The kernel is built automatically by the CI from the [linux kernel sources](https://mirrors.edge.kernel.org/pub/linux/kernel/v5.x/) version 5.4, using the latest kernel version for which a [real time patch](https://mirrors.edge.kernel.org/pub/linux/kernel/projects/rt/5.4/) is available. For more information on how the kernel is built, please review the `compile.bash` script.
It's `config` file is based on the config provided by a Unbuntu Bionic installation with two changes:
- The `preemption model` ist set to `Fully Preemptible Kernel (RT)`.
-`Compile the kernel with debug info (DEBUG_INFO)` is set to `no`.
Before the build, if the new kernel version contains new config keys, the corresponding values are set to their defaults.
## Installation
-**⚠ ATTENTION** Make sure secureboot is disabled. Currently, the compiled kernel is unsigned and thus, will not work with secureboot.
-**⚠ ATTENTION** The repository does not contain the kernel packges, they are built by the CI and and can be downloaded.
-[Download the latest kernel packages built by the CI](https://git-st.inf.tu-dresden.de/ceti/realtime-kernel/-/jobs/artifacts/ci/browse?job=build-kernel).
- Install the packages using `dpkg -i`.
## Verifying that the Realtime Kernel is Running
- Reboot after kernel installation, selecting the new kernel in the boot loader.
- Run `uname -a`, the result should contain the kernel version number from the installed `deb` package as well as `PREEMPT RT`.
## Set User Permissions
- Add a group named realtime and add the user controlling your robot to this group:
```
sudo addgroup realtime
sudo usermod -a -G realtime $(whoami)
```
- Add the following limits to the realtime group in /etc/security/limits.conf:
```
@realtime soft rtprio 99
@realtime soft priority 99
@realtime soft memlock 102400
@realtime hard rtprio 99
@realtime hard priority 99
@realtime hard memlock 102400
```
- Log off and on again to let the group assignment and realtime priorities take effect (or, to be safe, restart). Use the command `groups` to check if the the current user belongs to the realtime group.
