One of my "favorite" corner cases caused by systemd was that if an NIS user tried to login to the system, it would cause my X session to restart:
1. They changed the defaults for systemd-logind to disallow network access
2. When systemd-logind attempts to send a message to the NIS server, it instead hangs (or has a timeout greater than the systemd watchdog anyways)
3. The watchdog timer causes all systemd-logind services to be restart, which then tears down all of the child processes. My X session is a child process.
1. They changed the defaults for systemd-logind to disallow network access
2. When systemd-logind attempts to send a message to the NIS server, it instead hangs (or has a timeout greater than the systemd watchdog anyways)
3. The watchdog timer causes all systemd-logind services to be restart, which then tears down all of the child processes. My X session is a child process.