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

Re:FreeBSD's Linux emulation

[sfraggle]

They are entirely different things. FreeBSD's emulation does translation of the system calls into the corresponding FreeBSD ones; UML is a full Linux kernel running in user space.

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!

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.

Re:not for the humor impaired

[TheGreek]

AFAIK no other OS will offer this functionality.

Sorry, no.

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.

Re:Is there an parallel to FBSD's jail?

[autocracy]

Jail doesn't spawn an entire new virtual machine as a single process.

And yes, you can run many instances of UML.

Re:not for the humor impaired

[jbolden]

You forget MVS (even better than OS/400) which is based on running multiple virtual OSes of radically different types if needed all under extremely powerful management tools.

Still I agree 100% with your main point that while this is a big step up for Linux it ain't playing in the same ballpark yet.

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.

Re:Limitations

[Tom]

strace runs just fine.

I wanted to attach a few lines as proof here, but /. "junk filter" doesn't let me, no matter how much I try. Sorry, you'll have to verify for yourself.