The default networking for Debian installations without a desktop environment uses ifup and ifdown from the ifupdown package for managing network connectivity. Having more than one network manager running can cause conflicts.
Remove ifupdown to use a different network manager:
# apt purge ifupdown
Remove ifupdown from NetworkManager's plugin list:
# sed -i 's/plugins=ifupdown,keyfile/plugins=keyfile/' /etc/NetworkManager/NetworkManager.conf
Enable NetworkManager's service:
# systemctl enable NetworkManager.service
Reboot and you should have network connectivity established by NetworkManager if you are using Ethernet. If not, connections can be created with nm-applet, nmtui or nmcli.
Run nmcli to verify that your interface is connected. Expected output:
<interface>: connected to <connection name>
It should not say: <interface>: unmanaged
If NetworkManager is still not working, you may want to check for any other network managers that are running and remove / disable them. Another common one is systemd-networkd, which can be disabled through its service systemd-networkd.service.
systemctl statusand observe how it's belowsystem.slice.NetworkManager.serviceis subordinate to system.slice and I so see a user.slice before all that. But, I don't understand the ramifications of what you're trying to tell me. You see, up until now I've been spoiled by DEs, which set NetworkManager up for me. Now I'm trying to run AwesomeWM without any other DEs on the system and I'm a lost. I need a good tutorial on how to get NM up an running automatically, because that's the only way I know how to create VPN profiles. Although I set up a VPN profile with the nm_applet, I can't start the service.