chrony

packaged by Chainguard

Chainguard Container for chrony

Minimalist Wolfi-based image for chrony, an NTP client and server (chronyd and chronyc) that keeps the system clock synchronized.

Chainguard Containers are regularly-updated, secure-by-default container images.

Download this Container Image

For those with access, this container image is available on cgr.dev:

docker pull cgr.dev/ORGANIZATION/chrony:latest

Be sure to replace the ORGANIZATION placeholder with the name used for your organization's private repository within the Chainguard Registry.

Compatibility Notes

This image provides chrony, an implementation of the Network Time Protocol (NTP) written in C and licensed under the GNU General Public License v2.0. It tracks upstream chrony 4.9 and ships both chronyd (the daemon) and chronyc (the command-line control client).

The entrypoint is /usr/bin/chronyd with the default argument -d, which keeps the daemon in the foreground and logs to standard error. The default configuration file is /etc/chrony/chrony.conf.

The container starts as root because chronyd needs privileges to adjust the system clock and bind to port 123. After initialization, chronyd drops privileges to the chrony user (UID 65532). The state directory /var/lib/chrony is owned by that user; any volume mounted there must be writable by UID 65532.

This Chainguard build of chrony does not link an external crypto library, so NTS and SHA-2 based authentication are not available (-NTS -SECHASH).

Getting Started

To run chronyd as an NTP client that disciplines the host clock, grant the SYS_TIME capability:

docker run -d --name chronyd \
  --cap-add SYS_TIME \
  cgr.dev/ORGANIZATION/chrony:latest

To use your own configuration, mount it over the default and pass any arguments you need. Passing arguments replaces the default -d, so include it:

cat > chrony.conf <<'EOF'
pool pool.ntp.org iburst
driftfile /var/lib/chrony/drift
makestep 1.0 3
EOF

docker run -d --name chronyd \
  --cap-add SYS_TIME \
  -v "$PWD/chrony.conf:/etc/chrony/chrony.conf:ro" \
  cgr.dev/ORGANIZATION/chrony:latest -d -f /etc/chrony/chrony.conf

To run without modifying the system clock (for example, to serve time only or for testing), add -x:

docker run -d --name chronyd cgr.dev/ORGANIZATION/chrony:latest -d -x

To query the running daemon with chronyc:

docker exec chronyd chronyc tracking
docker exec chronyd chronyc sources -v

To validate a configuration file without starting the daemon:

docker run --rm -v "$PWD/chrony.conf:/etc/chrony/chrony.conf:ro" \
  cgr.dev/ORGANIZATION/chrony:latest -p -f /etc/chrony/chrony.conf

Configuration

Exposed ports

• 123/udp: NTP, when serving time to clients (requires an allow directive)
• 323/udp: chronyc command port on localhost

Volumes

• /var/lib/chrony: drift file and other persistent state. It must be writable by the chrony user (UID 65532).

Documentation and Resources

• chrony documentation
• chrony.conf reference
• chrony source (GitHub mirror)

What are Chainguard Containers?

Chainguard's free tier of Starter container images are built with Wolfi, our minimal Linux undistro.

All other Chainguard Containers are built with Chainguard OS, Chainguard's minimal Linux operating system designed to produce container images that meet the requirements of a more secure software supply chain.

The main features of Chainguard Containers include:

• Minimal design, without unnecessary software bloat
• Daily builds to ensure container images are up-to-date with available security patches
• High quality build-time SBOMs attesting to the provenance of all artifacts within the image
• Verifiable signatures provided by Sigstore
• Reproducible builds with Cosign and apko (read more about reproducibility)

For cases where you need container images with shells and package managers to build or debug, most Chainguard Containers come paired with a development, or -dev, variant.

In all other cases, including Chainguard Containers tagged as :latest or with a specific version number, the container images include only an open-source application and its runtime dependencies. These minimal container images typically do not contain a shell or package manager.

Although the -dev container image variants have similar security features as their more minimal versions, they include additional software that is typically not necessary in production environments. We recommend using multi-stage builds to copy artifacts from the -dev variant into a more minimal production image.

Need additional packages?

To improve security, Chainguard Containers include only essential dependencies. Need more packages? Chainguard customers can use Custom Assembly to add packages, either through the Console, chainctl, or API.

To use Custom Assembly in the Chainguard Console: navigate to the image you'd like to customize in your Organization's list of images, and click on the Customize image button at the top of the page.

Learn More

Refer to our Chainguard Containers documentation on Chainguard Academy. Chainguard also offers VMs and Libraries — contact us for access.

Trademarks

This software listing is packaged by Chainguard. The trademarks set forth in this offering are owned by their respective companies, and use of them does not imply any affiliation, sponsorship, or endorsement by such companies.