Docker : Where Are our Docker File stored ?

If we do following

1. Inside RedHat container
2. Spin a centos container
3. write a file /var/tmp/testfile inside it
4. stop & exit container
5. we can still see file in RedHat Container

We can see our tmp files there


Another way to start container

1. docker start
   
2. docker attach
   

Container names can be
a-z,A-Z,0-9,_ or -