MOSIX: A Cluster Load-Balancing Solution for Linux

Ibrahim introduces the MOSIX software package and describes how it was installed on an experimental Linux cluster in the Ericsson Systems Research Lab in Montréal.
Testing the Installation

After starting the 14 nodes as a MOSIX cluster, we wanted to test our installation. By default, all the diskless CPUs mount an NFS directory on PC1. So we placed the Linux kernel 2.2.14 source code directory under that NFS space, making it visible to all nodes, and we started the kernel compilation process using MExec/MPMake, the parallel make, a contributed software that assigns new processes to the best available cluster nodes (available for download from MOSIX web site).

Figures 3, 4, 5 and 6 show snapshots of mon, a MOSIX tool that shows the load on all the nodes. As Figure 3 shows, there was a high load on node 14 because it was the node on which the compilation started. A few seconds later, Figures 4 and 5 show less load on CPU 14, and then Figure 6 shows a good distribution of the load among all the nodes.

Figure 3, 4, 5 and 6. MOSIX at Work Distributing Loads


MOSIX supports configurations with large numbers of computers with minimal scaling overheads to impair the performance. You can have a simple low-end setup composed of several PCs connected via Ethernet, on the other hand, you can have larger configurations that include workstations and servers connected via higher speed LANs such as fast Ethernet. A high-end configuration may also include a large number of SMP and non-SMP workstations and servers connected via a high-performance LAN such as Gigabit-Ethernet.

Our last experiment will include testing MOSIX on a new self-contained NEBS-compliant cabinet that consists of 16 Pentium III processors powered with 512MB of RAM and running at 500MHz. Each CPU has two on-board Ethernet ports and is also paired with a four-port ZNYX Ethernet card (used to provide Ethernet redundancy). Eight of the CPUs have a RAID setup (RAID 0 and RAID 5) with three 18GB SCSI disks.

Getting MOSIX

MOSIX for Linux is subject to the GNU General Public License version 2, as published by the Free Software Foundation. It is available for download from the MOSIX web site (see Resources).

Uninstalling MOSIX

MOSIX allows us to do an uninstall and clean up the kernel source it modified. During the initial installation, mosix.install modifies the following system configuration files: /etc/inittab, /etc/inetd.conf, /etc/lilo.conf, /etc/rc.d/init.d/atd and /etc/cron.daily/slocate.cron.

The original contents of these files are saved with the .pre_mosix extension and the changes made to kernel files are logged to the mos_uninstall.log file in the kernel-source directory. To uninstall MOSIX, you run the command ./mosix.install uninstall and answer the questions. When you are asked if you want to clean the Linux kernel sources, answer “yes”. The script will then attempt to revert all the changes that were made during a previous MOSIX installation. At the end you need to reboot the node so start it as a plain Linux node.


Clustering offers several advantages that result in sharing the processing and the ability to achieve higher performance. If you are interested in clustering your servers with efficient load-balancing software and you need support for high performance, then MOSIX can certainly be useful for you. It is easy to install and configure, and it works.

However, our initial interest with MOSIX was to understand its algorithms and investigate the possibility of using it for efficient distribution of web traffic over multiple processors. We found that MOSIX is not directly suitable for the type of functionality we want for a near telecom-internet server that we are aiming to prototype, mainly because it is missing a front-end tool for transaction-oriented load balancing such as the HTTP requests.

There have been many requests to the MOSIX mailing list asking about HTTP traffic distribution with MOSIX. I believe that if the authors would add this functionality to MOSIX, MOSIX will be one of the most popular software packages for Linux clusters.