ubuntu14 docker无法启动并出现 Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

偶然一次输入docker ps的时候，出现 “Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?”错误，试过执行

 service docker start 命令，启动docker服务，

返回  docker start/running, process 2662，

但问题还是不能解决。

解决方法：查看docker日记

tail -5f /var/log/upstart/docker.log

output

time="2020-05-18T09:42:35.148670130+08:00" level=info msg="ClientConn switching  balancer to "pick_first"" module=grpc
time="2020-05-18T09:42:35.148707378+08:00" level=info msg="pickfirstBalancer: Ha ndleSubConnStateChange: 0xc420372530, CONNECTING" module=grpc
time="2020-05-18T09:42:35.148827393+08:00" level=info msg="pickfirstBalancer: Ha ndleSubConnStateChange: 0xc420372530, READY" module=grpc
time="2020-05-18T09:42:35.148849129+08:00" level=info msg="Loading containers: s tart."
Error starting daemon: Error initializing network controller: error obtaining co ntroller instance: failed to get bridge network configurations from store: error  while populating kmap: invalid database

出现上述黄色标注的错误，执行

rm -rf /var/lib/docker/network/files/*
service docker start
docker ps

不在出现“Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?”问题解决