As I was learning how to use Docker more fully, I came across a useful little command for seeing what distribution/version of Linux a container may be using.
cat /etc/issue
Running this command will print out something like this:
Ubuntu 18.04.4 LTS \n \l
It seems to be a pretty standard convention (as far as I can tell) across Linux distributions. This can be particularly helpful if you need to know what distribution/version of Linux a Docker container is running. You can execute this command against a running container by doing this:
docker exec name_or_id_of_container cat /etc/issue