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My laptop Lenovo T400 lost its wireless connection and couldn't detect the available wireless networks, immediately after I moved my laptop from one desk to another. I am not sure if moving it physically is the reason, but occasionally it is followed by losing wireless connection and detection.

I tried the following ways that I know to restart the wireless network card but couldn't make it work:

# 1st way
$ sudo ifdown wlan0
ifdown: interface wlan0 not configured
$ sudo ifup wlan0
Ignoring unknown interface wlan0=wlan0.

# 2nd way
$ sudo ifconfig wlan0 down
$ sudo ifconfig wlan0 up
SIOCSIFFLAGS: Operation not possible due to RF-kill

# 3rd way
$ sudo /etc/init.d/networking restart
 * Reconfiguring network interfaces...      [ OK ] 

I was wondering

  1. what the above three ways mean and how they differ from each other?
  2. Am I using them wrongly in order to restart my wireless network card and make it work?

Thanks and regards!

P.S. I have both Gnome network manager and WICD installed on my Ubuntu 10.10. But I have exited WICD, and it does not help.

Update: I followed the link The following command

$sudo lshw -C network

says my wlan0 is "Disabled", although it can find the wireless device wlan0 and gives information about it, such as the product name, vendor, phisal id, bus info, and clock frequency etc, which might suggests the wireless card is in place.

In such case, the link asks me to "Check that the device is on”:

Many wireless network devices can be turned on or off. Check to see if there is a hardware switch, some devices can be switched off from Windows and may need to be turned back on from Windows.

As I did not switch from Windows, I was wondering how I now check if there is a hardware switch? How can I turn my wireless network device on? Thanks!

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Could it be a hardware fault? Have you tried re-seating your wifi card, as it drops out occasionally when you move the system. – Matt Apr 6 '11 at 20:06
@Matt: Thanks! (1) I am not familiar with hardware. Is there some guide on how to open my laptop and identify my wifi card? (2) Meanwhile, are there some commands I can try to restart wifi card under Ubuntu? Are those I have tried relevant commands? Thanks! – Tim Apr 6 '11 at 20:24 page 105 on the pdf manual. Try Right click on Networking icon (nm-applet 0.6.6) in panel at top of screen; Untick Enable Networking; Right click on Networking icon... Retick Enable Networking; – Matt Apr 6 '11 at 20:35
I do not think the commands will help, try here starting with iwconfig… – Matt Apr 6 '11 at 20:50
@Matt: Thanks! (1) I followed the last link you gave, and found that my wlan0 is disabled. See my update to my post. So I guess I now need to turn my wireless device on and I wonder how? (2) just some more information: I have had the same problem before, and after reboot, the problem seemed go away. So I am not sure if my wifi card is not well seated. Thanks! – Tim Apr 6 '11 at 21:33
up vote 2 down vote accepted

I just found the solution. There is a hardware wireless switch in front of my laptop, which was switched off accidentally.

enter image description here

I hope this will be useful for others with similar problem. Thanks for all the helping!

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