added a comment - - edited
<Rich> how will this be exposed to users ? what would be a one-sentence overview of how the runtime signal is passed ?
<asaveljevs> When you do "zabbix_server --runtime-control config_cache_reload", this process parses zabbix_server PID file to find out the parent Zabbix process. Signal SIGUSR1 along with some information is sent to the parent process. Parent process analyses the information and determines to which child process the same signal should be sent. Then the parent process sends SIGUSR1 to the configuration syncer process.