Domain = user-id
Domain switch accomplished via file system
Each file has associated with it a domain bit (setuid bit)
When file is executed and setuid = on, then user-id is set to owner of the file being executed
When execution completes user-id is reset
Domain switch accomplished via passwords
su command temporarily switches to another user’s domain when other domain’s password provided
Domain switching via commands
sudo command prefix executes specified command in another domain (if original domain has privilege or password given)