Plan 9 has no super-user. Each server is responsible for maintaining its own security, usually permitting access only from the console, which is protected by a password. For example, file servers have a unique administrative user called adm, with special privileges that apply only to commands typed at the server’s physical console. These privileges concern the day-to-day maintenance of the server, such as adding new users and configuring disks and networks. The privileges do not include the ability to modify, examine, or change the permissions of any files. If a file is read-protected by a user, only that user may grant access to others.
http://plan9.bell-labs.com/sys/doc/9.html