docker quick start启动后镜像就消失了，刚启动时终端显示的命令如下：
bash: vmrun.exe: command not found
Running pre-create checks...
Creating machine...
(default) Copying C:\Users\hp\.docker\machine\cache\boot2docker.iso to C:\Users\hp\.docker\machine\machines\default\boot2docker.iso...
(default) Creating SSH key...
(default) Creating VM...
(default) Creating disk 'C:\Users\hp\.docker\machine\machines\default\default.vmdk'
(default) Virtual disk creation successful.
(default) Starting default...
(default) Waiting for VM to come online...
Waiting for machine to be running, this may take a few minutes...
Detecting operating system of created instance...
Waiting for SSH to be available...
Detecting the provisioner...
Provisioning with boot2docker...
Copying certs to the local machine directory...
Copying certs to the remote machine...
Setting Docker configuration on the remote daemon...
Checking connection to Docker...
Docker is up and running!
To see how to connect your Docker Client to the Docker Engine running on this virtual machine, run: C:\d_my_virtualMachine\Docker Toolbox\docker-machine.exe env default
我很确定输入了docker pull appium/appium ，然后docker images也看到了 appium/appium镜像，可是只要过一段时间或者再次关闭打开docker后结果就空空如也，如下：
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
请问这是为什么？怎么解决？我希望下次输入 docker images 能继续看到以前下载好的镜像，最好能找到以前下载的镜像。
