function login()
 local un,pw,cc = "","",false
 if #os.users() > 0 then
  repeat
   io.write("\f"..MOTD.."\n"..net.id.." login: ")
    un = io.read()
   io.write("Password: ")
    pw = io.read("*")
    cc = os.su(un,pw)
  until cc
  return true
 end
end