修改Docker镜像源之后，重启Docker，执行systemctl restart docker.service， 然后报故障：

li@raspberrypi:/etc/docker $ sudo systemctl start docker
Job for docker.service failed because the control process exited with error code.
See "systemctl status docker.service" and "journalctl -xeu docker.service" for details.

解决办法：
1.进入docker目录：

$ cd /etc/docker/

2.修改daemon文件类型：

$ sudo mv daemon.json daemon.conf

3.启动docker

$ sudo systemctl start docker

问题解决！