What you need to know about the real-time capable edition of Ubuntu 22.04
Don't rush in if you don't need it – there may be more cons than pros
Canonical has made a Real-time edition of Ubuntu 22.04 available on x86 and Arm… but only to Ubuntu Pro customers, and there are some potential issues you should know about.
The new real-time edition was announced on Valentine's Day [insert joke about loving a more responsive computer here]. The beta version appeared last year, a couple of months after the launch of 22.04 "Jammy Jellyfish" that April. The difference from standard Ubuntu is that this version integrates the out-of-tree PREEMPT_RT patches into kernel 5.15.
Canonical will shortly hold an online seminar to explain the new product.
This new edition follows Intel's acquisition of the real-time kernel developers Linutronix in February last year. This resulted in new investment into the pre-emptible kernel project, whose first patches went into kernel 2.5.4 in 2002. Now bigger results are appearing, and they're not limited to Intel processors or even to x86: there is also an Aarch64 version of Real-time Ubuntu. For now, the PREEMPT_RT patches are not part of the mainline kernel, although Intel is working to get them included soon – so Ubuntu is pushing the technology curve a little here.
In one way, the timing is a little unfortunate for Canonical: the second update to Jammy, version 22.04.2, is expected next week, and that will have kernel 5.19 from Ubuntu 22.10. This means that if you opt for Real-time Ubuntu, your systems will be held back to the older kernel version. That isn't a big problem, though: as we covered when it was released, kernel 5.15 is a LTS release and its projected end-of-life date isn't until October.
For now, the different kernel is the main difference. This isn't a new flavor or remix or anything: it's the same Ubuntu (Desktop, Server, or Core) but with a different kernel built with the RT patches. All you need is an Ubuntu Pro subscription, which, as we've covered, has been free for single users with up to five machines since last October.
Just the kernel won't make your machine suddenly real-time. The company told us:
It is important to understand a real-time kernel on its own will not necessarily make a system real-time. The rest of the hardware and configuration has to be set up for it. It takes careful understanding and tuning of the overall real-time stack, from the underlying silicon to the operating system, to the networking layer, and applications.
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Our first thought was that if you're not building 5G base stations or something, an obvious use of this might be Ubuntu Studio, the special edition for creatives which includes music composition and sequencing tools. Ubuntu Studio uses the existing low-latency kernel, and as it happens, in 2020 the Ubuntu Studio project actually warns against RT kernels:
For desktop computer usage, using a real-time kernel can cause security nightmares.
You may also see issues if you need proprietary drivers that need kernel modules – there are known issues with the Nvidia binary graphics drivers, for instance.
While this is good to see, and despite the long history of the development of the real-time kernel, we'd suggest holding back for now, unless you have an urgent need for real-time support – and keeping Real-time Ubuntu away from general-purpose desktops and servers. ®