DNS Questions

Address already in use

First identify which process is listening on port 53.

ss -ltup

Check the Local Address:Port column for listeners on port 53.

udp       UNCONN   0     0            127.0.0.54:domain           0.0.0.0:*         users:(("systemd-resolve",pid=556,fd=15))
udp       UNCONN   0     0         127.0.0.53%lo:domain           0.0.0.0:*         users:(("systemd-resolve",pid=556,fd=13))
tcp       LISTEN   0     4096         127.0.0.54:domain           0.0.0.0:*         users:(("systemd-resolve",pid=556,fd=16))
tcp       LISTEN   0     4096      127.0.0.53%lo:domain           0.0.0.0:*         users:(("systemd-resolve",pid=556,fd=14))
tcp       LISTEN   0     1024          127.0.0.1:39329            0.0.0.0:*         users:(("code-6609ac3d66",pid=196919,fd=9))

Output like this indicates that systemd-resolved is using the port. Stop it before starting Landscape:

systemctl stop systemd-resolved

To keep systemd-resolved disabled after a reboot, run:

systemctl stop systemd-resolved
systemctl disable systemd-resolved
systemctl mask systemd-resolved

To restore configuration:

systemctl unmask systemd-resolved
systemctl enable systemd-resolved
systemctl start systemd-resolved