I have a 64-bit processor running the 686 kernel and tried in the past, almost successfully, to migrate this to the full 64 bit. The 64 bit kernel can be installed, boots and runs fine.
From this thread, I dpkg --add-architecture amd64. Did not change any upgrades or anything. Just a "foreign architecture" can now be "printed." If I try to install the 64-bit kernel-headers, now the problems begin. Wants to remove all the cpp-4.6, g++-4.6 libstdc++6-4.6-dev and all the 32-bit linux headers currently installed (not the kernel images). In their place, would install cpp-4.6:amd64 and related packages ...:amd64 If multiarch is succeding, then this should not be removing any of this. The 32-bit libs are in one subfolder and the amd64 ones in another with lib and bin pointing to the ones of current architecture. No 32 bit applications are being removed or replaced and no 64 bit one installed. Note that in that past attempt without any --add-archtitecture stuff, I was able to install the 64 bit header leaving the 32-bit in place (so I could dkms the nvidia drivers, for instance). I chroot'ed and installed everything in the chroot. Then moved various folders around so stuff pointed to 64 bit stuff where appropriate, /lib folders done using rescue CD, and rebooted 64-bit. There were font issues so KDE came up unusable, and the 64-bit architecture was not set in for apt. So I moved everything back with only a few problems (my fault) afterwards. System got fixed up and still runs 32-bit until now. Would have hoped that a real multi-arch system would facilitate this, make a more sensible procedure for doint this, and even allow coexistance (not a requirement once 64-bit working).
