That error is system specific, I have never worked with RedHat but if systemctl doesn't work for you, try with this other command for checking the status of your shiny-server
/sbin/service shiny-server status
That error is system specific, I have never worked with RedHat but if systemctl doesn't work for you, try with this other command for checking the status of your shiny-server
/sbin/service shiny-server status