I remember looking at this circa 2016 - 2021 and letting go at that time, crony had just been released and systemd was still relatively new at that time.

• sudo systemctl status systemd-timesyncd
  • The default configuration is shown in /etc/systemd/timesyncd.conf (All the defaults are shown commented out)
  • Copy the default configuration in /etc/systemd/timesyncd.conf to /etc/systemd/timesyncd.conf.d/timesyncd.conf and modify options in /etc/systemd/timesyncd.conf.d/timesyncd.conf
• timedatectl timesync-status

ntp servers can be checked using the ntpdate command, which can be loaded in Debian with sudo apt install ntpsec-ntpdate

List of local ntp servers

chronyc can be used to query chronyd. The following are some key queries. Note chrony help will provide a list of available commands.

• sources -v will list information about the current sources
• tracking Display system time information
• nptdata display information about last valid measurement
• activity check how many NTP sources are online/offline
• serverstats Display statistics of the server
• authdata -v Display information about authentication

/etc/chrony/chrony.conf

# default config

=====docker chrony=====
++++Dockerfile|
<code>FROM alpine:latest

RUN apk update && \
apk --no-cache add \
chrony

EXPOSE 123/udp


#ENTRYPOINT [ "/bin/sh" ]
ENTRYPOINT [ "/usr/sbin/chronyd", "-d" ]
#ENTRYPOINT [ "/usr/sbin/chronyd", "-d", "-s" ]

docker-compose.yml

---
services:
  chrony:
    build: ./
    image: chrony:latest
    tty: true
    stdin_open: true
    container_name: chrony
    restart: 'always' # always | unless-stopped | no | on-failure [:max-retries]

#    volumes:
#      - '/mnt/docker_store/kea/.config:/app/'
#      - '/mnt/docker_store/kea/.config/log:/var/log/kea'
#    network_mode: host

    cap_add:
      - SYS_TIME

#    command: /bin/sh

• docker exec -ti chrony /bin/sh to get shell access to container

pool pool.ntp.org iburst initstepslew 10 pool.ntp.org driftfile /var/lib/chrony/chrony.drift rtcsync cmdport 0</code>++++

• STRATUMS IN THE NTP PROTOCOL: Understanding the hierarchy of servers
• chrony
• cturra/ntp (crony docker example)
• How to Install and Use Chrony in Linux
• configuring-ntp-server
• Arch chrony
• Steps to configure Chrony as NTP Server & Client (CentOS/RHEL 8)
• How to serve the Network Time Protocol with Chrony
• The Essential Guide to Using Chrony for NTP on Linux