Canonical has confirmed that there's a temporary restriction to its recently-released Ubuntu Server operating system images for the Raspberry Pi 4 single-board computer: They don't work on the 4GB RAM model, unless you restrict it to 3GB. The good news, though, is that a fix is in the works.
Canonical launched Ubuntu 19.10 "Eoan Ermine" last month, and brought with it native images for the Raspberry Pi 2, 3, and 4 families of single-board computers. Unfortunately, the company has found a bug in the Linux kernel which triggers only on the top-end Raspberry Pi 4 Model B with 4GB variant — and which prevents the USB ports from working.
"Due to a kernel bug, USB ports are not supported out of the box in the official arm64 image on the 4GB RAM version [of the Raspberry Pi 4]," Canonical's Galem Kayo explains. "Kernel fixes have been identified by Canonical engineers. We are currently testing these fixes extensively. We will push updates within weeks, following successful test completion."
At the same time, the company revealed its planned support roadmap for the Raspberry Pi family. "The Raspberry Pi has established itself as a most accessible platform for innovators in the embedded space," Kayo notes. "Canonical is dedicated to empowering innovators with open-source software. Consequently, Canonical endeavours to offer full official support for all the boards in the Raspberry Pi family. Canonical will therefore enable both Ubuntu Server and Ubuntu Core for existing and upcoming Pi boards," Ubuntu Core being the company's embedded Internet of Things variant of the Ubuntu Linux distribution.
For now, those running Ubuntu 19.10 on a Raspberry Pi 2, 3, or the 1GB and 2GB models of Raspberry Pi 4 need do nothing; anyone wishing to get up-and-running on the 4GB model will need to edit the file
/boot/firmware/usercfg.txt and insert the line:
While this will restore the USB ports to full functionality, it will also limit the Raspberry Pi 4 to using only 3GB of its available 4GB RAM. Once the kernel patch has been tested, merged, and distributed, all 4GB will be available at the same time as the USB ports.
More information is available on Kayo's blog post.