DisplayLink isn’t *quite* working in Ubuntu 21.04 (Hirsute)

[This article is obsolete, see the update here.]

Earlier, I wrote that the current DisplayLink release for Ubuntu was finally compatible with Ubuntu 21.04 (“Hirsute Hippo”). I’ve since learned that I wasn’t entirely correct.

It turns out that if you have a DisplayLink hub plugged into your Ubuntu 21.04 box when you boot it up, it works fine, but if you unplug the hub and plug it back in, it doesn’t recover, and as far as I can tell there’s no way to get it working again short of rebooting.

To fix this you have to revert to the 5.10 kernel that was released while Ubuntu 21.04 was in its beta-testing phase, before 21.04 switched to the 5.11 kernel.

Here’s a script to do that. Download this script, make it executable, run it as root, reboot, and then uninstall and reinstall the DisplayLink (to uninstall, run the installer with the argument “uninstall”).

	#!/bin/bash -e

	# You will probably need to adjust this script if you aren't using
	# the generic kernel.

	to_install=
	to_hold=
	pd=/tmp/packages.$$
	mkdir $pd

	# Get good Kernel packages

	while read package arch; do
	to_hold="$to_hold $package:$arch"
	if dpkg-query –show –showformat '${Package} ${Version} ${Status}\n' \
	$package:$arch 2>/dev/null \| grep -v deinstall \|
	grep -q -s '5\.10\.0-14\.15 '
	then
	continue
	fi
	deb_name="${package}_5.10.0-14.15_${arch}.deb"
	echo Downloading $deb_name
	curl –location –silent –output $pd/$deb_name \
	"https://launchpad.net/ubuntu/+archive/primary/+files/$deb_name"
	to_install="$to_install $pd/$deb_name"
	done < <(dpkg-query –show –showformat \
	'${Package} ${Architecture} ${Version} ${Source}\n' 'linux' \|
	awk '$4 == "linux" \|\| $4 == "linux-signed" {print $1, $2}' \|
	sed 's/-5\.[0-9.]-[0-9]/-5.10.0-14/' \| sort -u)

	# Get good Kernel meta-packages

	while read package arch version; do
	to_hold="$to_hold $package:$arch"
	if [ "$version" == "5.10.0.14.16" ]; then
	continue
	fi
	deb_name="${package}_5.10.0.14.16_${arch}.deb"
	echo Downloading $deb_name
	curl –location –silent –output $pd/$deb_name \
	"https://launchpad.net/ubuntu/+archive/primary/+files/$deb_name"
	to_install="$to_install $pd/$deb_name"
	done < <(dpkg-query –show –showformat \
	'${Package} ${Architecture} ${Version} ${Source}\n' 'linux' \|
	awk '$4 == "linux-meta" {print $1, $2, $3}')

	if [ -n "$to_install" ]; then
	apt-get install $to_install
	fi

	if [[ $(uname -r) =~ 5\.11 ]]; then
	echo
	echo "* NOTE NOTE NOTE *"
	echo
	echo "You need to reboot, select the 5.10 kernel during boot, and"
	echo "rerun this script."
	echo
	echo "Before rebooting, make sure GRUB_TIMEOUT is set to a non-zero value"
	echo "and GRUB_TIMEOUT_STYLE is set to 'menu' in /etc/default/grub, and if"
	echo "you have to change either of them, run 'sudo update-grub' before"
	echo "rebooting. Otherwise, you won't be able to easily select the 5.10"
	echo "kernel when you reboot."
	echo
	echo "* NOTE NOTE NOTE *"
	echo
	exit 1
	fi

	if [ -n "$to_hold" ]; then
	apt-mark hold $to_hold
	fi

	# Uninstalling the 5.11 kernel

	to_remove="$(dpkg-query –show –showformat \
	'${Package} ${Architecture} ${Version} ${Source} ${Status}\n' \
	'linux' \| grep -v deinstall \|
	awk '$4 == "linux" && $3 ~ /^5\.11/ {print $1 ":" $2}')"

	if [ -n "$to_remove" ]; then
	apt-get remove $to_remove
	fi

	rm -rf $pd