Flash Raspberry Pi OS

FIBER ships in two hardware variants, and the flashing procedure differs between them — pick the tab below that matches your device before you start:

FIBER (CM4)

The industrial version, based on the Raspberry Pi Compute Module 4. Uses rpiboot and a BOOT jumper to enter flashing mode.

FIBER Lite (Pi 5)

The Raspberry Pi 5 based bench-test variant. Flash a microSD card directly — no bootloader activation step.

FIBER (CM4)

1. Open the top cover of the FIBER device.

   tip

   There are four screws under the rubber feet.

2. Put jumper to the BOOT position (it has to be vertically aligned with the BOOT label on the PCB).

   tip

   This will allow the device to be switched to the bootloader mode.

3. Connect the PoE adapter (must be 802.3af compliant) to the wall socket.

4. Connect an Ethernet cable between the LAN port of the PoE adapter and your LAN router (unless WiFi connectivity is desired).

5. Connect the USB-B cable to HOST and the backside USB connector on the TARGET.

6. Install the rpiboot tool - follow the instructions from this GitHub repository:

   https://github.com/raspberrypi/usbboot

7. Connect an Ethernet cable between the PoE port of the PoE adapter and the Ethernet (RJ-45) connector of the TARGET.

8. Start the rpiboot tool.

   tip

   This should switch the TARGET to the bootloader mode. On the HOST, a new USB disk will appear.

9. Download, install, and launch the Raspberry Pi Imager tool.

10. In the Device step, select Raspberry Pi 4 (this includes Compute Module 4).

11. In the OS step, select Raspberry Pi OS (other).

12. Select Raspberry Pi OS Lite (64-bit).

13. In the Storage step, select the FIBER device (shown as RPi-MSD-0001 Media).

14. In the Customisation step, enter a hostname for your FIBER device (e.g. fiber).

15. In the Localisation section, select your location, time zone, and keyboard layout.

16. In the User section, enter a username and password.

    tip

    You can use fiber for username and hardwario for password.

    danger

    This is only recommended with public-key SSH authentication, otherwise use a strong passphrase.

17. Optional: In the Wi-Fi section, enter your wireless network's SSID and password.

18. In the Remote access section, enable SSH and select your preferred authentication method.

19. Optional: In the Raspberry Pi Connect section, you can enable remote access via Raspberry Pi Connect. For this guide, we leave it disabled.

20. Review the summary and click WRITE to start the flashing process.

21. Confirm the warning dialog by clicking I UNDERSTAND, ERASE AND WRITE.

22. Wait for the writing process to complete.

23. When finished, press the RESET button on the TARGET (located next to the USB connector).

24. Wait for the TARGET to boot and connect to the network.

    tip

    You may find the IP address of your TARGET from your DHCP server's leases.

FIBER Lite (Pi 5)

FIBER Lite uses a plain Raspberry Pi 5 — there is no bootloader-activation step, no BOOT jumper, and no rpiboot tool. You flash a microSD card directly, as with any standard Raspberry Pi.

tip

The screenshots below are reused from the Raspberry Pi Imager flow on the CM4-based FIBER (above), since the tool and most steps are identical regardless of device. A few steps look slightly different in practice: the Device picker shows Raspberry Pi 5 highlighted instead of Raspberry Pi 4, the Storage step lists your microSD card reader by its own name instead of RPi-MSD-0001 Media (that name is specific to the CM4's rpiboot USB boot mode, not used here), and the example hostname/username shown is fiber/fiber rather than fiber-lite/fiberlite — use the FIBER Lite values given in the steps below regardless of what the screenshot shows.

1. Download, install, and launch the Raspberry Pi Imager tool.

2. In the Device step, select Raspberry Pi 5.

3. In the OS step, select Raspberry Pi OS (other).

4. Select Raspberry Pi OS Lite (64-bit).

5. In the Storage step, select the microSD card for the FIBER Lite device.

6. In the Customisation step (gear icon, or Ctrl+Shift+X), enter a hostname for your FIBER Lite device (e.g. fiber-lite).

7. In the Localisation section, select your location, time zone, and keyboard layout.

8. In the User section, enter a username and password.

   tip

   You can use fiberlite for username and hardwario for password.

   danger

   This is only recommended with public-key SSH authentication, otherwise use a strong passphrase.

9. Optional: in the Wi-Fi section, enter your wireless network's SSID and password as a LAN fallback.

10. In the Remote access section, enable SSH and select your preferred authentication method.

11. Optional: in the Raspberry Pi Connect section, you can enable remote access via Raspberry Pi Connect. For this guide, we leave it disabled.

12. Review the summary and click WRITE to start flashing, then confirm the warning dialog.

13. Wait for the writing process to complete.

14. When writing completes, insert the microSD card into the FIBER Lite device and power it on.

15. Wait for the device to boot and connect to the network (30-90 seconds on first boot), then find its IP address. Try these in order:

    • Router/DHCP leases — check your router's admin page for a client named after the hostname you set (e.g. fiber-lite).

    • mDNS — ping raspberrypi.local or ping <hostname>.local (the hostname you set in Imager), if mDNS resolves on your network.

    • Network scan — from another machine on the same LAN/subnet:

      nmap -sn 192.168.1.0/24

      replacing 192.168.1.0/24 with your actual subnet. Look for a new host that wasn't there before you powered on the device.

    • Monitor + keyboard — as a last resort, connect a display and keyboard directly to the Pi and run hostname -I at the console.

    tip

    Skip the guesswork with a static IP. Instead of hunting for whatever address DHCP handed out, set one yourself before first boot: put the freshly flashed card back into your computer and create network-config at the root of the boot partition (bootfs, the small FAT volume — same partition as meta-data/user-data):

    network-config

    version: 2
    ethernets:
      eth0:
        dhcp4: false
        addresses:
          - 192.168.1.50/24
        gateway4: 192.168.1.1
        nameservers:
          addresses: [192.168.1.1, 1.1.1.1]

    Adjust the address, gateway, and subnet to match your network, then boot the device and SSH straight to 192.168.1.50 — no lease lookup or scan needed.

    This only applies on an instance's first boot, the same as user-data — see the cloud-init gotcha below. If you're adding this file to a card that has already booted once (so the account already exists), also bump instance-id in meta-data to a new value, otherwise cloud-init skips it as "already configured."

16. SSH into the device using the username and IP address (or hostname) from the previous steps:

    ssh fiberlite@<TARGET IP ADDRESS>

    Accept the host key fingerprint prompt on first connection, then enter the password you set in Imager. All commands in the rest of this guide are run from this SSH session, on the device itself.

danger

Cloud-init gotcha. Recent Raspberry Pi OS images use cloud-init instead of the older ssh-file/userconf.txt mechanism. If you ever need to hand-edit /boot/firmware/meta-data directly (instead of using Imager's Customisation dialog), the key must be instance-id (hyphen), not instance_id (underscore) — the underscored key is silently ignored, and cloud-init will skip user creation on every subsequent boot, causing "Permission denied" on SSH indefinitely even after fixing user-data. Always use Imager's own dialog for the username/ password/SSH settings; you should not need to touch cloud-init files by hand in normal use. If SSH connections are refused outright (no password prompt at all), or accepted but every password is rejected, see Troubleshooting in the sidebar.