Support for Debian Buster is dwindling so I decided to upgrade Debian.
(My pihole is a is a Proxmox container Debian 10 and Pihole Beta 6)
I just did the usual
apt update
apt upgrade
apt full-upgrade
change apt source list
/etc/apt/sources.list
deb http://deb.debian.org/debian bullseye main
deb-src http://deb.debian.org/debian bullseye main
deb http://security.debian.org/debian-security bullseye-security main
deb-src http://security.debian.org/debian-security bullseye-security main
deb http://deb.debian.org/debian bullseye-updates main
deb-src http://deb.debian.org/debian bullseye-updates main
and again
apt update
apt upgrade
apt full-upgrade
reboot
cat /etc/debian_version
11.9
Upgrade went well, without any errors
Pihole showed right away an error, "DNS server failure"
There were no entries in Pihole diagnoses.
# pihole status
[✓] FTL is listening on port 53
[✓] UDP (IPv4)
[✓] TCP (IPv4)
[✗] UDP (IPv6)
[✗] TCP (IPv6)
[✓] Pi-hole blocking is enabled
Restaring DNS resolver did absolutely nothing
pihole restartdns
[✓] Restarting DNS server
So I ran pihole repair
pihole -r
everything works now.
I will try to repeat the same steps on another Proxmox container, and probably sooner or later upgrade from Debian 11 to Debian 12. and update this post
Hope this helps someone upgrading OS