[conspire] "chiark’s skip-skip-cross-up-grade" (Debian 8 i386 directly to Debian 11 x86_64)

[Rick Moen]

This audacious -- and successful -- upgrade was performed on a noted
public Linux server in the UK.

https://diziet.dreamwidth.org/11840.html

At the begining, host "chiark" was on Debian 8 jessie -- 32bit.  The
end-state was Debian 11 bullseye -- 64-bit.  and he managed it while 
skipping intermediate releases (to save on downtime), exposure to 
packaging bugs in intermediate releases, and general opportunities to go
wrong.

However, this requires a _lot_ of confidence and planning.

Predictably, chiark's Mailman 2.1.x installation was A Problem, in that
Mailman2 got dropped at bullseye, replaced by the execrable and very
different Mailman3 packages.  The admin dealt with this infamous
headache by retaining the Mailman2 package from prior-to-bullseye
release Debian 10 buster.  A help, in this regard, that I'm happy to
hear about is Debian package "python-is-python2", which makes the
problem of Debian 11 bullseye having changed the meaning of
#!/usr/bin/python from Python 2 to Python 3 go away.  (That system
architecture change otherwise breaks Mailman 2.x and you reportedly have
to go around local-hotfixing the shebangs in all sorts of stuff in
/var/lib/mailman/bin/ .)

Some fancy footwork was required to keep his Exim config working, too.