debian squeeze kvm : /dev/net/tun operation not peritted

zswlb9999

(1)
sudo tunctl -t tap0 -u  peter
sudo chmod 666 /dev/net/tun

sudo ifconfig eth0 0.0.0.0 promisc
sudo ifconfig tap0 0.0.0.0 promisc

sudo brctl addbr br0
sudo brctl addif br0 eth0
sudo brctl addif br0 tap0
sudo ifconfig br0  192.168.2.8 up
sudo route add defaults gw 192.168.2.9   #网关可以上外网,
#至此可以ping局域网内的机器及网关
kvm -m 1024 -hda  /dev/sda5 -net nic  -net tap ifname=tap0  script=no -boot  c

提示:/dev/net/tun operation not peritted
ls -l /dev/kvm

crw-rw----  root:kvm  ,,,,,, /dev/kvm

ls -l /ev/net/tun
crw-rw-rw- 1 root kvm    /dev/net/run

运行完kvm -m 1024 -hda  /dev/sda5 -net nic  -net tap ifname=tap0  script=no -boot  c

提示:/dev/net/tun operation not peritted
即

ls -l /ev/net/tun
crw-rw-rw- 1 root kvm    /dev/net/tun

是哪里将  /dev/net/tun的2权限修改了?