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
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