Does Linux sends
init (PID 1 process) when it inherits orphaned zombie processes (processes that have not been reaped by its original parent)?
Yep. I tested it. And you can see where this happens in the Linux code.
Test: Start a nested shell. From elsewhere,
kill -s STOP the parent shell. Then
kill -s KILL the child shell and then the parent.
If you try this inside
gnome-terminal, for example, the reaper will not be PID 1. It will be a sub-reaper, the process
systemd handles signals using a signalfd. So when you run
strace -p on the systemd process, you will not see a signal being received. You will instead see that systemd wakes from epoll_wait() and performs a read() on a file descriptor.
You can confirm the file descriptor number is a signalfd using
ls -l /proc/<PID>/fd/<FD>. It will say