Today I put a usb drive to my raspberry pi to make a copy of the file. This is the first time I tried a usb. It pops up a window asking for authorization of root password. Don’t know the password, so tried the user Pi password “raspberry”. Of course it not work.
Actually we can change the root password with the following command.
sudo passwd root
Then input your password twice.
Use your new password to mount the USB.
It works perfectly.