The PFC100 only has 256MB of eMMC flash memory internally, of which only 32.6MB is available in root partition.
This is not enough storage for containers.
The work around is to prepare a special SD card to boot and run docker, which this procedure explains.
This requires many steps, and is not ideal.
This is not recommended for production use, only testing as SD cards are not as reliable as eMMC.
Question: Why can’t I install docker on the PFC100? Why does it fail when I try to install it?