classic networking stopped working after network-manager update

[Dennboy]

Dear all,

I'm running Armbian 21.02.1 on the nanopi neo3 (diagnostic: http://ix.io/3y5D) using /etc/network/interfaces and have network-manager disabled (`sudo systemctl disable network-manager.service` ). I occasionally use network-manager for a usb-wifi stick.

When I recently upgraded the packages it triggered a network-manager update. After a reboot the nanopi was not able to start is networking, it only got a 169.254.6.233 address. After analyzing the situation the network-manager update apparently removed the softlink `/etc/resolv.conf ->  /run/resolvconf/resolv.conf` and replaced it with a text file. Can network-manager be changed somehow, so that it keeps using the softlink instead of its own interpretation of /etc/resolv.conf?

 

Kind regards,

Dennis

[lanefu]

I'll give better answer later but yeah there's an option you can set in network manager.conf that lets you set resolver=files

[Dennboy]

Hi Ianefu,
Thanks for the pointer. It appears that rc-manager in `/etc/NetworkManager/NetworkManager.conf` is currently set to file, it probably needs to be set to something else to respect the softlink in /etc/resolv.conf. From the networkmanager.conf manpage :
 

	rc-manager
		Set the resolv.conf management mode. The default value depends on NetworkManager build options, and this version of NetworkManager was build with a default of "resolvconf". 
		Regardless of this setting, NetworkManager will always write resolv.conf to its runtime state directory /run/NetworkManager/resolv.conf.

From the description of the different options, it looks like it can be set to `symlink` or `resolvconf` to improve its behaviour, even `file` should not replace existing links... unless there is something in the network-manager debian package that does this...

 

Kind regards,

Dennis

[tparys]

If you know you're only using ifupdown, and never NetworkManager, you can always just disable it?

 

sudo systemctl stop NetworkManager
sudo systemctl disable NetworkManager

 

[Dennboy]

Hi tparys,

Yes, that is exactly my point. I had NetworkManager stopped and disabled, and during an apt update && apt upgrade, the linked /etc/resolv.conf was turned into a NetworkManager managed textfile, rendering 2 nanopi neo3's unreachable after reboot. I had to use debug-uart to repair the softlink.

Kind regards,

Dennis

[tparys]

Interesting. Doing some more digging into the debian postinst scripts. May be useful for you in the future if this becomes a continuing issue.

 

The resolvconf package touches this file after installation (/var/lib/dpkg/info/resolvconf.postinst), but only once (tracked via a file you can pre-place, and disable any action on its part).

 

# Linkify /etc/resolv.conf if appropriate
if [ ! -e /var/lib/resolvconf/linkified ] ; then

... <snip> ...
  
    ln -nsf ../run/resolvconf/resolv.conf /etc/resolv.conf
    # Make a record that we have created it
    :> /var/lib/resolvconf/linkified
fi

 

Looks like network-manager does too (/var/lib/dpkg/info/network-manager.postinst), but only if it's already a link.

 

SystemD appears to poke this file on a fresh installation (/var/lib/dpkg/info/systemd.postinst), but not on upgrade.

 

Might be useful to find out what /etc/resolv.conf is pointing to, and look for that pattern in /var/lib/dpkg/info? Might tell you which package is tripped you up, and how to prevent it from doing that in the future?