debug-kernel.md

Get cc-runtime Kernel logs

The cc-runtime launches a virtual machine when a new pod is created. This virtual machine (VM) uses a custom kernel inside the VM.

The kernel boot logs are disabled by default. However these logs may be desired when the kernel is customized by the end user, or if the virtual machine boot fails due to the kernel.

To provide a debug log of the kernel boot, Clear Containers supports an option to enable kernel boot logs using the configuration file.

1. Enable debug in configuration.toml

   $ enable_debug = true
   

2. Run a container to generate the logs

   $ sudo docker run -ti busybox true
   

3. Filter the kernel boot logs from the cc-proxy logs

   The cc-proxy logs show the sources of its collated information. To see the kernel boot logs, filter cc-proxy logs by the QEMU serial console. The QEMU serial console is represented by source=qemu.

   $ journalctl -u cc-proxy | grep source=qemu
   

4. Obtain logs using standalone cc-proxy

   In some cases it may be easier to run the cc-proxy standalone by first stopping the cc-proxy service and running it standalone to capture the logs.

   $ sudo systemctl stop cc-proxy
   $ sudo /usr/libexec/clear-containers/cc-proxy -log debug
   

   This will result in the cc-proxy log being printed on the terminal. This method can also be used to capture the logs in a specific cc-proxy file.

5. Connect to the Virtual machine console

   If the kernel boots successfully then the virtual machine console can be accessed for further debug.

   socat /run/virtcontainers/pods/<pod id>/console.sock