Probably video0 and video1 are listed persistently in udev. I mean the file named like /etc/udev/rules.d/*-android.rules (here I replaced some digits with "*"). Please try to clean this file from /dev/video* items. or you can try
sudo rm /dev/video0
sudo mv /dev/video1 /dev/video0
thanks for your reply.first,i check the /etc/udev/rules.d/* no file.beceuse i use ubuntu18.04 rootfs.
second,i try to sudo rm /dev/video*.then i plug in the usb camera,appear video2 node.
can you give me some advices,thanks!