From:"Sys Admin News" <> 
Subject: Sys Admin Magazine -- April 2003 News and Reviews
Date: Wed, 23 Apr 2003 09:31:34 -0700

	Sys Admin Magazine -- News and Reviews	 
		       April 2003

This month, Zonker reviews User-Mode Linux, which lets you run one 
or more virtual Linux systems that can be used for software testing, 
hosting, and just about anything else you'd want to do with Linux.
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Review: User-Mode Linux 
by Joe "Zonker" Brockmeier 

I've always been fascinated by the idea of running an operating 
system under another operating system. It's a cool hack to make a 
piece of hardware do double (or triple, or quadruple...) duty by 
running virtual machines. I've been hearing such good things about 
User-mode Linux (UML) that I had to give it a whirl. 

There are a few rough edges with UML. Overall, however, UML is a 
great piece of software that can come in very handy for Linux 
admins and developers. 

What's it good for? 

Other than the fun factor of running Linux under Linux, there are 
some very serious uses for UML. UML lets you tweak and torture a 
virtual system without having to risk your own stable system or 
maintain an extra system for testing. Instead, you can work with 
one or more UML virtual machines and do all the damage you want 
without worrying about trashing your system while testing device 
drivers and so on. If your job requires testing the latest and 
greatest development kernels, for example, UML is a great way to 
do that without having to use an unstable kernel for your 
workstation. There are a number of other testing scenarios where 
it's very helpful to be able to set up a slew of virtual machines 
instead of using multiple physical machines. 

Alternately, you can split a single system into a number of independent 
virtual machines. UML is already being used by several commercial 
hosting companies to provide virtual Linux hosts. UML is also a great 
educational tool that can provide students with their own virtual Linux 
machines instead of trying to provide each student with his own 
machine -- and students can have root on their systems without 
with other students. 

You can also use UML as a kind of sandbox for services. Running a 
process inside a UML machine means that it has no access to the 
outside machine. For example, say you want to provide FTP service 
for a few files, but don't want to run an FTP server on your Web 
server, and you don't want to deploy a second machine (which could be 
costly if you're using a co-location service of having to pay for 
hosting). Simply set up a UML virtual machine to provide FTP. If 
manages to find a vulnerability in your FTP server and exploit it, all 
he's got is access to a virtual machine that can be erased and 
with minimal difficulty. 

You can also use UML as a "honeypot" to distract crackers by providing 
easy-to-crack system. You can find some guidance for setting up a UML 
honeypot at 

To read the rest of Zonker's review, visit:
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