The VMS Disk Quota Utility (DISKQUOTA) was a standalone utility in
  versions of VMS prior to V5.0.  It is now a subset of the System
  Management (SYSMAN) Utility.

  Online help is available on DISKQUOTA commands from the SYSMAN Utility.
  To invoke SYSMAN, enter the following command in response to the DCL
  prompt:

     $  RUN SYS$SYSTEM:SYSMAN

  The utility responds with the prompt:

     SYSMAN>

  After you invoke SYSMAN, you can enter the command HELP DISKQUOTA.