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Merge pull request #1473 from killerspaz/kernel-module-docs
Updating documentation around kernel modules
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Josh Curl
GitHub
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__pycache__
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@@ -1,29 +0,0 @@
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---
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title: DKMS
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layout: os-default
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---
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## DKMS
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DKMS is supported by running the DKMS scripts inside a container. To compile any kernel modules, you first need to [install the kernel headers]({{site.baseurl}}/os/configuration/kernel-modules-kernel-headers/). After kernel headers are enabled, they are installed in `/lib/modules/$(uname -r)/build`. To deploy containers that runs DKMS, you will need to ensure that you bind mount in `/usr/src` and `/lib/modules`.
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### Docker Example
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```
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# Installing Kernel Headers for Docker
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$ sudo ros service enable kernel-headers
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$ sudo ros service up kernel-headers
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# Run a container in Docker and bind mount specific directories to run DKMS
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$ docker run -it -v /usr/src:/usr/src -v /lib/modules:/lib/modules ubuntu:15.10 sh -c 'apt-get update && apt-get install -y sysdig-dkms'
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```
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### System Docker Example
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```
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# Installing Kernel Headers for System Docker
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$ sudo ros service enable kernel-headers-system-docker
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$ sudo ros service up kernel-headers-system-docker
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# Run a container in System Docker and bind mount specific directories to run DKMS
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$ sudo system-docker run -it -v /usr/src:/usr/src -v /lib/modules:/lib/modules ubuntu:15.10 sh -c 'apt-get update && apt-get install -y sysdig-dkms'
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```
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@@ -1,13 +1,81 @@
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---
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title: Loading Kernel Modules in RancherOS
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title: DKMS / Loadable Kernel Modules in RancherOS
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layout: os-default
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---
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## Loading Kernel Modules
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---
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## Dynamic Kernel Module Support (DKMS) / Loadable Kernel Modules (LKM)
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Kernel modules can be automatically loaded with the `rancher.modules` cloud-config field.
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To compile any Kernel Modules, you first need to [deploy the Kernel Headers]({{site.baseurl}}/os/configuration/kernel-modules-kernel-headers/).
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### DKMS
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DKMS is supported by running the DKMS scripts inside a *privileged* container.
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> To deploy containers that compiles DKMS modules, you will need to ensure that you bind-mount `/usr/src` and `/lib/modules`.
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> To deploy containers that run any DKMS operations (i.e., `modprobe`), you will need to ensure that you bind-mount `/lib/modules`.
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By default, the `/lib/modules` folder is already available in the console deployed via [RancherOS System Services]({{site.baseurl}}/os/system-services/built-in-system-services/), but not `/usr/src`. You will likely need to [deploy your own container](#docker-example) for compilation purposes.
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To learn more about Docker's privileged mode, or to limit capabilities, please review the [Docker Runtime privilege and Linux capabilities documentation](https://docs.docker.com/engine/reference/run/#/runtime-privilege-and-linux-capabilities).
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#### cloud-config Example
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```yaml
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myservice:
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image: ...
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privileged: true
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volumes:
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- /lib/modules:/lib/modules
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- /usr/src:/usr/src
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```
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#### Docker Example
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> For one-off operations, it's useful to use `--rm` to clean up containers when operations complete.
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```bash
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$ sudo system-docker run -it --rm --name dkms-install -v /usr/src:/usr/src -v /lib/modules:/lib/modules ubuntu sh -c 'apt-get update && apt-get install -y sysdig-dkms'
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```
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The same approach can be utilized with the User Docker Daemon, just replace `sudo system-docker` with `docker`.
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### LKM Dependencies
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In some situations, another Kernel Module might need loading prior to any module you're trying to add.
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In this example, we'll reference the `v4l2loopback` DKMS module, which requires probing `videodev` into the Kernel space and is not on any filesystem by default.
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First, you must enable `kernel-extras`, then `modprobe` your dependencies and subsequent modules:
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```bash
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sudo ros service enable kernel-extras
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sudo ros service up -d kernel-extras
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```
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This will overlay all the compiled modules into `/lib/modules/$(uname -r)` that are configured in the default RancherOS Kernel config.
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Now you are ready to add your Modules into the Kernel space:
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```bash
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sudo modprobe videodev
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sudo modprobe v4l2loopback
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```
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To see which modules are pre-built, you can either do a listing of all `.ko` (kernel object) files, or review the Kernel config:
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```bash
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find /lib*/modules/$(uname -r) -name *.ko | less
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#or
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zcat /proc/config.gz | less
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```
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For more information regarding modifying the Kernel, please review the [Custom Kernels]({{site.baseurl}}/os/custom-builds/custom-kernels/) documentation.
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### Auto-Loading Modules
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Kernel Modules can be automatically loaded with the `rancher.modules` cloud-config field.
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```yaml
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#cloud-config
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@@ -17,16 +85,56 @@ rancher:
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This functionality is also available via a kernel parameter. For example, the btrfs module could be automatically loaded with `rancher.modules=[btrfs]` as a kernel parameter.
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### Loading Kernel Modules via a System Service
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### Ubuntu-based Kernel Manipulation
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Privileged containers can load kernel modules. In RancherOS, the kernel modules are in the standard `/lib/modules/$(uname -r)` folder. If you want to be able to run `modprobe` from a container, you will need to bind mount the `/lib/modules` into your container.
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```yaml
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myservice:
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image: ...
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privileged: true
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volumes:
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- /lib/modules:/lib/modules
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For images that are or derive from Ubuntu, you will need some small packages for `depmod`(`kmod`) and `modprobe`(`module-init-tools`):
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```bash
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sudo apt-get install kmod module-init-tools
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```
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By default, the `/lib/modules` folder is already available in the console.
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Most packages should already list these as dependencies in Aptitude, as well as `gcc` and related libs for packages that require compilation (which is most).
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### Troubleshooting
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Messing around with the Kernel can be tricky, so here's some common issues:
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#### kernel source for this kernel does not seem to be installed.
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Simply put, the Kernel Headers (or Source) cannot be found; enable them via the [Kernel Headers System Service]({{site.baseurl}}/os/configuration/kernel-modules-kernel-headers/).
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#### Operation not Permitted
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When inside a container, you might see similar to the following:
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```
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modprobe: ERROR: could not insert 'videodev': Operation not permitted
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```
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This is in reference to your container's privileges, not your user (i.e., `sudo` will not fix this).
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Instead, ensure you started the container with `--privileged` or the `cloud-config` setting described above.
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#### modprobe: ERROR: could not insert 'v4l2loopback': Unknown symbol in module, or unknown parameter (see dmesg)
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Again, using `v4l2loopback` as an example, but this can happen for any module.
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As stated, check out `dmesg` to see what the issue is. Chances are you'll see something like the following:
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```bash
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[ 322.734052] v4l2loopback: module verification failed: signature and/or required key missing - tainting kernel
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[ 322.734141] v4l2loopback: Unknown symbol video_ioctl2 (err 0)
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[ 322.734454] v4l2loopback: Unknown symbol v4l2_ctrl_handler_init_class (err 0)
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[ 322.734526] v4l2loopback: Unknown symbol video_devdata (err 0)
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[ 322.734563] v4l2loopback: Unknown symbol v4l2_ctrl_new_custom (err 0)
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[ 322.734599] v4l2loopback: Unknown symbol video_unregister_device (err 0)
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[ 322.734635] v4l2loopback: Unknown symbol video_device_alloc (err 0)
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[ 322.734696] v4l2loopback: Unknown symbol v4l2_device_register (err 0)
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[ 322.734732] v4l2loopback: Unknown symbol __video_register_device (err 0)
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[ 322.734765] v4l2loopback: Unknown symbol v4l2_ctrl_handler_free (err 0)
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[ 322.734796] v4l2loopback: Unknown symbol v4l2_device_unregister (err 0)
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[ 322.734828] v4l2loopback: Unknown symbol video_device_release (err 0)
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```
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This one can be trickier to evaluate, so start searching Google for symbol names to figure out which modules they derive from.
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In this example, `video_ioctl2` comes from `videodev` and can be simply inserted via the `kernel-extras` overlay described above.
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