You have been subscribed to a public bug: On xenial (systemd 229), 'systemctl mask NetworkManager' is ineffective; I can still start the service (and in fact it starts on boot). This may be due to an interaction with an init.d script with a different name ("network-manager").
root@test-paniikki:~# systemctl is-enabled NetworkManager network-manager enabled enabled root@test-paniikki:~# systemctl mask NetworkManager Created symlink from /etc/systemd/system/NetworkManager.service to /dev/null. root@test-paniikki:~# systemctl is-enabled NetworkManager network-manager masked masked root@test-paniikki:~# systemctl start NetworkManager; echo $? 0 root@test-paniikki:~# systemctl status --no-pager NetworkManager ● NetworkManager.service - Network Manager Loaded: loaded (/lib/systemd/system/NetworkManager.service; masked; vendor preset: enabled) Active: active (running) since Mon 2016-05-23 15:39:09 EEST; 9s ago Main PID: 6155 (NetworkManager) Tasks: 6 (limit: 512) CGroup: /system.slice/NetworkManager.service ├─6155 /usr/sbin/NetworkManager --no-daemon ├─6167 /sbin/dhclient -d -q -sf /usr/lib/NetworkManager/nm-dhcp-helper -pf /va... └─6182 /usr/sbin/dnsmasq --no-resolv --keep-in-foreground --no-hosts --bind-in... Only if 'network-manager' is also masked will the service fail to start: root@test-paniikki:~# systemctl mask network-manager Created symlink from /etc/systemd/system/network-manager.service to /dev/null. root@test-paniikki:~# systemctl stop NetworkManager root@test-paniikki:~# systemctl start NetworkManager Failed to start NetworkManager.service: Unit NetworkManager.service is masked. ** Affects: network-manager (Ubuntu) Importance: Undecided Status: Won't Fix -- masking NetworkManager ineffective without also masking network-manager https://bugs.launchpad.net/bugs/1584759 You received this bug notification because you are a member of Desktop Packages, which is subscribed to network-manager in Ubuntu. -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp