VMS 8.3 changed how file modification dates work

I've been chasing a nuisance problem for the past two days. I have an application that accesses files in a directory depending on their modification date. Sometimes I need to update one of these files, but I don't want the application to reprocess it. For many years (starting with Vax/VMS) I've used the "FILE" utility (submitted to Decus by Joe Meadows) to reset this date.

I recently ported part of this application to OpenVMS 8.3 on an Alpha DS20. This Alpha is part of a cluster that shares disks with my Vaxstation. I moved the files over, and reset the modification dates on the Vax. But, when I logged in to the Alpha, the files showed today as the modification date (using $DIR/DATE=MODIFIED on both system produced different results).

I started pulling my hair out! I checked file caching parameters, I checked the firmware rev on the MSA1000 SAN, everything seemed OK. The HP ITRC web site wasn't very helpful either. Finally a Google search brought up the VMS 8.2 New Features Manual. In it, under a section describing changes made for Posix compliance, HP mentions that the modification date displayed by the $DIRECTORY command is actually generated on the fly based on a new set of dates stored in an extended file header. In previous versions of VMS, the modification date was a part of the file's directory entry. Now there are 4 dates (revision date, accessed date, attributes date, and data modification date). The date displayed in a directory listing is the latest of these 4 dates.

But wait, it gets better. You can only see and modify these new dates if you also set the disk volume parameter /VOLUME_CHARACTERISTICS=ACCESS_DATES and this parameter is not set by default. If this parameter is not set, a $DIR/FULL shows the 4 new dates as blank! I modified the volume attributes, and saw that $FILE/REVISION_DATE was setting the data modification date, but then OpenVMS set the attributes date to today (which makes sense since the utility had indeed modified the file attributes).

Fortunately, there is a DCL command to override and set these dates (only on OpenVMS Alpha though, it's not implemented on the Vax). The command is $SET FILE/ATTRIBUTES=(ATTDATE=date,MODDATE=date). Using it I was able to see the same results for $DIR/DATE=MODIFIED on both the Vax and Alpha systems. Hooray!

Posted at 18:56 by Chris Wysocki   [/vms]   Comments | Perm Link |   |   Tweet