what is docker run -it flag?
docker run -it ubuntu:xenial /bin/bash starts the container in the interactive mode (hence -it flag) that allows you to interact with /bin/bash of the container. That means now you will have bash session inside the container, so you can ls, mkdir, or do any bash command inside the container.The key here is the word "interactive". If you omit the flag, the container still executes
/bin/bash but exits immediately. With the flag, the container executes /bin/bash then patiently waits for your input.