AUTHOR: Kevin Annies (kevinannies@hotmail.com)


DATE: 2003-08-15

LICENSE: GNU Free Documentation License Version 1.2

SYNOPSIS: Implement squashfs to create a compressed /usr image for a live cd.

DESCRIPTION:
This hint is a guide to creating a compressed /usr image as /usr usually tends 
to be the larget directory on a system. The user is then given a quick example 
of how to implement this on a Live CD by mounting the image at boot time.

ATTACHMENTS:
http://squashfs.sourceforge.net/

PREREQUISITES:
A complete LFS system
The kernel source code


HINT:

Introduction
To start with a full explanation of Squashfs can be found at the following 
link: http://squashfs.sourceforge.net/ if you have trouble undertanding this hint
If you are short of space on your 
machine or would like to create a live cd containing lots of software, this hint is ideal for you


				Acquiring Squashfs 

The source code can also be downloaded from this site	
				http://squashfs.sourceforge.net/

The package used in this hint is squashfs3.2-r2. The document 
located at www.artemio.net/projects/linuxdoc/squashfs/SquashFS-HOWTO.html was
refrenced and adapted to the circumstance of the hint.


			Patching and recompiling the Kernel

In order to use squashfs, the kernel needs to have a patch applied.Un pack the source tar ball. 
	tar xvfz squashfs3.2-r2.tar.gz


The patch can be found in /linux-2.6.16 of the source code directory. The patch we require 
is called: linux-2.6.16.27-utf8_input-1.patch 

Move the patch to the directory the kernel source is located at. apply the patch using the following command:

	patch -Np1 -i ../linux-2.6.16.27-utf8_input-1.patch

The menu driven kernel configuration must then be initiated again and squashfs must be 
selected within the supported file systems menu.


			Compiling mksquashfs
To compile the sourcecode, navigate to the /squashfs-tools directory within the sourcecode 
and type make. Following compilation, copy the executable file to a more appropriate directory:
	cp mksquashfs /usr/sbin

To check everything went accordingly, type mksquashfs and the help dialogue associated with 
the command will be displayed.


				Using Squashfs
On our system, /usr is by far the biggest directory. The most simple and logical approach 
would be to compress this directory and then uncompress and mount during the system boot. As /usr 
is not needed early during this boot process and exists generally as a read only directory this is 
a safe procedure.

A compressed file can be created using the following command from the top level root directory:
		mksquashfs /usr usr.sqsh

Depending on how large the /usr directory is, this command can take a while to execute so maybe go grab a cofee....
Once done, the resulting usr.sqsh file can be copied to the Live CD partition. The /usr directory on the CD must 
then be emptied:

		rm-fr $LIVECD/usr/*

Finally create a small start-up script  in $LIVECD/etc/rc.d/init.d called usr or something similar. 
 Insert the following text:

#!/bin/bash 

	  	mount /usr.sqsh /usr -o loop
  
Make the file executable. Next create a symbolic link:

		ln –l $LIVECD/etc/rc.d/init.d/usr $LIVECD/etc/rc.d/rcsysinitt/S35usr

This will trigger the kernel to mount the usr.sqsh image to the /usr directory during the 
system boot process. Upon logging on, the /usr directory will be fully populated and appear to be 
exactly as it was before we compressed it. 


Thats all there is to it. Please feel free to contact me if you have an alternative way of doing this.

As a final comment, I implemented this on a CD using an initrd using this procedure.

ACKNOWLEDGEMENTS:
  * Artemiy I. Pavlov - for writing the SquashFS HOWTO document
  * Micheal Hernandez - For writing the begginers guide to creating a Live CD hint

CHANGELOG:
[2007-04-11]
  * Initial hint.


