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WiFi Support

This guide will show you how to set up the Raspberry Pi's built-in WiFi module for use during initramfs. The steps here are intended for Ubuntu, slight changes will be necessary for Raspberry Pi OS.

Set up initramfs

Create the following files and customize them if necessary:

  • /etc/initramfs-tools/scripts/init-premount/a_enable_wireless

    #!/bin/sh
PREREQ=""
prereqs()
{
    echo "$PREREQ"
}

case $1 in
prereqs)
    prereqs
    exit 0
    ;;
esac

echo "Waiting for wlan device to come up..."
while [ ! -d "/sys/class/net/wlan0" ]; do
    sleep 1
done

echo "Initializing wpa-supplicant..."
/sbin/wpa_supplicant -i wlan0 -c /etc/wpa_supplicant.conf -P /run/initram-wpa_supplicant.pid -B

  • /etc/initramfs-tools/hooks/enable-wireless

    #!/bin/sh
set -e
PREREQ=""
prereqs()
{
    echo "${PREREQ}"
}
case "${1}" in
    prereqs)
        prereqs
        exit 0
        ;;
esac

. /usr/share/initramfs-tools/hook-functions

copy_exec /sbin/wpa_supplicant

# copy WiFi driver
copy_modules_dir kernel/drivers/net/wireless/broadcom/brcm80211/brcmfmac
# copy additional firmware files, ignoring error if they are already copied
for f in /lib/firmware/brcm/brcmfmac*; do
	copy_file firmware "$f" || true
done

copy_file config /etc/initramfs-tools/wpa_supplicant.conf /etc/wpa_supplicant.conf

  • /etc/initramfs-tools/scripts/init-bottom/kill_wireless

    #!/bin/sh
PREREQ=""
prereqs()
{
    echo "$PREREQ"
}

case $1 in
prereqs)
    prereqs
    exit 0
    ;;
esac

# allow the decrypted OS to handle WiFi on its own
echo "Stopping wlan device..."
kill $(cat /run/initram-wpa_supplicant.pid)
ip link set wlan0 down
# created by initramfs
# for some reason it lists wlan0 as ethernet, which breaks netplan - remove it
rm -f /run/netplan/wlan0.yaml

  • /etc/initramfs-tools/wpa_supplicant.conf

    ctrl_interface=/tmp/wpa_supplicant
country=GB

network={
    ssid="Foo"
    scan_ssid=1
    psk="Bar"
    key_mgmt=WPA-PSK
}

Chmod all scripts you just created:

chmod +x /etc/initramfs-tools/scripts/init-premount/a_enable_wireless
chmod +x /etc/initramfs-tools/hooks/enable-wireless
chmod +x /etc/initramfs-tools/scripts/init-bottom/kill_wireless

Set up WiFi for the decrypted OS. On Ubuntu, you do this by creating e.g. /etc/netplan/10-user.yaml:

network:
  version: 2
  ethernets:
    eth0:
      dhcp4: true
      optional: true
  wifis:
    wlan0:
      optional: true
      access-points:
        "Foo":
          password: "Bar"
      dhcp4: true

You're done! Follow the rest of the guide to finish building your initramfs.

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