Some others have mentioned the same kind of issue, but I've not found a solution that matches my issues exactly. Upon a reboot, the Pi-hole interface will load but is very sluggish. As the title says, pihole-FTL won't start and it says that port 53 is already in use. What I found from "netstat -tanp | grep LISTEN" is the following:
tcp 0 0 192.168.122.1:53 0.0.0.0:* LISTEN 1479/dnsmasq
192.168.122.1 is nowhere even close to the IP I'm using on the server, so I dug a little deeper and found the entry to be in /var/lib/libvirt/dnsmasq/default.conf, but the service is also disabled. I also confirmed that under Settings - DHCP, DHCP is not enabled. If I kill the running process, I can then start pihole-FTL.
[cshoults@pihole1 rc.d]$ sudo systemctl list-unit-files | grep dnsm
(partial configuration file)
##WARNING: THIS IS AN AUTO-GENERATED FILE. CHANGES TO IT ARE LIKELY TO BE
##OVERWRITTEN AND LOST. Changes to this configuration should be made using:
##virsh net-edit default
##or other application using the libvirt API.
##dnsmasq conf file created by libvirt
[cshoults@pihole1 rc.d]$ sudo systemctl status pihole-FTL.service
● pihole-FTL.service - LSB: pihole-FTL daemon
Loaded: loaded (/etc/rc.d/init.d/pihole-FTL; bad; vendor preset: disabled)
Active: active (exited) since Tue 2022-08-02 15:46:59 EDT; 31min ago
Process: 2310 ExecStart=/etc/rc.d/init.d/pihole-FTL start (code=exited, status=0/SUCCESS)
Aug 02 15:46:59 pihole1.battletech-live.net systemd: Starting LSB: pihole-FTL daemon...
Aug 02 15:46:59 pihole1.battletech-live.net pihole-FTL: Not running
Aug 02 15:46:59 pihole1.battletech-live.net su: (to pihole) root on none
Aug 02 15:46:59 pihole1.battletech-live.net pihole-FTL: FTL started!
Aug 02 15:46:59 pihole1.battletech-live.net systemd: Started LSB: pihole-FTL daemon.
CentOS 7, x86_64
The only things I've really done are to set up the OS, install Pi-hole, set up unbound and add adlists to Pi-hole.