# Nerves.Firmware.SSH

[![Hex version]( "Hex version")](

This project contains the necessary infrastruction to support "over-the-air"
firmware updates with Nerves by using

The default settings make it quick to integrate into Nerves projects for
development work. Later on, if your deployed devices can be reached by `ssh`,
it's even possible to use tools like Ansible or even shell scripts to update a
set of devices all at once.

## Installation

First, add `nerves_firmware_ssh` to your list of dependencies in `mix.exs`:

def deps do
  [{:nerves_firmware_ssh, "~> 0.3"}]

Next, update your `config/config.exs` with one or more authorized keys. These
come from files like your `~/.ssh/` or `~/.ssh/` that were
created when you created your `ssh` keys. If you haven't done this, the following
may be helpful. Here's an example:

config :nerves_firmware_ssh,
  authorized_keys: [
    "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAAAgQDBCdMwNo0xOE86il0DB2Tq4RCv07XvnV7W1uQBlOOE0ZZVjxmTIOiu8XcSLy0mHj11qX5pQH3Th6Jmyqdj",
    "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAACAQCaf37TM8GfNKcoDjoewa6021zln4GvmOiXqW6SRpF61uNWZXurPte1u8frrJX1P/hGxCL7YN3cV6eZqRiF"

Here's another way that may work well for you that avoids needing to commit your keys:

config :nerves_firmware_ssh,
  authorized_keys: [!(Path.join(System.user_home!, ".ssh/"))

The first firmware bundle that you create after adding `nerves_firmware_ssh`
will need to be installed in a non-ssh way. The usual route is to burn a MicroSD
card for most targets, but you may have another way of getting the new image
onto the device.

## Pushing firmware updates to devices

This project provides a `mix` task for updating devices. Here's an example:

mix upload [destination IP or hostname]

This task uses the current `mix` target and environment settings to find the
firmware bundle (`.fw` file) to upload. It does not build it, so you will need
to run `mix firmware` first.

The `upload` task has some limitations especially if `ssh` requires credentials.
If this task doesn't work for you, see the next section for
creating a shell script with the equivalent commands.

## Pushing firmware updates to devices via commandline ssh

Regular commandline `ssh` can push firmware to devices and is desirable if you
want to integrate firmware updates into other scripts or programs like Ansible.
To get started, run `mix` to generate a starter shell script with the ssh

mix firmware.gen.script

And then run:

./ [destination IP] [.fw file]

The destination IP and .fw file can frequently be guessed so the script
attempts to do that for you.

See the nerves_firmware_ssh protocol section below and the ssh(1) man page for
more details.

## Troubleshooting

If you're not able to connect, try the following:

1. Make sure that there's network connectivity and that you can ping the device.
2. Check that the authorized keys are set correctly. On the target, run
   `Application.get_all_env(:nerves_firmware_ssh)` and compare keys.
3. Are you trying to use OpenSSH's `ssh-agent`? See
   [ERL-469]( and try not using it.
4. Add `:runtime_tools` to the `:extra_applications` key in your `mix.exs` and
   run `:ssh_dbg.messages()` on the target and try to connect. You should get
   some diagnostic data from the Erlang `:ssh` application that may help.
5. File an [issue](
   or try the `#nerves` channel on the [Elixir Slack](

### Oops, I have the wrong keys on the device

Do not panic! You can temporarily change them if you have access to the console.
Here's what to do:


Application.put_env(:nerves_firmware_ssh, :authorized_keys, ["ssh-rsa AAAAB3NzaC1yc2EAA..."])


You should be able to update the devices firmware now.

## Device keys

Devices also have keys. This prevents man-in-the-middle attacks. For
development, `nerves_firmware_ssh` uses hardcoded device keys that are contained
in its `priv` directory. The private key portion is also in the clear in
source control, so you should not rely on device authentication in this default
configuration. This is for convenience since man-in-the-middle attacks and
device authentication are usually not concerns for everyday development tasks.

If your device uses `ssh` for other services (e.g., for providing a remote
command prompt), you'll likely want to use the same keys for both services. If
the `/etc/ssh` directory exists in the device's root filesystem,
`nerves_system_ssh` will automatically use keys from there. To generate them,
add a rootfs-additions directory to your project (see the [Nerves
and run something like the following:

mkdir -p rootfs-additions/etc/ssh
ssh-keygen -t rsa -f rootfs-additions/etc/ssh/ssh_host_rsa_key

This setup also hardcodes the ssh server keys for all devices and keeps them in
the clear, so it doesn't improve security, but makes working with devices more
convenient since there's one set of keys.

Another method is to either symlink `/etc/ssh` on the device to a writable
location on the device (Nerves devices have read-only root filesystems) or to
specify an alternative location for device keys in your `config.exs`:

config :nerves_firmware_ssh,
  authorized_keys: [
  system_dir: "/mnt/device/ssh"

This requires that you add a manufacturing step to your device production that
creates a public/private key pair, writes it to your device in a hypothetical
`/mnt/device` partition, and saves the public key portion. How to do this isn't
covered here.

## The nerves_firmware_ssh protocol

`nerves_firmware_ssh` makes use of the `ssh` subsystem feature for operation.
This is similar to `sftp`. The subsystem is named `nerves_firmware_ssh`. See the
`-s` option on [ssh(1)](

The data sent over `ssh` contains a header and then the contents of one or more
`.fw` files. The header is terminated by a newline (`\n`) and is a comma
separated list of operations. Currently supported operations are:

Operation         | Description
fwup($FILESIZE)   | Stream $FILESIZE bytes to [fwup]( on the device
reboot            | Reboot the device

After the header, all data required by operations in the header is concatenated
and streamed over. Here's an example header:


For this case, 10,000 bytes of data should be sent after the header. That data
will be streamed into `fwup`. After `fwup` completes, the device will be
rebooted. If any error occurs with the `fwup` step, processing stops and the
device will not be rebooted.

The data coming back from the server is the output of the invoked commands. This
is primarily textual output suitable for reading by humans. If automating
updates, this output should be logged to help debug update failures if any.

### Example manual invocation

Use `mix firmware.gen.script` to generate a script that's portable and has a few
workarounds for platforms. The general idea, though, is to do something like

FILESIZE=$(stat -c%s "$FILENAME")
printf "fwup:$FILESIZE,reboot\n" | cat - $FILENAME | ssh -s -p 8989 target_ip_addr nerves_firmware_ssh

## License

All source code is licensed under the
[Apache License, 2.0](