Clusters for Nothing and Nodes for Free

When the users are away, your company's legacy desktop systems can become a powerful temporary Linux cluster.
Those Old Machines

Usually, plenty of spare older computers can be found hiding in corners. Put an X server on one of them that is configured to be a terminal into the xdm service on the fast computers. With this machine, you can shut down the X servers on the fast computers and release their processor and memory resources back into the important workload. Alex's desktop computer, a 400MHz Pentium II, already had its X server indirecting over xdm's chooser. David's work keeps him roaming the building and relying on VNC, so he already was using Xvnc. Only Hoke needed to make minor changes to configuration files.

Next, install LTSP on one computer and set up all the other old computers to use diskless boots to become terminals too. Doing so eliminates the administration of all those operating systems. You now should have enough terminal stations that all your team members are using terminals, and all the fast compute nodes can stay in the stripped runlevel and be as efficient as possible. It doesn't take long to get those two features working, and an excellent time to work on this is whenever you're waiting on the running jobs.

There is no need to get the DHCP and TFTP components of LTSP working. Put the kernel on a floppy, together with SysLinux configured to trigger the non-boot DHCP, and mount the NFS root filesystem. Then, use that one floppy to do the one-time boot of the terminals. Reboots are needed infrequently, so the slowness of the floppy is fine.


Once the cluster and LTSP are both functional, we simply combine them. The short script shown in Listing 3 uses the NBI tools to put the patched kernel into /ltsp/i386/boot. Our DHCP server's filename parameter is a soft link, so we can change the LTSP kernel rapidly while testing upgrades. After copying the user-space tools into the client filesystem and renaming the init script as rc.openmosix, we add the few lines in Listing 4 to the LTSP startup script. Slower computers have MOSIX=N in the LTSP configuration file because they would not contribute much performance to the cluster.

One line in /ltsp/i386/etc/inittab:


calls a copy of Debian's shutdown binary using the script shown in Listing 5. This ensures that Ctrl-Alt-Del forces a clean disconnect from the cluster before rebooting.

Once you are confident that the LTSP-OpenMosix kernel is stable and not going to be changed, you can hand out floppies with the new kernel. The LTSP users won't see a difference, but your compute workload will.

If you would like to maintain the option of changing the kernel without having to hunt around the company to find all the old floppies, now is a good time to get the DHCP network boot working. The LTSP documentation describes how to configure Linux or UNIX servers, but our implementation was running on Microsoft Windows. David, who administers our Windows-based DNS and DHCP servers, set up Netboot in DHCP (Figure 1).

Figure 1. The three scope entries needed on a Windows DHCP server. Notice that the root path has the trailing slash workaround.

Microsoft DHCP appends a null to the NFSROOT, as discussed in LTSP mailing lists, so you need a soft link:

ln -s /ltsp/i386 /ltsp/i386/000


White Paper
Linux Management with Red Hat Satellite: Measuring Business Impact and ROI

Linux has become a key foundation for supporting today's rapidly growing IT environments. Linux is being used to deploy business applications and databases, trading on its reputation as a low-cost operating environment. For many IT organizations, Linux is a mainstay for deploying Web servers and has evolved from handling basic file, print, and utility workloads to running mission-critical applications and databases, physically, virtually, and in the cloud. As Linux grows in importance in terms of value to the business, managing Linux environments to high standards of service quality — availability, security, and performance — becomes an essential requirement for business success.

Learn More

Sponsored by Red Hat

White Paper
Private PaaS for the Agile Enterprise

If you already use virtualized infrastructure, you are well on your way to leveraging the power of the cloud. Virtualization offers the promise of limitless resources, but how do you manage that scalability when your DevOps team doesn’t scale? In today’s hypercompetitive markets, fast results can make a difference between leading the pack vs. obsolescence. Organizations need more benefits from cloud computing than just raw resources. They need agility, flexibility, convenience, ROI, and control.

Stackato private Platform-as-a-Service technology from ActiveState extends your private cloud infrastructure by creating a private PaaS to provide on-demand availability, flexibility, control, and ultimately, faster time-to-market for your enterprise.

Learn More

Sponsored by ActiveState