How to update all pulled Docker images that are tagged as latest

Recently, we moved a client to Docker and we needed to give them a way to automagically update all “latest” Docker images.
Since Docker does not have a single command to update all pulled images we used this one-liner to update all images at once:

docker images --format "{{.Repository}}:{{.Tag}}" | grep ':latest' | xargs -L1 docker pull;

The above command will:

  1. Print all images in the format RepositoryName:Tag
  2. Then it will filter all lines that end with the suffix :latest (which is the tag we are interested in)
  3. Finally, for each result (which is one per line) it will be fed  via the command xargs -L1 to the command docker pull

Please note that you cannot really update an existing container using docker commands, what you need to do is actually:

  1. Stop the container whose image was updated
  2. Delete it
  3. Recreate it using the parameters of the previous container

As you understand, it is a good practice to save all of your data in volumes outside the container to make the update process easy.

For example, below you will find the commands using which we updated the jwilder/nginx-proxy and the jrcs/letsencrypt-nginx-proxy-companion images along with the two containers that were using them:

docker container stop nginx-proxy nginx-letsencrypt;
docker container rm nginx-proxy nginx-letsencrypt;
docker run -d -p 443:443 \
     --name nginx-proxy \
     --net reverse-proxy \
     -v $HOME/certs:/etc/nginx/certs:ro \
     -v /etc/nginx/vhost.d \
     -v /usr/share/nginx/html \
     -v /var/run/docker.sock:/tmp/docker.sock:ro \
     -v $HOME/my_proxy.conf:/etc/nginx/conf.d/my_proxy.conf:ro \
     --label com.github.jrcs.letsencrypt_nginx_proxy_companion.nginx_proxy=true \

docker run -d \
     --name nginx-letsencrypt \
     --net reverse-proxy \
     --volumes-from nginx-proxy \
     -v $HOME/certs:/etc/nginx/certs:rw \
     -v /var/run/docker.sock:/var/run/docker.sock:ro \

[Video] Android OpenCV – Face Detection and Recognition Demo

Android OpenCV – Face Detection and Recognition Demo using Android NDK/JNI to load OpenCV library.

Google Play:

Get it on Google Play

Our application is based on the ‘Face Detection’ sample of OpenCV. The sample that is available for download from, you will notice that there are many versions there, we used version opencv- Refer to this ( introduction for more information.

How we sync files between two drives

We have two external hard disks that we use to keep backups of our data.
The way we do that is by using the command rsync that makes our life easy.

Specifically, we use the following command to synchronize the first hard disk with the second one:

rsync -avh --delete --progress "path/to/source" "path/to/destination";

rsync is a fast, versatile, remote (and local) file-copying tool, it is available in almost every system (GNU/Linux, Unix (MacOS as well) and Windows).

The parameters we use are the following:

  • -a, --archive enables archive mode which is equal to -rlptgoD (no -H,-A,-X)
    In more detail it enables all of the following options
    -r, --recursive recurse into directories
    -l, --links copy symlinks as symlinks
    -p, --perms preserve permissions
    -t, --times preserve modification times
    -g, --group preserve group
    -o, --owner preserve owner (super-user only)
    -D same as --devices --specials
    --devices preserve device files (super-user only)
    --specials preserve special files
  • -v, --verbose it increases verbosity of the output
  • -h, --human-readable outputs numbers in a human-readable format
  • --delete deletes extraneous files from destination directories
  • --progress shows progress during transfer

Install Required Plugins of Gillion | Multi-Concept Blog/Magazine & Shop WordPress Theme

For Gillion (the Multi-Concept Blog/Magazine & Shop WordPress Theme) to properly work, it needs the WPBakery Page Builder (formerly Visual Composer) and the Unison plugins. In a clients’ page, they did not get the message prompting to install the required plugins and could not find it again. Unison is available through WordPress Plugin Directory so that was easy to setup. On the other hand, WPBakery (and the Revolution slider) it is not available through the directory as it is a commercial product. After reading through the support forums we realised that they should not need to make a separate purchase of the plugin, the theme will be able to pull it automatically from a CDN of shufflehound (without getting support from the WPBakery team).

Solution: In case you are facing the same issue, you can find the installation link under the left side menu Appearance where a new option will be available called Install Plugins (the link will be similar to this We installed for them the two required plugins and their theme was operational.


CloudFlare does not allow port 22 (usual SSH port) on domain 2

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;