_____            _                 _____ _                _       _               _   
  / ____|          | |               / ____| |              | |     | |             | |  
 | |  __  ___ _ __ | |_ ___   ___   | |    | |__   ___  __ _| |_ ___| |__   ___  ___| |_ 
 | | |_ |/ _ \ '_ \| __/ _ \ / _ \  | |    | '_ \ / _ \/ _` | __/ __| '_ \ / _ \/ _ \ __|
 | |__| |  __/ | | | || (_) | (_) | | |____| | | |  __/ (_| | |_\__ \ | | |  __/  __/ |_ 
  \_____|\___|_| |_|\__\___/ \___/   \_____|_| |_|\___|\__,_|\__|___/_| |_|\___|\___|\__|
                                                                                         
                                                                                         
    

$ emerge -avuDN @world

Emerge ask for permission(-a), is verbose, (-u) check for package update, (--deep/D) update dependencies,(-N) new use is for NEW USE FLAGS and @world is for updating the /var/lib/portage/world.