WiFi country changed to US, how do I change it back?

Question

My EeePC running Ubuntu 14.04 suddenly didn't see my wireless network on channel 13 any more, about July 23 2014.

iw reg get says it's set to country US.

iw reg get on my other laptop running Ubuntu 12.04 and not updated for a while says country 00 and it works fine.

sudo iw reg set SE solves the problem but only until reboot, what is the correct way to fix this problem?

Solution

Set it permanently:

gksudo gedit /etc/default/crda

Use nano or kate or leafpad if you don't have the text editor gedit.

Change the last line to read:

REGDOMAIN=SE

Proofread carefully, save and close the text editor.