Ad-Hoc Computer Lab

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Ad-Hoc Computer Lab

Ad-Hoc Computer Lab

1 Introduction

A computer lab is usually a classroom of 20-30 computers, connected to a switch that makes a LAN. These computers are usually managed with LTSP, which reduces the hardware costs and the time and efforts needed for installing and maintaining all of them.

What if there is no computer lab but all the students have laptops? Can we build a similar infrastructure, based on WiFi? Yes we can, and in this article we will see how.

What if the students are not located on the same classroom but are distributed all over the world? Can we offer them some centralized services and build a virtual classroom? There may be many ways of doing it but we will see just one.

2 There Is No Computer Lab

In some computer science departments there are no computer labs anymore. Instead, the students are required to bring and use their own laptops. Let's see how we can build some kind of infrastructure in this case.

We will use the laptop of the teacher as a server, so let's assume that it has at least 4GB RAM. Actually we will install the server on a VirtualBox machine, which is the most easy and the most flexible way.

Note: Installing the server on a virtual machine provides isolation and encapsulation, so that the configurations of the server do not mess with the configurations of the rest of the laptop. This way the laptop can be used for other purposes as well.

2.1 Build a Wi-Fi LAN

We need a Wi-Fi LAN, so that the laptops can communicate with the server. Often there is some Wi-Fi access point nearby. By connecting to it, laptops will be able to communicate with each-other as well. In this case we have nothing to do.

If there is no Wi-Fi access point that can be used, we can create one with smartphone (Android or iPhone) and connect all the laptops to it.

Another way is to start a hotspot on one of the laptops (for example on the laptop of the teacher). It can be done easily with a script, like this:

wget https://gitlab.com/Virtual-LTSP/VirtualBox/raw/bionic/hotspot.sh
chmod +x hotspot.sh
./hotspot.sh start

The script hotspot.sh basically just calls the command nmcli with propper arguments:

nmcli dev wifi hotspot ifname "$ifname" ssid "$ssid" password "$pass"

2.2 Install a VirtualBox LTSP Server

The most easy way to install a LTSP server on a VirtualBox machine is to use the Virtual LTSP scripts:

  • Install virtualbox and vagrant: apt install virtualbox virtualbox-qt vagrant
  • Get the scripts:
    git clone https://gitlab.com/Virtual-LTSP/VirtualBox ltsp
    cd ltsp/
    
  • Edit settings.sh and make sure to:
    • set *DEVELOPMENT="no"*
    • set *GATEWAY="no"*
    • set LAN_IF to the name of the Wi-Fi interface (check them with ip addr)
    • change ADMIN_PASS, GUEST_PASS, GUAC_PASS
    • optionally change HOSTNAME and the PACKAGES that need to be installed on the clients
    • optionally change VM_BOX and VM_RAM, if you want to change the base system, or to allocate more RAM to the virtual machine
    • Start the installation with: ./server.sh build It takes a lot of time to download images and to install packages, so be patient.

Use ./server.sh halt to stop the server and ./server.sh up to start it again. Or go to ltsp-server/ and use vagrant halt and vagrant up. You can use vagrant ssh as well, to login to the server, if needed.

2.3 Start a VirtualBox LTSP Client

Students can create on the laptop a VirtualBox machine that boots from the network as a LTSP client.

Here are the steps for building it manually:

  1. Create a new VirtualBox machine, with 1GB RAM and no virtual hard disk.
  2. On the Settings of this machine, go to System settings, select Network on the Boot Order: and uncheck the other options.
  3. On the Network settings select a Bridged Adapter, and on the list select the Wi-Fi network interface (something like wlp2s0b1). Use the command ip addr to figure out the names of the network interfaces.

This VirtualBox machine will boot from the LTSP server through the Wi-Fi network.

You can also use this script to create and start automatically a VirtualBox LTSP client: https://gitlab.com/Virtual-LTSP/VirtualBox/blob/bionic/scripts/ltsp-client.sh

wget https://gitlab.com/Virtual-LTSP/VirtualBox/raw/bionic/scripts/ltsp-client.sh
chmod +x ltsp-client.sh
./ltsp-client.sh --help
ip link
./ltsp-client.sh start -m 1024 -i wlp2s0b1

2.4 LTSP Scenarios

2.4.1 Screen Sharing With Epoptes

The teacher can use Epoptes to share (broadcast) his screen with the students, or to watch what they are doing and help them (monitor and assist): http://www.epoptes.org/screenshots

The username of the teacher should be added to the group epoptes in order to be able to use it: adduser username epoptes . Or you can create another admin user, which automatically is added to this group:

cd ltsp-server/
vagrant ssh
sudo su
cd /host/scripts/
./create-admin-account.sh username password

2.4.2 Manage Student Accounts

The script scripts/users.sh can be used to create, export, import, backup and restore user accounts. Try it like this:

cd ltsp-server/
vagrant ssh
sudo su
cd /host/
script/users.sh --help
script/users.sh create user-list.txt
script/users.sh backup
script/users.sh restore backup/users-20190113.tgz

This is useful when you need to create lots of accounts. Also, when you need to rebuild the virtual LTSP server, you can backup user accounts before doing it and restore them afterwards.

2.4.3 Install New Applications On The Clients

Usually you list the packages that should be installed on the client on the variable PACKAGES on settings.sh:

# List of extra packages that need to be installed on the client.
# For example: ubuntu-edu-preschool, ubuntu-edu-primary, etc.
PACKAGES="
  vim
  geany
  xfce4-terminal
"

However, often you need to install more packages (or to remove some) after the server has been built. In this case you have to make these customizations on the chroot directory and then rebuild the client image:

cd ltsp-server/
vagrant ssh

sudo su
rm /opt/ltsp/i386/etc/resolv.conf
ltsp-chroot -mr

apt update
apt upgrade
apt install emacs
exit    # from chroot

ltsp-update-image
systemctl restart nbd-server

2.4.4 Customize The Guest Accounts

On settings.sh there are these variables:

# If GUEST_ACCOUNTS is "yes" then guest accounts are created and
# a "Login as Guest" button is provided on the clients. Everything
# on a guest account will be reset on login.
#
# If GUEST_AUTOLOGIN is "yes", then the client will automatically
# login to a guest account as soon as it boots.
#
# The account GUEST_USER is used as a template (skeleton) for the
# guest accounts. You can login to this account in order to customize
# and tweak all the guest accounts.
GUEST_ACCOUNTS="yes"
GUEST_AUTOLOGIN="no"
GUEST_USER="guest"
GUEST_PASS="pass1"

If you login to and customize the account of GUEST_USER (for example change the background), this will be applied to all the guest logins.

2.4.5 Change The RAM Of The Server

You can easily increase or decrease the RAM of the VirtualBox LSP server like this:

  • Stop the server with: ./server.sh halt (or cd ltsp-server/ ; vagrant halt)
  • Edit settings.sh and change VB_RAM
  • Start the server with: ./server.sh up (or cd ltsp-server/ ; vagrant up)

The same also works for changing LAN_IF (the network interface that is connected to the LAN). However for changing the other settings you need to rebuild the server (with ./server.sh build). If you want to preserve the user accounts, make sure to backup them first, and restore them after the rebuild.

2.5 Install Guacamole

Guacamole allows desktop access to a server from a web browser. When you install a virtual LTSP server, Guacamole is installed as well. This is the section about Guacamole on settings.sh:

# Access the server from the web with Guacamole
# https://guacamole.apache.org/doc/gug/using-guacamole.html
# It can be accessed on: https://127.0.0.1/guac/
# Comment out to disable installing Guacamole.
GUAC_ADMIN="admin"
GUAC_PASS="pass1"
#VNC_PORT="5901"
#VNC_WIDTH="1024"
#VNC_HEIGHT="768"
#VNC_DEPTH="24"

However you can install it on any bionic server, without having to install LTSP and other related things. It can be done like this:

wget https://gitlab.com/Virtual-LTSP/VirtualBox/raw/bionic/scripts/install-guacamole.sh
chmod +x install-guacamole.sh
./install-guacamole.sh

2.6 Guacamole Scenarios

2.6.1 Access Account From A Browser

Any user that has an account on the server can access the desktop of the server from a web browser. He can do it like this:

  • Open https://12.34.56.78/guac/ on the browser. Here 12.34.56.78 is the IP of the server, most probably something like 192.168.0.xy, or 10.42.0.1 if you started a hotspot from the laptop.
  • Click on the button "Login" without a username and password.
  • Click on the RDP connection.
  • Give the username and password of the account.

Note: I have noticed that sometimes the firewall has a glitch, especially when a hotspot is started, which prevents the server from being accessed from the clients. When this happens, I try ufw disable and then ufw enable, and the problem goes away somehow.

2.6.2 Teacher Sharing His Screen With The Students

This is useful when the teacher wants to demonstrate to the students how to do something, for example how to write a program. Usually a projector is used to show the desktop of the teacher, but this is a nice alternative too, especially when there is no projector available.

To be able to share the screen of his account, the teacher should enter in Guacamole with the username student or admin (and the corresponding password). This is different from the case above, where he could login in Guacamole even without a username and password.

Then he should go to his account by clicking on the RDP connection and giving the username and password of his account. Afterwards he should follow these steps:

  • Press Ctrl+Alt+Shift to open the Guacamole panel on the left side.
  • Click on the "Share" menu of the top and then on "Watch".
  • Right-click on the link that is displayed and copy it.
  • Open https://12.34.56.78/chat/ (or https://10.42.0.1/chat/) and post the link there to share it with the students.

Once the students open in browser the link of the shared Guacamole session they will be able to see the desktop of the teacher and what he is doing.

2.6.3 Students Collaborating With The Teacher And With Each-Other

The students can share their desktop too with the teacher and with other students. This is useful when a student is stuck and needs some help (for example he cannot find a bug in the program) or when the students are working in pairs or in groups.

To be able to share his desktop a student should login in Guacamole with the username student. Then he should follow the same steps as above, except that he should select "Collaborate" from the menu of "Share", instead of "Watch". The difference is that with "Collaborate" both parties (or all of them) can use the keyboard and mouse to work together, instead of just watching what the other person does.

Again they can use the chat (https://10.42.0.1/chat/) to share the link of the guacamole session with the others.

3 There Is No Classroom

Teaching online is becoming common nowadays. In this case the students may be distributed all over the world. But it can also be combined with traditional teaching, where the students sometimes meet in a classroom and sometimes meet online.

In this case the students are assumed to have a computer at home and good internet connection. The server will be a VPS on the cloud. It can also be located at the school/university, provided that there is good internet connection, however it is becoming increasingly more easy, cheaper and better to have it on the cloud.

3.1 Install A Docker Desktop Server On The Cloud

The server will be installed on a Docker container, with the help of docker-scripts.

Note: I have tried these installation steps on a server on Hetzner Cloud installed with Ubuntu-18.04, but it should be almost the same on other Linux servers.

3.1.1 Install Docker

Instructions for installing Docker on Ubuntu are here: https://docs.docker.com/install/linux/docker-ce/ubuntu/

  • Add the docker repository on the list of package repositories:
    apt update
    apt install \
        apt-transport-https \
        ca-certificates \
        curl \
        software-properties-common
    
    curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add -
    
    add-apt-repository \
       "deb [arch=amd64] https://download.docker.com/linux/ubuntu \
       $(lsb_release -cs) \
       stable"
    
  • Install the package docker-ce:
    apt update
    apt install docker-ce
    
  • Verify that Docker CE is installed correctly by running the hello-world image:
    docker container run hello-world
    

3.1.2 Install Docker-Scripts

DockerScripts is a shell script framework for Docker. It facilitates creating and maintaining docker containers.

Use these commands to install it:

apt install m4
git clone https://github.com/docker-scripts/ds /opt/docker-scripts/ds
cd /opt/docker-scripts/ds/
make install
ds
ds -h

3.1.3 Install Web Server Proxy

We need wsproxy in order to get and maintain the free letsencrypt SSL certificates. It can be installed like this:

  • Get its code: ds pull wsproxy
  • Init a container directory for it: ds init wsproxy @wsproxy
  • Customize the settings: cd /var/ds/wsproxy/; vim settings.sh
  • Build image, create the container and configure it: ds make

3.1.4 Build The Desktop Container

  • Get its code: ds pull desktop
  • Init a container directory for it: ds init desktop @desktop.example.org
  • Customize the settings: cd /var/ds/desktop.example.org/; vim settings.sh
  • Build image, create the container and configure it: ds make

3.2 Docker Server Scenarios

3.2.1 Install Additional Packages

You can go inside the docker container and install other packages with apt, like this:

cd /var/ds/desk.example.org/
ds shell
apt install ubuntu-edu-preschool ubuntu-edu-primary firefox
exit

However in case you rebuild the server you will have to install them again manually. To install them automatically on each rebuild of the server, create a file like /var/ds/desk.example.org/packages with a content like this:

RUN DEBIAN_FRONTEND=noninteractive \
    apt install --yes \
        ubuntu-edu-preschool \
        ubuntu-edu-primary \
        firefox

3.2.2 Manage Student Accounts

The script users.sh can be used to create, export, import, backup and restore user accounts. Try it like this:

cd /var/ds/desk.example.org/
ds shell

/app-scripts/users.sh --help
/app-scripts/users.sh create user-list.txt
/app-scripts/users.sh backup
/app-scripts/users.sh restore backup/users-20190113.tgz

3.2.3 Rebuild The Server

Before rebuilding the server you should make first a backup of the user accounts and homes, and after rebuilding it you should restore them:

cd /var/ds/desk.example.org/

ds shell
/app-scripts/users.sh backup
exit

ds make

ds shell
/app-scripts/users.sh restore backup/users-20190113.tgz
exit

3.3 Guacamole Scenarios

Guacamole is installed by default on the server and allows desktop access to the server from a web browser. Every application and everything runs on the server and the client does not consume any resources, except for a browser tab. This is very convenient because:

  • Does not require installation of any additional tools or applications, except a web browser.
  • It is cross-platform and universal. The desktop can be accessed from any system, on any architecture. This includes ChromeOS, RaspberryPi, tablets, smartphones, or any other not powerful computers.

Things that we can do with Guacamole on a cloud server are almost the same that we can do on a local server.

3.3.1 Access Account From A Browser

Any user that has an account on the server can access the desktop of the server from a web browser. He can do it like this:

  • Open https://desk.example.org:444/guac/ on the browser. Here the port 444 is the one that is forwarded to port 443 on settings.sh
  • Click on the button "Login" without a username and password.
  • Click on the RDP connection.
  • Give the username and password of the account.

3.3.2 Teacher Sharing His Screen With The Students

This is useful when the teacher wants to demonstrate to the students how to do something, for example how to write a program.

To be able to share the screen of his account, the teacher should enter in Guacamole with the username student or admin (and the corresponding password).

Then he should go to his account by clicking on the RDP connection and giving the username and password of his account. Afterwards he should follow these steps:

  • Press Ctrl+Alt+Shift to open the Guacamole panel on the left side.
  • Click on the "Share" menu of the top and then on "Watch".
  • Right-click on the link that is displayed and copy it.
  • Send the link to the students by email, instant message (chat), etc.

Once the students open in browser the link of the shared Guacamole session, they will be able to see the desktop of the teacher and what he is doing.

3.3.3 Students Collaborating With The Teacher And With Each-Other

The students can share their desktop too with the teacher and with other students. This is useful when a student is stuck and needs some help (for example he cannot find a bug in the program) or when the students are working in pairs or in groups.

To be able to share his desktop a student should login in Guacamole with the username student. Then he should follow the same steps as above, except that he should select "Collaborate" from the menu of "Share", instead of "Watch". The difference is that with "Collaborate" both parties (or all of them) can use the keyboard and mouse to work together, instead of just watching what the other person does.

Then they can use email or chat to share the link of the guacamole session with the others.

3.4 Making Videoconferences

Sharing the desktop with other people is most useful when you can also talk and discuss with them. This can be achieved even by phone calls, but videoconference applications are more useful, and there are plenty of them. I would suggest https://meet.jit.si/ for these reasons:

  • It is completely browser based and does not need any special tools or applications to be installed.
  • Working straight from the browser means also that it is also cross-platform and can be used on any system that has a browser (Linux, Windows, MacOS, ChromeOS, etc.)
  • It is completely free to use and does not have any limitations on the number of participants in a meeting.
  • It is very easy to use and does not even ask for users to register or have an account.
  • The software that it uses is free software and anybody can install it on his own server and build his own videoconference server.

Some other useful features that videoconference applications usually have are:

  • Instant messaging (chat), which can be useful for sharing url-s.
  • File sending and sharing.
  • Desktop sharing. With jitsi you can even share the view of a specific application or a specific tab of the browser.

Date: 2019-01-13

Author: Dashamir Hoxha

Created: 2019-04-17 Wed 16:50

Emacs 25.2.2 (Org mode 8.2.10)

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