## Using the XBox Controller with Ubuntu (the modern way)

If you want to get your Xbox One/ Xbox 360 running on ubuntu you basically have the choice between the in-kernel xpad driver and the userspace xboxdrv driver.

Most of the guides recommend using xboxdrv as xpad has been stagnating. However using xboxdrv has some disadvantages; as it runs as a daemon in userspace you have to manually take care of starting/ stopping it and giving your user access to the virtual devices it creates.
Xpad on the other hand just works as any other linux driver directly inside the kernel which is more  efficient and hassle free.

Fortunately while pushing SteamOS Valve has updated the xpad driver bringing it on par with xboxdrv:

• they added support for Xbox One Controller
• they fixed the communication protocol – no more blinking controller light

Update July 22, 2015

Unfortunately there are still several issues with the SteamOS driver. This follow-up post discusses them and the solutions in detail.

The bottom line is that I updated the official linux driver with chunks found in the SteamOS driver, as well as in several patches floating around the internet. Code and install instructions are available at Github.

## How to draw a line interpolating 2 colors with opencv

The build-in opencv line drawing function allows to draw a variety of lines. Unfortunately it does not allow drawing a gradient line interpolating the colors at its start and end.

However implementing this on our own is quite easy:


using namespace cv;

void line2(Mat& img, const Point& start, const Point& end,
const Scalar& c1,   const Scalar& c2) {
LineIterator iter(img, start, end, LINE_8);

for (int i = 0; i < iter.count; i++, iter++) {
double alpha = double(i) / iter.count;
// note: using img.at<T>(iter.pos()) is faster, but
// then you have to deal with mat type and channel number yourself
img(Rect(iter.pos(), Size(1, 1))) = c1 * (1.0 - alpha) + c2 * alpha;
}
}

## Introducing Sensors Unity

Sensors-Unity is a new lm-sensors GUI for the Unity Desktop. It allows monitoring the output of the sensors CLI utility while integrating with the Unity desktop. This means there is no GPU/ HDD support and no plotting.
If you need those you are probably better suited with psensor. However if you just need a overview of the sensor readings and if you appreciate a clean UI you should give it a shot.

Sensors Unity is available from this PPA

It is written in Python3 / GTK3 and uses sensors.py. You can contribute code or help translating via launchpad.

# Overview

In contrast to other applications the interface is designed around being a application. Instead of getting another indicator in the top-right, you get an icon in the launcher:

The idea is that you do not need the sensor information all the time. Instead you launch the app when you do. If you want to passively monitor some value you can minimize the app while selecting the value to display in the launcher icon.

To get the data libsensors is used which means that you need to get lm-sensors running before you will see anything.

However once the sensors command line utility works you will see the same results in Sensors-Unity as it shares the configuration in /etc/sensors3.conf.

# Configuration

Unfortunately configuring lm-sensors via /etc/sensors3.conf is quite poorly documented, so lets quickly recap the usage.

• /etc/sensors3.conf contains the configuration for all sensors known by lm-sensors
• however every mainboard can use each chip in a slightly different way
• therefore you can override /etc/sensors3.conf by placing your specific configuration in /etc/sensors.d/ (see this for details)
• you can find a list of these board specific configurations in the lm-sensors wiki
• to disable a sensor use the ignore statement
• #ignore everything from this chip
chip "acpitz-virtual-0"
ignore temp1
ignore temp2
• to change the label use the label statement
• chip "coretemp-*"
label temp1 "CPU Package"

## Sensors-Unity Specific Configuration

Sensors-Unity allows using the Pango Markup Language for sensor labels. For instance if you want “VAXG” instead of “CPU Graphics” to be displayed, you would write:

label in4 "V<sub>AXG</sub>"

In order not to interfere with other utilities and to allow per-user configuration of the labels/ sensors Sensors-Unity first tries to read ~/.config/sensors3.conf before continuing with the lm-sensors config lookup described above.

## introducing sensors.py

sensors.py is a new python wrapper for libsensors of the lm-sensors project. libsensors is what you want to use to programmatically read the sensor values of your PC with Linux instead of parsing the output of the sensors utility.

sensors.py is not the first wrapper – there are two alternatives, confusingly both named PySensors.

PySensors (ctypes) follows a similar approach to sensors.py by using ctypes. However instead of exposing the C API it tries to be a object-oriented(OO) abstraction, which unfortunately lacks many features and makes the mapping to the underlying API hard. Furthermore it does not support Python3.

PySensors (extension module)  does not use ctypes and thus is more efficient, but if you write a python script probably compiling a extension module is worse than losing some performance when reading the values.
Additionally there is python3 support and also some OO abstraction. The latter is somewhere in between the C API and proper OO: sensors_get_label(chip_name, feature) is ChipName.get_label(feature) instead of feature.get_label().

So what makes sensors.py immediately different is that it does not try to do any OO abstraction but instead gives you access to the raw C API. It only adds minor pythonification: you dont need to mess with pointers, errors are converted to exceptions and strings are correctly converted from/ to utf-8 for you.

However working with the C API directly is tiresome at times – therefore there is also an optional iterator API, which is best shown by a demo:

import sensors

sensors.init()

for chip in sensors.ChipIterator("coretemp-*"):

for feature in sensors.FeatureIterator(chip):
sfi = sensors.SubFeatureIterator(chip, feature)
vals = [sensors.get_value(chip, sf.number) for sf in sfi]
label = sensors.get_label(chip, feature)

print("\t"+label+": "+str(vals))

sensors.cleanup()

result:

coretemp-isa-0000 (ISA adapter)
Physical id 0: [38.0, 80.0, 100.0, 0.0]
Core 0: [37.0, 80.0, 100.0, 0.0]
Core 1: [35.0, 80.0, 100.0, 0.0]
Core 2: [38.0, 80.0, 100.0, 0.0]
Core 3: [36.0, 80.0, 100.0, 0.0]


for a more sophisticated example see the example.py in the repository.

## Replacing your desktop laptop with a ITX workstation

If you use your laptop as a desktop replacement, you will at some point get an external display and a mouse/ keyboard for more convenient usage.
At this point the laptop becomes only a small case of non-upgradable components.

Now you could as well replace your laptop by a real case of comparable size.  This will make your PC not only easily upgradable, but allow higher-end components while being more silent at the same time.

## Streaming the Screen on Android

In this post I want to discuss way of getting the screen content of your Android device to the TV or monitor. If you wonder why one might want to do such a thing – just think about playing some Android games with a bluetooth gamepad or watching a movie where your PC is not available.

Specifically I want to introduce SlimPort. SlimPort is a feature of Nexus devices which is unfortunately not covered much in reviews.
Basically SlimPort is DisplayPort over the Micro-USB connection of your device allowing you to mirror its display.

# But the future has arrived: we got Miracast!

One might wonder why one should go through the hassle of using a old-school HDMI cable.

# Building the program

To trigger a rebuild of the program simply execute

dpkg-buildpackage

To upload a package to a PPA you first need to sign it to prove that you are the author. To do this you have to execute the following in the <packagename><newversion> directory

debuild -S

sudo apt-get install dput

Now change to <somedir> and execute

dput ppa:<your_username>/<repository> <source.changes>

## Secure Owncloud setup

While the Owncloud Manual suggests enabling SSL, it unfortunately does not go into detail how to get a secure setup. The core problem is that the default SSL settings of Apache are not sane as in they do not enforce strong encryption. Furthermore the used default certificate will not match your server name and produce errors in the browser.

In the following a short guide in how to set-up a secure Apache 2.4 server for Owncloud will be presented.

## How to root Android using Ubuntu

update 26.02.2016 – instructions for Android 6 Marshmallow

# The Big Picture

Android consists of three parts relevant to rooting

2. recovery system
3. main system

typically only the main system is running, that is the Linux Kernel, the launcher, the phone app etc.. If we talk about rooting, that means we want to add an additional app to the main system which has access to secured parts of the system and acts as a gatekeeper for other apps that also want to get access.

The problem is the secured parts of the system are locked down – otherwise they would not be secure. This means that we can not simply install that app (e.g. an apk) from within the main system.

Therefore we have to go one level down. This is where the recovery system is. Typically you do not see it, as it is only active when the main system can not run – either because a system update is installed or because you do a factory reset.
As the recovery system can do a full system update, it means that it has also access to the secured parts of the main system – exactly what we need.
The stock recovery system obviously does not allow altering the main system – otherwise everybody could get your private date if you lose your phone.
So we need to replace it as well. But before that we have to talk about the bootloader.

The bootloader is a tiny piece of software which decides whether to start the recovery or the main system (or another main system, like Ubuntu Phone).
In the default configuration in only starts systems that it knows and trusts. In this configuration the bootloader is called locked.
Although this prevents malicious software to change the phone and spy on us, it also prevents us from replacing the recovery system. By the way, this concept is also coming to the PC where it is called UEFI secure-boot.

Here is a graphical overview of the Android components:

So what we need to do in order to get root access is

2. replace the recovery system
3. install a superuser app

Note that unlocking the bootloader also allows attackers to circumvent any of the android security features (PIN etc). It becomes possible to access all the files on the device using a different recovery system. (unless userdata is encrypted)
Therefore android will wipe all userdata when the bootloader state is changed from locked to unlocked.

So if you lose your unlocked device or it gets stolen, you better hope the thief is not tech savvy.

# Preparations

First you need to install the fastboot binary to be able to perform low-level communication with the device

apt-get install android-tools-fastboot

Next you have to allow non-root users to execute commands over USB, so you do not have to run fastboot as root. For this create the file

/etc/udev/rules.d/51-android.rules

with the following content

SUBSYSTEM=="usb", ATTR{idVendor}=="<VENDOR>", MODE="0666", GROUP="plugdev"

you can find the value for <VENDOR> on the page linked here.

Finally you have to reboot into fastboot mode. Usually there is a key combination you have to press on startup.

Remember this key combination as you will need some more times.

Samsung Devices however, like the Galaxy S3, do not support the fastboot mode – instead they have a download mode, which uses a proprietary Samsung protocol. To flash those you have to use the Heimdall tool. While this article does not cover the heimdall CLI calls, the general discussion still applies.

last warning: this will wipe all user data on the device

for google devices, like a Nexus 4 or Nexus 7 it is just do

fastboot oem unlock

if you have a Sony Xperia device, like a Xperia Z, you additionally have to request a unlock key and then do

fastboot oem unlock 0x<KEY>

where <KEY> is the key you obtained.

# Using AutoRoot to install SuperSU

There are several superuser apps to choose from for Android 4 and below. However the only superuser app working on Android 5/ Lollipop and above is SuperSU by Chainfire.

As there are devices like the Nexus 5X shipping with Android 6/ Marshmallow, I will describe this method first.

Chainfire created an “installer” called AutoRoot that includes the fastboot utility and will perform the unlocking step described above. However if you have read this far, you probably also want to understand the rest of the process.

fastboot boot image/CF-Auto-Root-hammerhead-hammerhead-nexus5.img

the command above will not flash anything on your device, but just upload the image and immediately start it. The image contains a script to modify the main system (change startup to get around SELinux) and install the superuser app.

If everything goes well, you can now just reboot your phone and you are done.

You could lock your bootloader again now to make your device more secure. However the next Android update will remove root again and repeating the rooting procedure will wipe userdata – so you have to balance security update vs. the risk of your device being stolen. For the latter case you still have the option to enable encryption of userdata though.

Android over the air (OTA) updates contain only the changes to the current system. In order to verify that the update succeeded Android computes a checksum of the patched system and reverts to the old state otherwise.

As SuperSU has changed the boot image to start itself, the updates obviously will fail. So to install an OTA update you will have to grab a factory image and restore the boot partition using the included boot.img

fastboot flash boot boot.img

after this you will have to patch the boot partition again using the procedure described above.

Also note that if you use apps that change the system partition (like AdAway that changes the hosts file), you will have to revert those changes as well in order for the OTA update to succeed.

# Optional: Replacing the Recovery System

If you want some advanced features, like backing up all your installed apks, you can permanently replace the recovery image on your device. However this will most likely prevent you from installing OTA updates.
There are two prominent alternative recovery systems with the ability to install apps

Clock Work Mod (CWM) is probably most known so we will use that one. From the Website linked above download the recovery image which fits your phone.
Here you have the choice between the ordinary recovery which uses the volume buttons of your device for navigation and the touch recovery which supports the touch screen.

fastboot flash recovery <RECOVERY>.img

where <RECOVERY> is the name of the file you downloaded. For instance for a Nexus 5 and CWM 6.0.4.5 it would be

fastboot flash recovery recovery-clockwork-6.0.4.5-hammerhead.img

## restoring stock recovery

If you have a Google Nexus Device, you can grab the factory images here.  There you will find a image of the stock recovery. You can restore it by

fastboot flash recovery recovery.img

# Alternative superuser apps

If you run a device with Android older than 5/ Lollipop you have some alternatives to SuperSU:

I would recommend getting Superuser by CWM, as it is open source and also nag-free as there is no “pro” version of it. There is even a pull-request which might make it also work with Android 5 in the future.

To install the app we need to get this zip archive and copy it to the device. Then we need to reboot into fastboot mode and then select “Recovery Mode” to get to the recovery system. Once in Recovery mode select

install zip -> choose zip from /sdcard

then browse and select the “superuser.zip” you just copied.

Once installed select

Go Back -> reboot system now

Once the system has started you should have a “Superuser” App on your device. Congratulations, you are done.