Hi Falk, hi everybody,
First: I am glad to help you.
At the moment I run a 32Bit singlecored Linux VServer
(184.108.40.206-skas3-kernelsendpagefixed) in uid-based cgroup scheduling
with 3 concurrent instances of an uml-kernel (with one TUN-network
each) and a "share-16" performanceconsuming task (as the idle
Each uml-kernel runs under a seperate user (user 1 shares : 1024 for
the IPv6 testrouter(linux 2.6.24), user 2 and 3 share: 512 for a SAMBA
testserver and a crosscompile environment(linux 2.30.5)) for about 24h
and all 3 seem to be stable. (but the router and the server currently
havn't much load)
I use (limited) shm on the host (384MB RAM / 512 MB SWAP), so
memory-operations are speed up vast. ("shm on /dev/shm type tmpfs
For now I know 2 things about them (both uml-linux-versions):
1) The UML-implemented (in guestsystems) COW-Filesystem won't work
correct and produces more and more bad-sectors over timer (so only use
real images for each uml)
2) The "advanced syscall emulation patch for ptrace" seems to be
buggy (maybe in host AND guest) and leads to crashes - so I patched the
uml-kernels to don't use this
(perhaps this also can be achieved through uml-commandline?)
In performaces criterias the uml is only compareable with the
host-performance, if only one process is active in UML (tested with
UML-conextswitching seems to cost enormous cpu. (But no problem, the
host-cgroup scheduler makes it fair under the 3 UMLs)
Long story short:
UML is a great thing to virtualize your linux, for example if you need
safe environments with rootright (compile environment) - without
compromising your productive system, to test Software or to host cheap
and small servers for small usergroups. It is a great way to decouple
and detach systems.
btw.: How do you feel about UML, what bugs had you discovered? - I am
thankful about all kind of information.
-Thanks in advance, Stephan Bärwolf
Falk Husemann schrieb:
you just made my day. I was ranting about why Debian lenny didn't
contain the skas-patch anymore and there was no recent working patch
out. Even started looking at OpenVZ.
So can you let me and the list know if and how stable it works? I'm
interested in performance when used with uml_switch and TUN and lots of
concurrent instances. Any experience so far?
On Sep 15, 2009, at 12:04 PM, Stephan Bärwolf wrote:
Because I needed the SKAS3-Patch for the Linux (Host)Kernel 220.127.116.11, I
patched this version.
So perhaps anybody else would like to take it - here is it.
The patch can be downloaded at
file is also in the attachments.
Sincerly, Stephan Bärwolf - Ilmenau/Thuringia/Germany
This is a SKAS3 patch for Linux 18.104.22.168. If you have any questions or
problems, please ask on the uml-user list (URL below).
-- Stephan Baerwolf <email@example.com>
The usual maintainer of such patches:
--Ryan Finnie <firstname.lastname@example.org>