Prowlarr is unable to connect to indexer, please check your DNS settings and ensure IPv6 is working or disabled

This occurred on a Debian Linux server, where the issue appeared to stem from the standard DNS settings for the network failing to resolve. It was determined that utilizing Google's DNS servers might resolve the problem. A temporary solution involved modifying the "/etc/resolv.conf" file to include the entries "8.8.8.8" and "8.8.4.4," which successfully resolved the issue until a network DNS restart erased these changes.

In order to make the DNS server changes persistent across reboots, a proposed solution was to update the "dns-nameservers" configuration in the "/etc/network/interfaces" file. However, attempting this approach did not yield the desired results.

The challenge stemmed from the fact that the "resolv.conf" file was consistently overwritten whenever the network manager daemon was started or restarted.

To maintain a static DNS configuration, the suggested course of action was to incorporate the following line into the "/etc/network/interfaces" file, using the desired DNS server IP addresses:

dns-nameservers xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx

In this example, "xxx.xxx.xxx.xxx" should be substituted with the desired DNS server's IP address. Google's DNS addresses, such as "8.8.8.8" and "8.8.4.4," could be used as an illustration.  This failed to work.

To ensure that modifications persisted after a reboot, the following command was employed to prevent the "resolv.conf" or any other specified file from being overwritten:

chattr -V +i filename (e.g., chattr -V +i /etc/resolv.conf)

To reverse this protective change, the subsequent command was used:

chattr -i filename (to re-enable insert permissions for the file)

Consequently, this approach ensured that the changes endured after a reboot. It is worth noting that subsequent testing of all indexers and then synchronization with application indexers was required from within Prowlarr for the network changes to take effect.