Launching an Ubuntu Environment with Docker

If standard development tools like gdb and valgrind are not available on your computer, you can create a virtual machine from which to access them.

Installing Prerequisite Software

First, install the following tools on your computer:

Docker
- Windows
  - If you have the Windows Subsystem for Linux (WSL) installed, select the option during the installation to use WSL. If you have VirtualBox or another virtualization software installed (or otherwise do not have WSL installed), choose Hyper-V.
- Mac
  - The Mac download page will ask if you want to install the x86 or Apple Silicon version of the software. If you are running an ARM processor, choose the Apple Silicon version. If you aren’t sure, click the Apple menu at the top left, and choose “About this Mac.” If it says Intel, it’s an x86/x64 installation, and if it says M1 or M2, it’s an ARM installation.
Git
- Windows
- Mac
  - Open a terminal and execute sudo port install git if you have MacPorts installed, or brew install git if you have Homebrew installed.
  - If you don’t have either MacPorts or Homebrew installed (or if the command above fails), run the command sudo xcode-select –install in your terminal, and then download and install either MacPorts or Homebrew, and then re-run the appropriate install command above.

Creating an SSH Key to Log Into Your Virtual Machine

Next, open a terminal and run the following command, if you don’t already have an SSH public key on your system.

ssh-keygen -t ed25519

Follow the prompts and it will create a public key file within your home directory called ~/.ssh/id_rsa.pub (as well as another file in that same directory called id_rsa, which is your associated private key; don’t share that file with anyone!). You will use the contents of this file later; to copy these contents, type the following command, and copy the output to your clipboard:

cat ~/.ssh/id_rsa.pub

Using Docker

Launch the Docker Desktop tool. You will be prompted to accept the license agreement and log in (and perhaps create a Docker account) the first time you launch it.

Now, launch the terminal, where we will create our virtual image. Run this command to gain access to the ubuntu base image (which we will customize):

docker pull ubuntu

Creating a Dockerfile

Create a file named Dockerfile with the following contents, making sure to set the ENV variables at the beginning of the file with your host SSH public key id_rsa.pub file contents, and a password for the default account on the guest:

# Use the official image as a parent image
FROM ubuntu

# Specify the SSH public key as a string variable (replace with your public key)
ENV SSH_PUBLIC_KEY="<paste the contents of your id_rsa.pub file here>"

# Specify the password for user and root user as a string variable (replace with your desired password)
ENV USER_PASSWORD="<put a good password that you'll remember here>"

# Update the system, install OpenSSH Server, and set up users
RUN apt-get update && apt-get upgrade -y && \
    apt-get install -y openssh-server openssh-client aptitude sudo && \
    apt-get install -y git build-essential libc6-dbg gdb valgrind vim && \
    apt-get install -y inetutils-ping traceroute python3 python3-pip

# Create user and set password for user and root user
RUN useradd -rm -d /home/ubuntu -s /bin/bash -g root -G sudo -u 1000 ubuntu && \
    echo "ubuntu:$USER_PASSWORD" | chpasswd && \
    echo "root:$USER_PASSWORD" | chpasswd

# Set up the ubuntu user's environment to generate core files in the current directory
RUN echo "ulimit -c unlimited" >> /home/ubuntu/.bashrc
RUN sysctl -w kernel.core_pattern=core.%u.%p.%t

# Set up configuration for SSH
RUN mkdir -p /var/run/sshd && \
    sed -i 's/PermitRootLogin prohibit-password/PermitRootLogin no/' /etc/ssh/sshd_config && \
    sed -i 's/#PasswordAuthentication yes/PasswordAuthentication no/' /etc/ssh/sshd_config && \
    sed 's@session\s*required\s*pam_loginuid.so@session optional pam_loginuid.so@g' -i /etc/pam.d/sshd && \
    echo "export VISIBLE=now" >> /etc/profile

# Copy the SSH public key to the authorized_keys file of the ubuntu user
RUN mkdir -p /home/ubuntu/.ssh && \
    echo "$SSH_PUBLIC_KEY" >> /home/ubuntu/.ssh/authorized_keys && \
    chown -R ubuntu:root /home/ubuntu/.ssh && \
    chmod 700 /home/ubuntu/.ssh && \
    chmod 600 /home/ubuntu/.ssh/authorized_keys

# Generate an SSH key pair during image build for the ubuntu user
RUN ssh-keygen -t rsa -b 2048 -f /home/ubuntu/.ssh/id_rsa -N "" && \
    chown -R ubuntu:root /home/ubuntu/.ssh

# Create a volume at the SHARE_PATH
VOLUME ["/home/ubuntu/shared"]

# Expose the SSH port
EXPOSE 22

# Run SSH
CMD ["/usr/sbin/sshd", "-D"]

Building the Image

Build this custom image with the following command:

docker build -t ubuntu-ssh .

Launching the Image

To start the image, run the following command (which you can skip to once you’ve built the image above):

docker run -d -v /c/Users/<your user name>/Desktop:/home/ubuntu/shared/desktop -p 2222:22 --privileged ubuntu-ssh 

The path including <your user name> allows you to share a local directory within your virtual image home directory! This example will mount your local Desktop directory at /home/ubuntu/shared/desktop, but you can select other possibilities here. Feel free to specify this or omit the entire -v parameter to skip it.

Logging into the Image

You can log into the image using ssh:

ssh ubuntu@localhost -p 2222

A password is not required, since we provided our ssh key.

Enabling Access to GitHub

Log into GitHub, and copy both the contents of your local computer id_rsa.pub and the contents of your guest id_rsa.pub to the SSH Keys section of GitHub’s settings. To list the contents of your virtual image public key file, type the following command while logged into the virtual machine (just like you did earlier on the host), and copy the resulting output:

cat ~/.ssh/id_rsa.pub

Quickstart: Launching a Vanilla Ubuntu Image

You can quickly spin up an Ubuntu instance by typing:

docker pull ubuntu
docker run -it ubuntu

However, this will not have incoming SSH access or any of the software packages we use. You’ll have to install those manually.

CS376

Operating Systems