Switch raspbian to 64bit - raspbian

Question

I switched my raspian to 64bit by adding arm_64bit=1 to /boot/config.txt. It worked in that sense, that the kernel now is 64bit.
When I want to install packages (docker in my case), I want to use it the 64bit version, but it installs the 32bit version. As it turns out, the package manager still is set to 32bit:
$ dpkg --print-architecture
armhf
How can I make the package manager install 64bit packages?

Answer 1

$ dpkg --print-architecture
i386
# dpkg --add-architecture arm64
$ dpkg --print-foreign-architectures
amd64
# apt-get update
# apt-get download gcc-4.6-base:arm64 libgcc1:arm64 libc6:arm64 \
libselinux1:arm64 zlib1g:arm64 libbz2-1.0:arm64 dpkg:arm64
# dpkg -i gcc-4.6-base*.deb libgcc*.deb libc*.deb libselinux*.deb \
libbz2*.deb zlib*.deb dpkg*.deb
$ dpkg --print-architecture
arm64
$ dpkg --print-foreign-architectures
i386
Some of your packages are then amd64, but most will remain i386. apt-get upgrade will take care of some packages, apt-get -f install will repair some of errors, but still most packages will remain i386. If you want to cope with this, then skip the tricky part ;)
Using dpkg --get-selections | grep :i386 will return all your packages, that you will still have to migrate.
My next idea was to do:
# apt-get install `dpkg --get-selections \
| grep i386 \
| awk {'gsub(/:i386/, ":amd64"); print $1'}`
But it turned out to be a bad idea: some packages are not available in amd64 (e.g. libc6-i686), apt-get will be confused, and a lot of packages will be installed in both versions. A lot of manual work in aptitude is to be done.