[Gentoo]bind named could not configure root hints from 'named.ca': file not found

bind named could not configure root hints from 'named.ca': file not found

/etc/bind/ 下面有沒有named.ca這個file 
沒有 

dig @a.root-servers.net . ns > named.ca

/etc/init.d/named restart
還是error

在/var/bind下
cp named.cache named.ca
/etc/init.d/named restart
成功。