Realtime Kernel for Ubuntu 18.4

These are deb packages built for Ubuntu Bionic. The packages are created following advice from Stackoverflow and the Panda manuals.

Information

The kernel is built automatically by the CI from the linux kernel sources version 5.4, using the latest kernel version for which a real time patch 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 is 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.

⚠️ ATTENTION The packages are designed for Ubuntu 18.4 only. While they may also work on newser versions of Ubuntu, we recommend to compile them yourself. You can use the provided shell script, which (using Ubuntu) reuqires the following packages build-essential curl bison flex bc rsync kmod cpio lsb-release libssl-dev. For increased compatibility, replace the config file provided here with a new configuration based on your system's current configuration. In this case, you must use a config tool like make menuconfig to set the preemption model to Fully Preemptible Kernel (RT). For more information, also consult Stackoverflow and the Panda manuals.

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 as individual files(https://git-st.inf.tu-dresden.de/ceti/realtime-kernel/-/jobs/artifacts/master/browse?job=build-kernel) as archive(https://git-st.inf.tu-dresden.de/ceti/realtime-kernel/-/jobs/artifacts/master/download?job=build-kernel).
• Install all three packages using sudo dpkg -i <package-file-name>.

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.