suid bit on an executable is ignored during boot process.
I have an executable /usr/local/bin/process_monitor which is owned by the user engineer.
I have set the SUID bit with chmod u+s. I have a scripts which calls this executable passing the required parameters. Upon bootup my script is called from another in /etc/rc5.d. Process_monitor and other processes it forks are ran as root. If I manualy execute this script from when logged in as root process_monitor is ran as engineer being the owner as expected.