Fern must be run with root privileges:
Here is a step-by-step guide to troubleshooting and fixing this issue. 1. Check for Hardware Compatibility Kali Linux Fern Wifi Cracker No Wireless Interface Was Found
This creates a monitor interface like wlan0mon . Fern must be run with root privileges: Here
Or:
Sometimes, Kali’s Network Manager grabs hold of the Wi-Fi card, preventing Fern from switching it into Monitor Mode. You can clear these "zombie" processes using airmon-ng : sudo airmon-ng check kill Use code with caution. Kali Linux Fern Wifi Cracker No Wireless Interface Was Found