ubuntu WiFi: operation not possible due to RF-kill《转载》

Some people have been experiencing WiFi problems with Ubuntu 10.10 since an update that happend just before Christmas 2010. The problem seems to be a bug in a kernel module, which prevents the rfkill's soft and hard block from syncing correctly.

In practice that means you can press your laptop's WiFi button as often as you want, it doesn't change anything. Your wireless adapter will always appear as disabled. If you try to start the wireless interface manually you get the following error message:

sk@ubuntu:~# sudo ifconfig wlan0 up
SIOCSIFFLAGS: Operation not possible due to RF-kill

If you do a rfkill list all you should get an output similar to this:

sk@ubuntu:~$ sudo rfkill list all
0: hp-wifi: Wireless LAN
Soft blocked: yes
Hard blocked: no
1: phy0: Wireless LAN
Soft blocked: yes
Hard blocked: no

Depending on the state of your WiFi button the Hard blocked will either be yes or no. Press the WiFi button and run rfkill list all again to make sure the value for Hard blocked changes.

The actual problem is, that the Soft blocked value is always set to yes, because for some reason the syncing between the hardware block and the software block doesn't work as supposed. To override this behavior, you can just run rfkill unblock wifi and it should work again. Double check by entering rfkill list all again and make sure it looks like this, with all values set to no:

sk@ubuntu:~$ sudo rfkill list all
0: hp-wifi: Wireless LAN
Soft blocked: no
Hard blocked: no
1: phy0: Wireless LAN
Soft blocked: no
Hard blocked: no

If you then run ifconfig wlan0 up (or enable the wireless via your desktop's network manager) you should be able to connect to a wireless network again without any further issues.

The configuration, which I've been using:

Compaq Presario CQ60
Atheros AR5001 Wireless Network Adapter
Ubuntu 10.10

I also read, that some people could fix it, by turning off the WiFi button during the boot process and then switch it on again, once the system is up and running. It seems that the system expects the hard block to be set to off. This is still a bug, but it could explain why then the soft block didn't sync with the hard block any more.

《FROM:http://blog.csdn.net/cat_lover/article/details/7088873》

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UBUNTU14.04也出现过同样的问题，按如上操作后重新启动电脑才能连接到WIFI。

操作步骤是这个的，首先按笔记本电脑的快捷键或开关关闭无线网，然后执行sudo rfkill list all---->ifconfig wlan0 up--->重启电脑。

查看网卡启用状态：

执行ifconfig -a 显示所有网卡信息，不加-a参数，只能查启用的网卡。
例如：网卡名 eth0
启用网卡命名 ifconfig eth0 up
禁用网卡命名 ifconfig eth0 down