>> root 17606 1 0 21:26 pts/9 00:00:00 idled Reply to myself, master sends Term signal to all process group, including idled, although ppid is 1.
Problem here was that idled was being launched by root. So sending it a signal from cyrus user will not work. Looking into code, I needed to add libcap "--with-libcap" to configure and recompile. This makes become_cyrus success before START section and idled being launched now by cyrus user.
