According to https://github.com/rstudio/shiny-server/wiki/Building-Shiny-Server-from-Source , the executable file is located at /usr/local/shiny-server/bin/shiny-server and we made a link to /usr/bin/shiny-server. This is why, I think the service should execute /usr/bin/shiny-server instead of /opt/shiny-server/bin/shiny-server
According to https://github.com/rstudio/shiny-server/wiki/Building-Shiny-Server-from-Source , the executable file is located at /usr/local/shiny-server/bin/shiny-server and we made a link to /usr/bin/shiny-server. This is why, I think the service should execute /usr/bin/shiny-server instead of /opt/shiny-server/bin/shiny-server