Code:
root@bt:~# ifconfig
eth0      Link encap:Ethernet  HWaddr 08:00:27:da:55:1d
          inet addr:10.0.2.15  Bcast:10.0.2.255  Mask:255.255.255.0
          inet6 addr: fe80::a00:27ff:feda:551d/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:3874 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2786 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:4498281 (4.4 MB)  TX bytes:262193 (262.1 KB)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:431 errors:0 dropped:0 overruns:0 frame:0
          TX packets:431 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:146286 (146.2 KB)  TX bytes:146286 (146.2 KB)

root@bt:~# iwconfig
lo        no wireless extensions.

eth0      no wireless extensions.

wmaster0  no wireless extensions.

wlan0     IEEE 802.11bg  ESSID:""
          Mode:Managed  Frequency:2.412 GHz  Access Point: Not-Associated
          Tx-Power=0 dBm
          Retry min limit:7   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          Link Quality:0  Signal level:0  Noise level:0
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0

root@bt:~# airmon-ng


Interface       Chipset         Driver

wlan0           Ralink 2573 USB rt73usb - [phy0]

root@bt:~# airmon-ng start wlan0


Found 1 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
6229    dhclient


Interface       Chipset         Driver

wlan0           Ralink 2573 USB rt73usb - [phy0]SIOCSIFFLAGS: No such file or directory

                                (monitor mode enabled on mon0)

root@bt:~# airmon-ng


Interface       Chipset         Driver

wlan0           Ralink 2573 USB rt73usb - [phy0]
mon0            Ralink 2573 USB rt73usb - [phy0]

root@bt:~# airodump-ng mon0
ioctl(SIOCSIFFLAGS) failed: No such file or directory
root@bt:~#
I use <<Back|Track on VirtualBox, thanks !