I am using Ubuntu 16.04 and I have installed driver for External Wifi Adaptor of Model USB TP-Link TL-WN821N wireless adapter (Realtek rtl8192cu) by following the answers present In ubuntu 14.04, why does my internet connection keep disconnecting?. But this works fine for 14.04 while it doesn't works for 16.04 and I have used following command sudo add-apt-repository ppa:hanipouspilot/rtlwifi sudo apt-get update sudo apt-get install rtl8192eu-dkms rtlwifi-new-dkms linux-firmware and installed the driver, it works fine. But when I remove the external Wifi Adapter it says, server not found. It only works only after restarting the computer. Are there any solution ???