Here an Ubuntu related example for
/etc/hostapd/hostapd.conf
# Lose the comment after its line
ssid=MY_SSID
interface=wlan0 # The interface name of the card
driver=hostap # The card driver
macaddr_acl=0
accept_mac_file=/etc/hostapd.accept
deny_mac_file=/etc/hostapd.deny
ieee8021x=1 # Use 802.1X authentication
wep_key_len_broadcast=13
wep_key_len_unicast=13
wep_rekey_period=300 # WEP rekeying interval
own_ip_addr=10.10.10.100 # The interface IP
nas_identifier=some_name
auth_server_addr=127.0.0.1 # Where is the radius server
auth_server_port=1812 # The port the radius server runs on
auth_server_shared_secret=supersecretradiuskey # This is used to authenticate the hostapd to the radius server so none can use your raduis server
acct_server_addr=127.0.0.1 # Where is the radius server
acct_server_port=1813 # Where the accounting port is (I think)
acct_server_shared_secret=supersecretradiuskey # Same as above