好久没有启动虚拟机了，在virtualbox里面运行docker报错。

怀疑是docker服务没有起来，于是：

systemctl start docker & systemctl enable docker

结果提示：

Job for docker.service failed because the control process exited with error code. See "systemctl status docker.service" and "journalctl -xe" for details.

详细定位：

systemctl status docker

提示：

9月 05 11:20:45 master-node systemd[1]: docker.service: main process exited, code=exited, status=1/FAILURE
9月 05 11:20:45 master-node systemd[1]: Failed to start Docker Application Container Engine.
9月 05 11:20:45 master-node systemd[1]: Unit docker.service entered failed state.
9月 05 11:20:45 master-node systemd[1]: docker.service failed.
9月 05 11:20:47 master-node systemd[1]: docker.service holdoff time over, scheduling restart.
9月 05 11:20:47 master-node systemd[1]: Stopped Docker Application Container Engine.
9月 05 11:20:47 master-node systemd[1]: start request repeated too quickly for docker.service
9月 05 11:20:47 master-node systemd[1]: Failed to start Docker Application Container Engine.
9月 05 11:20:47 master-node systemd[1]: Unit docker.service entered failed state.
9月 05 11:20:47 master-node systemd[1]: docker.service failed.

想起了以前貌似遇到过这个问题，当时是配置了国内镜像。

解决方法是将/etc/docker/daemon.json，修改文件后缀为.conf。即可正常启动docker 服务

定位到上述目录发现daemon.conf已经存在，但同时原来的daemon.json也存在。于是果断删除后者。

再次启动，成功