The User-mode Linux Kernel Home Page
User-Mode Linux is 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.
User-Mode Linux gives you a virtual machine that may have more
hardware and software virtual resources than your actual, physical
computer. Disk storage for the virtual machine is entirely contained
inside a single file on your physical machine. You can assign your
virtual machine only the hardware access you want it to have. With
properly limited access, nothing you do on the virtual machine can
change or damage your real computer, or its software.
Here are some of the things that UML is used for:
Hosting of virtual servers
Experimenting with new kernels and distributions
It's written by me, and covers UML pretty comprehensively.
the publisher and
this one for 64-bit systems) and
filesystem (80M, uncompressing to 1.6G) (or this
host% bunzip2 linux-2.6.24-rc7.bz2 FedoraCore5-x86-root_fs.bz2
Run UML as follows:
host% chmod 755 ./linux-2.6.24-rc7
host% ./linux-2.6.24-rc7 ubda=FedoraCore5-x86-root_fs mem=128M
Log in as root, no password needed:
Fedora Core release 5 (Bordeaux)
Kernel 2.6.19-rc7 on an i686
localhost login: root
When you're done, shut it down:
[root@localhost ~]# halt
Broadcast message from root (tty0) (Tue Apr 4 17:18:01 2006):
The system is going down for system halt NOW!
INIT: Switching to runlevel: 0
INIT: Sending processes the TERM signal
"Panic - Failed to open 'root_fs', errno = 2"
"F_SETLK failed, file already locked by pid n"
UML exits after a few lines of output
"Kernel panic - not syncing: Kernel mode signal 7"
"handle_trap - failed to wait at end of syscall"
On x86_64, processes randomly segfault
Hang after 'VFS: Mounted root...'
For a lot more (and a lot less organized) information, see the
old UML site.
This project is hosted at
which provides a number of useful services:
This web site is hosted at SourceForge
Bug reports may be sent to either list.
Searchable list archives exist at MARC
uml-devel) and gmane
IRC (see www.irchelp.org/ for more
information on IRC) - #uml on irc.oftc.net is where I hang out 2-3
days a week. It's good for general UML questions and chit-chat.
#kernelnewbies on oftc.net is a also good place for UML questions
and discussion that relate to kernel development in general.
: A network simualation tool for UML - contains its own
: Virtual Distributed Ethernet - layers a virtual ethernet
: Virtual Network User-Mode-Linux
Robert P. J. Day's
UML on Fedora Wiki
ISTS and Bill Stearns for sponsoring the security work in UML
Stearns for many forms of support since nearly the start of the
HP contributed a
nice IA64 workstation to the UML project.
hiring me in 2004 to work on UML full-time