Putting a Raspberry Pi 1 SD card into a Pi 3

I have an older Raspberry Pi 1B (not the 1B+, really the older 1B¹). It has two USB ports and a standard-size SD card (no microSD yet). But I have gotten a Raspberry 3B that I needed for school, and I didn't want to reuse my old Pi that I used as sensor and sound server.

Well, the newer Pi has many improvements, like built-in wifi and less visible lights. As it has built-in wifi and my room only has one Ethernet connection, I won't have to use a switch² anymore, meaning a lot less flickering lights at night!

It turns out moving the installed SD card to the new Pi isn't as simple as just pulling it out of the old one and inserting it to the new one. It needs some software adjustments too (which will allow it to run both on the Pi 1 and the Pi 3). Between version 1 and 2, the CPU got an update from ARMv6 to ARMv7 which means a new kernel is needed (but fortunately not new userland). The Pi 3 uses ARMv8 but is compatible with the kernel from the Pi 2.

Here is what you'll need to change:

1. Install the new kernel.

    # apt-get install linux-image-rpi2-rpfv
   

2. Adjust config.txt. The bootloader has to know where to load the right kernel from! This is a minimal example:

   [pi1]
   kernel=vmlinuz-4.4.0-1-rpi
   initramfs initrd.img-4.4.0-1-rpi followkernel
   
   [pi3]
   kernel=vmlinuz-4.4.0-1-rpi2
   initramfs initrd.img-4.4.0-1-rpi2 followkernel
   

3. Change eth0 to eth1 in /etc/network/interfaces. I don't know why this is needed, but apparently it's eth1 on the newer Pi. A possible reason is that the system recognizes the new ethernet controller is a different one from the last (it's a completely different device, after all). Just do it, to be sure.

   I have changed it in such a way that it works on both devices (with wifi not yet configured).

    auto lo
    iface lo inet loopback
   
    # Pi 1
    allow-hotplug eth0
    iface eth0 inet dhcp
   
    # Pi 3
    allow-hotplug eth1
    iface eth1 inet dhcp
   

4. Install wireless-related drivers and software.

    # apt-get install firmware-brcm80211 pi-bluetooth wpasupplicant
   

5. Set up wifi. If you want to log into the device headlessly, you probably want to do this (so that at least wifi OR ethernet works - if one of them fails).

   Add this to your /etc/network/interfaces:

    allow-hotplug wlan0
    iface wlan0 inet manual
    wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
    iface default inet dhcp
   

   Create the file /etc/wpa_supplicant/wpa_supplicant.conf with the following contents:

    country=NL
    ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
    update_config=1
   
    network={
            ssid="foo"
            psk="bar"
            key_mgmt=WPA-PSK
    }
   

   Adjust the country code, the SSID, and the password for your network.

This should be it! It took me a few tries and some googling to get this right, especially the network part. I first tried with just ethernet, which of course didn't work due to the network device name change. When I set up wifi (while running on the old Pi 1), I could finally log into the 'new' system.

I hope this saves someone some trouble.