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For an embedded usecase I want my Pi users to be able to temporarily "switch off" WLAN/Wifi. Does ifdown wlan0 only bring down the interface or does it also switch of the WLAN sender/receiver? What additional steps do I need to take in order to temporarily switch off wlan TX/RX completely?

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ifdown wlan0 prevents the OS from initiating any TX/RX operation on the interface. The RPi shouldn't be transmitting anything at this point, and you won't be able to scan for wireless networks until you bring the interface up again.

Depending on what you want to achieve, you may also want to disable Bluetooth, since WiFi and Bluetooth share the antenna and parts of the transceiver.

If you want to guarantee that no communication takes place (as much as you can guarantee something on a closed-source hardware), you'll have to disable WLAN and BT drivers in /etc/modprobe.conf and reboot:

#wifi
blacklist brcmfmac
blacklist brcmutil
#bt
blacklist btbcm
blacklist hci_uart

This will prevent the firmware from being uploaded into the adapter.

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    SInce I only need temporary switch-off -- kind of "flight mode" -- it should be sufficient for me to bring the interface down. – TheDiveO Aug 16 '17 at 9:59
  • To be really on the safe side, I'm now using rfkill block 0 to disable Wifi on the TX/RX level. – TheDiveO Aug 16 '17 at 10:05
  • @TheDiveO Good point about rfkill – Dmitry Grigoryev Aug 16 '17 at 10:56
  • The advantage of rfkill is (at least I think so) that it also works when the firmware alrady has been downloaded. – TheDiveO Aug 16 '17 at 10:59
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    @TheDiveO According to the manpage, ifconfig will attempt to disable reception if supported by the driver. I doubt rfkill can do anything in addition to that. – Dmitry Grigoryev Aug 16 '17 at 11:20

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