[CentOS] [External] Re: Unexpected /etc/resolv.conf updates on CentOS 7

Thu Oct 14 06:25:57 UTC 2021
Toralf Lund <toralf.lund at pgs.com>

On 13/10/2021 20:06, J Martin Rushton via CentOS wrote:
> If you just want to tell NM to clear off and leave your resolv.conf 
> alone do the following:

I might possibly be able to set up a workaround based on that, but it's 
not what I really want. Ideally I want NetworkManager to update 
resolv.conf, but only if it actually set up a new connection and/or got 
new information. Which is what it seemed to do in the past, but then 
something changed...

- Toralf

> If you don't want it to touch the contents of the file then remove all 
> DNSx= parameters from all ifcfg files and add PEERDNS=“no” instead. 
> Now you are solely responsible for setting the content of 
> /etc/resolv.conf yourself.
> You may also have to edit /etc/NetworkManager/NetworkManager.conf and 
> add dns=none to the [main] section.
> On 13/10/2021 18:24, Toralf Lund wrote:
>> Hi
>> Does here anyone know exactly when NetworkManager creates or is 
>> supposed to create /etc/resolv.conf for a network connection? Is 
>> there a way I can control it, or alternatively, is there a good way 
>> to debug the functionality?
>> I thought that there would simply be an update whenever a connection 
>> was established, and an addresses/network info was received (if using 
>> DHCP), and that the information would pretty much be left alone after 
>> that. However, I've lately found that a new file gets written every 
>> few hours even though there is no connection change (that I can 
>> detect), i.e. the same link is up all along. Does anyone have any 
>> ideas why that might happen? I thought at first that the updates 
>> could be linked to DHCP lease renewal, but on closer inspection, that 
>> does not seem to be the case. I don't see anything in the system log 
>> related to networking at the points where a new file gets written.
>> I get the above behaviour for my home Wifi net. It seemed to start 
>> after I switched to a new router, but that might be coincidental. 
>> It's a problem for me because I'm also using "commercial" VPN 
>> software (not integrated with NetworkManager) that will create it's 
>> own resolv.conf file; it replaces data e.g. from Network Manager when 
>> VPN is enabled, and restores it on disable. If NetworkManager 
>> "refreshes" the information in the mean time, the DNS config for VPN 
>> is lost, and the link doesn't work as expected...
>> This is on a CentOS 7 system with all the latest updates.
>> - Toralf
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