[mathiasgredal]

Just use bsdtar, which will convert a tar archive to cpio: https://unix.stackexchange.com/a/581014

I have used it to convert docker images to Linux bootable initramfs archives for Rpi4.

[akdev1l]

Do you have link to that conversion? I wanna use containers to provision the pis, such a pain.

[zygology]

I've had good luck making environments in a qemu user chroot, then you can more or less just copy the whole filesystem to a SD card and boot it, considering the boot partition of course.