I'm running KDE Neon which is Ubuntu 18.04 Bionic (LTS) with the latest KDE desktop packages on top of it.
Since upgrading to this from Xenial I have lost the ability for processes to survive SSH session disconnects... specifically nohup, tmux, screen, byobu and all their children are killed when disconnecting.
Here's a simple test to demonstrate the problem
# connect over ssh cd /tmp nohup watch date & ps -ef | grep watch # disconnect and reconnect ps -ef | grep watch # process is gone
I tried reverting tmux and byobu to older versions before discovering nohup was also effected. This leads me to believe that it's either SSHd config or systemd.
Apparently systemd decided to change it's default behaviour to nuke all users processes when a user disconnects some time ago. I tried to revert the behaviour by editing /etc/systemd/logind.conf and setting KillUserProcesses=no and then rebooting (service systemd-logind restart didn't work). It didn't work... I'm at my wits end.