Operating system

Time to breathe life into the hardware. You'll write Raspberry Pi OS to the SSD on your regular computer, pre-configure it with a user and SSH access, and boot the Pi for the very first time, all without ever connecting a screen or keyboard to it.

Which operating system?

Which flavour of Linux belongs on a node? You'll use Raspberry Pi OS Lite (64-bit): a minimal, headless Debian-based system with no desktop environment. No wasted RAM on things you'll never see.

It's based on Debian 13 "Trixie", the current Debian stable release (since August 2025) and the same OS that powers a good slice of the internet's servers. Trixie gets security updates well into the 2030s. Because the guide only uses standard Debian commands, everything you learn here also applies to other Debian machines.

Install Raspberry Pi Imager

The official Raspberry Pi Imager handles the whole "write OS to SSD" dance with a friendly interface. This guide was written against v1.9.4; any recent version works.

Download the Imager for your OS (macOS, Windows, or Linux), install it, and launch it.

Flash the operating system

Plug the external SSD into your regular computer, then walk through the Imager one step at a time.

1. In the "Raspberry Pi device" section, click "Choose device" and select your model, Raspberry Pi 5 (or Pi 4).
2. In the "Operating system" section, click "Choose OS" and select "Raspberry Pi OS (64-bit)" right at the top of the list.
3. In the "Storage" section, click "Choose storage" and pick your external SSD. Double-check, this drive will be wiped.
4. Click "NEXT". When the Imager asks about "Use OS customisation", click "EDIT SETTINGS".

Pre-configure the system

This is the clever part: you can set the hostname, create your user, hand over your Wi-Fi credentials, and enable SSH before the Pi even boots once. That's what "headless" means in practice. Sounds like black magic, but it's really just a small config file that the Pi reads on first boot.

On the "General" tab:

• Set hostname, choose a name for your node, for example raspibolt. The Pi then answers to raspibolt.local from any device on the same network that speaks mDNS (most do).
• Set username and password, turn this on, enter the username admin, and use your password [A]. Every command in this guide assumes the user is called admin.
• Configure wifi, only if you plan to connect over Wi-Fi. Enter the SSID and password, and set the two-letter country code (e.g. US, DE, CH). Leave this blank if you'll use Ethernet, which, if you're sitting near the router, is what you want.
• Set locale settings, pick your timezone and keyboard layout.

On the "Services" tab:

• Enable SSH, check the box and select "Use password authentication". This lets you reach the Pi over the network in the next section.

On the "Options" tab:

• Optional: uncheck "Enable telemetry" if you'd rather not send usage data to the Raspberry Pi Foundation.

Click "SAVE" to lock in the settings.

Write to the SSD

Back on the main screen, the Imager asks "Use OS customisation?". Click "YES". Read the final warning, confirm you picked the right drive, and click "YES" again to start writing.

The Imager writes the operating system and verifies every byte. When it reports "Success", safely eject the SSD.

Boot your Pi

1. Plug the SSD into a USB 3 port on the Pi (the blue ones, USB 2 ports are not fast enough).
2. If you skipped the Wi-Fi settings, connect an Ethernet cable.
3. Power the Pi on by plugging in the USB-C power supply.

The Pi boots straight from the SSD. No microSD card needed.

Is it alive?

Keep an eye on the two LEDs on the Pi:

• A solid red LED means the Pi is powered.
• A flickering green LED means the SSD is being read, exactly what you want. Boot takes 20-40 seconds on an SSD.
• A solid green LED that never flickers usually means the Pi didn't find anything bootable and is sitting there waiting.

If the green LED is flickering, you're in business. Move on to the next page. Done.

If your Pi refuses to boot from USB

Some older Pi 4 boards shipped with a bootloader that can't boot from USB. You fix this once, using a microSD card, and then the Pi will happily boot from USB forever after.

1. Grab a microSD card (any size, the data is erased).
2. On your regular computer, launch Raspberry Pi Imager.
3. Click "Choose device" and pick your Pi model.
4. Click "Choose OS" → "Misc utility images" → "Bootloader" → pick your Pi family → "USB Boot".
5. Click "Choose storage" and select the microSD card.
6. Click "NEXT" → "YES" to write the bootloader.
7. Boot the Pi from this microSD card. When the green LED blinks steadily, disconnect power, remove the microSD, and reboot with the SSD attached.

Your Pi should now boot from the SSD.