[Beowulf] cluster os

[Tim Cutts]

In practice, at Sanger we haven't made very heavy use of the ability of Debian to upgrade from release to release.  We use FAI to install the boxes, so frankly it's faster and less hassle to just reinstall them from scratch when the next release comes out.

For some complicated bespoke systems, I have done the manual upgrade, and I've even done that across debian-derived distros.

Officially, you're not supposed to be able to use apt to upgrade a system from Debian to Ubuntu, for example, but I have done it in the past - I worked out a documented procedure for doing a dist-upgrade from Debian Lenny to Ubuntu Lucid, for example.  At one point, you do have to force downgrade packages which are newer in the original os than they are in the target, which led to the following one liner of which I am perversely proud:

aptitude search -F '%p' ~i | xargs -n 1 apt-cache policy | sed -n -e '
/^[a-z0-9.-]*:$/{h;d;}
/\*\*\*/{
  n
  /^  *500 /d
  /^  *100 /{
    n
    /^  *[^ ]/{x;s/:/\/lucid/p;x;}
  }
  /^[a-z0-9.-]*:$/{h;d;}
}
' | xargs apt-get -y --force-yes install


Gotta love sed for resulting in completely impenetrable commands.  I did try to do it in a more readable way using the python APT bindings, but that was actually much harder.

Tim