PREEMPT_RT Linux Kernel

To get good real-time performance on Linux, we recommend using a Linux kernel with the PREEMPT_RT patch. Unfortunately, this requires one to build the kernel from source (at least on Ubuntu). We provide some help for this in the following.

Note that this page only covers installation of the kernel, for further real-time-related configuration of the system see Real Time Setup.

Unfortunately, Nvidia does not support the PREEMPT_RT patch, so you may not be able to use Nvidia drivers (and thus also no CUDA) when using this kernel.

An alternative may be the “lowlatency” kernel. It is easier to install and works with Nvidia drivers but has weaker real-time capabilities (see Alternative: The Low Latency Kernel).

Install PREEMPT_RT Kernel

To install the patched kernel on Ubuntu, you may use our script install_rt_preempt_kernel.sh. It is tested for Ubuntu 18.04 but may also work with other recent versions.

Before running the script, you may want to modify it a bit, though:

• The VERSION_ variables at the top refer to the kernel version that will be installed. Usually you can leave the default values. See preempt_rt_versions for available versions in case you want to change it.

Then simply execute the script in a terminal. Internally, sudo is used in some steps, so the user executing it needs to have sudo-permission.

In the beginning (after downloading some things) you will be asked to manually adjust some configuration settings. Before entering the menu, the script prints the following instructions:

Please apply the following configurations in the next step:

General setup [Enter]
  Local version - append to kernel release: [Enter] Add '-preempt-rt'

General setup [Enter]
  Preemption Model (Voluntary Kernel Preemption (Desktop)) [Enter]
    Fully Preemptible Kernel (RT) [Enter] #Select

However, depending on the kernel version the “Preemption Model” setting may be found in the “Processor type and features” menu instead.

The script will automatically download, build and install the kernel. This will take a while.

Boot with the PREEMPT_RT Kernel

Once the PREEMPT_RT kernel is installed, you need to reboot and select the “preempt-rt” kernel in the GRUB menu (go to “Advanced options for Ubuntu”, it should be listed there).

When the system is running, you can check which kernel is running with uname -a. It should print something containing “PREEMPT_RT”.

Select PREEMPT_RT Kernel by Default

You can configure GRUB to automatically select this kernel by setting GRUB_DEFAULT in /etc/default/grub. For this, first the identifier of the kernel needs to be determined. Open a terminal and run

cat /boot/grub/grub.cfg | grep -w -e menuentry -e submenu

It should print something like this:

menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-1a26991b-b045-48dd-bb12-064a2725b80b' {
submenu 'Advanced options for Ubuntu' $menuentry_id_option 'gnulinux-advanced-1a26991b-b045-48dd-bb12-064a2725b80b' {
    menuentry 'Ubuntu, with Linux 5.4.93-rt51-preempt-rt' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-5.4.93-rt51-preempt-rt-advanced-1a26991b-b045-48dd-bb12-064a2725b80b' {
    menuentry 'Ubuntu, with Linux 5.4.93-rt51-preempt-rt (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-5.4.93-rt51-preempt-rt-recovery-1a26991b-b045-48dd-bb12-064a2725b80b' {
    menuentry 'Ubuntu, with Linux 5.4.0-65-generic' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-5.4.0-65-generic-advanced-1a26991b-b045-48dd-bb12-064a2725b80b' {
    menuentry 'Ubuntu, with Linux 5.4.0-65-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-5.4.0-65-generic-recovery-1a26991b-b045-48dd-bb12-064a2725b80b' {

For GRUB_DEFAULT the path full submenu/menuentry is needed, using the id of each step (the last part in the line, “gnulinux-…”), separated by “>”. In this specific case, the setting for starting the rt-kernel would be:

GRUB_DEFAULT = "gnulinux-advanced-1a26991b-b045-48dd-bb12-064a2725b80b>gnulinux-5.4.93-rt51-preempt-rt-advanced-471e9718-013f-4cbb-91a7-d22635173b70"

After saving the changes in /etc/default/grub you need to run the following command for the changes to become active:

sudo update-grub

Then reboot and verify that the correct kernel is used.