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Difference between OpenVMS "Revised" date and "Modified" date

 

Difference between OpenVMS "Revised" date and "Modified" date

As a long-time OpenVMS user, I am surprised that I cannot explain the purpose of the "Modified" date in a DIR/FULL command.

It appears that the "Revised:" date gets updated whenever anything about the file is changed - including data modification, permission changes, or other file attribute changes.

The OpenVMS help is woefully unclear on explaining this when I do HELP DIR/DATE.  

Apparently, on the DIR /DATE switch, the MODIFIED setting actually shows the "Revised" date and the DATA_MODIFIED setting supposedly shows the "Modified" date.

However, the "Modified" date does NOT appear to get changed when data is modified - instead the "Revised" date gets modified!!!

Does anybody have a good explanation for the purpose of the "Modified" date?

I have a customer that is trying to check that files have not been tampered with (i.e. their data has not been modified) but because the "Revised" date includes even file attribute and file permission/access changes, I am unclear how to see if the file's contents have actually been modified.

Anyone know?

2 REPLIES 2
Steven Schweda
Honored Contributor

Re: Difference between OpenVMS "Revised" date and "Modified" date

> [...] OpenVMS [...]

   Version?  Hardware architecture?

> Does anybody have a good explanation for the purpose of the "Modified"
> date?

   Not I, but there is more documentation for VMS than you'll find in
HELP.

> I have a customer that is trying to check that files have not been
> tampered with (i.e. their data has not been modified) [...]

   My standards are pretty low, but even I would not rely on those file
attributes for that purpose.  I have some confidence that I could write
a program which, when run with sufficient privilege, could fiddle with
any of these values (and the file data).

   There are various checksum programs lying around, including the one
obvious built-in:

      help checksum

   Also, if you have an OPENSSL.EXE anywhere, then you get a choice from
a bunch of algorithms.  For example:

alp $ OPENSSL dgst -sha256 login.com;0
SHA256(login.com;0)= 09c47f265bccea084fbfe1824aebcb9867631692c97188418be8594d2ed2e01c

alp $ OPENSSL dgst -sha256 login.com;-1
SHA256(login.com;-1)= c357b3680094791470978b9e5cbe281fa22fd0da728adea259d4e7c40e30275c

   Looks modified to me.  Who cares about dates?  Of course, any
checksum scheme requires you to know what the right answers are.

Re: Difference between OpenVMS "Revised" date and "Modified" date

My OpenVMS system is an Integrity server - HP rx1620  (1.60GHz/3.0MB) - running OpenVMS V8.3-1H1

My customer in question has an Integrity HP rx2800 i2 running OpenVMS 8.4

With that being said, I think I discovered the answer to my question (or at least part of the answer).

Apparently, somewhere around OpenVMS 8.3, date handling was changed such that "access dates" (i.e. "Accessed", "Attributes", and "Modified" dates in a DIR/FULL) are not shown by default.

Instead, you need to use the following command to enable the "access dates":

$ SET VOLUME/VOLUME_CHARACTERISTICS=ACCESS_DATES dev:

Once I did the above command on my OpenVMS system disk, lo and behold, those dates become visible!

There is also a "delta time" option that can be specified with the above command - but I am not sure whether I should mess with that or not.

At least part of the mystery is now solved!