Plkmod is a Linux kernel module that runs on all PlanetLab nodes, currently over 160 machines at 65 sites world-wide. It is based primarily on the resource isolation research that produced the Scout OS, a configurable, communication-oriented operating system targeted at network appliances. The module also incorporates several Scout libraries (e.g., the Map library, Scout's general-purpose hashing tool).
Plkmod also draws heavily on techniques developed for the SILK (Scout in Linux Kernel) project. The original SILK prototype featured a complete Scout kernel (including Scout's native protocol stack) running in a virtual machine, which in turn was loaded into Linux as a kernel module and replaced Linux's networking subsystem. In contrast, Plkmod leverages Linux's more functional and up-to-date protocols, while overlaying a Scout-path-like structure on top of them. Plkmod also includes the resource scheduling framework originally developed for SILK. Since Plkmod evolved directly from SILK, and since "SILK" is a better name than "Plkmod", in the rest of these pages we refer to the current PlanetLab kernel module as SILK (and the original version of SILK as "the SILK prototype").