v0lkan/docker-i-t-trivia.md

## docker-i-t-trivia.md

      
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              docker-i-t-trivia.md
            
          
    docker run -i -t --name nodejs ubuntu:latest /bin/bash
So here, -i stands for interactive mode and -t will allocate a pseudo terminal for us.
Some more trivia about these flags.
-i keeps STDIN open even if not attached and it allows piping (or “composition”).
Since -i keeps STDIN open even if not attached, it allows for composition (piping).
So for example
docker run ubuntu printf "line1\nline2" \
    | docker run -i ubuntu grep line2 \
    | docker run -i ubuntu sed 's/line2/line3/g'
Or, for a simpler example,
echo hello | docker run -i busybox cat
  hello
The -t option goes back to how Unix/Linux handles terminal access:
In the past, a terminal was a hardline connection. Terminals had physical device drivers which were real pieces of equipment.
Once generalized networks came into use, a pseudo-terminal driver was developed.
The pseudo-terminal driver is a layer of abstraction that helps the end user interact with the terminal.
So, with that background, when you do a docker run container (without any -i or -t flag), you basically get a STDOUT stream. So this works:
docker run ubuntu echo "hello" | cat
With -i you add a STDIN to docker too, so…
echo "hello" | docker run -i busybox cat
…works as well.
And with -t you add the pseudo-tty driver to the container, so you can type stuff from your keyboard into the container process; this is what you want (*typically combined with -i as in -it**) when you want to interact with the container.
The -i -t makes the container start to look like a terminal connection session.
If you are interested in how Docker actually does what it does, there is no better way than reading the source to learn more about it.