HP OpenVMS Systems

ask the wizard
Content starts here

What happens when PID wraps?

» close window

The Question is:

I have always beleived that OpenVMS PID's are unique for as long as the system
 is booted and are only re-used after a reboot.  Is this true?  And if so, is
 there any limit to PID's - i.e. the 8 hex digits normally displayed?  What
 would happen if this lim
it were reached?
I know 8 billion unique processes should be enough for anyone and we are not in
 imminent danger of hitting this limit, but I would still be interested in the
 'what if' scenario, particularly as a few UNIX-types are siting this as a
 weakness with OpenVMS

The Answer is :

  With OpenVMS, the PID format (both external and internal PID varieties
  in the current model) formats are undocumented and subject to change
  without notice.  The current format of the external and internal PIDs
  are listed in the OpenVMS Internals and Data Structures Manual (IDSM),
  though the OpenVMS Wizard strongly discourages any dependencies on PID
  format be implemented in any application software.
  As for what happens when the PID itself wraps, well, nothing particularly
  interesting happens.
  The value wraps.
  Continous OpenVMS system uptimes of fifteen or more years are known to
  have occured on customer systems, so there is some experience with very
  extended system uptimes.
  With the wrapping of the PID, you will have the potential for duplicate
  PIDs in accounting and auditing files, particularly if you have not
  recreated new versions of the accounting and auditing logs during the
  intervening years.  That said, due to the construction of the PID, you
  cannot and will not have duplicate PIDs active on the same system or
  same cluster at the same time.  Also due to the construction of the
  PID, a very long time will transpire between any particular uses of any
  particular PID value.
  UNIX has a very similar process identification (PID) construct.

answer written or last revised on ( 25-JAN-2001 )

» close window