Authors: David Fernández (david at dit.upm.es) Fermín Galán (galan at dit.upm.es) version 1.7, June 4th, 2004
So, if you want to use as many virtual networks as your physical
host could cope, use at least bridge-utils 0.9.7 (available just as
tarball at http://sourceforge.net/projects/bridge/ at time of
this writting) and Linux Kernel 2.6.5.
Linux Kernels for VNUML
How can I know which kernel options were used when compiling a UML linux kernel?
Just execute the kernel with "--showconfig" option. For example, to know if a UML linux kernel has IPv6 support just type:
> linux --showconfig | grep IPV6
About root filesystems
I have changed the filesystem used by a virtual machine, but when I start the simulation it seems to use the old one.
If you are using "COW" filesystems as recommended, you have to delete the old cow file before starting the simulation with the new filesystem. The reason is that cow files save a reference to the root file system they are derived from. To delete a cow file you can use the "purge" option ("-P") of vnumlparser.pl.
I am using "root_fs_tutorial" root filesystem and I see that Apache web server (or any other service) is not automatically started when the virtual machine boots, why? How can I make it start from the beginning?
Most of the services are not started from the beginning to speed up virtual machines boot up process during the scenario start-up (-t option). It is recommended to start the services you need using "<exec>" commands inside your VNUML specification. For example, to start apache2, you can include the following command:
<exec seq="start" type="verbatim">/etc/init.d/apache2 start</exec>
Alternatively, you can use "update-rc.d" command to restore the scripts that start apache2 during boot process. Just start the rootfilesystem in direct mode as described in update rootfilesystem example, login into the virtual machine through the console or using ssh and type the following command:
update-rc.d apache2 defaults
Starting the simulation (-t option)
When I build a scenario, I get the following message when booting each virtual machine:
Checking for the skas3 patch in the host: - /proc/mm...not found - PTRACE_FAULTINFO...not found - PTRACE_LDT...not found UML running in SKAS0 mode
Then the process stops, apparently hanging, but if I press CTRL+C it continues and, finally, the scenario is set up properly. Can this be avoided?
This is a known problem that happens with some guest UML kernels and host kernel combinations. If you are using a modern UML guest kernel (like 18.104.22.168) the problem doesn't use to occur, but otherwise you can test some of the following:
The recommended solution is the third one. As a proof, I'm using a 2.6.21 kernel, CONFIG_COMPAT_VDSO=y and the hanging does not occurs. However, further confirmation by other users would be helpful :)
I'm trying to build the simple.xml example that comes with the VNUML software, but I'm getting the following error:
Checking for the skas3 patch in the host: - /proc/mm...not found - PTRACE_FAULTINFO...not found - PTRACE_LDT...not found UML running in SKAS0 mode Xlib: connection to ":0.0" refused by server Xlib: No protocol specified xterm Xt error: Can't open display: :0.0 Boot timeout for virtual machine uml1 reached. Abort, Retry, or Continue? [A/r/c]:
and the virtual machine xterm never pops up. I'm executing vnumlparser.pl as root (either directly or through sudo).
Try the following:
vnumlparser.pl -P simple.xml -v vnumlparser.pl -t simple.xml -v -u root
If using '-u root' works, the problem seems to be that the 'vnuml' user has no permissions in your X server. Note that, although you were launching vnumlparser.pl as root, some actions (in particular, the launching of the xterm) are performed by 'vnuml' user.
There are two possible solutions:
There are several causes that can prevent a simulation from start correctly. If that happens you can:
<boot> <con0>xterm</con0> </boot>
Each virtual machine console will be opened in a different xterminal.
<boot> <con0>pts</con0> </boot>
and start the simulation using: "vnuml -t name.xml -e screen.cfg" and access the consoles using: "screen -c screen.cfg".
ping (IP address on the eth0 interface in the virtual machine)
From the virtual machine:
ping (IP address on the vm-eth0 interface in the host)
Conflict between IP addresses in the host enviroment and thoses used in the management interfaces is a common cause of problems. To avoid conflict, use a proper <offset>
VNUML over different Linux distributions
How can I install VNUML over X linux distribution?.
See Howto page for some detailed recipes to install VNUML over some common linux distributions