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3. Running VMs as systemd services

crun-vm also enables you to define a systemd service corresponding to a VM, and thus manage it through systemd. This relies on Podman's Quadlet feature, through which you can define systemd unit files for containers.

Tip

This means that system containers and VMs can both be deployed and managed using the same tooling, i.e., systemd!

Here, we overview how you can create Quadlet-powered systemd services to manage VMs. Make sure you have installed both crun-vm and Podman (see 1. Installing crun-vm).

Navigation
  1. Installing crun-vm
  2. Running VMs with Podman or Docker
  3. Running VMs as systemd services
  4. Running VMs in Kubernetes
  5. crun-vm(1) man page

Creating a systemd service for a VM

The easiest way to do this is using Podlet, a tool that can generate a systemd unit file corresponding to a given podman-run command. (Follow the instructions at https://github.com/containers/podlet to install Podlet.) This means we can apply it to the podman-run commands we use to launch VMs.

For instance, say you're using this command to launch a VM that runs a web service (see 2. Running VMs with Podman or Docker to learn how crun-vm can be used with Podman):

$ podman run --runtime crun-vm --detach -p 8000:80 quay.io/crun-vm/example-http-server:latest

To convert this invocation into an equivalent systemd container unit definition, you would run:

$ podlet \
    --install \
    --wanted-by default.target \
    podman run --runtime crun-vm --detach -p 8000:80 quay.io/crun-vm/example-http-server:latest
#example-http-server.container
[Container]
Image=quay.io/crun-vm/example-http-server:latest
PublishPort=8000:80
GlobalArgs=--runtime crun-vm

[Install]
WantedBy=default.target

The --install, --wanted-by default.target options configure the service to run automatically on boot.

Finally, to actually install this unit definition, you would instead run (using sudo to become root):

$ sudo podlet \
    --name my-web-service \
    --unit-directory \
    --install \
    --wanted-by default.target \
    podman run --runtime crun-vm --detach -p 8000:80 quay.io/crun-vm/example-http-server:latest
Wrote to file: /etc/containers/systemd/my-web-service.container

$ systemctl daemon-reload  # load the new service

With this, your web server VM becomes a systemd service:

$ sudo systemctl status my-web-service
○ my-web-service.service
     Loaded: loaded (/etc/containers/systemd/my-web-service.container; generated)
    Drop-In: /usr/lib/systemd/system/service.d
             └─10-timeout-abort.conf
     Active: inactive (dead)

$ sudo systemctl start my-web-service  # start the service without having to reboot

$ sudo systemctl status my-web-service
● my-web-service.service
     Loaded: loaded (/etc/containers/systemd/my-web-service.container; generated)
    Drop-In: /usr/lib/systemd/system/service.d
             └─10-timeout-abort.conf
     Active: active (running) since Tue 2024-04-30 21:14:36 WEST; 4s ago
   Main PID: 1531707 (conmon)
      Tasks: 48 (limit: 76805)
     Memory: 1.1G (peak: 1.1G)
        CPU: 11.768s
[...]

$ curl localhost:8000
<!DOCTYPE HTML>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Directory listing for /</title>
</head>
<body>
[...]

Further information

See this article for additional information on Podman Quadlet, and the podman-systemd.unit(5) man page for the reference format of container unit files.

The podlet commands provides several options to further customize the generated container unit file. Run podlet -h to know more.