The Road to Windows

Most Elixir developers prefer Mac or Linux, but Windows is historically the platform of choice for embedded development. Therefore as Nerves continues to grow, a Windows solution is needed.

There are 2 fundamental approaches to Nerves-on-Windows:

  1. Pretend it’s Unix
  2. Run it as a Windows app

Unfortunately, there is no “silver bullet”–each approach has its trade-offs.

Pretend its Unix

There are several ways to make Windows pretend its Unix:

  1. Cygwin
  2. Mingw
  3. Linux VM
    1. WSL
    2. Docker
    3. Virtualized (Virtual Box / VMWare)

At present, there really aren’t any solutions that leverage Cygwin or Mingw. Virtualized solutions tend to act like Native Linux, so we will focus on WSL and Docker.

WSL

Mac users have long enjoyed a robust Unix environment. With Windows 10, Microsoft has finally decided to follow suite with is Windows for Linux Subsystem. Unfortunately there are several distinct versions of Windows 10, each with their distinct version of Ubuntu.

  1. Original Release - No WSL
  2. Anniversary Update - WSL is in its infancy @ Ubuntu 14.04. Cannot run Erlang and thus Elixir
  3. Creators Update - WSL updated to Ubuntu 16.04. First Version that runs Elixir
  4. Fall Creators Update - Additional features that don’t impact Elixir/Nerves

Updating Windows between these releases is problematic (at best), but if your machine can run Creators Update (or later), Nerves becomes a 1st class citizen.

  • The Good
    • Nerves can run all steps except firmware.burn the same as Mac and Linux
  • The Bad
    • No access to SD Cards from WSL
    • Choice of git directory has consequences
    • /mnt/c/* - Permission issues will abound
    • ~/* - Can’t access files via Windows Editors

Docker

Docker on Windows comes in 2 distinct flavors:

  1. Docker Toolbox - Uses Virtualbox to create a Linux VM. Supports Windows 7+
  2. Docker for Windows - Uses Hyper-V to create a Linux VM. Windows Anniversary

Update+ (Note that Original Release is officially supported, severe issues are common. You Have Been Warned)

  • The Good
    • Same as WSL
    • Can use “volumes” which are Linux Native FS. This preserves file case and permissions.
    • Expose volumes via Samba for Windows Editors
  • The Bad
    • No access to SD Cards (same as WSL)
    • Docker Toolbox has same issues as WSL ~/* files
    • Docker for Windows has same issues as /mnt/c/* for non-volumes
    • Git over Samba has issues tracking execute permissions

Run as Windows

The second major approach is to run Nerves “natively” on Windows the same way its run on Mac. Since Windows is not a Unix OS, there are some extra catches.

  1. Paths: The modules which setup the cross-compiler have to be modified to support Windows-style paths
  2. Symbolic links: Windows has progressively adds symbolic links over the last several versions, but they still operate differently than their Unix counter-parts. The major sticking point is that Windows does not allow the creation of symbolic links to a location that does not exist. This causes huge issues when trying to unpack a nerves_system archive, as the symbolic links may occur before the files that they reference
  3. File Case Sensitivity: The Linux kernel has files that differs only in case. This makes it hard to even unpack on a Windows file system
  4. Ecosystem: Many dependencies (accidentally??) require a unix environment to compile

Installation

WSL

If you are running Windows 10 Creator’s Update, then the choice is easy: use WSL. Tim Mecklem has a great video here.

Note: To avoid pain, always run “git” from WSL.

Docker

For previous version of Windows, Docker Toolbox works fairly well, and gives an environment close to WSL. The CROPS project has step-by-step instructions here.

The above link will get you going with a “Base” Ubuntu 16 image. We still need to create a dockerfile that has Elixir + Nerves dependencies.

First we will need to create a file named “Dockerfile” with the following contents:

FROM crops/poky
WORKDIR /tmp
USER root

RUN apt-get update &&\
    apt-get install -y squashfs-tools docbook-xsl inotify-tools vim emacs npm nodejs nodejs-legacy software-properties-common python-software-properties &&\
    add-apt-repository ppa:git-core/ppa &&\
    apt-get update &&\
    apt-get install -y git &&\
    rm -rf /var/lib/apt/lists/*

RUN wget https://packages.erlang-solutions.com/erlang-solutions_1.0_all.deb &&\
    dpkg -i erlang-solutions_1.0_all.deb &&\
    rm erlang-solutions_1.0_all.deb

# Everything below will likely need to be updated periodically.
RUN npm install -g n &&\
    n lts &&\
    apt-get remove -y nodejs nodejs-legacy

RUN wget https://github.com/fhunleth/fwup/releases/download/v0.19.0/fwup_0.19.0_amd64.deb &&\
    dpkg -i fwup_0.19.0_amd64.deb &&\
    rm fwup_0.19.0_amd64.deb

RUN apt-get update &&\
    apt-get install -y esl-erlang=1:20.2.2 elixir=1.5.2-1 &&\
    rm -rf /var/lib/apt/lists/*

RUN HOME=/etc/skel mix local.hex --force &&\
    HOME=/etc/skel mix local.rebar --force &&\
    HOME=/etc/skel mix archive.install https://github.com/nerves-project/archives/raw/master/nerves_bootstrap.ez --force

The build process creates no artifacts in the local directory, so the file can be put anywhere

Once you have your Dockerfile, use it to create a image named nerves_developer:

docker build nerves_developer .

Also create a volume to persist your home directory:

docker volume create myhome

# This will copy ssh keys into the new home directory
docker create -v  myhome:/home/pokyuser --name busybox_container busybox
# Note there is a bug where docker cp can't use full paths that map back to /c/*, so workaround with pushd
pushd $HOME
docker cp .ssh  busybox_container:/home/pokyuser

echo "Copying .gitconfig"
docker cp .gitconfig busybox_container:/home/pokyuser
popd

echo "Copying .bashrc"
docker cp .bashrc busybox_container:/home/pokyuser

docker run -it --rm -v myhome:/home/pokyuser busybox chown -R 1000:1000 /home/pokyuser
docker run -it --rm -v myhome:/home/pokyuser busybox chmod -R 700 /home/pokyuser/.ssh
docker rm busybox_container

Finally run the container from your nerves_developer image:

docker run --rm -it --hostname docker -p 4000:4000 -p 9100-9109:9100-9109 -v myhome:/home/pokyuser -v myvolume:/workdir nerves_developer --workdir=/workdir

Docker commands are very verbose. Here is a quick breakdown:

  • “run” a new container interactively (-it) from nerves_developer image and delete it (–rm) when done
  • Set the host name of the container to “docker” (–hostname docker). This comes into play when doing distributed Erlang stuff
  • Expose the ports (-p) 4000, 9100-9109. 4000 is the default for Phoenix, and 910x is for Distributed Erlang
  • Mount volumes (-v). Docker containers do not save state, so to make directories permanent we have to mount them as a “volume”.
  • The CROPS scripts expect a workdir to be specifed. We use their convention and chose /workdir

Finally, to access files from Windows programs, mount /workdir as a network drive

net use a: \\192.168.99.100\workdir

Docker - Advanced

The above setup will create a new temporary container each time the command is run, and cleanup after it exits. What if you want a single container with multiple shells attached? This is easily done. :

Instead of the “run” command, we first need to “create” a new container nerves_dev from your nerves_developer image:

docker create -t --user usersetup -v myvolume:/workdir --name nerves_dev --hostname docker -v myhome:/home/pokyuser -p 4000:4000 -p 9100-9109:9100-9109 nerves_developer --workdir=/workdir

You should recognized most of the options from before. The only new one is “–user”, which lets us specify the user to run the container as. The usersetup user is part of the CROPS ecosystem.

Finally, attach a new shell to the container. You can attach as many shells desired, and they will all share the same container

docker exec -it -u pokyuser nerves_dev poky-launch.sh /workdir bash -l

Docker - Transparent Proxy

Docker’s main advantage over WSL is its support for creating a “Transparent” proxy. This is needed in many corporate environments where firewalls interfere with the SSL Certificate checks that are done by mix, npm and other package managers. See github/chameleonsocks if this pertains to you.

Burning SD Cards and GUIs

Neither WSL or Docker allow GUIs or direct burning of SD Cards. Thus we will need to install the native windows tools for this. The easiest way is to install Chocolately

Next install fwup and elixir packages:

  • fwup bat choco install fwup
  • elixir bat choco install elixir

SD Card

To burn an SD Card, you must run “fwup” from a Windows Command Prompt with Administrator priviledges.

  • Launch a new Command Prompt as Administrator
  • (Docker Only) The Administrator does not have access to mapped drives of the normal user, so you must re-mount the Samba share: bat net use a: \\192.168.99.100\workdir
  • (WSL Only) Copy the .fw file to your Windows Desktop
  • Finally, run fwup to burn the SD Card. Docker: bat a: cd <path to nerves project> fwup -a -i _build\<target>\dev\nerves\images\myfirmware.fw -t complete WSL: bat cd Desktop fwup -a -i myfirmware.fw -t complete

Erlang GUIs

Erlang ships with a variety of GUI applications to help with debugging. The most useful of these is Observer

Launching this on Windows is 2 step process

  • Launch your app with distribution enabled:
  iex --sname my_app --cookie cookie --erl "-kernel inet_dist_listen_min 9100 inet_dist_listen_max 9109" -S mix
  • Create a new file named inetrc to let erlang find our docker app
  {host,{192,168,99,100}, ["docker"]}.
  • From Windows, Launch Observer
  ERL_INETRC=inetrc iex --sname observer --cookie cookie -e ":observer.start()"
  • Finally attach to the remote node
    • select Nodes->Connect Nodes”
    • type ‘my_app@docker’

Note even though we have named the node “docker”, the above procedure should work for WSL as well.

Conclusion

WSL is a great way to get Nerves running on Windows. For older versions of Windows, or Windows in a corporate network, Docker can provide a similar experience

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