Device shows up as ????? in ADB I am running Ubuntu on my computer and I plugged in my tablet to flash TWRP to it. I enter adb devices and here is the output:

juniorRubyist@juniorRubyist-iMac:~$ adb devices
List of devices attached 
????????????    no permissions

...


Why is it doing this. I have a Kindle Fire 1st Generation, it says that it will ask to authorize ADB, but it will not. It has ADB enabled (I think) and everything.
This is the same for me on Ubuntu. These commands should solve it:

sudo adb kill-server
sudo adb devices