$ sudo usbtop
Error while capturing traffic from usbmon1: usbmon1: Can't open USB bus file /sys/kernel/debug/usbmon/1t: No such file or directory
Error while capturing traffic from usbmon2: usbmon2: Can't open USB bus file /sys/kernel/debug/usbmon/2t: No such file or directory
Error while capturing traffic from usbmon3: usbmon3: Can't open USB bus file /sys/kernel/debug/usbmon/3t: No such file or directory
Error while capturing traffic from usbmon4: usbmon4: Can't open USB bus file /sys/kernel/debug/usbmon/4t: No such file or directory
Error while capturing traffic from usbmon5: usbmon5: Can't open USB bus file /sys/kernel/debug/usbmon/5t: No such file or directory
Error while capturing traffic from usbmon6: usbmon6: Can't open USB bus file /sys/kernel/debug/usbmon/6t: No such file or directory
FATAL ERROR: couldn't open any USB buses with pcap. Did you load the usbmon module (sudo modprobe usbmon)?
You might also need to run this software as root.
It'd be nice to coalesced the above errors into one, as they have a single
well-known cause. The current spam is so long that an inattentive reader
might miss the modprobe suggestion (as I did).
But, as usbtop already needs root, why not just load the module yourself?
As reported in https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=906132 usbtop insists on manual loading of the usbmon module even when running as root: