How can I get Docker Linux container information from within the container itself?

Unless overridden, the hostname seems to be the short container id in Docker 1.12

root@d2258e6dec11:/project# cat /etc/hostname
d2258e6dec11

Externally

$ docker ps -a
CONTAINER ID        IMAGE               COMMAND             CREATED                 STATUS                      PORTS               NAMES
d2258e6dec11        300518d26271        "bash"              5 minutes ago       

$ docker -v
Docker version 1.12.0, build 8eab29e, experimental

I've found out that the container id can be found in /proc/self/cgroup

So you can get the id with :

cat /proc/self/cgroup | grep -o  -e "docker-.*.scope" | head -n 1 | sed "s/docker-\(.*\).scope/\\1/"

You can communicate with docker from inside of a container using unix socket via Docker Remote API:

https://docs.docker.com/engine/reference/api/docker_remote_api/

In a container, you can find out a shortedned docker id by examining $HOSTNAME env var. According to doc, there is a small chance of collision, I think that for small number of container, you do not have to worry about it. I don't know how to get full id directly.

You can inspect container similar way as outlined in banyan answer:

GET /containers/4abbef615af7/json HTTP/1.1

Response:

HTTP/1.1 200 OK
Content-Type: application/json

{
         "Id": "4abbef615af7......  ",
         "Created": "2013.....",
         ...
}

Alternatively, you can transfer docker id to the container in a file. The file is located on "mounted volume" so it is transfered to container:

docker run -t -i -cidfile /mydir/host1.txt -v /mydir:/mydir ubuntu /bin/bash

The docker id (shortened) will be in file /mydir/host1.txt in the container.