apt wants to downgrade packages with pin-priority less than 1000

[Alon Swartz]

Hi Guys,

Firstly, let me introduce myself, I am one of the developers for TurnKey
Linux, an opensource project that develops a family of lightweight
installable Ubuntu based Live CD appliances optimized for various
server-type tasks.

Now, down to business...

Summary
-------

apt will attempt to downgrade an installed package if the pin-priority
of the package is greater than 99.

apt will not downgrade when pin-priorty is 99 or below because the
already installed package automatically gets a priority of 100.

According to the apt_preferences manpage (mentioned several times), apt
will *never* downgrade a package unless the priority of an available
version exceeds 1000.

Details
-------

I came across this issue because our package repository has not yet been
updated with the latest package, but the latest package has been
installed on the system.

Although this shouldn't matter, apt seems to be breaking its own rules
(unless I am missing something...)

My testing system:
    Ubuntu 8.04.1 (Hardy)
    apt 0.7.9ubuntu17.1 for i386 compiled on Oct 27 2008 18:11:08

# dpkg -s drupal5 |grep Version
Version: 5.12-2

# cat /etc/apt/preferences
Package: drupal5
Pin: release o=turnkeylinux
Pin-Priority: 999

Note: the pin-priority can be anything larger than 99 to reproduce this,
and the same situation happens with other packages.

# apt-cache policy drupal5
drupal5:
  Installed: 5.12-2
  Candidate: 5.10-3
  Package pin: 5.10-3
  Version table:
 *** 5.12-2 999
        100 /var/lib/dpkg/status
     5.10-3 999
        500 http://archive.turnkeylinux.org hardy-security/universe Packages
     5.7-1ubuntu1.1 999
        500 http://archive.ubuntu.com hardy-security/universe Packages

# apt-get install drupal5
...
The following packages will be DOWNGRADED:
  drupal5

In other words, the installed version is 5.12-2 but apt wants to
downgrade to the eariler version 5.10-3.

Is this a bug in apt, a bug in the documentation, or am I
mis-understanding something?


Cheers,
Alon Swartz


-- 
Website: http://www.turnkeylinux.org
Launchpad: https://launchpad.net/~alonswartz