User-Mode Linux Merged Into 2.5 Kernel

An anonymous reader writes "With little fanfare, User Mode-Linux (UML) has been merged into Linus' BitKeeper tree. The merge followed a patch by UML author Jeff Dike, resynching UML with the 2.5.34 development kernel. From the UML homepage, User-Mode Linux provides you with a virtual machine that offers 'a safe, secure way of running Linux versions and Linux processes. Run buggy software, experiment with new Linux kernels or distributions, and poke around in the internals of Linux, all without risking your main Linux setup.'" There's more UML resources available at the community site.

Comments

Good stuff.

[Lukey Boy]

I recently found a beautiful use for user mode linux - changing distributions with a minimum of downtime.

I have a RedHat box that's colocated that I wanted to move over to Debian - so I installed UML and loaded Debian onto one partition, got everything set up correctly and told LILO to boot off the new slice. After a few minutes of praying Debian came up running all the correct services.

Thanks to the UML team!

not for the humor impaired

[dboyles]

User-Mode Linux provides you with a virtual machine that offers 'a safe, secure way of running Linux versions and Linux processes. Run buggy software, experiment with new Linux kernels or distributions, and poke around in the internals of Linux, all without risking your main Linux setup.'

Finally, something that will get Linux accepted as a viable desktop operating system for all levels of users!

Honeypot

[GigsVT]

I imagine there are honeypot applications for something like this. You could make a cracker totally believe they had broken in when in reality they are just in a UML.

For the ultra paranoid you could also make a backup copy of your whole UML partition and only run services in that, periodically restoring it from backup, and copying in the new data that is stored on the real OS. If you got broken into, it wouldn't really matter.

Re:What Are Some Other Uses?

[kgasso]

In our office (Wholesale/Virtual ISP), we've been experimenting with UML for a while as a decent alternative to trying to virtualize every service and allowing some of our reselling ISPs to have their own username space - something I don't even want to attempt with Apache and most FTP servers.

So far it's been fairly stable, after working out a few quirks. Definitely worth the trouble of getting everything set up. Makes backups on the UML servers stupidly-simple too.

Congrats to the UML developers on clearing this hurdle, and here's to hoping it betters future development on the project!

Imagine...

[stor]

A Beowu*smack* ow.

Cheers
Stor

Re:FreeBSD's Linux "emulation"

[Anonymous Coward]

Comparing UML to FreeBSD's API redirector (usually misnamed "Linux emulation") is like comparing Windows running in VMware to WINE. VMWare runs the true full blown MS-Windows while WINE redirects the calls to approbate native calls/code. Likewise, UML runs the true full blown Linux kernel while FreeBSD just redirects the calls to native calls/code.

UML adds more layers before a system call makes it to the hardware than simple API redirection. For example, for a program running in UML to read from the CD-ROM, the real kernel only provides access to the block device and the UML kernel translates the block device/ISO9660 accordingly for the file access calls. In UML, reading of the structures as following ISO9660 is done is *user space*. FreeBSD's API redirector breaks the block device structures from ISO9660 to approbate formats for file system calls all in the FreeBSD kernel. FreeBSD's Linux "emulator" does not achieve the same redefination of what occures in user space as opposed to kernel space at all. If FreeBSD can't run Linux binaries faster than UML then something is very wrong. However, it would be interesting to see if FreeBSD's API redirector could run UML and see if UML runs faster on top of FreeBSD or on top of Linux.

UML = Unified Modeling Language

[WindowsTroll]

The use of TLA's (Three Letter Acronyms) has become so rampant that it is hard to find things which aren't referred to by their TLA. In many cases, the same TLA has more than one meaning, so the users of the acronym are able to keep the context straight. In this case, where the software sector has a standard definition of UML, reusing the acronyn will only spread confusion

If I were to create a software application called Great New Utility and referred to it as GNU, people would rightly be upset at me for trying to usurp an already common use of an acronym. In this case, I would probably be violating a trademark. The acronym of UML is already trademarked by Object Management Group, and has a common and well known usage.

Well documented.

[tshak]

One of the great things about UML - unlike a lot of other OSS projects - is that it's very well documented. Thanks to the UML diagrams on UML, there is no confusion as to what UML is or what it does.

Re:I don't get it

[pabs]

$iptables -t filter -A FORWARD -i tap0 -j in-throttle
$iptables -t filter -A in-throttle -m limit --limit 5000/sec -j RETURN

Thank you, drive through.

Another important use

[fireboy1919]

There are several products that require a custom kernel, and this could certainly benefit all of them.

The one I'm thinking of right now is Win4lin, the cheapest, fastest Windows VM for Linux right now; it needs a kernel with its own patches, and they distribute patches for Debian, Slackware, Mandrake, and Vanilla kernels. My distro (Gentoo) makes a kernel which is known for its speed, but which I'm not using right now because of this (I can't even patch the Vanilla kernel to that level because it the Win4lin patch conflicts with Gentoo's patches).