This OpenJDK implementation may require procfs(5) mounted on /proc for some
applications.
If you have not done it yet, please do the following:
mount -t procfs proc /proc
To make it permanent, you need the following lines in /etc/fstab:
proc /proc procfs rw 0 0
Reason:
Version JAVA_DEFAULT is updated from 8 to 21.
No specific action should be needed, just a heads-up to test before
deploying to production as this is quite a big step in versions.