Doing a mass downgrade

[Lloyd Zusman <ljz@asfast.com>]

I'm using the priorities in /etc/apt/preferences to control the software
base from which I'm updating my system.  I had 'testing' set to the
highest priority for a long time.  But recently, I made the mistake of
setting 'unstable' to be the highest priority, which meant that my daily
upgrade runs from "aptitude" started bringing in a lot of 'sid'
packages.

Well, needless to say, my system is now unstable, and now I'd like to
back out all of these 'unstable' packages.  The problem is that I'm not
sure which packages I have upgraded to 'unstable', and which ones are
still either 'stable' or 'testing' packages.

What is the recommended way to do a mass downgrade so that all my
'unstable' packages get downgraded to 'testing' versions?  I have
already reset the priorities in /etc/apt/preferences so that 'testing'
has the highest priority, 'stable' has the next highest, and 'unstable'
has the lowest (my current /etc/apt/preferences listing follows).

So now what should I do to perform the mass downgrade?

I apologize if this question was answered here recently.  One side
effect of my newly created system instability is that I lost lots of my
archived email messages, including many from this mailing list.

Thanks in advance for any pointers and suggestions you can offer.


Current /etc/apt/preferences

 Package: *
 Pin: release a=stable
 Pin-Priority: 500

 Package: *
 Pin: release a=testing
 Pin-Priority: 600

 Package: *
 Pin: release a=unstable
 Pin-Priority: 5

-- 
 Lloyd Zusman
 ljz@asfast.com