1. Introduction

1.1 Address space

On Intel based machine there are normally two address space:

• kernel space
• user space

In the kernel space there are kernel's process only.
In the user space there are user's process only. User can be normal user or privileged user (root).

1.2 User mode linux (UML)

Linux provides a nice Linux only virtual machine that works in user mode: its name is user-mode-linux.

With this tool it's possible to boot more linux instance on the same host, and no any root privileges are required. This means that a normal user can run multiple linux instance and work as an administrator WITHOUT any risk of damaging the host's system.