About this container

This container runs OpenNTPD on Alpine Linux. More about NTP can be found at:

http://www.ntp.org

Running from Docker Hub

Pull and run -- it's this simple.

# pull from docker hub
$> docker pull cturra/ntp

# run ntp
$> docker run --name=ntp             \
              --restart=always       \
              --detach=true          \
              --publish=123:123/udp  \
              --cap-add=SYS_NICE     \
              --cap-add=SYS_RESOURCE \
              --cap-add=SYS_TIME     \
              cturra/ntp

Building and Running with Docker Compose

Using the docker-compose.yml file included in this git repo, you can build the container yourself (should you choose to). *Note: this docker-compose files uses the 3.4 compose format, which requires Docker Engine release 17.09.0+

# build ntp
$> docker-compose build ntp

# run ntp
$> docker-compose up -d ntp

# (optional) check the ntp logs
$> docker-compose logs ntp

Building and Running with Docker Engine

Using the vars file in this git repo, you can update any of the variables to reflect your environment. Once updated, simply execute the build then run scripts.

# build ntp
$> ./build.sh

# run ntp
$> ./run.sh

Configure NTP Servers

By default, this container uses CloudFlare's time server (time.cloudflare.com). If you'd like to use one or more different NTP server(s), you can pass this container an NTP_SERVERS environment variable. This can be done by updating the vars, docker-compose.yml files or manually passing --env=NTP_SERVERS="..." to docker run.

Below are some examples of how to configure common NTP Servers.

Do note, to configure more than one server, you must use a comma delimited list WITHOUT spaces.

# (default) cloudflare
NTP_SERVERS="time.cloudflare.com"

# google
NTP_SEVERS="time1.google.com,time2.google.com,time3.google.com,time4.google.com"

# alibaba
NTP_SERVERS="ntp1.aliyun.com,ntp2.aliyun.com,ntp3.aliyun.com,ntp4.aliyun.com"

Test NTP

From any machine that has ntpdate you can query your new NTP container with the follow command:

$> ntpdate -q <DOCKER_HOST_IP>

Here is a sample output from my environment:

$> ntpdate -q 10.13.13.9
server 10.13.13.9, stratum 3, offset 0.010089, delay 0.02585
17 Sep 15:20:52 ntpdate[14186]: adjust time server 10.13.13.9 offset 0.010089 sec

If you see a message, like the following, it's likely the clock is not yet synchronized.

$> ntpdate -q 10.13.13.9
server 10.13.13.9, stratum 16, offset 0.005689, delay 0.02837
11 Dec 09:47:53 ntpdate[26030]: no server suitable for synchronization found

To see details on the ntpd status, you can check with the below command on your docker host:

$> docker exec ntp ntpctl -s status
1/1 peers valid, clock synced, stratum 4

Here is how you can see a peer list to verify the state of each ntp server configured:

$> docker exec ntp ntpctl -s peers
peer
   wt tl st  next  poll          offset       delay      jitter
162.159.200.1 time.cloudflare.com
 *  1 10  3   26s   32s    -44088.078ms    14.829ms     2.924ms