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How awesome is User Mode Linux!!?

Posted: Wed May 24, 2006 6:10 pm
by Chris Corbyn
Just compiled and ran this baby ( 2.6.16.18 ) on my poor-man's intel celeron laptop.

I was expecting performance to be a bit slack on this hardware when I load up a Virtual Environment.... it's running almost natively. Been using a VDS for a while now but never actually bothered to see how it all works from the UML side of it - pretty neat :) Oh the things that excite me :?

Posted: Wed May 24, 2006 7:20 pm
by Weirdan
What is UML? Is it something like jails in FreeBSD?

Posted: Thu May 25, 2006 4:17 am
by Chris Corbyn
Weirdan wrote:What is UML? Is it something like jails in FreeBSD?
UML can do Jailing/sandboxing yes.

UML is a version of the Linux kernel which is modified to run as a set of proccesses inside linux itself, rather than by itself. It means that you can install linux inside itself and play around with things - Think Virtual Machine, but nothing needs to be emulated.

Very useful for development I would guess :)

Posted: Thu May 25, 2006 4:32 am
by Weirdan
Very useful for development I would guess Smile
Seems it is :)

Posted: Thu May 25, 2006 4:40 am
by Chris Corbyn
It used to be the case that you needed to download a kernel (normal one) then apply the UML patches to it.

Kernel versions newer than 2.6.9 now actually have the UML architecture built-in.

You just do `make ARCH=um menuconfig' then choose the host processor type and compile the kernel. The result is a binary (~6MB) which you can execute to "boot" a linux installation.

Posted: Thu May 25, 2006 8:01 am
by Roja
Weirdan wrote:What is UML? Is it something like jails in FreeBSD?
Its a little different. UML is higher-level (its actually kernel level, although not ring-0). Jails on the other hand are below-kernel level sandboxing.

Imagine that jails are closely similar to rooms in a house. If a room floods, the house will be affected. UML is more like multiple houses in a neighborhood - if one floods, it might not have an impact on the other houses.

Of course, neither is a sure thing, and both aim for the same goal - segregation of information to reduce impact beyond its scope.

Also complicating the issue is that Linux also has chroots, although nowhere near as secure as BSD's jails.

Posted: Thu May 25, 2006 9:21 am
by Weirdan
Ahha, thanks for explanation.