You execute the AUTOGEN command procedure when your system is installed,
  upgraded, or whenever you make significant  changes  to  your  workload.
  AUTOGEN performs some or all  of  the  following functions depending  on
  which phases of AUTOGEN are executed:

   o Collects the following types of data:

     - Feedback data (on the running system)
     - Hardware configuration characteristics
     - User-supplied SYSGEN parameter information
     - DIGITAL-supplied SYSGEN parameter information

   o Calculates appropriate new values for SYSGEN parameters
   o Creates a new installed image list
   o Calculates the sizes of system page, swap, and dump files
   o Resets system parameter values and file sizes if necessary
   o Optionally shuts down and reboots the system

  To invoke AUTOGEN, log in to the system manager's account  and  use  the
  following command syntax:

  $ @SYS$UPDATE:AUTOGEN [start-phase] [end-phase] [execution-mode]

  You can enter up to three parameters  to  perform  the  desired  AUTOGEN
  operation. All parameters are optional; however, if you do not supply an
  option in parameter 1, you must enter a null argument (that is, "" ).

  For detailed information on AUTOGEN parameter options   and instructions
  for performing AUTOGEN operations, enter the word HELP in parameter 1 of
  the command line.