Hola, he tenido algunos problemas para poner a mi tarjeta en modo monitor. He usado el comando

# sudo airmon-ng start wla0(interface) y me aparece este mensaje.

Found 5 processes that could cause trouble.
If airodump-ng, aireplay-ng or airtun-ng stops working after
a short period of time, you may want to kill (some of) them!

PID Name
894 avahi-daemon
895 avahi-daemon
919 wpa_supplicant
3816    dhclient
3917    NetworkManager
Process with PID 3816 (dhclient) is running on interface wlan0


Interface   Chipset     Driver

wlan0       Atheros     ath5k - [phy0]


Help please :)