Good day, all. Here are a few notes on using your virtual machine on Zaphod. They're not intended to be a complete guide to using Linux, but a few notes on how your virtual machine is set up.

Sharing the system

While User-Mode Linux and the host system will do their best to share resources evenly, keep in mind that you are sharing a physical box.

What you get

Your virtual machine has:

Note that all of the above are completely negotiable - I'm happy to extend any of the above limits.

Simple math with 25+ users and the above limits shows we are oversubscribing on memory and disk; that's not a problem. I've talked quite a bit with Jeff Dike and we agree that since not everyone is going to use all the resources given, we can quite reasonably share this way.

I would like to sincerely encourage you to put anything you need to store somewhere under /home. If you later decide to upgrade to a new Redhat or simply want to move to a new distribution, it's trivial to carry the files in /home along. Anything in / needs to be identified and manually carried over, and that takes a bit of time.

If you know you're going to be creating content that wouyld normally fall in a directory under /, the best approach is to make a directory under /home, move the files there, delete the old directory, and make a symlink to the corresponding directory. For example:

mkdir /home/var/named
mv /var/named/* /home/var/named
rmdir /var/named
ln -sf ../../home/var/named /var/named

Now all your files get actually saved in /home, making it much easier to do things like replace a root filesystem, should you ever want to.

/shared is for files you'd like to make available to anyone else with a virtual machine on Zaphod. /pub is for files you're willing to share with anyone in the world. At some point I'll set up directories to which each of us can write under those two and set up a virtual machine that will publish aything in /pub via web, ftp, and rsync.

Applications and distributions

If you're missing Linux rpm packages, they're all available in /pub/mirrors/rh73updates or /pub/mirrors/rh73 . You can install them with

rpm -Uvh /pub/mirrors/rh73updates/name_of_package.rpm
rpm -Uvh /pub/mirrors/rh73/name_of_package.rpm

If you'd like to use a distribution other than Redhat 7.3, no problem! Take a look at the distributions available at . If one of those appeals to you, I can pull those in. If you have a UML root filesystem from some other location I can get those too. Please let me know.

You should be able to run any applications that would run on a normal linux system, with the exception of a very small number of programs that need to talk directly to hardware (hwclock, X windows servers, scanner applications, fdisk, hardware probe tools, etc.). To run command line apps, simply ssh to your system and run them:

[wstearns@sparrow wstearns]$ whoami
[wstearns@sparrow wstearns]$ mcedit
#Midnight commander's editor starts up.

To run X windows (graphical applications), just run them with an ampersand at the end to get your prompt back:

[wstearns@sparrow wstearns]$ xclock &
[1] 6974
[wstearns@sparrow wstearns]$ 

SSH will carry the graphical output back to your own box; see for more info.


The files you store in in / and /home can be snapshotted. If you get to a point where the system is set up just the way you want it, I can make copies of your root and /home filesystems. Think of them as backups in case of emergency. Also, we can roll back you system to the last good snapshot if you are ever broken into or lose some crucial files.

As drive space fills, old backups will be the first things I'll ask people about removing. :-)

To actually do this, you'll shut down your virtual machine with the halt command, I'll make copies of your filesystems, and then start your machine back up again.


You get a single IP address for your virtual machine. Any servers you run can be found at that address. Your IP address will be 66.59.11.X, where X is between 160 and 191.

If you'd like a second virtual machine for some reason, or if you simply don't need to run your own servers, I have an unlimited number of private addresses that can be assigned to your machines. We can set up networking in such a way that you can ssh to them.


If you come across any problems or have any requests, please let me know. William Stearns <>.