归根到底是ubuntu自带的network-manager太糟糕了！

1. check whether the device is recognized

      lspci | grep -i net
      [03:00.0 Network controller: Qualcomm Atheros AR9485 Wireless Network Adapter (rev 01)
      04:00.2 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit       Ethernet Controller (rev 0a)]
    2.  replace NetworkManager with wicd
       sudo apt-get install wicd
       sudo apt-get purge network-manager
       sudo /etc/init.d/wicd start
    3. install latest wireless net drivers
          download latest backports-3.10.17-1 from https://www.kernel.org/pub/linux/kernel/projects/backports/stable/3.10.17/
          unzip and cd into backports-3.10.17-1
          make defconfig-ath9k    //as my driver's AR9485
          make defconfig-ath9k install
          sudo modprobe ath9k
          add a file: sudo gedit /etc/modprobe.d/ath9k.conf
          add this in the new file: options ath9k nohwcrypt=1
          reboot
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4 . sudo rm -r /etc/NetworkManager //可选，慎用
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