... mainly Programming, Technology, Android, Linux

Most of you have probably heard of Viber and most likely use it with your smartphone. Here is a nice blog post for simple instructions on how to get it working in Fedora 20. I will just list the steps here as well just in case the blog gets unavailable:

1. Download and extract

http://download.cdn.viber.com/cdn/desktop/Linux/Viber.zip

in a place of your choice. I placed it in an /opt/viber folder 2. Change the ownership of your viber directory to your user by issuing the commands: cd /opt sudo chown -Rf user:user viber

where user is your username 3. make Viber and Viber.sh executable by changing their permission by issuing the commands: chmod +x /opt/viber/Viber chmod +x /opt/viber/Viber.sh 4. Test by running Viber.sh shell script:

cd /opt/viber/ ./Viber.sh

5. Optionally you can create an application launcher to place in your panel (see in previous posts)

KeePass is a very nice application that can be used to keep all your passwords safe in one place. Personally I have in my dropbox a KeePass portable folder so I can access my password database from anywhere. The only thing that you should be aware of is to use a really strong password to encrypt the KeePass database file which will be the only one that you will then have to remember.

In order to run KeePass in Fedora 20 here is what you should do:

1. Download KeePass 2.x portable from

http://keepass.info/download.html

2. Extract it in a folder of your choice

3. Install mono-core and mono-winforms by issuing the commands:

sudo yum install mono-core.x86_64 mono-winforms.x86_64

4. Execute KeePass by issuing the command:

mono KeePass.exe

5. Optionally you can create a custom application launcher to put in your panel (see previous post)

In order to login to a remote server using SSH with no password but a KEY-based login here are the steps you should follow.

1. If not already present create an ssh directory and change its permissions:

mkdir ~/.ssh chmod 700 ~/.ssh

2. Generate your key pair. If you only have (or think is enough) access to your computer you can leave the password field empty when prompted. This way you will not be bothered with entering it every time you want to connect to the remote server but of course is somewhat less secure. Issue the command:

ssh-keygen -t rsa -b 4096

3. Finally you need to copy your public key to the server machine. Issue the command:

ssh-copy-id <username>@<host>

where <username> is your username in the server machine and <host> the hostname of the server machine.

4. Now you can test if you can connect with SSH without using any password. It should only prompt you for a password if you have used a password to encrypt-protect your key in step #2.

5. If you succeeded in step #4 you can now disable password authentication which is higly recommended. To do that look for the following edit your sshd_config file:

sudo vi /etc/ssh/sshd_config

look for a line that looks like

#PasswordAuthentication yes

and replace it with a line that looks like this:

PasswordAuthentication no

Save and restart the ssh service

sudo service ssh restart

You can read a more detailed description here but it all summarizes to the instructions above.

Troubleshooting:

If when trying to connect after doing all steps above you get the following error:

Agent admitted failure to sign using the key.

Then just issue the command

ssh-add

Recently I tried to create custom application launchers for the Cinnamon desktop environment in Fedora 20 to place in the panel. 

If you don't have any launcher in the panel (which will be the case in the beginning) the easiest way is to right click one in the menu and select "Add to panel" (you can also add it to desktop and to favorites).

After you do that and the launcher is already in the panel, you can add a custom one just by right clicking on an existing one and selecting "Add". Of course right clicking the panel itself and having the same option would in my opinion make much more sense!

For the command line lovers the same thing would be accomplished by running the following command:

python /usr/lib/cinnamon-desktop-editor/cinnamon-desktop-editor.py -mpanel-launcher

In that way I managed to add two custom launchers, one for android studio and one for viber (instruction posts will follow) but when I tried to do the same for a command that had parameters it did not work!

To be more specific: I wanted to make a shortcut to run KeePass (a greate app) with the mono framework and the command was

mono /install_dir/KeePass.exe

The weird thing was that after I was filling the "Name", "Command" and choosing an icon nothing was happening! There was no error but nothing was added in the panel either. Even by running it in the command line did not reveal any errors! :)

After some searching I found that apart from the normal place that most of the application launchers are in the system /usr/share/applications/  and in which you should put launchers that you want to be system wide available there is another folder in which the cinnamon  creates and saves the custom launchers:

~/.cinnamon/panel-launchers/

In there I found several launchers named cinnamon-custom-launcher-1.desktop, cinnamon-custom-launcher-2.desktop etc which were indeed my custom launchers but much more than the ones I was looking in the panel (actually there were as many as the tries I had done to create them). What had happened?

Apparently, the python script mentioned in the beginning has a bug in which when you put a space in the command of the launcher it is escaped with \\ characters which results in a non valid content for a .desktop file.

The solution? Just delete the duplicate .desktop files and only keep one in which you should delete the \\ characters so that the specific line looks like the following:

Exec=mono ~/KeePass/KeePass.exe

After you reboot or restart the display manager you will have the launcher in place!

I am assuming that you have a properly installed and working camera and a printer to print the “patterns” or whichever way of having a printed copy of the patterns.

1. Download and install the latest Java SE from http://java.sun.com/javase/downloads/index.jsp

2. Download and install the latest NetBeans IDE from http://netbeans.org/

3. Download the latest Java Media Framework from http://java.sun.com/javase/technologies/desktop/media/jmf/ (near the bottom of the page is the link Download JMF). Choose Windows as the platform, check the box and click Continue. In the next screen click on the first file jmf-2_1_1e-windows-i586.exe (Windows Performance Pack) to download it. Double click and follow setup instructions to install it.

4. Download the latest version of the zip binaries file Java 3D for windows (at the time these instructions were written this was j3d-1_5_2-windows-i586.zip) from https://java3d.dev.java.net/binary-builds.html

5. Download the latest NyARToolkit zip file from the NyARToolkit for Java - NyARToolkit Core section (at the time these instructions were written this was NyARToolkit-2.4.2.zip) from  http://sourceforge.jp/projects/nyartoolkit/releases/

By now you must have installed the required Java SE, NetBeans IDE and Java Media Framework and you must also have the j3d-1_5_2-windows-i586.zip and the NyARToolkit zip files downloaded somewhere.

6. Create a new Java Application project in NetBeans. Name it as you wish, say JNyAR.

7. Unzip the NyARToolkit zip file somewhere and copy and paste the following folders in the src folder of the project you just created:

a) [NyARToolkit-2.4.2]/src/jp

b) [NyARToolkit-2.4.2]/src.utils/java3d/jp

c) [NyARToolkit-2.4.2]/src.utils/jmf/jp

d) [NyARToolkit-2.4.2]/sample/java3d/jp

e) [NyARToolkit-2.4.2]/sample/jmf/jp

Be careful to copy only the jp folder of each path mentioned above. When copying and pasting the folder from the paths b, c, d and e windows will tell you that there is a jp folder already. Choose to overwrite.

8. Create a lib folder in the JNyAR project. Unzip the j3d zip file somewhere. There will be another zip file called j3d-jre.zip. Unzip it also somewhere (I created the folder C:\Program Files\Java\j3d-1.5.2 and unzipped it in there) and copy the 3 jar files that are inside the /lib/ext folder (j3dcore.jar, j3dutils.jar, vecmath.jar) in the lib folder of your NetBeans project.

9. Add to the end of the PATH variable the path to the bin folder of the j3d you unzipped in step 8. In my case I added the text ‘;C:\Program Files\Java\j3d-1.5.2\bin’ (without the ‘’). Also the installation process of the Java Media Framework should have changed the CLASSPATH variable adding the path to the JMF installation folder and should have added a JMFHOME variable.

*Warning: Be care full when you mess up with the system variables.

10. Right click in the Libraries of your NetBeans project and choose Add JAR/Folder. Choose the 3 .jars you copied in step 8 from the /lib folder and click open. This will add the jars to the classpath of your project.

11. Do the same as in step 10 but this time choose the jars located in the [Path to installed JMF] \lib (for me that was the jars located in folder C:\Program Files\Java\JMF2.1.1e\lib)

12. Finally, copy the Data folder of the NyARToolkit zip file in the same folder that the NetBeansProjects  folder resides (or if you prefer put it inside the project folder but change the path of the variables that use the files in the Data folder accordingly - like for example the variables CARCODE_FILE and PARAM_FILE in class NyARJava3D.java)

13. You are done. If all have gone well you should be able to build the project without errors. Print the file pattHiro.pdf, run the file jp/nyatla/nyartoolkit/java3d/sample/NyARJava3D.java and when the image from the camera appears hold the paper in front of the camera.