You might be familiar with the /etc/resolv.conf file and configuring it by manually specifying the desired name servers for DNS resolution.
However, the configuration within /etc/resolv.conf can also be dynamically managed by various programs such as NetworkManager, resolvconf, rdnssd, and systemd-resolved.
If any of the aforementioned programs are actively managing /etc/resolv.conf, attempting to modify the file without disabling the program’s control may result in your changes being overwritten after a few minutes or reverted upon system reboot.
Identifying which program currently controls your /etc/resolv.conf
If you closely examine the file, you should find comments indicating the program that is currently managing the /etc/resolv.conf file.
Example1 (when using “resolvconf”)
Example2 (when using “systemd-resolved”)
About systemd-resolved
systemd-resolved can be configured by editing /etc/systemd/resolved.conf and/or by using drop-in .conf files in /etc/systemd/resolved.conf.d/
systemd-resolved has four different modes (stub, uplink, static, foreign) for handling the DNS resolution file (/etc/resolv.conf), with stub mode being the default and recommended option.
About “stub” mode
1) /run/systemd/resolve/stub-resolv.conf is the stub resolver configuration file, dynamically created. The file typically contains the local stub address 127.0.0.53 as the sole DNS server and includes a list of search domains for domain search suffixes.
2) The address 127.0.0.53 is the loopback address where systemd-resolved operates as a local stub resolver.
3) When DNS resolution is needed, the request first goes to the local stub resolver at 127.0.0.53, which then forwards the DNS query request to the appropriate DNS server configured in the file /etc/systemd/resolved.conf.
4) The file /etc/resolv.conf is often symbolically linked (symlinked) to /run/systemd/resolve/stub-resolv.conf.
Enabling only systemd-resolved (“stub” mode) for managing DNS
$ ls -la /etc/resolv.conf
$ mv /etc/resolv.conf /etc/resolv.conf.BAK
$ ln -s /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf
$ systemctl restart systemd-resolved
$ resolvectl
NOTE:
If multiple programs or services are attempting to manage the /etc/resolv.conf file simultaneously, conflicts and inconsistencies can arise. The /etc/resolv.conf file is a critical configuration file for DNS resolution, and having multiple sources trying to control it can lead to unexpected behavior.
On systems using systemd-resolved, it’s recommended to let systemd-resolved manage resolv.conf and to avoid interference from other programs unless necessary.
