Upgrading RaspiOS to arm64

Can I upgrade my Raspberry Pi 4-powered k3s cluster to arm64? Without rebuilding everything? tl;dr: no.

$ uname -a
Linux rpi405 5.10.63-v7l+ #1496 SMP Wed Dec 1 15:58:56 GMT 2021 armv7l GNU/Linux

sudo rpi-update

sudo vi /boot/config.txt

In the [pi4] section, add arm_64bit=1. Reboot.

$ uname -a
Linux rpi405 5.10.87-v8+ #1502 SMP PREEMPT Fri Dec 17 15:15:12 GMT 2021 aarch64 GNU/Linux

$ dpkg --print-architecture
armhf

64-bit kernel. 32-bit userland.

How to upgrade userland to 64-bit? Just don’t bother:

I have done it successfully, just for the fun of it, but it’s difficult, time-consuming, and really isn’t worth the hassle. So much so that I haven’t bothered to write it up, and it was long enough ago that I forget the gotchas.

Much, much better to reinstall. The usual –get-selections | –set-selections dance, with a backup of /etc, is easier, cleaner, less error-prone, and much more likely to result in a working system. But yes: it can be done. Just don’t bother.

Vladimir over at rpi4cluster.com went with 64-bit Ubuntu 20.10.