This is a re-release of the 4th Edition of Plan 9 from Bell Labs. 4th Edition was originally released by Lucent Technologies in 2002. Itwas released under the terms the Lucent Public License Version 1.02.4th Edition continues the development of the same ideas, but in manyways represents the base of what most people think of as "modern" Plan9 today. The ubiquitous file protocol, 9P, got its first revision, to9P2000, which caused changes to many parts of the system. It also sawthe debut of venti(8) and fossil(4), which began replacing thevenerable old file server, fs(4). Authentication largely moved to aseparate agent, factotum(4). Updates moved to replica, and the wikiwas created. The original release notes for this edition can be foundat /sys/doc/release4.ms. While this release is a recognizable ancestor of the latest Plan 9available, it is still quite old, and this release is mostly foreducational and research purposes. The file protocol andauthentication mechanisms are continued in modern Plan 9, though, soresearchers looking to run this should have an easier time than withall previous releases. The only changes between this release and the original 4th Editionrelease are the new NOTICE, LICENSE, and README files, and moving theold ones. In particular, any copyright notices attributing things toLucent Technologies or Bell Labs, or notices on restrictions of theiruse, should be read as historical; all such rights have beentransferred to the Plan 9 Foundation and released as open source.Parts (notably, the fonts) maintain trademark and copyright to theirrespective parties (such as Bigelow & Holmes Inc.) and were includedin Plan 9 by permission; those copyrights are unaffected by thetransfer to Plan 9 Foundation and remain in effect per the terms foundin this distribution.