docker-ubuntu - a mini-ubuntu that has systemd with SSH configured.

Why?

  The official `library/ubuntu` image does not contain SSHD running
  by default as well as systemd. Thus, this images replicates a little 
  better the environment of an ubuntu machine. The tradeoff is that
  it requires more privileges and volume mounting the cgroup virtual
  filesystem.

Usage:

  1.  Default password
    
      The easiest way to get `cirocosta/ubuntu` running is using
      the default password for the `ubuntu` or `root` user.

          docker run \
            --privileged \
            --security-opt seccomp=unconfined \
            --tmpfs /run \
            --tmpfs /run/lock \
            --volume /sys/fs/cgroup:/sys/fs/cgroup:ro \
            --detach \
            --publish 2222:22 \
            cirocosta/ubuntu
          
          ssh root@localhost -p 2222
          Password: root

          ssh ubuntu@localhost -p 2222
          Password: ubuntu

  2.  Public and Private keys
    
      As the image represents a mini version of ubuntu and runs
      a normal sshd process you can mount your public key into
      /root/.ssh/authorized_keys and use your own private key.

          ssh-keygen -t rsa -b 4096 -C "test@test.com" -f ./key.rsa -P ""

            Generating public/private rsa key pair.
            Your identification has been saved in ./key.rsa.
            Your public key has been saved in ./key.rsa.pub.
            ...

          tree ./ 
            .
            ├── key.rsa
            └── key.rsa.pub

          chmod 400 ./key.rsa

          docker run \
            --privileged \
            --security-opt seccomp=unconfined \
            --tmpfs /run \
            --tmpfs /run/lock \
            --volume /sys/fs/cgroup:/sys/fs/cgroup:ro \
            --volume `pwd`/mykeys/key.rsa.pub:/root/.ssh/authorized_keys:ro \
            --detach \
            --publish 2222:22 \
            cirocosta/ubuntu
          
          ssh -i ./key.rsa root@localhost -p 2222

          ps.:  when you volume mount the file `key.rsa.pub` you might 
                have problems due to permissions (you'll mount the file
                having the permissions from the user that created the 
                file). Make sure you adjust the permissions or, if you're
                mounting for root, that you create the key file as root.