CloudFlare does not allow port 22 (usual SSH port) on domain

When you try to connect via ssh on a domain for which you are using CloudFlare as a HTTP proxy, you will get the following error:

$ ssh [email protected]
 ssh_exchange_identification: Connection closed by remote host

You have a few options to resolve for this issue:

  1. Either connect directly to the IP of the machine.
  2. Or, setup a CNAME record with no HTTP proxy for the SSH (so that you do not need to remember the IP).
    This solution does not offer any additional benefits than connecting directly to the IP of the server.
    To do that, you need to visit the configure DNS page for your site: e.g.,
    then create the CNAME named ssh, use as target your domain (e.g. and disable HTTP proxy by clicking on the orange cloud and making it gray before pressing the Add Record button.

    Then, you will be able to connect via ssh [email protected].
  3. Last solution but not least is configuring your server to listen for SSH on one of the ports of CloudFlare that are open.
    When this post was written, the following ports were available/open for any site in CloudFlare:
    For requests made via HTTP:


    For requests made via HTTPS:


    At the time, we were using an Ubuntu GNU/Linux server, to instruct Ubuntu SSHD to listen to multiple ports we edited the file /etc/ssh/sshd_config and right after the lines:

    # What ports, IPs and protocols we listen for
    Port 22

    we added another line with the new port we wanted to use:

    # What ports, IPs and protocols we listen for
    Port 22
    Port 2053

    After restarting the service
    service ssh restart;
    we were able to connect to our page as follows:
    ssh -p 2053 [email protected];


JetPack: Cannot Verify Site Ownership using pinterest

Recently, we tried to verify the ownership of a site running WordPress with JetPack in Pinterest.

As the instructions say, we logged in to Pinterest and visited the settings page to Claim Website paragraph.

Using the meta tag solution we received a code similar to the one below:

<meta name="p:domain_verify" content="8525e3384b3545fb80b9e21f0910de21"/>

When we tried to add the code in the JetPack site verification page ( we got the following error:
Error updating settings. Invalid parameter(s): pinterest (Status 400).

To resolve the issue, we just added a space character right before the end of the tag /> and our code became:

<meta name="p:domain_verify" content="8525e3384b3545fb80b9e21f0910de21" />

Trying again, it worked properly!

ffmpeg: Create a video countdown

The code below was used to generate the video countdown timers that are available in the following playlist using ffmpeg:

#This example will create a 3 second video, with 100 frames per second and it will print the elapsed and remaining times using a two second accuracy.
ffmpeg -loop 1 -i ~/Pictures/Black-Background.png -c:v libx264 -r $fps -t $seconds -pix_fmt yuv420p -vf "fps=$fps,drawtext=fontfile='/usr/share/fonts/urw-base35/C059-Bold.otf':fontcolor=yellow:fontsize=$upperFont:x=(w-text_w)/2:y=(h-text_h)/2:text='%{eif\:($seconds-t)\:d}.%{eif\:(mod($seconds-t, 1)*pow(10,$mantissaDigits))\:d\:$mantissaDigits}',drawtext=fontfile='/usr/share/fonts/urw-base35/C059-Bold.otf':fontcolor=yellow:fontsize=$lowerFont:x=(w-text_w)/2:y=((h-text_h)/2)+$upperFont:text='Elapsed\: %{eif\:(t)\:d}.%{eif\:(mod(t, 1)*pow(10,$mantissaDigits))\:d\:$mantissaDigits}'" "$seconds seconds countdown timer.mp4";


  • We used a single black frame for the background that defined the size of the video frame as well.
  • Using the fps variable we defined the number of Frames per Second for the video.
  • The seconds variable defined the number of seconds the duration of the video should be.
  • The mantissaDigits variable defines how many decimal digits should be shown after the dot.
  • upperFont and lowerFont define the size of the fonts in the upper row and the lower one respectively.
  • We used the drawtext directive twice to write to the frames.

Notes on the first drawtext:

  • fontfile='/usr/share/fonts/urw-base35/C059-Bold.otf' defines the font to be used for the text.
  • fontcolor=yellow defines the color of the font of the text.
  • fontsize=$upperFont defines the size of the font of the text.
  • x=(w-text_w)/2 defines the X-coordinate of the location for the text on the frame, here we center the text horizontally on the frame.
  • y=(h-text_h)/2 defines the Y-coordinate of the location for the text on the frame, here we center the text vertically on the frame.
  • text='%{eif\:($seconds-t)\:d}.%{eif\:(mod($seconds-t, 1)*pow(10,$mantissaDigits))\:d\:$mantissaDigits}' We print the remaining seconds for the video to finish with specific decimal digit accuracy.

Notes on the second drawtext:

  • drawtext=fontfile='/usr/share/fonts/urw-base35/C059-Bold.otf' defines the font to be used for the text.
  • fontcolor=yellow defines the color of the font of the text.
  • fontsize=$lowerFont defines the size of the font of the text.
  • x=(w-text_w)/2 defines the X-coordinate of the location for the text on the frame, here we center the text horizontally on the frame.
  • y=((h-text_h)/2)+$upperFont defines the Y-coordinate of the location for the text on the frame, here shift the text from the vertical center  of the frame.
  • text='Elapsed\: %{eif\:(t)\:d}.%{eif\:(mod(t, 1)*pow(10,$mantissaDigits))\:d\:$mantissaDigits}' We print the elapsed seconds since the video started with specific decimal digit accuracy.

LibreOffice Calc: get the distinct/unique values in a column or a list of elements

These videos demonstrate how to get the distinct/unique values in a column or a list of elements in LibreOffice Calc.

Procedure to get the distinct values in a column or a list of elements:

  1. Select the column (or the list of data) that you want to process
  2. Click on the top menu Data
    then click on the option group More Filters
    and finally on the option Standard Filter...
  3. In the new window, change the Field Name on the first row to - none -
  4. Click on the Options label and enable the No duplications checkbox
  5. Finally press the OK button

Video demonstrating how to get the distinct values in a column:

Video demonstrating how to get the distinct values in a list of elements:

Fedora 27: Install OBS Studio

In order to record a few desktop sessions on our Fedora GNU/Linux machine, we decided to use the OBS Studio as it appeared to be a very powerful tool.
Unfortunately, this software does not ship with the official repositories so we had to install it from the repository using the following commands.

#Enable access to both the free and the nonfree repository
#free repository: for Open Source Software (as defined by the Fedora Licensing Guidelines) which the Fedora project cannot ship due to other reasons
#nonfree repository: for redistributable software that is not Open Source Software (as defined by the Fedora Licensing Guidelines); this includes software with publicly available source-code that has "no commercial use"-like restrictions 
sudo dnf install$(rpm -E %fedora).noarch.rpm$(rpm -E %fedora).noarch.rpm;

#Perform the installation
sudo dnf install obs-studio;


RPM Fusion provides software that the Fedora Project or Red Hat don’t want to ship. That software is provided as precompiled RPMs.

Codecs in Fedora

By default Fedora does not ship with several codecs whose license is not free.
So we had to install a few packages manually and be able to playback or process sever multimedia formats.

Specifically we installed the following plugins and libraries for GStreamer (needed for the Totem Movie Player):

  1. gstreamer1-libav: This package provides libav-based GStreamer plug-ins.
    Libav is a free software project, forked from FFmpeg in 2011, that produces libraries and programs for handling multimedia data.
  2. gstreamer1-plugins-good: GStreamer Good Plugins is a collection of well-supported plugins of good quality and under the LGPL license.
  3. gstreamer-ffmpeg: This package provides FFmpeg-based GStreamer plug-ins.

GStreamer is a streaming media framework, based on graphs of filters which operate on media data. Applications using this library can do anything from real-time sound processing to playing videos, and just about anything else media-related. Its plugin-based architecture means that new data types or processing capabilities can be added simply by installing new plugins.

The command to install these packages was:

sudo dnf install gstreamer1-plugins-good gstreamer-ffmpeg gstreamer1-libav;

Additional h264 – h.264 Codec – Optional

Following, we decided to install the OpenH264 codec implementation and its extensions for Firefox and gstreamer.

Cisco provides an OpenH264 codec (as a source and a binary), which is their of implementation H.264 codec, and they cover all licensing fees for all parties using their binary. This codec allows you to use H.264 in WebRTC with gstreamer and Firefox. It does not enable generic H.264 playback, only WebRTC.

The code source is available at under a BSD license. The binary is released under this agreement from Cisco:

Upstream Firefox versions download and install the OpenH264 plugin by default automatically. Due to it’s binary nature, Fedora disables this automatic download.


To install the codec we performed the three following steps:

sudo dnf config-manager --set-enabled fedora-cisco-openh264;

sudo dnf upgrade;

sudo dnf install gstreamer1-plugin-openh264 mozilla-openh264;

# Afterwards you need open Firefox, go to menu -> Add-ons -> Plugins and enable OpenH264 plugin.

Bonus: Black Screen Issue

If you are having issues with the OBS Studio black screen bug, have a look at this post, it may be able to help you.

Compiling openbts-umts on Ubuntu 15.04

Below are the steps we followed to compile OpenBTS-UMTS on Ubuntu 15.04.
There could be a chance that we installed a couple of extra system packages while troubleshooting the installation but it works and we did not include some heavy system service as well so it should be OK.

sudo apt-get install build-essential libuhd autoconf libtool libdevel libzmq-dev libzmq libzmq-dev libzmq-dev libosip2-dev libortp-dev libusb-dev libusb-1.0 libtool-bin libsqlite3-dev libboost-dev libreadline-dev;
git clone;
cd OpenBTS-UMTS/;
git submodule init;
git submodule update;
#First we need to setup ASN1C compiler
tar -xf asn1c-0.9.23.tar.gz;
cd vlm-asn1c-0959ffb/;
make check;
sudo make install;
cd ..;
#Finally, we can proceed with compiling openbts-umts
sudo make install;

Compiling gr-gsm on Ubuntu 14.04 LTS

Below are the steps that we followed to compile gr-gsm on Ubuntu 14.04 LTS.

sudo apt-get update;
sudo apt-get install build-essential python-dev git python-pip;
sudo pip install PyBOMBS;
sudo pybombs prefix init /usr/local -a default_prx;
sudo pybombs config default_prefix default_prx;
sudo pybombs recipes add gr-recipes git+;
sudo pybombs recipes add gr-etcetera git+;
sudo pybombs install gr-gsm;
sudo ldconfig;

Building wireshark-2.4.2 on CentOS 7 (64bit)

Recently we were trying to compile WireShark from source on a CentOS 7 (64bit) with GTK3 disabled (./configure --disable-gtk3;).

As seen in the truncated logs below we got some errors.
To resolve them we had to install a few packages using yum.
Specifically, our solution involved the installation of the following:

sudo yum install libgcrypt-devel qt5-qttools-devel libpcap-devel -y;

Truncated logs:

checking for libgcrypt-config... no
checking for LIBGCRYPT - version >= 1.4.2... no
configure: error: libgcrypt not found; install libgcrypt-devel package for your system
libgcrypt-devel.i686 libgcrypt-devel.x86_64 
[[email protected] wireshark-2.4.2]$ sudo yum install libgcrypt-devel -y

checking for lrelease-qt5... no
checking for lrelease... no
configure: error: I couldn't find lrelease-qt5 or lrelease; make sure it's installed and in your path
[[email protected] wireshark-2.4.2]$ sudo yum install qt5-qttools-devel

checking whether to use libpcap for packet capture... yes
checking for pcap-config... no
checking for extraneous pcap header directories... not found
checking pcap.h usability... no
checking pcap.h presence... no
checking for pcap.h... no
configure: error: Header file pcap.h not found; if you installed libpcap
from source, did you also do "make install-incl", and if you installed a
binary package of libpcap, is there also a developer's package of libpcap,
and did you also install that package?
[[email protected] wireshark-2.4.2]$ sudo yum install libpcap-devel

[[email protected] wireshark-2.4.2]$ ./configure --disable-gtk3


Fedora 27: Setup stackskills-dl

A couple of days ago we were asked to setup stackskills-dl on a Fedora 27 (x64).
Apparently stackskills-dl is a Ruby script that allows a registered user to download the StackSkills tutorials for which the user has access to.

Following the instructions at are not enough to get the application running as the json gem and the Ruby development files appear to be missing from the filesystem.

Solution: Below are the steps we followed to setup stackskills-dl and make it operational:

sudo dnf install gem ruby-devel youtube-dl wget;
gem install json;
gem install bundler;
git clone;
cd stackskills-dl/;
bundle install;

After the above steps were completed, we were able to use stackskills-dl from the clone/installation folder normally:

[[email protected] stackskills-dl]$ ruby stackskills_dl.rb -u "[email protected]" -p "e#rf54HTw3se!fe678f." -s;
Loaded login credentials from environment variables.
Login Successfully.
Finding from your list of courses
Number of courses found: 1

[[email protected] stackskills-dl]$ ruby stackskills_dl.rb --help
Usage: ruby stackskills_dl.rb [options]
-u, --email NAME Email
-p, --password PASSWORD Password
-c, --course COURSE_URL Course URL in ID.
-s, --course-slug COURSE_SLUG Course URL in slug.

With out the Ruby json gem you would get the following error:

[[email protected] stackskills-dl]$ ruby stackskills_dl.rb --help;
/usr/share/rubygems/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- json (LoadError)
from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:55:in `require'
from /home/george/.gem/ruby/2.4.0/gems/mime-types-2.99.1/lib/mime/types/loader.rb:226:in `load_from_json'
from /home/george/.gem/ruby/2.4.0/gems/mime-types-2.99.1/lib/mime/types/loader.rb:63:in `block in load_json'
from /home/george/.gem/ruby/2.4.0/gems/mime-types-2.99.1/lib/mime/types/loader.rb:62:in `each'
from /home/george/.gem/ruby/2.4.0/gems/mime-types-2.99.1/lib/mime/types/loader.rb:62:in `load_json'
from /home/george/.gem/ruby/2.4.0/gems/mime-types-2.99.1/lib/mime/types/loader.rb:88:in `load'
from /home/george/.gem/ruby/2.4.0/gems/mime-types-2.99.1/lib/mime/types/loader.rb:113:in `load'
from /home/george/.gem/ruby/2.4.0/gems/mime-types-2.99.1/lib/mime/types.rb:296:in `load_default_mime_types'
from /home/george/.gem/ruby/2.4.0/gems/mime-types-2.99.1/lib/mime/types.rb:323:in `<class:Types>'
from /home/george/.gem/ruby/2.4.0/gems/mime-types-2.99.1/lib/mime/types.rb:63:in `<top (required)>'
from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:55:in `require'
from /home/george/.gem/ruby/2.4.0/gems/mechanize-2.7.4/lib/mechanize/pluggable_parsers.rb:5:in `<top (required)>'
from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:55:in `require'
from /home/george/.gem/ruby/2.4.0/gems/mechanize-2.7.4/lib/mechanize.rb:1361:in `<top (required)>'
from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:133:in `require'
from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:133:in `rescue in require'
from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:40:in `require'
from /home/george/Videos/stackskills-dl/lib/course_finder.rb:1:in `<top (required)>'
from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:55:in `require'
from stackskills_dl.rb:4:in `<main>'

An attempt to use images in WP-Polls

Recently we needed to make a poll with images in WordPress.
On our system we only had WP-Polls installed and we decided to go along with it despite its drawbacks.

Drawbacks of using WP-Polls:

  • Does not support polls with images directly.
  • Does not allow you to configure ‘Poll Options’ per poll.
    For example, either all polls are logged by username or none is.


In any case, we only needed one poll for a very specific task so we decided to ignore those limitations and see what we could do with the current vanilla code of WP-Polls ( WP-Polls 2.73.8 (retrieved on 2017 Dec 18) (27 downloads) ).

What we did was the following:

A: We configured the system to only allow registered users to vote and set the vote logging to be per username

B: We modified the templates below to receive the poll answers as URIs for images.

Voting Form Body:

<li><input type="%POLL_CHECKBOX_RADIO%" id="poll-answer-%POLL_ANSWER_ID%" name="poll_%POLL_ID%" value="%POLL_ANSWER_ID%" /> <label for="poll-answer-%POLL_ANSWER_ID%"><img src="%POLL_ANSWER%" />%POLL_ANSWER%</label></li>

Result Body:
Displayed When The User HAS NOT Voted

<li><img src="%POLL_ANSWER%" />%POLL_ANSWER% <small>(%POLL_ANSWER_PERCENTAGE%%, %POLL_ANSWER_VOTES% Votes)</small><div class="pollbar" style="width: %POLL_ANSWER_IMAGEWIDTH%%" title="%POLL_ANSWER_TEXT% (%POLL_ANSWER_PERCENTAGE%% | %POLL_ANSWER_VOTES% Votes)"></div></li>

Result Body:
Displayed When The User HAS Voted

<li><img src="%POLL_ANSWER%" /><strong><i>%POLL_ANSWER% <small>(%POLL_ANSWER_PERCENTAGE%%, %POLL_ANSWER_VOTES% Votes)</small></i></strong><div class="pollbar" style="width: %POLL_ANSWER_IMAGEWIDTH%%" title="You Have Voted For This Choice - %POLL_ANSWER_TEXT% (%POLL_ANSWER_PERCENTAGE%% | %POLL_ANSWER_VOTES% Votes)"></div></li>

These two changes produced the following result:

Vote for the best filter

  • (36%, 23 Votes)
  • (30%, 19 Votes)
  • (23%, 15 Votes)
  • (8%, 5 Votes)
  • (2%, 1 Votes)
  • (2%, 1 Votes)
  • (0%, 0 Votes)
  • (0%, 0 Votes)

Total Voters: 64

Loading ... Loading ...

We did not fiddle with the CCS of the site to make the polls look better or anything as it was OK for the scenario that we cared about.