[CentOS] NetworkManager and /etc/resolv.conf

Sat Nov 17 16:31:11 UTC 2018
Alice Wonder <alice at domblogger.net>

On 11/17/2018 07:01 AM, Alice Wonder wrote:
> On 11/17/2018 06:43 AM, Alice Wonder wrote:
>> CentOS 7.5 image running on linode.
>> unbound running on localhost.
>> Have to use a cron job once a minute to keep /etc/resolv.conf using 
>> the localhost for name resolution - whenever NetworkManager gets 
>> restarted (usually only a system boot) it gets over-written.
>> It seems every distro has a different way of preventing NetworkManager 
>> from replacing that file.
>> I found instructions for Fedora that said create 
>> /etc/NetworkManager/conf.d/no-dns.conf containing
>> [main]
>> dns=none
>> That doesn't seem to have any effect.
>> Poking around, I find a file on boot seems to be created called
>> /var/run/NetworkManager/resolv.conf
>> It has most of the contents of what ends up in /etc/resolv.conf - 
>> except w/o the last line, which just reads rotate in generated 
>> /etc/resolv.conf.
>> It says it's generated by NetworkManager (both /etc/resolv.conf and 
>> the one in /var/run/NetworkManager) but neither are specific enough to 
>> indicate what is causing them to be created so I can turn it off.
>> Anyone know how to tell NetworkManager to just not create that file?
>> Using a cron job to overwrite it once a minute works but there must be 
>> a proper way.
>> I really wish KISS was a design goal when designing system configuration.
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> Just found this -
> # cat dhclient-exit-hooks
> echo 'options rotate' >> /etc/resolv.conf
> That's where the last line in /etc/resolv.conf is coming from.

Okay replacing the contents of dhclient-exit-hooks with

echo -e 'nameserver\nnameserver ::1' > /etc/resolv.conf

seems to do what I need.

I hope RHEL/CentOS 8 do networking better, as in, not have spaghetti 
scripts called here and there making something that should be a config 
option hard to do.

With DNS the only way to trust results is if the zone is signed and 
local resolver validates. You can't ever trust external nameservers 
defined by dhcp to validate. So there's very valid reasons to want to 
use local unbound.