Clean up netplan stuff after dropbear-initramfs

dropbear-netplan-fix

#!/bin/sh

: <<'README'

This is a fix for a well-known problem [1] with dropbear-initramfs+netplan
combo.

When dropbear starts, it enables networking [2]. This results in netplan configs
for available ifaces created under /run/netplan. After unlocking, the configs
are still there preventing networkmanager from picking ifaces up: by default,
ifaces matched by the IFDOWN variable are only put down. So to make it clean, we
have to explicitly drop the netplan stuff.

Put this script under /etc/initramfs-tools/scripts/init-bottom/ and update
initramfs.

[1] https://bugs.launchpad.net/ubuntu/+source/dropbear/+bug/1813394
[2] configure_networking() from /usr/share/initramfs-tools/scripts/functions

README

PREREQ="dropbear"

prereqs() {
    echo "$PREREQ"
}

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


IFDOWN="*"
CONF=/etc/dropbear/dropbear.conf
[ ! -e "$CONF" ] || . "$CONF"

if [ "$BOOT" != nfs ] && [ "$IFDOWN" != none ]; then
    for IFACE in /sys/class/net/$IFDOWN; do
        [ -e "$IFACE" ] || continue

        PLAN="/run/netplan/${IFACE##*/}.yaml"
        [ ! -e "$PLAN" ] || rm "$PLAN"
    done
fi

Awesome, works flawlessly.