User-mode Linux at IMADA

In the following we describe how to install and use User-mode Linux (UML) for DM14 at IMADA. If you have any problems, have a look at the FAQ.

All the files mentioned below, can also be found here.

How to install User-mode Linux at IMADA

cd /home/DM14/<login>

where <login> is your IMADA/MIP login. Next, get the source code for Linux and all the other necessary files for DM14 by writing

tar xvjf ../dm14/linux-2.6.10.tar.bz2

Enter the directory containing the kernel source files:

cd linux-2.6.10

To make this a working copy of UML, you also need to have a configuration file (.config), a root file system (root_fs), and some extra files (ummake and run_linux).

cp ../../dm14/{.config,root_fs.bz2} ../../dm14/bin/* .
bunzip2 root_fs.bz2

You are now ready to start using UML.

How to compile User-mode Linux

Usually you will compile UML using the following command:

make ARCH=um linux

Have a look at man make, if you want to know what make does. ARCH=um ensures that the kernel you are building is a UML kernel.

You can also compile UML using this command instead:

./ummake linux

ummake is a small script which makes the compilation run faster. Apart from this, ummake is basically the same as make ARCH=um. Have a look at the file itself to see, what it actually does.

How to run User-mode Linux

Due to problems with NFS, the root file system for UML needs to be kept at /tmp and not in /home/DM14/<login>/... To make life easier for you, you can use the following small script to run UML. This script copies your root file system from the current directory to /tmp and then runs UML.

./run_linux

When running UML, you can login using the user name root with no password. All files from /home/DM14/ are also available in the directory /home/DM14/ inside UML. To stop the UML system you can run the command halt.

Frequently asked questions (FAQ)

When I try to run UML, I get the following error. Why?

<snip>
Failed to lock '/tmp/root_fs_<login>', err = 11
Initializing stdio console driver
VFS: Cannot open root device "98:0" or unknown-block(98,0)
Please append a correct "root=" boot option
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(98,0)
</snip>

This is most likely because you are trying to run two UML processes at the same time. Kill all running UML processes with the command killall -9 linux. Next, try to run UML again using ./run_linux. If this does not work, you can also try to delete your root file system in /tmp by using rm /tmp/root_fs_<login>.

Changes I make inside UML in the root file systems, sometimes seems to be lost when I run UML the next time?

The root file system is only saved in the temporary directory /tmp. Occasionally, the contents of this directory is deleted, and a fresh copy of the root file system is copied by run_linux to /tmp. If you want to preserve the changes you have made, you need to copy the changed root file system from /tmp to your own directory, i.e.,

cp /tmp/root_fs_<login>
    /home/DM14/<login>/linux-2.6.10/root_fs

How can I avoid UML running xterms? I want to run UML at IMADA using Putty from my Windows machine without X at home.

To do this both /etc/inittab in the root file system and the configuration of UML needs to be changed slightly. The easiest way to do this is to use the modified files that already have been made available:

cd /home/DM14/<login>/linux-2.6.10
rm root_fs /tmp/root_fs
bunzip2 < ../../dm14/root_fs_noxterm.bz2 > root_fs
cp ../../dm14/.config_noxterm .config
./ummake clean