# First get ID of running container
$ docker ps
CONTAINER ID        ...
5776d1849024        ...

# Next we take a snapshot of the docker container by first pausing (-p) the container
$ docker commit -p 5776d1849024 mysql
e09f9ac65c8b3...

# The commit arg saves the entire snapshot as a docker image with a name mysql:
$ docker images
REPOSITORY                      TAG                 IMAGE ID            ...
mysql                           latest              5776d1849024        ...

# To save to a docker repo:
$ docker login
$ docker push mysql

# To save as tarball:
$ docker save -o mysql.tar mysql