Mendel Development Tool (mdt)

Mendel Development Tool (mdt) is a command-line tool that lets you communicate with a device running Mendel Linux. The mdt command facilitates a variety of device actions such as opening a shell, installing Debian packages, pushing and pulling files, and more.

Install MDT

The server-side component that runs on the Mendel device is included with the Mendel system image. So you only need to install the mdt client on your host computer.

You can install it with pip as follows:

pip3 install --user mendel-development-tool
Note: The --user flag installs the mdt executable in your user directory. On Linux, that's ~/.local/bin/. On a Mac, it's something like /Users/yourname/Library/Python/3.7/bin/. If you remove that flag, it requires root access and will install at /usr/local/bin. So make sure that the appropriate path is in your PATH environment variable.

If you prefer apt-get then you can also use that:

# Add the repo:
echo "deb coral-mdt-stable main" | sudo tee /etc/apt/sources.list.d/mdt.list

# Add Google keys
curl | sudo apt-key add -

# Then install the package:
sudo apt-get update

sudo apt-get install mendel-development-tool

Connect to a board's shell

MDT can access the shell on any Mendel device that's visible on your network, but the easiest option is to connect with a USB-C cable as shown in figure 1.

Figure 1. The USB-C data and power cables connected to the board

Then if you have just one device, run this command:

mdt shell

If multiple devices are available, you need to specify the name or IP address (you can list all devices with mdt devices).

Internally, this is a normal SSH connection using OpenSSH with key-based authentication. So before you can connect to the device shell with MDT or any other SSH tools, you must push a public key to the device's /home/mendel/.ssh/authorized_keys file. If no such key exists there, the mdt shell command creates it and pushes it (you can also do this manually with mdt genkey and then mdt pushkey). This key created by MDT is PEM-formatted, passwordless, and saved on your host computer at ~/.config/mdt/keys/mdt.key (this key is used only when connecting with mdt shell).

If you prefer to use other SSH tools, simply generate your own key and then push that one to the device with mdt pushkey. For example, run the following on your host computer:

Note: This command requires that you already established a secure connection with MDT as per above.
# Follow steps to create key

mdt pushkey ~/.ssh/

ssh mendel@

MDT commands

The following table provides a reference of the available commands you can use with mdt using this syntax:

mdt subcommand arguments
Note: You can also use mdt help and man mdt for information about what commands are available in your version of MDT.
Subcommand Description
devices Returns a list of device names and IP addresses found on the local network segment. Also indicates if a given device is marked as your default.

Uses the preferred-device variable, which contains the device name you want as your default. It can be set to an IPv4 address to bypass the mDNS lookup.

Note: MDT uses a python implementation of mDNS ZeroConf for discovery, so it does not require a running Avahi daemon.

wait-for-device Waits for a device to be discovered on the network.
get variable-name Returns the value currently set for a given variable name. Some useful variables are:
  • preferred-device: set this to your preferred device name to default most commands to manipulating this specific device. This can be set to an IPv4 address to bypass the mDNS lookup.
  • username: set this to the username that should be used to connect to a device with. Defaults to 'mendel'.
  • password: set this to the password to use to login to a new device with. Defaults to 'mendel'. Only used during the initial setup phase of pushing an SSH key to the board.

If no variable name is provided, 'mdt get' will print out the list of all known stored variables and their values. Note: default values are not printed.

set variable-name Sets the value for a given variable name. See example variables for the corresponding get command above.

Note that setting a variable to the empty string does not clear it back to the default value. Use mdt clear for that.

clear variable-name Clears the value for a given variable name, resetting it back to its default value.
genkey Generates an SSH key and stores it to disk on the Mendel device.

If you already have an MDT key, this replaces it, effectively locking you out from any boards that require authentication using that existing key. You must also remove the keys previously stored on the Mendel device in $HOME/.ssh/authorized_keys and restart the mdt-keymaster service on the device before you can re-push any newly generated keys.

pushkey path-to-ssh-public-key Copies an SSH public key to the Mendel device's ~/.ssh/authorized_keys file. If an MDT private key is provided, will push the public half of that key to the device's authorized_keys file. If no public key is provided, it attempts to push MDTs previously generated public key from ~/.config/mdt/keys/mdt.key.
setkey path-to-private-key Copies a PEM-format SSH private key into the Mendel device's MDT keystore for use with authentication later.
resetkeys device-or-ip-address Resets a device to it's pre-MDT state by removing all MDT keys and restarting the mdt-keymaster on the device so that new keys can be pushed again.
shell [device-or-ip-address] Opens an interactive shell to either your preferred device or to the first device found. If device-or-ip-address is specified, shell attempts to connect to that device name or directly to the IP address provided instead.

Uses the variables preferred-device, username, and password (see the get command above).

If no SSH key is available on disk (you didn't run genkey before running shell), this will implicitly run genkey for you. Additionally, it will attempt to connect to a device by doing the following:
1. Attempt a connection using your SSH key only, with no password.
2. If the connection attempt failed due to authentication, will attempt to push the key to the device by using the default login credentials in the 'username' and 'password' variables.
3. Installs your SSH key to the device after logging in.
4. Disconnects and reconnects using the SSH key.

exec [shell-command...] Opens a non-interactive shell to either your preferred device or to the first device found, runs a shell command and returns the output and the exit code.

If no SSH key is available on disk, it follows the same steps as the shell command.

install deb-package-file Installs a given Debian package file to the connected device via mdt-install-package. Uses the variables preferred-device, username, and password (see the get command above).

Note: if the package provided has dependencies that are not already installed on the device, this will require internet connectivity to fetch and install those dependencies.

push local-filename... remote-destination Pushes (copies) a local file or set of files to the remote device. Uses the variables preferred-device, username, and password (see the get command above).
pull remote-filename... local-destination Pulls (copies) a set of files from the remote device to a local path. Uses the variables preferred-device, username, and password (see the get command above).
reboot Reboots a device.
reboot-bootloader Reboots a device into the bootloader.
version Prints which version of MDT this is.