lo
Then come the hardest (and yet funniest) part. Copy the necessary applications to ~/flop/tree/bin and ~/flop/tree/sbin. Please copy the most important things only (cause space is limited!). The following files are starting-point for you:
for ~/flop/tree/bin:
bash cp dmesg mkdir mv rmdir touch cat date echo ls mount rm sleep
and for ~/flop/tree/sbin:
halt ifconfig insmod reboot route
You don't need login or mingetty because there won't be any login prompt :)
NOTE: Surely you need insmod if you add module support for the kernel.
Create a symbolic link ~/flop/tree/sbin/init to point to /bin/bash. The kernel expects to find this file, so if you don't have one, system will be halted.
Installation to the floppy is performed using install-flop script (provided in the next section). The script assumes you want to create the floppy in /dev/fd0 .If this is not what you want, modify the script as necessary.
NOTE: Even though you can do it manually, I find the script is very handy.
Your Linux in a floppy is ready !
This is the installation script. Create the file using your own favorite editor, save it, and don't forget to make it executable.