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QEMU: A Review

What is QEMU? It's a free software "processor emulator", which means it's capable of running applications written for other systems natively on your current operating system. The QEMU virtual CPU core library is released underneath the GNU LGPL. QEMU is capable of running a guest operating system on top of your current operating system, in the same manner as applications such as VirtualBox OSE and Vmware Workstation. At its current state, QEMU is capable of launching Linux or Darwin/Mac OS X processes compiled for one CPU on another CPU; it can also boot a myriad of guest operating systems, including Linux, Microsoft Windows, DOS, Solaris, and BSD. Hardware platforms, such as x86, amd64, alpha, mips, and sparc can be emulated. QEMU can be installed from most of the Linux packaging systems.

Like VirtualBox OSE, QEMU can be a great tool for launching Windows on your current Linux desktop. If you have certain Windows applications with which you cannot part ways, QEMU can be used to start up Windows as a guest operating system on your Linux desktop; as with any guest operating system, QEMU will create a window in which that operating system will reside; the entire operating system is sustained within the QEMU launched window. Below is a screen shot of QEMU running Damn Small Linux on top of the Ubuntu Gutsy Gibbon desktop.

QEMU has two modes of operation. In "user mode emulation", QEMU is able to run Linux or Darwin/Mac OS X processes seamlessly within another CPU. This is often used to run your favorite Linux applications directly within a Windows environment; unlike "system mode emulation" (where an entire operating system is emulated on your current desktop), user mode emulation does not create a wrapper around the entire operating system from which you are launching your applications; instead, your applications are run directly on the desktop. This is similar to Wine for Linux, wherein Windows applications are run directly on a Linux desktop.

QEMU is a command line tool. For a graphical front end, there are two useful GUI tools. Try the Qemu-Launcher. The Qemu-Launcher provides a front-end to basic and advanced operations for QEMU. You can create, save, and run multiple virtual machine configurations. Or as an alternative, you can try the qemulator, which also let's you create, set up, and run virtual machines. Both of these tools can be found in many of the Linux packaging systems.

What are the perks?

Very fast, applications may run in real time
Support for Linux binaries for other architextures
Can save and restore the state of the machine
Improved performance with the KQEMU kernel module
Command line tools allow full control of QEMU
Remote control of emulated machine through VNC server
USB tablet support

What does it lack?

Lacks accelerated graphic drivers
May provide incomplete support for some operating systems/architectures

Overall, QEMU is a really powerful CPU emulator. It can be a useful tool for running Linux applications or Linux operating systems on another system, such as Windows, as well as a way to virtual run the Windows operating system on your native Linux desktop. For more information on QEMU, vist the QEMU home page. Check back with LinuxHow2, we're going to continue writing articles on various different virtual machine applications.

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