This dissertation will aim to explain the conception of a Linux mini-distribution that will provide an emergency rescue and recovery solution to most systems.

 

In case of a crash or of a failure of a system, we need a tool that can be installed within a few minutes and without the need to erase the contents of the hard-drive in order to backup some data, gain access to the configuration files or temporary run some services.

 

This distribution will hold on a CD-ROM and will be easily bootable from the CD.

 

It will provide common and useful administrative and network applications and services. The following applications, among others, will be implemented:

-          Shell

-          Base commands (ls, ps, cp, rm etc.)

-          Text editor

-          Disks management utilities (Fdisk, Lilo etc.)

-          Networking applications (Ftp, Telnet, SSH etc.)

-          Update, Upgrade and packages installation (APT)

 

It is enough typing searching for “Linux mini distribution” on Google to see that there are many “custom” distributions existing that can even hold on a single floppy disk for some of them.

 

 

The aim here is not to make a simple boot disk containing basic commands, but to get a complete distribution by integrating the necessary applications in order to provide the following services:

-         access to a crashed machine drive and to its network;

-         temporary replacement of some services usually provides by a station that has crashed or that is being maintained;

-         regular workstation services.

 

 

We can find several mini distributions by searching in Google, will compare three distributions among them: Linux On A Floppy (LOAF), Linux Router Project (LRP) and Fresco.

 

Some common characteristics of these distributions is that they are quite small, they run on PCs with minimal requirements, they are specialized and therefore have restricted functionalities.

 

For out project we have decides to explain how to build a more complex distribution, also loaded in a ramdisk, but having more functionalities in order to compete with distributions such as Debian, Suze or Redhat.

 

LOAF is a distribution created by Eric Benoit, it holds on a floppy disk and can run on a 386 PC with only 4MB of RAM. It provides a text editor and basic modules such as Lynx, Ftp, Telnet and Ssh. It

Cette distribution a été crée par Eric Benoit, elle tient sur une disquette et est capable de fonctionner sur pc 386 avec seulement 4 Mo de RAM.

Elle possède un éditeur  ainsi que des modules de bases tel que lynx, ftp, telnet et ssh. It is a polyvalent distribution but its funcionalities are restricted.

 

LRP and FREESCO are network oriented distributions. They also fit on one floppy disk and allow creating routers, terminal servers and other embedded applications.

These distributions do not have text editors; it is not possible to add scripts anyway. Their configuration is guided and easy, nevertheless, they do not support many network cards which makes them not usable in many cases.

 

 

This distribution is based on system V. Init system V is the program loaded by the kernel at during the system start-up. Its main purpose is to load the different processes necessary to the start-up (gettys, NFS daemons, FTP daemons…).

 

In order to be able to download and install new packages, drivers or to customize the distribution, the apt-get or yum module will be included. There is no need to include all packages possible on the CD-ROM and to load them all – even if most useful ones would fit - since the administrator can download and install packages depending on its needs. This way, the programs loaded in the ramdisk is limited to what is strictly necessary and the distribution is really scalable.

 

This distribution uses bash, its role is to reed your commands and then to execute them if they are “internal” like cd or to find and execute the program that they belong to if they are “external” like cp or startx. Bash has also several options like command completion or an history of executed commands that make its use more comfortable.

 

The scripts launched by init are usually Shell scripts executed by bash. Having an own programming language in parallel with system utilities available from the command line if a very powerful combination.

 

This type of distribution can be situated in between simple boot disks and a distribution such as Knoppix. It has much more capacities than a regular boot disk, but is not intended to be used as an office distribution. The use of a CD-ROM to load the distribution is much faster and more reliable than the use of floppy disks. It allows having a bigger system although it is limited by the amount of RAM since the distribution is stored in a ramdisk while we still need some RAM memory for executing processes.

 

The distribution includes numerous tools that support most filesystems and network debugging tools. Modules for Telnet, FTP, an SSH server and support for many network cards are included. HTTP text navigation and basic networking elements such as ping, traceroute, and DHCP client or port scan tools are integrated.

 

As stated before, installation of new modules is very easy using Apt-get or Yum and does not require re-compile the kernel.

Nevertheless, new modules installation is temporary, since they are loaded in the ramdisk.  If all the data is lost when the computer is shut down, it is still possible to save the configuration files to a USB key or any storage device in order to recover them for a new installation.

 

To make its use friendlier, it is possible to open six consoles and to switch between them like on any distribution.

 

A last important point is that we have to consider the number and the size of the package we will use for each service we want to provide. Indeed, if we want them to fit in the ramdisk they should be as light as possible.

 

The distribution requires a PC equipped with a compatible i386 processor. A Pentium processor or above with 128 Mo of RAM memory is recommended because of the ramdisk.

 

Although the mini-distribution requires a CD-ROM drive and a PC with a BIOS that support booting from CD-ROM (generalized since 1997), the distribution supports a wide range of peripherals.

	LOAF	LRP et FREESCO	PROJET
Media	Floppy disk	Floppy disk	CD-ROM
Sofware	VI, network tools	Network tools, IP modules, masquerading	Most common tools and possibly any with APT
Evolution	NO	NO	YES with APT

 

 

 

Before making a bootable CD-ROM of the image, we need to build our file system and the distribution. We will keep in mind that the distribution must not exceed the size of a CD-ROM (650 or 700 MB).

 

During the boot process, the kernel is loaded first, and then it initializes device drivers and its internal data structures. Once it has been done, the root file system needs to be loaded and mounted. Here, our root file system must be loaded into RAM memory as if it was a disk, which is called a ramdisk.

 

To build our distribution, we need a boot system that will load a root file system into a ramdisk. We will start by creating the file system and then we will see how to include the boot system and make the whole of it bootable on a CD-ROM.