Set wifi txpower from /etc/network/interfaces

Question

I am trying to configure my wifi to reliably connect at start-up on a headless device.

I currently have done this with a simple entry in /etc/network/interfaces, along the lines of

auto wlan0
iface wlan0 inet static
    wpa-ssid <my ssid>
    wpa-psk <my psk>
    address <address>
    netmaks <netmask>
    gateway <gateway>

Now I also need to set txpower (which also requires me to set the region (reg) as I understand it).

I can do this from the command line with iw reg set ... and iwconfig wlan0 txpower .... However, what I need is for these values to be reliably set on startup.

I have looked in what I believe is the documentation for configuring wifi in /etc/interfaces, which is /usr/share/doc/wpasupplicant/README.modes.gz, but this does not seem to have any information on setting transmit power.

How can I achieve this?

Answer 1

Try the up option described under "IFACE OPTIONS" here: http://manpages.ubuntu.com/manpages/precise/man5/interfaces.5.html

It, and similar options like pre-up, etc. allow you to execute arbitrary commands at various points during the configuration of your interface. So your /etc/network/interfaces might look like

auto wlan0
iface wlan0 inet static
    wpa-ssid <my ssid>
    wpa-psk <my psk>
    address <address>
    netmaks <netmask>
    gateway <gateway>

    # Command options with the same label (e.g. "up", "pre-up") are executed in the
    #  order in which they're specified.
    up iw reg set ...
    up iwconfig wlan0 txpower ...

    # If you have `rfkill` installed and want to disable (all) WiFi transmission
    #  while this interface is down.
    post-down rfkill wifi

You should also be able to use the option wireless-txpower ... since you have the wireless-tools (i.e. iwconfig) package installed, but I'm not sure how the sequencing of your commands would work in that case. Some (sparse) information on the wireless-[ ] options here: http://manpages.ubuntu.com/manpages/precise/man7/wireless.7.html