Simple initialization for devices running Nerves
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README.md

nerves_init_gadget

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This project provides the basics for getting started with Nerves. This includes bringing up networking, over-the-air firmware updates and many other little things that make using Nerves a little better. At some point your project may outgrow nerves_init_gadget and when that happens, you can use it as an example.

By design, this project is mostly dependences and only a little "glue" code. Here's a summary of what you get:

  • Basic network initialization for USB gadget devices (Raspberry Pi Zero and Beaglebone) and wired and wireless Ethernet
  • mDNS support to advertise a name like nerves.local or nerves-1234.local if devices have serial numbers
  • Device detection, filesystem mounting, and basic device control from nerves_runtime
  • Over-the-air firmware updates using nerves_firmware_ssh
  • Easy setup of Erlang distribution to support remsh, Observer and other debug and tracing tools
  • Access to the IEx console via ssh and transfer files with sftp
  • IEx helpers for a happier commandline experience
  • Logging via ring_logger
  • shoehorn-aware instructions to reduce the number of SDCard reprogrammings that you need to do in regular development.

Installation for a new project

To modify an existing Nerves project, please see the next section.

If you haven't set up your environment for Nerves, go to the Nerves Project Installation instructions and come back.

Make sure that your Nerves archive is up-to-date. The Nerves archive contains the new project generator:

mix local.nerves

# or if you don't have it yet
mix archive.install hex nerves_bootstrap

Create a new project using the generator:

mix nerves.new mygadget --init-gadget

The defaults should work for most people. However, it's good to check.

Open up config/config.exs and look for the ssh key section. If the device doesn't have your ssh public key installed, then firmware updates and ssh console access won't work. The default operation is to insert the contents of ~/.ssh/id_rsa.pub. You can add as many public keys as you'd like or copy/paste them manually into the list. See nerves_firmware_ssh for more details.

IEx prompt access and firmware updates use completely separate modules and TCP ports. Prompt access is via the normal ssh port (port 22). Firmware updates use the ssh protocol but on port 8989.

The next section to review is the nerves_init_gadget configuration. This one depends on the device that you're using. The most important configuration key is ifname. Set that to the Ethernet interface for your device. For the Raspberry Pi Zero and Beaglebone Black, "usb0" is a virtual Ethernet device going over USB. For other boards, "eth0" is the wired Ethernet interface and "wlan0" is the Wireless interface.

The next key is the address_method. If using "usb0", your choices are :linklocal or :dhcpd. The former configures the device with a link-local address and the latter configures a static IP address and starts a DHCP server that gives an address to your computer. We're having better luck with DHCP than link-local support on laptops. If you're using a wired or wireless Ethernet interface, you can use :linklocal or :dhcpd if you'd like or you can use :dhcp to have your device get it's own IP address. The configuration is done via nerves_network so when you start getting too fancy, you may need to consult the documentation there.

See the configuration section below for the other parameters.

Finally, run the usual Elixir and Nerves build steps:

# Modify the target name for your board. See the mix.exs for the options
export MIX_TARGET=rpi0

mix deps.get
mix firmware

# Copy the firmware to a MicroSD card (or change this to how you do the
# first-time load of software onto your device.)
mix firmware.burn

Since debugging ssh is particularly painful, take this opportunity to double check the authorized key one last time.

find . -name sys.config

# This should print out the configuration that was compiled into the image. If
# you have multiple ones since you've been compiling for more than one device,
# pick the one that makes sense. The following is the one that I had:

cat ./_build/rpi0/dev/rel/mygadget/releases/0.1.0/sys.config

Now you should be able to boot the device and push firmware updates to it. See the sections below for doing this and troubleshooting.

Installation for an existing project

These instructions assume that your existing project is configured to expose a virtual Ethernet adapter and virtual serial port on the target. The official nerves_system_rpi0 does this.

This project works well with shoehorn. It's not mandatory, but it's pretty convenient since it can handle your application crashing during development without forcing you to re-burn an SDCard. Since other instructions assume that it's around, update your mix.exs deps with it too:

def deps do
  [
    {:shoehorn, "~> 0.4"},
    {:nerves_init_gadget, "~> 0.3"}
  ]
end

Shoehorn requires a plugin to the distillery configuration, so add it to your rel/config.exs (replace :your_app):

release :your_app do
  plugin Shoehorn
  ...
end

Now, add the following configuration to your config/config.exs:

config :shoehorn,
  init: [:nerves_runtime, :nerves_init_gadget],
  app: Mix.Project.config()[:app]

The final configuration item is to set up authorized keys for pushing firmware updates to the device. This is documented in more detail at nerves_firmware_ssh. Basically, the device will need to know the ssh public keys for all of the users that are allowed to update the firmware. Copy the contents of the id_rsa.pub, etc. files from your ~/.ssh directory or add something like this:

config :nerves_firmware_ssh,
  authorized_keys: [
    File.read!(Path.join(System.user_home!, ".ssh/id_rsa.pub"))
  ]

The last change to the config.exs is to enable ring_logger. Like many aspects of nerves_init_gadget, this is optional and you can use the default Elixir logger or a logger of your choosing if you'd like.

config :logger, backends: [RingLogger]

That's it! Now you can do the normal Nerves development procedure for building and installing the image to your device:

export MIX_TARGET=rpi0  # modify if necessary

# You shouldn't need to run this line unless you skipped this step
# when running `mix nerves.new` to create your project initially.
mix nerves.release.init

mix deps.get
mix firmware
mix firmware.burn

Using

Connect your device over the USB port with your computer (if using a RPi0, it is very important to use the port labeled "USB" and not the one labeled "PWR"). Give your device a few seconds to boot and initialize the virtual Ethernet interface going through the USB cable. On your computer, run ping to see that it's working:

ping nerves.local

If you're using Ubuntu and ping doesn't work, check the Network Settings for the usb0 interface and set the IPv4 Method to "Link-Local Only". Depending on your kernel settings for "Predictable Network Interface Naming", the interface might be called enp0s26u1u2 or some variation thereof. Be aware that the NetworkManager tool may have trouble holding on to configured settings for this network interface between unplugging and replugging.

If the network still doesn't work, check that the virtual serial port to the device works and see the troubleshooting section.

To update firmware from now on, just run the following:

MIX_TARGET=rpi0 mix firmware.push nerves.local

Change MIX_TARGET to whatever you're using to build the firmware. Assuming everything completes successfully, the device will reboot with the new firmware.

If you have a password-protected ssh private key, mix firmware.push currently isn't able to prompt for the password or use the ssh-agent. This means that you either need to pass your password in cleartext on the commandline (ugh), create a new public/private key pair, or use commandline ssh. For commandline ssh, take a look at the upload.sh script from nerves_firmware_ssh for an example.

If you have your private key stored in a file with a different name than id_dsa, id_rsa, or identity, chances are that mix firmware push will not find them. Use upload.sh in this case as well.

Configuration

You may customize nerves_init_gadget using your config.exs:

config :nerves_init_gadget,
  ifname: "usb0",
  address_method: :dhcpd,
  mdns_domain: "nerves.local",
  node_name: nil,
  node_host: :mdns_domain

The above are the defaults and should work for most users. The following sections go into more detail on the individual options.

:ifname

This sets the network interface to configure and monitor on the device. For gadget use, this is almost aways usb0. If you'd like to use nerves_init_gadget on a real Ethernet interface or WiFi, modify this to eth0 or wlan0. You'll probably want to change the :address_method to :dhcp. For wireless use, you'll need to supply a default configuration to specify the SSID to associate with. See the nerves_network docs for details.

:address_method

This sets how an IP address should be assigned to the network interface. You may specify the following:

  • :linklocal - assign a link-local IP address
  • :dhcp - send a DHCP discovery request on the network to get assigned an IP address
  • :dhcpd - set an automatically calculated IP address and start a DHCP server to assign an address to the other side of the link. See OneDHCPD

:mdns_domain

This is the mDNS name for finding the device. It defaults to nerves.local. This is very convenient when there's only one device on the network.

If you don't want mDNS, set this to nil.

You can set this to :hostname and the mDNS name will be set to the hostname.local. The official Nerves systems all generate semi-unique hostnames for devices. This makes it possible to discover devices via mDNS and also to connect to them. Note that if your network uses DHCP, Nerves lists its hostname in the DHCP request so if your router supports it, you may be able to connect to the device via the hostname as well.

:node_name

This is the node name for Erlang distribution. If specified (non-nil), nerves_init_gadget will start epmd and configure the node as :<name>@<host>. See the next option for the host part.

Currently only long names are supported (i.e., no snames).

:node_host

This is the host part of the node name when using Erlang distribution. You may specify a string to use as a host name or one of the following atoms:

  • :ip - Set the host part to :ifname's assigned IP address.
  • :dhcp - Set the host part to the host name registered by dhcp.
  • :mdns_domain Set the host part to the value advertised by mDNS.

The default is :mdns_domain so that the following remsh invocation works:

iex --name me@0.0.0.0 --cookie acookie --remsh node_name@nerves.local

:ssh_console_port

By default, nerves_init_gadget will start an IEx console on port 22 or whatever port is specified with this option. The SFTP subsystem is also enabled so that you can transfer files back and forth as well. To disable this feature, set :ssh_console_port to nil. This console will use the same ssh public keys as those configured for :nerves_firmware_ssh. Usernames are ignored. Connect by running:

ssh nerves.local

To exit the SSH session, type ~.. This is an ssh escape sequence (See the ssh man page for other escape sequences). Typing Ctrl+D or logoff at the IEx prompt to exit the session won't work.

Troubleshooting

If things aren't working, try the following to figure out what's wrong:

  1. Check that you're plugged into the right USB port on the target. The Raspberry Pi Zero, for example, has two USB ports but one of them is only for power.
  2. Check that the USB cable works (some cables are power-only and don't have the data lines hooked up). Try connecting to the virtual serial port using picocom or screen to get to the IEx prompt. Depending on your host system the virtual serial port may be named /dev/ttyUSB0, /dev/ttyACM0, or some variation of that.
  3. Check your host machine's Ethernet settings. You'll want to make sure that link-local addressing is enabled on the virtual Ethernet interface. Static addresses won't work. DHCP addressing should eventually work since link-local addressing is what happens when DHCP fails. The IP address that's assigned to the virtual Ethernet interface should be in the 169.254.0.0/16 subnet.
  4. Reboot the target and connect over the virtual serial port as soon as it allows. Watch the log messages to see that an IP address is assigned to the virtual Ethernet port. Try pinging that directly. If nothing is assigned, it's possible that something is wrong with the Ethernet gadget device drivers but that's more advanced to debug and shouldn't be an issue if you haven't modified the official Nerves systems.
  5. If you're having trouble with firmware updates, check out the nerves_firmware_ssh troubleshooting steps.
  6. If all else fails, please file an issue or try the #nerves channel on the Elixir Slack. Inevitably someone else will hit your problem too and we'd like to improve the experience for future users.

FAQ

What should I put in my config for Raspberry Pi 3 w/ wired Ethernet

Try this if you're on a DHCP-enabled network:

config :nerves_init_gadget,
  ifname: "eth0",
  address_method: :dhcp,
  node_name: "murphy"

This also starts up Erlang distribution with a node name of "murphy". Get your cookie from rel/vm.args (look for the -setcookie line) and run the following to connect to your device:

iex --name me@0.0.0.0 --cookie acookie --remsh murphy@nerves.local

How do I register a callback before the system reboots

If you need to save data or notify the user of an impending reboot or power off, take a look at OTP's Application.stop/1 and Application.prep_stop/1 callbacks. Reboots and shutdowns initiated through Nerves.Runtime.reboot/0 or Nerves.Runtime.poweroff/0 have a timer that restricts how long the OTP shut down process can take. This prevents shutdown hangs. The timer duration is specified in erlinit.config.

Why do I see x\360~ when I reboot

You may also see things like this:

x\360~
** (SyntaxError) iex:4: invalid sigil delimiter: "\360" (column 3, codepoint U+00F0). The available delimiters are: //, ||, "", '', (), [], {}, <>

You're probably also using Linux. This is ModemManager probing the serial port to see if there's a modem. ModemManager prevents anything from using the serial port until it gives up on finding a modem at the other end. This takes a second or two and leaves junk behind at the IEx prompt.

Check out the ModemManager description to see whether this software is even something that you want. Here's a popular solution:

sudo apt remove modemmanager

License

This code is licensed under the Apache License 2.0.