When I try to start airmon-ng, I get the following output
# airmon-ng start wlan0 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 993 avahi-daemon 994 NetworkManager 999 avahi-daemon 1539 wpa_supplicant 4568 dhclient Process with PID 4568 (dhclient) is running on interface wlan0 Interface Chipset Driver wlan0 Broadcom b43 - [phy0]
When I kill those processes with
kill -9 993 994 999 1539 4568
it doesn't help. airodump-ng and aireplay-ng won't work.