OS: Debian 11 (testing)
IP: 192.168.1.30 (ntp.fortier-family.com)

apt-get install ntp
sntp --version
vi /etc/ntp.conf

choose a pool close : https://support.ntp.org/bin/view/Servers/NTPPoolServers

server 0.ch.pool.ntp.org
server 1.ch.pool.ntp.org
server 2.ch.pool.ntp.org
server 3.ch.pool.ntp.org

systemctl restart ntp
systemctl status ntp

...kernel reports TIME_ERROR: 0x2041: Clock Unsynchronized

 ufw allow from any to any port 123 proto udp

 apt install -y firewalld
firewall-cmd --add-service={ssh,ntp} --permanent
firewall-cmd --reload

 ntpdate ntp.fortier-family.com

→ NTP

• https://help.ui.com/hc/en-us/articles/220066768-UniFi-Network-How-to-Install-and-Update-via-APT-on-Debian-or-Ubuntu
• https://community.ui.com/questions/Java-Home-Directory-Fail-Issue-on-Ubuntu-RESOLVED/1faea5fd-6eda-4be9-a12f-676ef6be2529
• https://community.ui.com/questions/UniFi-Installation-Scripts-or-UniFi-Easy-Update-Script-or-UniFi-Lets-Encrypt-or-UniFi-Easy-Encrypt-/ccbc7530-dd61-40a7-82ec-22b17f027776
• https://vitux.com/how-to-install-ntp-server-and-client-on-ubuntu/
• https://linuxize.com/post/how-to-set-or-change-timezone-on-ubuntu-20-04/
• https://davidshomelab.com/unifi-controller-setup-on-ubuntu-20-04lts/