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Originally these techniques were devised for use with VMWare, but many
of them really apply to many virtual computing environments. Some
tips have been removed since the original version because they were VMWare
specific and no longer apply to the current version of VMWare.
Configuration
- Edit configuration files to remove all directory information from path
names and place all files related to the virtual machine in a single
directory - this makes the Virtual Machine (VM) independent of directory location,
and therefore more portable, just change to the directory before executing VMWare
for the directory's VM
- Rename vmware configuration files for each VM to a common name such
as "vmware.cfg" to make it easier to write shell scripts that handle all
of your virtual machines.
Execution Environment
- Set variable "TMPDIR" in order to change temporary file directory (defaults
to "/tmp"). Important if your "/tmp" directory is on a small or nearly
full file system. Example: export TMPDIR=/home/vmware/tmp
- Use "esd" (enlightened sound daemon) to share audio output between host
and virtual computers. Start esd running on host system, then execute
vmware using esddsp. This allows multiple virtual computers to share
the sound card.
Display
- Headless operation can be setup using VNC, a free software package allowing
remote access to a variety of computer operating systems. The VNC software
includes a virtual Xserver that does not make use of a video display adapter.
To access the display, you can use any of their VNC clients which are available
for Mac, Linux, Windows, Java (i.e. your web browser!).
- I don't know if overall performance is faster for VMWare, but for at least
some of my Linux VM's I get a more responsive X display by configuring XDM in
the VM to provide "remote" X display access, and then run X "remotely"
from the host computer. Though I have not yet tried to measure performance,
this appears to be faster even then full screen mode. Note: if the
host computer does not have access to all of the fonts on the VM, your
display may look a little different for some applications. This should
definitely be faster when running Linux/UNIX in a virtual computer inside
of non-VMWare virtual computer products.
- If you need console mode access for running interactive scripts from
the host computer, or don't need/want a virtual display for the VM, you can
configure Linux based VM's to support a serial console and tie it into a virtual
serial port on the host computer. Linux provides a series of virtual
serial connections with the names of the form: "/dev/pty[p|q|r|s][0-9a-f]"
for each "/dev/ptyXX" device name, there is a "/dev/ttyXX" which provides the
other end of the serial link. To make use of these "serial" ports with
VMWare, you configure your VM serial port to be of type "TTY" and specify the
path for an unused "/dev/ptyXX" device, then when you wish to communicate
with the machine using the serial console you connect to the corresponding
"/dev/ttyXX" device. For example, you might configure a VM to use
"/dev/ptyr7" as it's serial port, in order talk to this machine you could use
your favorite modem program and tell it to connect to "/dev/ttyr7".
Alternatively if you wish to run a script from the host computer which
talks to the VM, you could use "chat", "expect", or some other program to
communicate using this virtual serial port.
Disks
- Information and startup scripts can be passed to virtual machines by
statically or dynamically creating virtual floppy disks which are used
as the default floppy drive when the virtual machine boots. When doing
this you may want to reconfigure the virtual machine BIOS to boot first from
something other than the floppy, and then add a script to the VM's hard
disk which processes the information passed on the floppy. To create
the virtual floppy, create an empty file the size of a real floppy disk using
the "dd" command, use "mke2fs" or other appropriate filesystem creation
program to create a file system on the empty file, then using the "loop" option
to the mount command you can mount this virtual file system on a local directory,
copy files to it and unmount it when you are done. To use this disk
in your VM, the VM configuration file must have it's floppy disk configured
to be of type "file" and the name you give the file must match the name for
the floppy filename specified in the configuration file.
- If you use multiple virtual machines which need a common, unchanging core
configuration, you can install all common data on a single virtual hard drive,
then configure all virtual machines which need the data to reference the
virtual hard drive as read-only/non-persistent. Even if the virtual
computer environment doesn't support this, it may be possible to safely
do this by configuring all of the guest operating systems to treat the disk
as read only, such as setting the "ro" option for this drive in the /etc/fstab
file in Linux guest operating systems.
Networking
Some virtual computer environments provide what amounts to
virtual network "hubs", allowing you to create one or more independent
private networks that can only be shared by other virtual machines
configured to use the same hub. These have some valuable
uses including:
- Creating a secure well partitioned firewall network complete with DMZ,
all hosted on a single computer.
- Experimenting with and modeling computing clusters.
Performance
- System Overload -- some client operating systems such as Windows 95,
DOS, etc. never sleep/stop, their idle state consumes all available cpu,
so it may be desirable to use "nice" or "renice" on these virtual machines
to lower their priority (though I think VMWare may already do something
to handle this problem, it certainly applies to other virtual computer
products).
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Debian Linux.