I ran the following Docker command from a Git Bash shell on Windows 10:
docker pull ruby:1.9.3
to get the following output (I removed a couple lines for clarity):
1.9.3: Pulling from library/ruby
...
Digest: sha256:c296bd581b8c1ee0585a77cafc0b14342356cea30a10fa2c9f82370909665149
Status: Image is up to date for ruby:1.9.3
So it looks like everything "just worked" and I've now got a Ruby 1.9.3 Docker image.
But where did this image come from? When I look at library/ruby at Docker Hub or at the associated GitHub repo, I don't see any mention of a 1.9.3 tag. There are numerous third-party images on Docker Hub targeting Ruby 1.9.3, and I'm concerned that I've downloaded one of them rather than an "official" image from the Ruby or Docker teams. I'd also like to find this image's source so I can see what's in its Dockerfile. Is this image just not mentioned in the official pages linked above? I'm quite new to the Ruby world so any input helps!
It's actually available, but not visible in Dockerhub:
You can see it via the API:
https://hub.docker.com/v2/repositories/library/ruby/tags/1.9.3/
The fact that it pulls from library/x, means that it's an official version.