Proxmox DNS failure from a rogue resolvconf package

Problem

After upgrading a node from PVE 8.3 to 8.4, DNS resolution broke — name lookups failed even though /etc/resolv.conf looked correct and the network was otherwise up.

Cause

A resolvconf package had been pulled in and was managing /etc/resolv.conf, overwriting the working nameserver config. On Proxmox the file should be static, not managed by resolvconf.

Fix

Find what owns the file and remove the offending package:

cat /etc/resolv.conf # confirm it points somewhere wrong dpkg -l | grep resolvconf apt remove resolvconf

Then restore a static resolv.conf with a working nameserver:

echo "nameserver 1.1.1.1" > /etc/resolv.conf

Re-test with ping to a hostname. Watch for anything else (systemd-resolved, a DHCP hook) that might rewrite the file on reboot.