How to run hostap as a radius srever?

[why]

Hi, all. Can someone tell me how to run hostap as a radius srever? Thank you! Here is my conf:
eap_server=1
eap_user_file=/home/wlan/wlan/hostapd-0.7.3/hostapd/hostapd-ap.eap_user
ca_cert=/home/wlan/wlan/hostapd-0.7.3/hostapd/demoCA/newcerts/ca.crt.pem
server_cert=/home/wlan/wlan/hostapd-0.7.3/hostapd/demoCA/newcerts/server.crt.pem
private_key=/home/wlan/wlan/hostapd-0.7.3/hostapd/demoCA/newcerts/serverkey.prv
private_key_passwd=wlanwlan
#dh_file=/home/wlan/wlan/hostapd-0.7.3/hostapd/hostapd.dh.pem

radius_server_clients=/etc/hostapd.radius_clients
radius_server_auth_port=1812

I run "./hostapd ./hostapd-as.conf -B", but it says"Could not read interface as0 flags: No such device nl80211 driver initialization failed."
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