1.TL 2Preface to the Fourth (2002) Edition 3.LP 4Plan 9 continues to grow and adapt. 5The fourth major release of the system 6incorporates a number of changes, but the most central 7is the conversion to a new version of the 9P file system 8protocol. 9This new version was motivated by a desire to support 10files with name elements longer than 27 bytes (the old 11.CW NAMELEN ), 12but the opportunity was taken to change a number of other things 13about the protocol, 14making it more efficient, more flexible, and easier to encapsulate. 15One simple but indispensable new feature made possible by the protocol 16change is that the system now records the user who last modified a file; 17try 18.CW ls 19.CW -m 20to identify the culprit. 21.LP 22Many aspects of system security have been improved. 23The new security agent 24.I factotum (4) 25maintains user passwords, while 26.I secstore (4) 27keeps them safe and enables single sign-on to multiple domains and machines 28using a variety of secure protocols and services. 29.LP 30Throughout the system, components have been rewritten and interfaces 31modified to eliminate restrictions, improve performance, and clarify design. 32The full list is too long to include here, but significant changes have occurred 33in a number of system calls 34.I wait (2), ( 35.I stat (2), 36.I mount (2), 37and 38.I errstr (2)), 39the thread library 40.I thread (2)), ( 41formatted printing 42.I print (2) ( 43and 44.I fmtinstall (2)), 45security 46(many pages in section 2, including 47.I auth (2), 48.I authsrv (2)), 49and many others. 50.LP 51The changes are sweeping and are accompanied by many new programs, tools, 52services, 53and libraries. 54See the manual pages and the accompanying documents for more information. 55.LP 56.sp 57.in 3i 58Bell Labs 59.br 60Computing Science Research Center 61.br 62Murray Hill NJ 63.br 64April, 2002 65