systemd-networkd - No networking in recovery mode

Running UbuntuGnome 17.04 I am not enable to start networking in recovery mode, because there is an unknown group "power" in message bus configuration file error when NetworkManager is trying to connect. NetworkManager won't connect.

I am using a Wireless Lan Adapter: Bus 003 Device 004: ID 0bda:8172 Realtek Semiconductor Corp. RTL8191SU 802.11n WLAN Adapter. In an older Version of Ubuntu Gnome it was possible to enable networking using this adapter.

EDIT:

I could solve the 'unknown group "power" in message bus configuration file' error due to cd /etc/dbus-1/system.d and find . | xargs grep 'power'. It showed up that thermald seems to not work properly. Purging it temporarily the error was not shown up. But NetworkManager didn't connect as well. Running root from recovery it tells me that nmcli can not be found. But it is installed and works properly running the system in graphic mode as user. Any ideas how to solve this?

EDIT:

I decided to use systemd-networkd for running as root in recovery. I disabled Network-Manager and enabled systemd-networkd as well as systemd-resolved. I could start systemd-networkd. But I don't know how to scan for wifi and connect to it. Or maybe just connect to it with typing in the needed informations... Any ideas?

Thanks a lot

2 Answers

1: Boot to recovery mode

2: Drop to a root shell prompt (read only)

3: Remount file system to read and write:

mount --options remount,rw /
mount --all

4: Add dns server just to be safe that DNS will work:

vi /etc/resolv.conf

add

nameserver 8.8.8.8

(8.8.8.8 is the Google DNS server)

5: Reboot and get into a root shell again with read/write access Remount to read and write:

mount --options remount,rw /
mount --all

6: Stop networking:

systemctl stop network-manager

7: Setup wireless connection and scan:

ifconfig wlan_name up
iwlist wlan_name scan

8: Create wpa configuration file and connect:

wpa_passphrase NETWORK_ID WIRELESS_KEY > /home/(username)/wpa.conf
wpa_supplicant -B -i wlan_name -c /home/(username)/wpa.conf

Ignore any IOCSIWENCODEEXT and SIOCSIWGENIE errors, and finally run:

dhclient wlan_name

If you don't want to create a file to save your config, use these commands instead:

iwconfig wlan_name essid NETWORK_ID key s:WIRELESS_KEY
dhclient wlan_name

Source:

First find out the name of your wirless interface using ifconfig. Then run:

ifconfig wlan_name up

where wlan_name is the name of your wireless interface.

This will enable your wireless interface. There won't be an output. Next thing you have to do is to search for the wireless networks near you.

iwlist wlan_name scan 

You will see a list of wireless networks in your area. Find out the wireless network you want to connect to and run the following:

iwconfig wlan0 essid NETWORK_ID key s:PASSWORD

where NETWORK_ID with the name (SSID) of the network and PASSWORD is the network passphrase.