The Question is:
How can I startup VMS cleanly, bypassing all the startup files
The Answer is :
You will not want to bypass all startup files, as the standard system
startup files (including SYS$SYSTEM:STARTUP.COM) establish the context
needed for system operations.
If you wish to bypass the site-specific files (including the file
SYS$MANAGER:SYSTARTUP_VMS.COM), please see the OpenVMS documentation
for details on the conversationsal bootstrap; specifically, please
see the emergency startup and shutdown sections of the OpenVMS System
Managers' Essentials manual.
General information on conversational bootstraps -- particularly in
the context of a forgotten system password -- is also included in the
OpenVMS Frequently Asked Questions (FAQ) documentation.
In particular, the usual approach is a conversational bootstrap,
and to then set the system parameter STARTUP_P1 to "MIN.