Jack itself uses a lot of CPU
I'm testing in Ubuntu 12.04, but I don't think that that can make any difference (?).
No it doesn't.
The current year is 2018 not 2012. Are you using a six year old distribution?
Yes. On purpose. For compatibility reasons, because anything you build on any Linux system uses the glibc from that system. And on any other distro that has an older glibc you can't run it. I am using the latest gcc compiler etc, so that's all new - and you yourself are at 14.04 which isn't the latest either
. But yes, this is on purpose. Best way to maintain compatibility over a large range of distro's. In fact, despite using this really old build environment I STILL had to make some changes (hacks, basically) to make things work in CentOS 6, which is still supported and used.