Easytether and Networkmanager

Easytether is a nice application you can use to tether your Android phone regardless of restrictions put in place by your carrier.  It consists of an app for the phone, as well as a program you run on your computer.  The two then talk to each other using the phone’s USB debugging abilities (ie, through ADB, which is integrated).  On the computer-side, Linux, Windows, and OS X are supported, and you can even use it with a Raspberry Pi.

I use this to occasionally tether my laptop, which runs Xubuntu.  On GNU/Linux, the PC-side application works by creating a tun (virtual) interface.  You start it from the command line like this ($ indicating the command prompt):

$ sudo easytether-usb

When I first did this (must have been a few years ago), Networkmanager would immediately detect the interface and manage it, so I didn’t really have to do anything else.  As soon as I started the program, I’d have a network connection.   This does not work with Xubuntu 16.04, however – the interface comes up, but I have to configure it manually.  No big deal, but now after running the above I have to do this:

$ sudo dhclient easytether-tap

Or this instead of dhclient, to do it manually:

$ sudo ifconfig easytether-tap 192.168.117.2
$ sudo route add default gw 192.168.117.1$ sudo sh -c ‘echo “nameserver 8.8.8.8” >> /etc/resolv.conf’

That works fine, but it’s kind of a pain.  Networkmanager is fairly capable these days, and it would be nice to make it do some of this for us again.  The reason it doesn’t is that, with the current version (1.2.0-0ubuntu0.16.04.2 on this machine), virtual interfaces that it didn’t create itself are ignored by default.  Luckily, there is a way we can make a new connection and automate things.  Unfortunately, this doesn’t seem to be possible with the panel applet in Xubuntu, but we can do it from the command line using nmcli.

In the above lines, easytether-tap is the default name of the virtual interface that the PC application creates.  First, let’s create a new connection named ‘phone’ that uses this interface.  Then, we’ll add a DNS server.  (Note that the below lines can be done as a normal user, no sudo needed.)

$ nmcli connection add ifname easytether-tap con-name phone type tun mode tap ip4 192.168.117.2 gw4 192.168.117.1
$ nmcli con mod phone +ipv4.dns 8.8.8.8

You could of course name it something other than phone.  Note that that configures the interface manually, which I just did for simplicity.  Also, 8.8.8.8 is Google’s public DNS, and you could substitute a different server IP.  Now, assuming you have easytether-usb started like in the first command in this post, you can bring the interface up like this:

$ nmcli connection up phone

And then bring it down like this:

$ nmcli connection down phone

And that’s it!  But, we still have to start easytether-usb when we plug the phone in.  It’s possible to automate that, too, using Networkmanager’s dispatcher scripts.  I created the following script, and saved it as 90easytether.sh:

#!/bin/bash

IFACE=$1
STATUS=$2

if [ “$IFACE” == “easytether-tap” ]
then
case “$STATUS” in
pre-up)
logger -s “Starting easytether-usb daemon”
easytether-usb
;;
down)
logger -s “Stopping easytether-usb daemon”
killall easytether-usb
;;
esac
fi

Now, move the script into the dispatcher.d directory, then change the ownership and permissions, and create a symlink to the script in the pre-up directory:

$ sudo mv 90easytether.sh /etc/NetworkManager/dispatcher.d/
$ cd /etc/NetworkManager/dispatcher.d
$ sudo chown root:root 90easytether.sh$ sudo chmod 755 90easytether.sh
$ cd pre-up.d/
$ sudo ln -s /etc/NetworkManager/dispatcher.d/90easytether.sh ./

Now, we need to start the dispatcher service, an enable it on boot:

$ sudo systemctl start NetworkManager-dispatcher.service
$ sudo systemctl enable NetworkManager-dispatcher.service

I also found I needed to restart Networkmanager itself:

$ sudo systemctl restart network-manager.service

Basically, that script is triggered by the pre-up and down actions, and starts and kills easytether-usb for us.  The symlink was necessary because Networkmanager needs anything that acts on this to be in the pre-up.d directory.  Now, you plug in your phone, then use the nmcli commands from above to bring the interface up and down, and that’s it!

One caveat: You need to be able to use USB debugging on your phone.  Also, you may have to confirm on your phone that you want to be able to connect from your PC or laptop first.  I also find that I have to mount my phone (IE, click on the icon on the desktop and browse to it in the file manager) before easytether-usb will connect.  Make sure you get Easytether working manually like at the beginning of this post, and you should be fine.  Have fun!

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