Merge pull request clearcontainers#595 from mcastelino/topic/docs

Docs: Add documentation for obtaining VM Kernel logs

docs/debug-kernel.md

@@ -0,0 +1,46 @@
+# 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.