Real-time Linux Playground

This repo contains experimental code to play with Real-time Linux and other RTOS.

Ubuntu

Real-time Ubuntu will be supported on LTS and interim versions. See https://documentation.ubuntu.com/real-time/en/latest/reference/releases/. The LTS versions have been created by Canonical merging the PREEMPT_RT patches into kernel. The latest interim version 25.04 (Kernel 6.14) does rely on fully merged PREEMPT_RT into kernel 6.12 (09/2024).

Note: Real-time Ubuntu requires a Ubuntu Pro subscription, which is available for free for personal use. See Ubuntu Pro.

Installation Ubuntu 24.04 LTS (Noble Numbat)

Ubuntu 24.04 LTS has been installed on an Parallels (20.3.1) VM (2 cores, 4 GB RAM, 64 GB disk) on a MacBook Pro M1 MAX (32 GB RAM).

• Create new VM of Parallels type "Ubuntu 24.04 ARM64" with defaults
• Install Parallel Tools Installation Agent
• Update all software packages

Note: I am aware that reliable stress and latency tests of Real-time capabilities should be done on bare metal, this VM was just used for simple development.

# check kernel version
# expected: 6.8.0-40-generic, 6.8.0-60-generic
uname -r

# make sure latest Ubuntu Pro client is installed
sudo apt update && sudo apt install ubuntu-advantage-tools
# attach your installation to your subscription
sudo pro attach <free-personal-token>
pro status

# enable real time
sudo pro enable realtime-kernel
One moment, checking your subscription first
No variant specified. To specify a variant, use the variant option.
Auto-selecting generic variant. Proceed? (y/N) y
The Real-time kernel is an Ubuntu kernel with PREEMPT_RT patches integrated.

This will change your kernel. To revert to your original kernel, you will need
to make the change manually.

Do you want to continue? [ default = Yes ]: (Y/n) y
Configuring APT access to Real-time kernel
Updating Real-time kernel package lists
Updating standard Ubuntu package lists
Installing Real-time kernel packages
Real-time kernel enabled
A reboot is required to complete install.

# a reboot is necessary
reboot

# check if Real-time kernel is installed
# expected: 6.8.1-1022-realtime
uname -r

Installation Ubuntu 25.04 (Plucky Puffin)

Ubuntu 25.04 has been installed on an Intel NUC8 (Intel Core i7 x 8, 64 GiB RAM, 1 TB SSD). Ubuntu is updated to latest packages.

# check kernel version
uname -r

# for interim versions, universe repo is needed. Not needed for LTS versions
sudo add-apt-repository universe
sudo apt update
sudo apt install ubuntu-realtime

# make sure latest Ubuntu Pro client is installed
sudo apt update && sudo apt install ubuntu-advantage-tools
# attach your installation to your subscription
sudo pro attach <free-personal-token>
pro status

# enable real time
# This seems to fail, even checking realtime feature does show "disabled"
# But after reboot it seems that realtime kernel has been installed
# Created bug for Canonical: https://github.com/canonical/ubuntu-pro-client/issues/3447
sudo pro enable realtime-kernel
One moment, checking your subscription first
Real-time kernel is not available for Ubuntu 25.04 (Plucky Puffin).
Could not enable Real-time kernel.

# After reboot it seems that realtime kernel has been installed
reboot

# check if Real-time kernel is installed
# expected: 6.14.0-1002-realtime
uname -r

Testing

Follow Ubuntu tutorial here: https://documentation.ubuntu.com/real-time/en/latest/tutorial/first-rt-app/.

Notes:

• All Ubuntu samples run as expected also in VM
• Samples require to be run as root using sudo as sched_setscheduler needs root privileges. Otherwise you will see in strace a failed call: sched_setscheduler(20759, SCHED_FIFO, [89]) = -1 EPERM (Operation not permitted)
• Thread sanitizer did not work reliably even with latest compilers (gcc13, clang TODO version here).
  • For more details see https://stackoverflow.com/questions/77850769/fatal-threadsanitizer-unexpected-memory-mapping-when-running-on-linux-kernels
  • A call with sudo sysctl vm.mmap_rnd_bits=28 can enable that temporarily on Linux, but is not persisted by default.
  • TODO test that on 25.04, with clang as well

TODO stress testing

Ubuntu Core

TODO after Ubuntu is working

References

Real-time Linux in general:

• https://wiki.linuxfoundation.org/realtime/start
• https://wiki.linuxfoundation.org/realtime/preempt_rt_versions
• https://www.linutronix.de/blog/A-Checklist-for-Real-Time-Applications-in-Linux
• Final merge commit

Ubuntu:

• https://ubuntu.com/real-time
• https://documentation.ubuntu.com/real-time/en/latest/
• https://documentation.ubuntu.com/real-time/en/latest/how-to/uc-image-creation/
• https://packages.ubuntu.com/source/plucky/linux-realtime
• https://ubuntu.com/pro/dashboard
• https://documentation.ubuntu.com/pro-client/en/latest/howtoguides/enable_realtime_kernel/
• https://ubuntu.com/blog/real-time-kernel-technical

C/C++ best practices:

• https://best.openssf.org/Compiler-Hardening-Guides/Compiler-Options-Hardening-Guide-for-C-and-C++.html