Running a Linux Web Server on an Android device

Summary

With the GnuRoot program, it's possible to run a linux operating system on Android without "rooting" the device. With this ability, servers like Sinatra, Rails, Node, etc. can run webapps on localhost. With the help of a NPM library called localtunnel, it's possible to expose the local server to the broader internet.

Step 1: Make sure there is available hard drive space

There should be at least 1GB of available hard drive space to store the Linux OS. It is also possible to install to an SD card, but I didn't try it because the performance is inferior.

Step 2: Install GnuRoot Debian

Download GnuRoot Debian on the play store. It's a 60 MB download.

Step 3: Install Linux

Open the program and click "install/reinstall". This will compile and install the Linux operating system. Once the installation is finished, the GnuRoot program will close.

Note on some buggy UI stuff

Note that the GnuRoot app has a little bug where the terminal window doesn't show up after it's been backgrounded and re-opened. When re-opening the app after backgrounding it, get back to the terminal by pressing the back button. If the installation screen is just black (empty), that means the installation is complete

Step 4: Setup Linux environment

Open the GnuRoot app, and switch to the "launch" tab. Click "launch" to start the terminal.

The first thing you should run is

apt-get update

This updates the package list, which is needed to install programs.

It's probably a good idea to also run apt-get upgrade at this point, which will make sure the OS is up-to-date with the last fetched package list.

Next,

apt-get install build-essential

This installs tools for the C language and is required to install many other programs.

Installing is easy enough. Run

apt-get install ruby ruby-dev

This sets up the ruby, irb, and gem commands.

Next, install Sinatra, which is the simple web server I'll use. Optionally run

echo "gem: --no-document" >> .gemrc

to prevent gems from installing documentation (which takes forever). Install Sinatra with

gem install sinatra

Next install NodeJs with

apt-get install nodejs

One might alternatively use a PPA for this, but for simplicity's sake this tutorial just uses the standard package. Some libraries will expect a binary called node, but on linux it is actually called nodejs. To preempt these errors, run

ln -s /usr/bin/nodejs /usr/bin/node

Which will let node be used as an alias for nodejs.

Next, install NPM, the package manager for Node, with

apt-get intall npm

Finally, install localtunnel with

npm install -g localtunnel

Step 5: Write & run web server

Start by writing instructions for a simple webserver. Run

echo "require 'sinatra'; get('/') { 'hello world' }" >> app.rb

Run the web server with ruby app.rb &. The ampersand will background the process.

Run the localtunnel listener with lt --port 4567. After a few seconds, a url will be printed. Enter this url in any web browser to see "hello world" as a response.

Caveats

There is an issue with firewall and localtunnel. It only works for a few minutes. But then it exits with an error. See this thread for more info.