Real-Time Linux Foundation publishes list of real-time Linux projects
Variants
There are many groups spread around the world developing modifications to the Linux kernel in order to provide a real time operating system, either as hard, soft or firm real time.
Hard Real Time
Soft Real Time
Firm Real Time
If you want to make your variant available here, please write an email to Peter Wurmsdobler with the variant title, a description and a link to it.
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Hard Real Time
An operating system is considered to be hard real time if all time constraints imposed by the external world, so-called deadlines, are strictly met within a predefined tolerance, both for a priori deadlines which can be scheduled, and for sporadic deadlines such as interrupts, i.e. the worst case must be within the tolerance, e.g. a real time process is scheduled within a tolerance of 1ms any time when it ought to and the interrupt response time for any interrupt issued by a preselected device is less than 100us, too. This OS property is required for safety critical applications where missing a deadline has catastrophic consequences.
RT-Linux -- Real Time Linux
RT-Linux is the original hard real time Linux variant developed by Professor Victor Yodaiken at New Mexico Institute of Mining Technology. It patches the kernel to trap promiscuous disabling interrupts and replaces them with software macros under the direction of a real time executive.
Position papers for Real-Time Linux Workshops 2001 , 2000 and 1999 .
Official website is .
Services provided by FSMLabs and LynuxWorks .
Additional information.
RTAI -- Real Time Application Interface
RTAI is a non-conforming hard real time Linux variant utilizing the real time hardware abstraction layer concept and the same basic idea of disabling hard interrupts. It was developed by Professor Paulo Mantegazza at the Department of Aerospace Engineering at Milan Polytechnic.
Position papers for Real-Time Linux Workshops 2000 and 1999 .
Official website is .
Services provided by LINEO .
Additional information.
RedHawk Linux
RedHawk Linux is a real-time variant based on the Red Hat distribution. RedHawk achieves real-time performance by replacing the Red Hat kernel with a 2.4.18 based Linux variant that contains real-time performance enhancements that have been previously released in the open source world as well as new real-time enhancements developed by Concurrent. The kernel is fully-preemptable and has the low latency patches. CPU shielding is a new approach that allows certain processors in an SMP system to be designated as "shielded" from the background activity of Linux. High-priority real-time processes that execute on a shielded CPU have a guaranteed worst-case interrupt response time of less than 200 microseconds. The RedHawk kernel also supports modifications that allow the non-intrusive operation of Concurrent's NightStar real-time application development tool set.
Official website is
http://www.ccur.com/realtime/index.htm .
Services provided by Concurrent Computer Corporation .
Soft Real Time
An operating system is considered to be soft real time if all time contraints imposed by the external world, so-called deadlines, are met in a statistical sense, i.e the mean value of schedule time deviation is less than a predefined tolerance, e.g. a process is scheduled within a mean tolerance of 1ms, but it may happen, that sometimes the scheduling delay is bigger. This OS property is used for multimedia applications where missing a deadline has no catastrophic consequences.
Linux/RK -- The ressource kernel
Linux/RK is the portable Linux resource kernel developed by Professor Ragunathan Rajkumar at Carnegie Mellon. This variant supports quality of service with regard to CPU utilization, network bandwidth and/or disk bandwidth.
Position paper for Real-Time Linux Workshop 2000 and 1999 .
Official website is .
Services provided by TimeSys .
Additional information.
RED-Linux
RED-Linux is the real time and embedded Linux solution from Professor Kwei Jay Lin at the University of California. In this variant, the simple fixed priority scheduler is replace by a general scheduling framework offering fixed priority, rate monotonic and earliest deadline first schemes.
Position paper for Real-Time Linux Workshop 1999 .
Official website is .
Services provided by Redsonic .
Additional information.
SMART-Linux
SMART-Linux is adaptive kernel capable of reacting to system load and adapting real time behavior to guarantee quality of service. It was developed by Professor Dilma Silva at the University of Sao Paulo, Brazil.
Paper for Real-Time Linux Workshop 1999.
Official website is .
ART-Linux
ART-Linux is a Real-Time extension to Linux, developed by Youichi Ishiwata at ETL and is inspired by RT-Linux.
Official website is .
Additional information.
Linux-SRT
Linux-SRT is an extension to the Linux kernel which improves the performance of "soft real-time" applications such as in multimedia.
Official website is .
Additional information.
QLinux
QLinux is a Linux kernel implementation that provides Quality of Service (QoS) guarantees for "soft real-time" Linux performance in applications such as multimedia, data collection, etc.
Official website is .
Additional information.
Firm Real Time
This is a mixture of soft realtime and hard realtime.
KURT -- Kansas University Real Time
is the Kansas University firm real time variant developed by Professor Douglas Niehaus for ATM traffic solutions using a timing patch.
Paper for Real-Time Linux Workshop 1999 .
Official website is .
Additional information,
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