在执行 docker ps 等命令的时候，报错： error during connect: Get https://192.168.99.100:2376/v1.37/images/json

error during connect: Get https://192.168.99.100:2376/v1.37/images/json: dial tcp 192.168.99.100:2376: connectex: A conn
ection attempt failed because the connected party did not properly respond after a period of time, or established connec
tion failed because connected host has failed to respond.

处理方案：

查看 Oracle VM VirtualBox ，会发现 default 虚拟机已经关闭了，此时需要开启就好了。

或者在 cmd 中执行命令开启

# 开启
docker-machine start default

# 关闭
docker-machine stop default

图中为执行操作