Get Docker up and running on the RaspberryPi (ARMv6) in four steps
Failed to start docker.service: Unit docker.service is masked.
systemctl unmask docker.service
systemctl unmask docker.socket
systemctl start docker.service
If you got the message,
WARNING: Your kernel does not support cgroup swap limit. WARNING: Your
kernel does not support swap limit capabilities. Limitation discarded.
Add cgroup_enable=memory swapaccount=1
to /boot/cmdline.txt