To reduce the risk of lawsuits due to a patent covering certain techniques used in RTLinux, the competing Real Time Application Interface (RTAI) project has changed the license associated with portions of RTAI from LGPL to GPL. The change in license was quietly phased in as part of the RTAI-24.1.8 release. This LinuxDevices.com article by Rick Lehrbaum and Kevin Dankwardt, which includes a statement from RTAI project leader Paolo Mantegazza, explains why the change was made, and what its implications are. Lehrbaum and Dankwardt write . . .

“Based on the change in license, the RTAI team now believes that the new partly-GPL RTAI is covered by the terms of Version 2 of the Open RTLinux Patent License, which says: 'The Patented Process may be used, without any payment of a royalty, with two types of software.' Specifically, the partly-GPL version of RTAI would appear to fall within the first type described in the patent license. A statement from Free Software Foundation counsel Eben Moglen apparently supports that position.”

“However, while the change in the license status of portions of RTAI hopefully eliminates the possibility that all RTAI users might be required to purchase a license to use the RTLinux patent, it introduces a new concern, based on what is sometimes referred to as the 'viral effect' of GPL. Namely: Does the change in license of portions of RTAI, from LGPL to GPL, require that the source code of proprietary applications based on RTAI be made available to those who request it? . . .”

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