If you have not configured your LXC or VM to automatically start Calibre-Web or if you need to manually start Calibre-Web after it has stopped, you need to run this command (This may need to be modified to apply to where you installed Calibre-Web on your LXC.)

nohup /opt/calibre-web/venv/bin/cps

Information about installing Calibre-Web including on how to configure your LXC or VM to automatically start Calibre-Web can be found at Install Calibre Web in a Container