Testing and Virtualization
CentOS 5.3 is available as a free download from the CentOS project or from one of its mirrors via www.centos.org. The CentOS project doesn't offer support beyond community resources, although the project maintains a directory of companies offering support services. What's more, because of CentOS' closeness to Red Hat's supported enterprise Linux product, migration barriers from CentOS to the Red Hat platform would be low if an organization decided to purchase Red Hat's support. The CentOS distribution spans six CDs or one DVD, and is available in versions for the x86 and x86_64 processor architectures. The distribution is also available in a slim, 8.3MB network install image. I used this image in some of my tests to boot a new system before pulling down the packages I needed from one of the CentOS mirror sites.Virtualization As a reflection of Red Hat's Linux development efforts, it isn't a surprise to see that many of the enhancements in CentOS 5.3 focus on virtualization. These improvements are targeted largely at scalability on large host machines, including support for host systems with as many as 126 processors and 1TB of RAM, and support for guest instances with as many as 32 processors and 80GB of RAM. CentOS 5.3 taps Xen 3.0.3 as its default hypervisor, but I could opt for KVM as a virtualization option by installing packages from the CentOS project's "extra" repository. As with the Xen implementation that ships with Novell's SLES 11, CentOS offers a more Spartan feature set compared with purpose-built virtualization products such as VMware's ESX Server. Still, I was able to roll out new, fully virtualized Linux or Windows guest instances very easily, as well as install Linux guests in higher-performance paravirtualized mode. CentOS 5.3 ships with a Linux alternative to Sun's DTrace system-tracing framework called SystemTap. I've found SystemTap rougher around the edges than DTrace, particularly on CentOS. Right from the start, SystemTap requires more setup steps than DTrace, including installing additional packages. One of these packages, containing kernel debug info, wasn't available in the regular CentOS repositories. After following the instructions for CentOS at the SystemTap project site, I was able to run the example scripts provided at the site to tease out information about the workings of my test machine. I was able to pipe the output of one script, which tracked disk and CPU utilization, to the data-and-function-plotting Gnuplot to visualize the information. Elsewhere on the development front, CentOS 5.3 ships with OpenJDK, the fully open-source release of Sun's Java Platform, Standard Edition. I was also pleased to see that CentOS 5.3 now offers support for block-level disk encryption as an install-time option-an important option for notebook deployments because it can keep data inaccessible in case of lost or stolen machines. Executive Editor Jason Brooks can be reached at email@example.com.
I tested the 32-bit version of CentOS 5.3 from a virtual machine with 1GB of RAM hosted by Sun Microsystems' VirtualBox desktop virtualization application. I tested the x86_64 version of CentOS on a dual-core AMD Athlon 64 server with 4GB of RAM, as well as on a paravirtualized virtual machine hosted under CentOS's Xen hypervisor.