/lib/recovery-mode/options/network is in friendly-recovery 0.2.38.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 | #!/bin/sh
if [ "$1" = "test" ]; then
  . /lib/recovery-mode/l10n.sh
  echo $(eval_gettext "Enable networking")
  exit 0
fi
# Check for existing connectivity
check_connectivity() {
    ip route get 1.2.3.4 >/dev/null 2>&1
    retval_route=$?
    grep ^nameserver -q /etc/resolv.conf
    retval_resolve=$?
    if [ "$retval_route" = "0" ] && [ "$retval_resolve" ]; then
        exit 0
    fi
}
# Try handling networking using systemd
if [ -d /run/systemd/system ]; then
    for i in dbus.socket systemd-resolved.service networking.service systemd-networkd.service NetworkManager.service; do
	systemctl is-enabled -q $i && systemctl start $i
    done
    /lib/systemd/systemd-networkd-wait-online && exit 0	
fi
# Start by trying to bring everything up
ifup -a
check_connectivity
# Then try Network Manager
if type NetworkManager >/dev/null 2>&1; then
    echo "Trying to start NetworkManager..."
    mkdir -p /run/dbus
    chown messagebus:messagebus /run/dbus
    dbus-daemon --system --nopidfile
    NetworkManager
    trap "killall dbus-daemon NetworkManager" EXIT HUP INT QUIT PIPE
    timeout=15
    while [ $timeout -ge 0 ]; do
        check_connectivity
        sleep 1
        timeout=$((timeout-1))
    done
fi
# Try running dhclient on everything else
cd /sys/class/net/
for interface in *; do
    dhclient -1 $interface
    check_connectivity
done
exit 0
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