Cooperative Linux
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Cooperative Linux, or coLinux for short, is a piece of software that enables the Linux kernel to run under Microsoft Windows without significant runtime overhead.
The application was developed by Dan Aloni, a first year B.Sc student in Computer Science, with the help of other developers.
The coLinux package installs a port of the Linux kernel and a virtual network device and can run simultaneously under a version of the Windows operating system such as Windows 2000 or Windows XP. It does not use a virtual PC such as VMware. X Window or X Servers will not run under coLinux directly, but you can install an X Server under Windows, such as Cygwin/X and use KDE or GNOME and almost any other Linux application and Distibution. Debian and Gentoo are especially popular with the coLinux users. Applications such as MySQL are also known to work well. This allows a user to safely learn Linux without going to the trouble of wiping out existing operating systems, creating a separate partition.
Cooperative Linux utilizes the rather underused concept of a Cooperative Virtual Machine (CVM), in contrast to traditional VMs that are unprivileged and being under the complete control of the host machine.
The term Cooperative is used to describe two entities working in parallel, e.g. coroutines. In that sense the most plain description of Cooperative Linux is turning two operating system kernels into two big coroutines. In that mode, each kernel has its own complete CPU context and address space, and each kernel decides when to give control back to its partner.
However, only one of the two kernels has control on the physical hardware, where the other is provided only with virtual hardware abstraction. The host can be every OS kernel that exports basic primitives that provide the Cooperative Linux portable driver to run in CPL0 mode (ring 0) and allocate memory.
The special CPL0 approach in Cooperative Linux makes it significantly different than traditional virtualization solutions such as VMware, plex86, Virtual PC, and other methods such as Xen. All of these approaches work by running the guest OS in a less privileged mode than of the host kernel. This approach allowed for the extensive simplification of Cooperative Linux's design and its short early-beta development cycle which lasted only one month, starting from scratch by modifying the vanilla Linux 2.4.23-pre9 release until reaching to the point where KDE could run.
The only downsides to the CPL0 approach is stability and security. If it's unstable, it has the potential to crash the system. However, measures can be taken, such as cleanly shutting it down on the first internal Oops or panic. Another disadvantage is security. Acquiring root user access on a Cooperative Linux machine can potentially lead to root on the host machine if the attacker loads specially crafted kernel module or uses some very elaborated exploit in case which the Cooperative Linux kernel was compiled without module support.
Most of the changes in the Cooperative Linux patch are on the i386 tree -- the only supported architecture for Cooperative at the time of this writing. The other changes are mostly additions of virtual drivers: cobd (block device), conet (network), and cocon (console). Most of the changes in the i386 tree involve the initialization and setup code. It is a goal of the Cooperative Linux kernel design to remain as close as possible to the standalone i386 kernel, so all changes are localized and minimized as much as possible.
See also
External links
- coLinux Sourceforge page (http://sourceforge.net/projects/colinux/)
- coLinux Home page (http://www.colinux.org/)
- coLinux wiki (http://www.colinux.org/wiki/index.php/coLinuxFAQ)
- Slashdot discussion about coLinux (http://developers.slashdot.org/developers/04/04/12/211236.shtml?tid=106)
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