How to Reinstall Home Assistant Green: Recover the OS via microSD

If your Home Assistant Green fails to boot after a botched update, broken add-ons, or file corruption, a clean reset is usually the best remedy. Since the operating system resides on the internal 32 GB eMMC storage, you can restore it using the built-in microSD card slot. In this guide, I’ll walk you through flashing a fresh operating system onto the internal storage via microSD.

What you need

• Hardware: Home Assistant Green, power supply (12 V DC), Ethernet cable connected to a router with internet access.
• Storage medium: A working microSD card (the slot is intended solely for recovery purposes).
• Software: The official installer image from the GitHub repository NabuCasa/buildroot-installer (e.g. green-installer-*.img, approx. 73 MB) and flashing software on your PC. If you want to know how to flash images to memory cards, check out our guide on Raspberry Pi OS installieren: Anleitung mit dem Imager.
• Optional: A monitor with an HDMI cable to diagnose error messages.

Caution: Reinstalling will overwrite the internal storage, erasing any existing configurations. Whenever possible, create a backup beforehand.

1. Download the correct installer image

Do not download the standard HAOS image; instead, grab the lightweight Green installer image (approx. 73 MB) from the GitHub releases under NabuCasa/buildroot-installer. A full system image on the microSD won’t be transferred to internal storage; the device will incorrectly attempt to boot directly from the card instead.

2. Prepare and flash the microSD card

Flash the downloaded image to your microSD card. Make sure to use a reliable, preferably new card—bad sectors can cause the subsequent write process to the internal eMMC storage to fail.

3. Start the recovery on Home Assistant Green

1. Disconnect the Home Assistant Green from power.
2. Plug in the Ethernet cable. The installer strictly requires an active internet connection to download the latest operating system version from the stable channel.
3. Insert the prepared microSD card into the Green’s card slot.
4. Reconnect the power supply. The system will now boot from the memory card and run the haos-flash script, overwriting the internal mmcblk0 storage.

4. Remove the microSD card

Once the transfer is complete, the status LEDs will turn off. Briefly disconnect the device from power, remove the microSD card, and reboot the Green with only the Ethernet cable and power supply connected.

Did it work?

After a brief wait, the freshly installed Home Assistant OS will boot. You can access the initial setup as usual via your browser over the local network.

Troubleshooting

• Download fails (curl error): If the installer aborts with errors after 1 to 2 hours, check your internet connection. The installer fetches the OS directly from GitHub.
• Write error on mmcblk: If a connected HDMI display reports read errors or haos-flash aborts, the culprit is almost always an unreliable microSD card. Try using a different card.
• System boots from the card instead of flashing: You flashed the standard OS image rather than the buildroot installer. Make sure to use the green-installer-*.img file.
• Resetting with an intact CLI: If you still have console access via keyboard and monitor, you can alternatively reset the system directly with a terminal command:

os datadisk wipe

os datadisk wipe

Confirm the prompt locally by typing YES to wipe the internal storage without needing a microSD card.

Once the reinstallation is complete, you can restore your latest backup or start building your smart home from scratch.

Sources: Forum: Home Assistant Community, home-assistant.io, community.home-assistant.io, raspberry.tips, community.simon42.com