Docker安裝完啓動時提示Failed to start docker.service: Unit docker.service is masked.

Ubutntu安裝完docker後，執行

sudo service docker start

提示

Failed to start docker.service: Unit docker.service is masked.

解決方案：

執行以下三條指令

systemctl unmask docker.service
systemctl unmask docker.socket
systemctl start docker.service