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To learn, I am writing my own caching DNS server (à la dnsmasq, but in Python instead). From DHCP, NetworkManager obtains upstream nameservers and places them in /etc/resolv.conf. My system also looks in /etc/resolv.conf to find nameservers to query.

I need to place my own DNS server (127.0.0.1) in /etc/resolv.conf so my system will query it, but NetworkManager will overwrite the file. If I disallow/configure NetworkManager not to overwrite /etc/resolv.conf, my DNS server will not be able to find caching nameservers because NetworkManager doesn't write them there.

It seems that /etc/resolv.conf symlinks to /var/run/NetworkManager/resolv.conf, so I guess I could have my DNS server find upstream servers there? I'd just chattr -i /etc/resolv.conf to prevent NetworkManager from overwriting it. Is this how I'm supposed to do it, or is there a better way?

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chattr will work. It tells NM to leave resolv.conf alone. Alternatively, seerc-manager in man NetworkManager.conf.

NM will always write to it's internal resolv.conf in var/run, so you could scrape that. Or you use nmcli -f all device show, or use a dispatcher script (man NetworkManager).

Finally, you could write your own DNS plugin. But that requires you to rebuild NM from source, and the plugin API is not public/stable either.

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  • Thanks for mentioning so many good options! Reading about rc-manager in man networkmanager.conf, I see it will always write to the runtime directory regardless of what it does with /etc. That's exactly what I needed and the easiest option. I didn't think of trying to get it from nmcli, and I didn't know NM has dispatcher scripts. And that explains how dnsmasq does it, since NM has a specific dnsmasq setting (i.e. must be a plugin). Thanks again!
    – Luc
    Apr 12 '17 at 7:05

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