🥇Installation of ROS in IMG image of Ubuntu for a single-board computer

Introduktion

Recently, while working on my thesis, I encountered the need to create an Ubuntu image for a single-board computer with ROS already installed (Robot Operating System – the operating system for robots). In short, the thesis is dedicated to managing a group of robots. The robots are equipped with two wheels and three range finders. All of this is controlled from ROS, which runs on the ODROID-C2 board.

Robot Ladybug. Sorry for the poor quality of the photo

There was neither time nor desire to install ROS on each robot individually, which is why the need for a system image with ROS already installed arose. While browsing the internet, I found several approaches to how this could be done.
In general, all the solutions I found can be divided into the following groups.

Programs that create an image from a ready and configured system (Distroshare Ubuntu Imager, linux live kit, linux respin, systemback, etc.)
Projects that allow you to build your own image (yocto, linux from scratch)
Building an image manually (liveCD customization og the Russian equivalent, plus artikel på habr)

Using solutions from the first group seemed to be the simplest and most attractive option, but I couldn't create a live system image for ODROID. The solutions from the second group also didn't work for me due to a sufficiently high entry threshold. Manual building based on available tutorials also wasn't suitable, since there was no compressed file system in my image.
As a result, after coming across a video about chroot (chroot — change root, video link at the end of the post) and its capabilities, I decided to use it. I will describe my specific case of customizing Ubuntu for robotics developers.

Udgangsdata:

The entire process of modifying the image (except for writing to the SD card using balenaEtcher) was carried out in the Ubuntu 18.04 operating system.
The operating system I modified the build of – Ubuntu 18.04.3 mate desktop version.
The machine where the assembled system is supposed to run – ODROID-C2.

Preparing the image

Download the Ubuntu image for ODROID from den officielle hjemmeside
Unpack the archive
```
unxz –kv
```
Create a directory where we will mount the image
```
mkdir mnt
```
Determine the partition where the file system is located
```
file
```
Look for a partition with a file system in ext2, ext3, or ext4 format. We need the address of the beginning of the partition (highlighted in red in the screenshot):

Bemærkning. Filsystemets placering kan også ses ved hjælp af værktøjet parted.
Vi monterer billedet
```
sudo mount -o loop,offset=$((264192*512))  mnt/
```
Den nødvendige partition starter fra blok 264192 (dine tal kan variere), størrelsen af hver blok er 512 bytes, så vi ganger dem sammen for at få offsettet i bytes.
Gå ind i mappen med det monterede system og chroot ind i det
```
cd mnt/
sudo chroot ~/livecd/mnt/ bin/sh
```
~/livecd/mnt — den fulde sti til mappen med det monterede system
bin/sh — et shell (kan også erstattes med bin/bash)
Nu kan vi begynde at installere de nødvendige pakker og applikationer.

Installation af ROS

Jeg installerede den nyeste version af ROS (ROS Melodic) i henhold til den officielle tutorial.

Opdaterer pakkelisten

sudo apt-get update

Her stødte jeg på en fejl:

Err:6 http://deb.odroid.in/c2 bionic InRelease
De følgende signaturer var ugyldige: EXPKEYSIG 5360FB9DAB19BAC9 Mauro Ribeiro (mdrjr)

Den relaterer sig til, at nøglen til signaturen af pakkematerialet er udløbet. For at opdatere nøglerne indtaster vi:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys AB19BAC9

Forbereder systemet til installation af ROS

sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -sc) main" > /etc/apt/sources.list.d/ros-latest.list'

sudo apt-key adv --keyserver 'hkp://keyserver.ubuntu.com:80' --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654

sudo apt update

Installerer ROS
Desværre kunne jeg ikke installere desktop-versionen af ROS, så jeg installerede kun de grundlæggende pakker:
```
sudo apt install ros-melodic-ros-base
apt search ros-melodic
```
Bemærk 1. Under installationen opstod der nogle gange en fejl:
```
dpkg: error: failed to write status database record about 'iputils-ping' to '/var/lib/dpkg/status': No space left on device
```
Det blev rettet ved at rydde cachen for apt-værktøjet:
```
sudo apt-get clean; sudo apt-get autoclean
```
Bemærk 2. Efter installationen virker det ikke at source kommandoen:
```
source /opt/ros/melodic/setup.bash
```
for vi har ikke kørt bash, så det skal IKKE indtastes i terminalen.

Installerer nødvendige afhængigheder

sudo apt install python-rosdep python-rosinstall python-rosinstall-generator python-wstool build-essential

sudo apt install python-rosdep

sudo rosdep init
rosdep update

Sætter adgangsrettighederne
Da vi har chrooted ind og faktisk udfører alle handlinger som root i det samlede system, vil ROS også kun blive kørt med superbrugerrettigheder.
Ved forsøg på at køre roscore uden sudo opstår der en fejl:

Traceback (most recent call last): File "/opt/ros/melodic/lib/python2.7/dist-packages/roslaunch/__init__.py", line 230, in main write_pid_file(options.pid_fn, options.core, options.port) File "/opt/ros/melodic/lib/python2.7/dist-packages/roslaunch/__init__.py", line 106, in write_pid_file with open(pid_fn, "w") as f: IOError: [Errno 13] Permission denied: '/home/user/.ros/roscore-11311.pid'

For the error not to occur, we will recursively change the permissions of the user's home directory ROS. To do this, type:

sudo rosdep fix-permissions

Install the packages rviz and rqt

sudo apt-get install ros-melodic-rqt ros-melodic-rviz

De sidste detaljer

Exit from chroot:
```
sigreturn
```
Unmount the image
```
cd ..
sudo umount mnt/
```
We will pack the system image into an archive
```
xz –ckv1
```

All done! Now using balenaEtcher you can write the system image to the SD card, insert it into ODROID-C2, and you will have Ubuntu with ROS installed!

Links: