conmon-v3

An OCI container runtime monitor.

Conmon is a monitoring program and communication tool between a container manager (like Podman or CRI-O) and an OCI runtime (like runc or crun) for a single container.

Upon being launched, conmon (usually) double-forks to daemonize and detach from the parent that launched it. It then launches the runtime as its child. This allows managing processes to die in the foreground, but still be able to watch over and connect to the child process (the container).

While the container runs, conmon does two things:

• Provides a socket for attaching to the container, holding open the container's standard streams and forwarding them over the socket.
• Writes the contents of the container's streams to a log file (or to the systemd journal) so they can be read after the container's death.

Finally, upon the containers death, conmon will record its exit time and code to be read by the managing programs.

Written in Rust and designed to have a low memory footprint, conmon is intended to be run by a container managing library. Essentially, conmon is the smallest daemon a container can have.

In most cases, conmon should be packaged with your favorite container manager. However, if you'd like to try building it from source, follow the steps below.

Run Podman with conmon-v3

To test conmon-v3 on Fedora, CentOS or RHEL, do the following:

$ sudo dnf copr enable rhcontainerbot/podman-next
$ sudo dnf install conmon-v3
$ sudo dnf copr disable rhcontainerbot/podman-next

It is important to disable the copr repository after the installation, otherwise any future dnf update installs the latest unreleased versions of Podman and other tools.

To update conmon-v3 to latest version, enable the repository using the command line option:

$ sudo dnf --enablerepo=copr:copr.fedorainfracloud.org:rhcontainerbot:podman-next update conmon-v3

To switch Podman to conmon-v3, edit the /usr/share/containers/containers.conf and change the conmon_path option like this:

conmon_path = [
  "/usr/bin/conmon-v3"
]

To verify that Podman is really using the conmon-v3, run the podman info command like this:

$ podman info|grep conmon
  conmon:
    package: conmon-v3-3.0.0-1.20260324101217195131.main.fc43.x86_64
    path: /usr/bin/conmon-v3
    version: 'conmon version 3.0.0-dev, commit: <commit_hash>'

Dependencies

These dependencies are required for the build:

Fedora, CentOS, RHEL, and related distributions:

sudo yum install -y \
  rust \
  make \
  cargo

Debian, Ubuntu, and related distributions:

sudo apt-get install \
  rust \
  make \
  cargo

Build

Once all the dependencies are installed:

make

There are three options for installation, depending on your environment. Each can have the PREFIX overridden. The PREFIX defaults to /usr/local for most Linux distributions.

• make install installs to $PREFIX/bin, for adding conmon to the path.

Note, to run conmon, you'll also need to have an OCI compliant runtime installed, like runc or crun.