busybox 1.36.1 is currently failing to build across all architectures in Ubuntu [1] due to the removal of the CBQ (class based queue) headers from the current kernel in [2]. I've worked around this temporarily by simply patching the defines back in, in a compatibility header (see debdiff in [3]) but I'd guess a more permanent solution is desired? [1]: https://launchpad.net/ubuntu/+source/busybox/1:1.36.1-6ubuntu2/+build/28036868 [2]: https://github.com/torvalds/linux/commit/33241dca486264193ed68167c8eeae1fb197f3df [3]: https://bugs.launchpad.net/ubuntu/+source/busybox/+bug/2062414