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Command line script to flash SD card images of any kind.

Note that for some devices (e.g. Raspberry Pi), at the end of the flashing process the tool tries to customize the SD card e.g. it configures a hostname or WiFi. And with a cloud-init enabled image you can do much more like adding users, SSH keys etc.

The typical workflow looks like this:


  1. Run flash
  2. Insert SD card to your notebook
  3. Press RETURN
  4. Eject SD card and insert it to your Raspberry Pi - done!

This script can

  • download a compressed SD card from the internet or from S3
  • use a local SD card image, either compressed or uncompressed
  • wait until a SD card is plugged in
  • search for a SD card plugged into your Computer
  • show progress bar while flashing (if pv is installed)
  • copy an optional cloud-init user-data and meta-data file into the boot partition of the SD image
  • copy an optional config.txt file into the boot partition of the SD image (eg. to enable onboard WiFi)
  • copy an optional device-init.yaml or occidentalis.txt file into the boot partition of the SD image (for older HypriotOS versions)
  • copy an optional custom file into the boot partition of the SD image
  • optional set the hostname of this SD image
  • optional set the WiFi settings as well
  • play a little sound after flashing
  • unplugs the SD card

At the moment only Mac OS X and Linux is supported.


Download the appropriate version for Linux or Mac with this command

curl -LO
chmod +x flash
sudo mv flash /usr/local/bin/flash

Install Dependencies

The flash script needs optional tools

  • curl - if you want to flash directly with an HTTP URL
  • aws - if you want to flash directly from an AWS S3 bucket
  • pv - to see a progress bar while flashing with the dd command
  • unzip - to extract zip files.
  • hdparm - to run the program


brew install pv
brew install awscli

Linux (Debian/Ubuntu)

sudo apt-get install -y pv curl python-pip unzip hdparm
sudo pip install awscli


$ flash --help
usage: flash [options] [name-of-rpi.img]

Flash a local or remote Raspberry Pi SD card image.

   --help|-h      Show this message
   --bootconf|-C  Copy this config file to /boot/config.txt
   --config|-c    Copy this config file to /boot/device-init.yaml (or occidentalis.txt)
   --hostname|-n  Set hostname for this SD image
   --ssid|-s      Set WiFi SSID for this SD image
   --password|-p  Set WiFI password for this SD image
   --clusterlab|-l Start Cluster-Lab on boot: true or false
   --device|-d    Card device to flash to (e.g. /dev/disk2)
   --force|-f     Force flash without security prompt (for automation)
   --userdata|-u  Copy this cloud-init config file to /boot/user-data
   --metadata|-m  Copy this cloud-init config file to /boot/meta-data
   --file|-F      Copy this custom file to /boot


The strength of the flash tool is that it can insert some configuration files that gives you the best first boot experience to customize the hostname, WiFi and even user logins and SSH keys automatically.


With HypriotOS v1.7.0 and higher the options --userdata and --metadata can be used to copy both cloud-init config files into the FAT partition.

This is an example how to create our default user with a password.

# vim: syntax=yaml
hostname: black-pearl
manage_etc_hosts: true

  - name: pirate
    gecos: "Hypriot Pirate"
    shell: /bin/bash
    groups: users,docker,video
    plain_text_passwd: hypriot
    lock_passwd: false
    ssh_pwauth: true
    chpasswd: { expire: false }

package_upgrade: false

Please have a look at the sample folder, our guest blogpost Bootstrapping a Cloud with Cloud-Init and HypriotOS or at the cloud-init documentation how to do more things like using SSH keys, running additional commands etc.


The option --bootconf can be used to copy a config.txt into the SD image before it is unplugged.

With this option it is possible to change some memory, camera, video settings etc. See the config.txt documentation at for more details.

The boot config file config.txt has name/value pairs such as:



For HypriotOS older than v1.7.0 the option --config can be used to copy a device-init.yaml into the SD image before it is unplugged. This YAML file can be read by newer HyperiotOS SD images.

The config file device-init.yaml should look like

hostname: black-pearl
      ssid: "MyNetwork"
      password: "secret_password"

If you don't want to set any wifi settings, comment out or remove the wlan0, ssid and password.

HypriotOS 1.12.0 and higher has the /etc/ file symlinked to the boot partition. Flash tool updates this timestamp with the current time (UTC timezone). This fixes problems running commands that communicate with the internet with a wrong initial date on first boot.

Use cases

Flash a compressed SD image from the internet


Flash and change the hostname

This works only for SD card images that already have occi installed.

flash --hostname mypi hypriot.img

Then unplug the SD card from your computer, plug it into your Pi and boot your Pi. After a while the Pi can be found via Bonjour/avahi and you can log in with

ssh pi@mypi.local

Onboard WiFi

The options --userdata and --bootconf must be used to disable UART and enable onboard WiFi for Raspberry Pi 3 and Pi 0. For external WiFi sticks you do not need to specify the -bootconf option.

flash --userdata sample/wlan-user-data.yaml --bootconf sample/no-uart-config.txt hypriotos-rpi-v1.12.0.img

Automating flash

For non-interactive usage, you can predefine the user input in the flash command with the -d and -f options:

flash -d /dev/mmcblk0 -f hypriotos-rpi-v1.12.0.img


Pull requests and other feedback is always welcome. The flash tool should fit our all needs and environments.

To develop the flash scripts you need either a Linux or macOS machine to test locally. On a Mac you can use Docker to run the Linux tests in a container and if you dare you can run the macOS tests directly. On a Linux machine you can not test the macOS variant directly. But in every case you can send a pull request and push code to GitHub and the CI pipeline with CircleCI (Linux) and TravisCI (macOS) will test your code for both platforms.

Local development

The flash script are checked with the shellcheck static analysis tool.

The integration tests can be run locally on macOS or Linux. We use BATS which is installed with NPM package. So you would need Node.js to setup a local development environment. As the flash script runs dd and some commands with sudo it is recommended to use the isolated test environment with Docker or run this local tests in a macOS / Linux VM.

npm install
npm test

Isolated tests with Docker

If you do not want to install all these development tools (shellcheck, bats, node) and don't trust the flash script enough, you can use Docker instead and run the shellcheck and integration tests in a much safer test environment.

All you need is Docker and make installed to run the following tests.


The flash script are checked with the shellcheck static analysis tool.

make shellcheck

Integration tests

The flash script also have BATS integration tests. You don't have to install everything on your development machine. It should be enough to test the Linux variant in a Docker container and then run the macOS tests with TravisCI.

make test

Test Linux from Mac

For manual tests of the Linux version on a Mac there is a Vagrant environment. It can be used to investigate Linux problems when you don't have a baremetal Linux machine. With some help I found a way to spin up a VirtualBox Vagrant box with Ubuntu that maps the internal Apple SD card reader into the VM. Thanks to Flexshot for the helper functions I found in NextThingCo/CHIP-SDK#15.

Check the vendor ID and product ID in "About this Mac" -> System Report ... -> Card Reader. I found the vendor ID 0x05ac and product ID 0x8406 can be found in the Vagrantfile.

vagrant up --provider virtualbox
vagrant ssh
cd /vagrant