Thursday, December 22, 2016

Copying streams to video/audio files using vlc

If you ever need to save a stream (either audio or video) to a file, you can do it by using vlc.

You will find more details here:

Wednesday, December 7, 2016

Wifi analyzer

If by any chance, you would like to see what is the wifi state around you, in order for example to pick the best channel for your own wireless device, and you do not have a wifi analyzer in an android device, you do not need to look far.

NetworkManager has got you covered. Just execute:
nmcli d wifi

on your linux console and you are done.

Saturday, November 26, 2016

Gimp and rule of thirds guides

Ever wanted to use rule of thirds guides in gimp?

Here is a simple guide that works just fine:

Friday, November 25, 2016

Realtek gigabit usb ethernet card with usb hub

Just got this ethernet/hub combo and I was unable to make it work. I was getting the following error:

[ 265.335354] usb 1-1.1.3: Manufacturer: Realtek
[  265.335358] usb 1-1.1.3: SerialNumber: 00E14C3600C8
[  265.428826] usb 1-1.1.3: reset high-speed USB device number 19 using ehci-pci
[  265.567413] r8152 1-1.1.3:1.0 eth1: v1.08.2
[  267.113732] r8152 1-1.1.3:1.0 enx00e14c3600c8: renamed from eth1
[  267.139576] IPv6: ADDRCONF(NETDEV_UP): enx00e14c3600c8: link is not ready
[  267.197045] IPv6: ADDRCONF(NETDEV_UP): enx00e14c3600c8: link is not ready

and no connectivity.

After some digging, I discovered that my network card is a Realtek 0bda:8153, this card is supported by the driver r8152 that already existed in my system.

Some more digging brought this on surface:

In short it seems that tlp tries to save power for me by blocking my network card. The solution is to add the following

USB_BLACKLIST="0bda:8153" in /etc/default/tlp and reconnect the card. After that everything works as expected.

Typing the € symbol in a linux system

For infrequent users:

If you use English (US) keyboard layout and you don't want to change it, the the fastest way would be to use Ctrl+Shift+U key combination and then type 20ac followed by Space(or Enter) which will turn into .

The Xorg solution:

In your keyboard layout settings choose Options -> Add currency signs to certain keys then choose the key you can use to activate that option by changing the option Key to choose 3rd level (or 4th depending on which level your currency symbol is. you can get the full keycodes by using xmodmap -pke in console)
For this you can choose use Win key, its useless in Linux anyway, so you might as well find some use for it.

The console solution:

xmodmap -e "keycode 13 = 4 EuroSign 4 EuroSign"
xmodmap -e "keycode 13 = 4 dollar 4 dollar"
xmodmap -pke > .xmodmap
xmodmap .xmodmap

Now if you want, for example, to change the $ sign (which you can type it using Shift+4 shortcut when you have an US English keyboard) with sign, you can use the following command in terminal in terminal:
From now you can type using Shift+4 shortcut.
To switch back to $ sign, use:
To get this change for every session, create a file called .xmodmap, with the following command:
Then, create a file called .xinitrc in your home directory, containing the following line/command:
In the same mode you can set any other key combination to type symbol. Use xmodmap -pke command to see all keycodes and their map assignment.

Monday, October 31, 2016

Presenting pdf with next slide and timer

Finding a tool that is not heavy weight in order to do presentations is not as easy as it seems.
But on Ubuntu pdf-presenter-console dies the job quite well.
Just provide a pdf.
The pdf can be easily generated by markdown using pandoc or your pdf generator of choice.

The project name is pdfpc and can be found on github

Saturday, October 29, 2016

An alternative to lens flare correction

If your lens tends to create monochromatic spherical flares, one of mine does, then you can get rid of the flare by selecting it, going to levels, selecting the color channel (blue in my case) and fiddle a bit with the middle slider.
That can help you sort out the flare without an issue.

Lens flare correction with gimp

Got a photo that has flare?

It can be corrected with gimp. Check out this article. I am copying the text here so it wont dissappear if the post goes away.

After purchasing a glorious new Nikon D40X Digital SLR Camera online today, I was inspired to fix up a couple images.
So, I was trying to get rid of the obvious flaw in the following picture, and I found a pretty easy way to do it with GIMP.
Now, I’m no expert at GIMP or anything, but all I did was select the region in question using the lasso, like so:
Then, I used the Colors -> Components -> Channel Mixer tool to bend it to my will (make sure you grow your selection to encompass the whole flare using the Select -> Grow tool):
Notice how in the preview window the blemish isn’t visible?  That’s what you want.  Now, hit OK.
So, now all we have is a little bit of a color/contrast issue.  Let’s fix that up with the Colors -> Color Balance tool:
Now, if you look closely, you can still see just a tiny bit of brightness, but that’s alright with me – it’s much better than the blue crap.  Here’s the end result:
And there you have it: how to remove those annoying lens flares with GIMP.

Sunday, October 16, 2016

Thursday, October 6, 2016

Getting webex to run on linux

It can mess up your system, so why not use docker instead?

Get this image
command: docker pull dnk8n/docker-webex

close all running firefox instances

start image

sudo docker run -it \
    --env DISPLAY=unix$DISPLAY \
    --privileged \
    --name=docker-webex \
    --volume /dev/snd:/dev/snd \
    --volume /tmp/.X11-unix:/tmp/.X11-unix \
    dnk8n/docker-webex:latest $1

if firefox is already open and you want to maintain your existing session

sudo docker run -it \
    --env DISPLAY=unix$DISPLAY \
    --privileged \
    --name=docker-webex \
    --volume /dev/snd:/dev/snd \
    --volume /tmp/.X11-unix:/tmp/.X11-unix \
    dnk8n/docker-webex:latest $1 \
    /usr/bin/firefox --no-remote

make sure there is no whitespace after \ otherwise the multiline commands wont work

Wednesday, October 5, 2016

The last unicorn, by Peter S Beagle

A nice book with a rather poetic style and multiple references to the power of the stories.

Finetuning an adafruit pir sensor

These sensors are a bit tricky to calibrate, so this web site is quite handy

Saturday, September 3, 2016

Weaverley by sir Walter Scott

Just finished the first novel of Scott, with the title Weaverley.
It is one of the classic books of Scottish literature and narrates the story of an English gentleman of the name Weaverley, that serves as an officer in the English army during the Jacobite civil war.

Apart from the very long editorial, which may or may not exist in different versions of the book, and the somewhat flowery style of sir Scott, the book is captivating. It is describing the social structure in the scottish highlands during the civil war and also describes how the war itself affected the future generations of Scotland.

Overall a very interesting reading to anyone who is interested in understanding the complicated history of Scotland.

Wednesday, August 10, 2016

Resizing disk space in Virtualbox virtual machine

If you need to increase your disk space in a virtual machine, if your disk is in vmdk format then you need to execute the following steps:

First you need to convert your disk to vdi by cloning.
Vdi can be resized and replace the vmdk disk in place. Just remove the vmdk in the settings
Internal partition needs to be resized this can be done by using the gparted iso:

Add the gparted as a cd iso and boot from it, resize the partition. In the next boot the system will recognize the new capacity

Vdi cloning and disk increase can be done with the following two commands:
  • VBoxManage clonehd "/home/nickapos/VirtualBox VMs/NCRWin7/NCRWin7-2016-06-27-disk1.vmdk" "/home/nickapos/VirtualBox VMs/NCRWin7/win7clone.vdi" --format vdi
  • VBoxManage modifyhd "/home/nickapos/VirtualBox VMs/NCRWin7/win7clone.vdi" --resize 100000

After that we are ready to boot. This will work with windows as well as linux. If you need to export your vm, there is a chance that Virtualbox will convert the image back to vmdk

Monday, August 1, 2016

Ubuntu ufw and docker

If you are using a system with ufw and at the same time are using docker, please keep in mind that docker manipulates the iptables rules in order to allow access to its services.

That means that it will open ports that you never intended to open to the world.
In order to disable this, you need to add the  --iptables=false in its arguments and restart it.

Saturday, July 30, 2016

Haskell in Docker

This is for my functional programming friends.

If you want to try haskell, or try a different version of haskell than the one you have on your system, you can use one of the official  haskell docker containers.

All you need is Docker and the following two commands:

docker pull haskell
docker run --rm --interactive --tty haskell

and you are done, you are in ghc interactive mode

Thursday, July 28, 2016

Merging git branches while keeping some files from the old branch

Lets say we have master and experimental branch.
Master has evolved and we would like to merge its changes in the experimental branch, that has not yet lost its value.

But there are some files in the experimental branch we would like to keep.

How can we do that?

First we need to create our own merge driver. A merge driver is the command that is responsible for the actual merging of the files. In this case we need a driver that does not do anything to the files we want to preserve.

We can accomplish that by using this command:

git config --global merge.ours.driver true

This driver will always return true for every file that meets a specific pattern. What is this pattern and how do we configure it?

We need to create a file called .gitattributes in our project, version it, and add as contents the pattern of the files we would like to keep from being merged:

echo 'email.json merge=ours' >> .gitattributes
git add .gitattributes
git commit -m 'chore: Preserve email.json during merges'

This will protect a file called email.json from being merged.

After that we execute
git merge -

to complete the merge.

If you need more details please check this link:

Wednesday, July 27, 2016

Inspecting a docker container.

It is very common to perceive a docker container as a black box, you do now know what is in there, and very rightly so. That is what a container is all about.
But what happens when you want to actually finetune its deployment? What happens when you want to find out if there are multiple ports or volumes defined, in it. What are the hashes that are being used in your system?

All these can be retrieved by using the docker inspect command:

docker inspect grafana

And this is the output:

        "Id": "6280c5bb41b8a5410d0d35b478e1617d77c332df503b32271cebdc5aadc68579",
        "Created": "2016-07-27T17:32:56.328619446Z",
        "Path": "/",
        "Args": [],
        "State": {
            "Status": "running",
            "Running": true,
            "Paused": false,
            "Restarting": false,
            "OOMKilled": false,
            "Dead": false,
            "Pid": 8153,
            "ExitCode": 0,
            "Error": "",
            "StartedAt": "2016-07-27T17:32:57.239316798Z",
            "FinishedAt": "0001-01-01T00:00:00Z"
        "Image": "sha256:932c5bca836b177b4f2071fd1061d8649f74fb510fe51b5e2d466a0e4856f10a",
        "ResolvConfPath": "/zfspool1/docker/containers/6280c5bb41b8a5410d0d35b478e1617d77c332df503b32271cebdc5aadc68579/resolv.conf",
        "HostnamePath": "/zfspool1/docker/containers/6280c5bb41b8a5410d0d35b478e1617d77c332df503b32271cebdc5aadc68579/hostname",
        "HostsPath": "/zfspool1/docker/containers/6280c5bb41b8a5410d0d35b478e1617d77c332df503b32271cebdc5aadc68579/hosts",
        "LogPath": "/zfspool1/docker/containers/6280c5bb41b8a5410d0d35b478e1617d77c332df503b32271cebdc5aadc68579/6280c5bb41b8a5410d0d35b478e1617d77c332df503b32271cebdc5aadc68579-json.log",
        "Name": "/grafana",
        "RestartCount": 0,
        "Driver": "aufs",
        "MountLabel": "",
        "ProcessLabel": "",
        "AppArmorProfile": "",
        "ExecIDs": null,
        "HostConfig": {
            "Binds": null,
            "ContainerIDFile": "",
            "LogConfig": {
                "Type": "json-file",
                "Config": {}
            "NetworkMode": "default",
            "PortBindings": {
                "3000/tcp": [
                        "HostIp": "",
                        "HostPort": "3000"
            "RestartPolicy": {
                "Name": "no",
                "MaximumRetryCount": 0
            "AutoRemove": false,
            "VolumeDriver": "",
            "VolumesFrom": [
            "CapAdd": null,
            "CapDrop": null,
            "Dns": [],
            "DnsOptions": [],
            "DnsSearch": [],
            "ExtraHosts": null,
            "GroupAdd": null,
            "IpcMode": "",
            "Cgroup": "",
            "Links": null,
            "OomScoreAdj": 0,
            "PidMode": "",
            "Privileged": false,
            "PublishAllPorts": false,
            "ReadonlyRootfs": false,
            "SecurityOpt": null,
            "StorageOpt": null,
            "UTSMode": "",
            "UsernsMode": "",
            "ShmSize": 67108864,
            "ConsoleSize": [
            "Isolation": "",
            "CpuShares": 0,
            "Memory": 0,
            "CgroupParent": "",
            "BlkioWeight": 0,
            "BlkioWeightDevice": null,
            "BlkioDeviceReadBps": null,
            "BlkioDeviceWriteBps": null,
            "BlkioDeviceReadIOps": null,
            "BlkioDeviceWriteIOps": null,
            "CpuPeriod": 0,
            "CpuQuota": 0,
            "CpusetCpus": "",
            "CpusetMems": "",
            "Devices": [],
            "DiskQuota": 0,
            "KernelMemory": 0,
            "MemoryReservation": 0,
            "MemorySwap": 0,
            "MemorySwappiness": -1,
            "OomKillDisable": false,
            "PidsLimit": 0,
            "Ulimits": null,
            "CpuCount": 0,
            "CpuPercent": 0,
            "BlkioIOps": 0,
            "BlkioBps": 0,
            "SandboxSize": 0
        "GraphDriver": {
            "Name": "aufs",
            "Data": null
        "Mounts": [
                "Name": "b68a5fe8f6e8c817bfacbbd8004e2452411673bd631e09564873a58badc0ac3d",
                "Source": "/zfspool1/docker/volumes/b68a5fe8f6e8c817bfacbbd8004e2452411673bd631e09564873a58badc0ac3d/_data",
                "Destination": "/etc/grafana",
                "Driver": "local",
                "Mode": "",
                "RW": true,
                "Propagation": ""
                "Source": "/zfspool1/grafana-volume",
                "Destination": "/var/lib/grafana",
                "Mode": "",
                "RW": true,
                "Propagation": "rprivate"
                "Name": "ac220948e55e4e65ac9905b480bf1150aa8732a0ab6b094a8269032921478775",
                "Source": "/zfspool1/docker/volumes/ac220948e55e4e65ac9905b480bf1150aa8732a0ab6b094a8269032921478775/_data",
                "Destination": "/var/lib/grafana/plugins",
                "Driver": "local",
                "Mode": "",
                "RW": true,
                "Propagation": ""
                "Name": "7be07c6927bbe12d0957a05a8bf3284a6e10c0ec9152646b85c2583e47a2ac6e",
                "Source": "/zfspool1/docker/volumes/7be07c6927bbe12d0957a05a8bf3284a6e10c0ec9152646b85c2583e47a2ac6e/_data",
                "Destination": "/var/log/grafana",
                "Driver": "local",
                "Mode": "",
                "RW": true,
                "Propagation": ""
        "Config": {
            "Hostname": "6280c5bb41b8",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "ExposedPorts": {
                "3000/tcp": {}
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": [
            "Cmd": null,
            "Image": "grafana/grafana",
            "Volumes": {
                "/etc/grafana": {},
                "/var/lib/grafana": {},
                "/var/lib/grafana/plugins": {},
                "/var/log/grafana": {}
            "WorkingDir": "",
            "Entrypoint": [
            "OnBuild": null,
            "Labels": {}
        "NetworkSettings": {
            "Bridge": "",
            "SandboxID": "121cb533502a3613ed086db64b3291c6dcaf2808fa97499c5bd1aac95a913593",
            "HairpinMode": false,
            "LinkLocalIPv6Address": "",
            "LinkLocalIPv6PrefixLen": 0,
            "Ports": {
                "3000/tcp": [
                        "HostIp": "",
                        "HostPort": "3000"
            "SandboxKey": "/var/run/docker/netns/121cb533502a",
            "SecondaryIPAddresses": null,
            "SecondaryIPv6Addresses": null,
            "EndpointID": "bd06a65e45743a62d86509ff4ec49b38f78e8c23c5dc45c74c3cdfb98c840c21",
            "Gateway": "",
            "GlobalIPv6Address": "",
            "GlobalIPv6PrefixLen": 0,
            "IPAddress": "",
            "IPPrefixLen": 16,
            "IPv6Gateway": "",
            "MacAddress": "02:42:ac:11:00:02",
            "Networks": {
                "bridge": {
                    "IPAMConfig": null,
                    "Links": null,
                    "Aliases": null,
                    "NetworkID": "8312143de9ee482776c4b923b71d695687244fc9ac28ec8d151bd7678a9240ae",
                    "EndpointID": "bd06a65e45743a62d86509ff4ec49b38f78e8c23c5dc45c74c3cdfb98c840c21",
                    "Gateway": "",
                    "IPAddress": "",
                    "IPPrefixLen": 16,
                    "IPv6Gateway": "",
                    "GlobalIPv6Address": "",
                    "GlobalIPv6PrefixLen": 0,
                    "MacAddress": "02:42:ac:11:00:02"

Sunday, July 24, 2016

Setting up a freebsd box with Vagrant

It makes sense to be able to spin up a freebsd system to use as for test of new ideas and concepts. It is also a good way for one to familiarize himself with the platform and experiment with new settings and technologies.

One of the easiest ways to do this is to use Vagrant. All it is needed is the following Vagrantfile:

# -*- mode: ruby -*-"
# vi: set ft=ruby :

box_type  = "freebsd/FreeBSD-10.3-RELEASE"

Vagrant.configure("2") do |config| = "#{box_type}"
  config.vm.synced_folder ".", "/vagrant", :disabled => true
  config.vbguest.auto_update = false = "sh"
  config.vm.base_mac = "080027D14C66"

  config.vm.provider :virtualbox do |vb|
    vb.customize ["modifyvm", :id, "--memory", "1024"]
    vb.customize ["modifyvm", :id, "--cpus", "1"]
    vb.customize ["modifyvm", :id, "--hwvirtex", "on"]
    vb.customize ["modifyvm", :id, "--audio", "none"]
    vb.customize ["modifyvm", :id, "--nictype1", "virtio"]
    vb.customize ["modifyvm", :id, "--nictype2", "virtio"]


Saturday, July 23, 2016

Installing latex packages with greek support for ubuntu 16.04

It is natural for things to evolve, and that is true for package names in linux distributions. So the good old tetex package family has evolved to texlive in ubuntu and what used to be one big package has been split to multiple smaller.
So in order to compile my latex files with Greek support and all, i need to install the following packages (and their dependencies) in ubuntu 16.04:

  • texlive
  • texlive-latex-extra
  • texlive-lang-greek

Tuesday, July 12, 2016

Autojump usage

Autojump is a tool that allows us to navigate our filesystem faster when using the command line.
It does all that by keeping statistics of which folders we visit most frequently and by making that available to us through some handy shortcuts.

There are multiple integrations with various shells, and an autojump plugin bundled with my oh-my-zsh.


We can install autojump using our package manager:
sudo apt-get install autojump

After that we need to source its initialization file. There are different files for each mainstream shell, so for zsh in ubuntu this line should do the trick:

[[ -s /usr/share/autojump/autojump.zsh ]] && . /usr/share/autojump/autojump.zsh

copy that in your .zshrc and do a
. ~/.zshrc

you are ready to use autojump now.


See statistics:
autojump -s


j dir

Open a directory in file browser instead of navigating:

jo dir

Autojump website:

Autojump usage

Autojump is a tool that allows us to navigate our filesystem faster when using the command line.
It does all that by keeping statistics of which folders we visit most frequently and by making that available to us through some handy shortcuts.

There are multiple integrations with various shells, and an autojump plugin bundled with my oh-my-zsh.


We can install autojump using our package manager:
sudo apt-get install autojump

After that we need to source its initialization file. There are different files for each mainstream shell, so for zsh in ubuntu this line should do the trick:

[[ -s /usr/share/autojump/autojump.zsh ]] && . /usr/share/autojump/autojump.zsh

copy that in your .zshrc and do a
. ~/.zshrc

you are ready to use autojump now.


See statistics:
autojump -s


j dir

Open a directory in file browser instead of navigating:

jo dir

Autojump website:

Thursday, July 7, 2016

Cleaning up docker device mapper

Docker device mapper is an alternative storage backend to aufs.
During everyday operation lots of images are downloaded that are never  deleted , so the device mapper may end up taking a lot of space in your system, unless you remember to clean it up regularly.

You can see the details about your docker instance by executing

sudo  docker info

This command will tell you what backend you are using and how much space is allocated to it.

After executing a container, you may want to clean up the images it downloaded in order for it to run. People usually forget to do this and eventually they end up taking a lot of space.

An easy way to clean any unused images and cleanup your device mapper is by executing the following command:

sudo docker images -a|awk '{print $3}'|xargs sudo docker rmi

In the past there was a bug that prevented docker from releasing the disk space. This has been now resolved and you should have no issues if you are running a newer kernel than 3.13

Monday, June 27, 2016

An alternative to dynamic dns using consul

If you have a remote system, behind a dynamic IP and need to access it, you can use one of the dynamic DNS providers.
What happens if your dynamic DNS suddenly stops working?

There is an alternative, provided you have access to a consul server.

You can set up your system to push its IP to the consul server (either the service backend, or the Key/Value store).

The following example is using the KV store

You can use the following commands in your remote system:

First of all you need to retrieve your external IP:

EXTERNAL_IP=$(curl "")

and then you need to push it to your consul server

curl -X PUT -d "$EXTERNAL_IP" http://consul-server/v1/kv/keyname/externalIP

You can set up this to be executed every now and then in order to update the key every time it changes by your provider.

these data can then be consumed by another script from any other system that need access to your remote system:

curl -s http://consul-server/v1/kv/keyname/externalIP|grep -Po '"Value":.*?[^\\]",'|awk -F: '{print $2}'|tr -d '",'|base64 -d|tr -d '%'

to retrieve the IP of the remote system.
You can then use this either directly, or put it in /etc/hosts or any other system you like.

Just keep in mind that you also need to execute this often since your ISP will change the remote IP relatively often (e.g a couple times per day)

Wednesday, May 25, 2016

Http proxying through an ssl tunnel

I have found useful in the past the use of a simple http proxy in one location (e.g tinyproxy), that listens on a local port (e.g localhost:8888)

And an ssl tunnel to that system that effectively maps a local port (e.g 8080) to the remote one.
Assuming the proxy on the other side is up and running, we can do the following:

ssh  -L 8080:localhost:8888 remote-server-with-proxy-service

Now we can configure one of our local browsers to use local port 8080 and access the proxy on the other side.
A useful trick if we need to access services geographically restricted (e.g tv streaming etc)

Sunday, May 22, 2016

Haskell in production

Interested in haskell in production?  Take a look at this

Saturday, May 14, 2016

LiquidCrystal Displays compatible with the Hitachi HD44780 driver and arduino pin mapping

These lcds are cheap and retro and work with most arduino boards even if you do not have i2c. They are using a bunch of digital pins for the communication.
The full details about the various pins can be found here.

There is an arduino shield that can be used for fast prototyping with a weird (at least for me) pin mapping. The pin mapping the shield is using is: lcd(8, 9, 4, 5, 6, 7).

However if you buy a naked lcd, you can wire it up any way you like. Unfortunately if you are using the shield to develop your app and have a different pin mapping in your naked lcd, that means that you need to modify the code between debugging and normal mode, or wire your lcd in the same way with the shield.

Most code examples out there are using the shield mapping as well.

Anyway. The lcd has 16 pins. Some of them can be wired only one way:

  • VSS (pin 1) -> Ground
  • VDD (pin 2) -> 5Volt
  • V0 (pin 3) -> 10K resistor/pot (this pin controls the contrast)
  • R/W (pin 5) -> Ground
  • A (pin15) -> 10K resistor/pot (this pin controls the backlight)
  • K (pin 16) -> Ground

and there are another 6 data pins that can be wired any way we like. The shield mapping is the following:

  • RS (pin 4) -> Digital pin 8
  • E (pin 6) -> Digital pin 9
  • D4 (pin11) -> Digital pin 4
  • D5 (pin12) -> Digital pin 5
  • D6 (pin13) -> Digital pin 6
  • D7 (pin14) -> Digital pin 7
The pins D0 up to D4 are not being used, since we are using the screen in 4bit mode.

This mapping should allow you to have the same mapping between your development environment and your final setup.

Friday, May 13, 2016

Cleaning hazy photos

Using gimp, multiple passes of the unsharpen mask filter with a radius of 50 and an amount of 0.2 will usually do the trick. After a certain point noise is introduced, so caution is needed.

The documentation for the filter can be found here

Saturday, May 7, 2016

Verifying https key and certificate match

Sometimes it is difficult to verify if your https key matches your https certificate.

In these cases you can use the following commands:

openssl x509 -noout -modulus -in /etc/yourcertificate.crt | openssl md5 
openssl rsa -noout -modulus -in /etc/private.key | openssl md5

Also keep in mind that the CN name of the certificate sign request (CSR) needs to match the CN of the certificate.

If you have more than one domain entries in the certificate, the first one is the CN. Multiple https virtualhost definitions (including the default ssl.conf) may confuse apache.

Tuesday, April 26, 2016

Holy Island: A DCI Ryan Mystery by LJ Ross

This book was a best seller when it was released in 2015. It is  a detective novel, with pagan cult highlights. Not too deep, but a good and easy read nevertheless.

Thursday, April 21, 2016

Using bus pirate to communicate with chips

Check this post
The bus pirate can be connected to a Linux box using a terminal emulator or multiplexer (screen and tmux should work fine)
It can also be used as a logic analyser using an opensource java based tool

Another article with usage instruction

Wednesday, April 20, 2016

Dynamic dns update with new server

Some time ago i posted a link to an article about how to set up a dynamic dns server with a raspberry pi. There is an update to that article here.
I will include the content of the article here for archival purposes:

In a previous post quite sometime back we explained how to configure a DynDNS service on your Raspberry pi or any similar unix system. This is no different, except for the super easy way of doing the similar thing.

Here we would be using the free DynDNS service of

Step. 1
Goto to and sign up

Step. 2
Verify the registered email to activate the service

Step. 3
Add a zone in your account (e.g.:
You can add your own host (which you might have bought separately), in that case you will also need to update the name-servers after this step.

Step. 4
Setup a cron job to update your dynamic ip to dns4e
sudo crontab -e

In the editor add the following line on a new line to update your DNS every 10 minutes
*/10 * * * * curl '<zone address>/a' --user '<Public Key>:<Secret Key>' --data '' -X POST

That's all, you should be able to reach out to your hosted server via the zone address you just configured after the DNS propagates.

Note: If your raspberry pi or unix box is behind a router or firewall then you might have to do port forwarding accordingly to enable the outside world to reach your server.

Tuesday, April 19, 2016

High current usb charging devices

It seems that in order for some devices to detect a charger as high current,  the data pins need to be short circuited. This will not work with Apple devices so a data voltage mapping need to be done in that case.

Thursday, April 14, 2016

Dirk Pitt 6, A night probe

As the series progress, they get better. This one is a spy storie. Multiple storylines, and a few unbelievable twists, but enjoyable.

Monday, April 11, 2016

Λεονάρντο ντα βιντσι δια την ζωγραφιά

Νομίζω ότι αυτό είναι ένα από τα πιο ενδιαφέροντα βιβλία που έχω δει τον τελευταίο καιρό :παναγιώτης-ιωάννου-διά-την-ζωγραφ/

Resizing disks in vms

This is a classic pain in the butt, and this blog explains how to do it.

I am going to copy and paste the content, just in case it disappears in the future.

VirtualBox : Extend Virtual Disk and File System

Related articles.

Extend Virtual Disk

If the virtual disk is defined as dynamically allocated (Dynamically allocated differencing storage), the existing disk is extended using the VBoxManage modifyhd command. The approach is similar on Linux and Windows. The --resize option assumes a size is specified in megabytes. If you want to specify the size in bytes, use the --resizebytes option.
The examples below show how to resize a virtual disk to 40G on Linux and Windows.
$ cd /u01/VirtualBox/ol6-112/
$ VBoxManage modifyhd ol6-112.vdi --resize 40960


C:\>cd "C:\Users\myuser\VirtualBox VMs\ol6-112"
C:\Users\myuser\VirtualBox VMs>"C:\Program Files\Oracle\VirtualBox\VBoxManage" modifyhd ol6-112.vdi --resize 40960

C:\Users\myuser\VirtualBox VMs>
If this command gives an error, saying the disk is already registered, use the UUID presented in the error in place of the file name, as shown below.
$ VBoxManage modifyhd ./ol6-112.vdi --resize 40960
VBoxManage: error: Cannot register the hard disk '/u01/VirtualBox/ol6-112/ol6-112.vdi' {fc63137b-c779-41a2-b0a3-5fb5788e77cc} because a hard disk '/u01/VirtualBox/ol6-112/ol6-112.vdi' with UUID {fc63137b-c779-41a2-b0a3-5fb5788e77cc} already exists
VBoxManage: error: Details: code NS_ERROR_INVALID_ARG (0x80070057), component VirtualBox, interface IVirtualBox, callee nsISupports
VBoxManage: error: Context: "OpenMedium(Bstr(pszFilenameOrUuid).raw(), enmDevType, enmAccessMode, fForceNewUuidOnOpen, pMedium.asOutParam())" at line 178 of file VBoxManageDisk.cpp

$ VBoxManage modifyhd fc63137b-c779-41a2-b0a3-5fb5788e77cc --resize 40960

Create Virtual Disk

Rather than extending an existing virtual disk, you can create a new virtual disk and associate it with the virtual machine to provide the extra space. The following text shows how this can be done in Linux and Windows.
$ cd /u01/VirtualBox/ol6-112/
$ VBoxManage createhd --filename ol6-112b.vdi --resize --size 10240
Disk image created. UUID: 34d7532e-cd4c-4bf8-88e3-5207aca1e343

$ VBoxManage storageattach ol6-112 --storagectl "SATA" --port 1 --device 0 \
    --type hdd --medium ol6-112b.vdi --mtype normal


C:\>cd "C:\Users\myuser\VirtualBox VMs\ol6-112"
C:\Users\myuser\VirtualBox VMs>"C:\Program Files\Oracle\VirtualBox\VBoxManage" createhd ^
     --filename ol6-112b.vdi --size 10240
Disk image created. UUID: 532fa35b-a437-4a07-8f4a-5503e9049cb6

C:\Users\myuser\VirtualBox VMs>"C:\Program Files\Oracle\VirtualBox\VBoxManage" storageattach ol6-112 ^
    --storagectl "SATA" --port 1 --device 0 ^
    --type hdd --medium ol6-112b.vdi --mtype normal

C:\Users\myuser\VirtualBox VMs>
When you start the virtual machine the disk will be visible to the OS. If you can't see it, you will need to force a rescan for SCSI devices. There are two methods to achieve this. The first involves echoing wildcards to the individual SCSI host(s).
# ls /sys/class/scsi_host/
host0  host1  host2

# echo "- - -" > /sys/class/scsi_host/host0/scan
# echo "- - -" > /sys/class/scsi_host/host1/scan
# echo "- - -" > /sys/class/scsi_host/host2/scan
The second involves echoing the value "1" to the SCSI device rescan file.
# ls /sys/class/scsi_device
1:0:0:0  2:0:0:0

# echo 1 > /sys/class/scsi_device/1:0:0:0/device/rescan
# echo 1 > /sys/class/scsi_device/2:0:0:0/device/rescan
Within a few seconds the device should be visible to the Linux OS. If in doubt, reboot the VM.

Partition the New Space

Start the virtual machine and check the current file system sizes. We plan to add space to the root file system.
# df -h
Filesystem            Size  Used Avail Use% Mounted on
                       26G   19G  5.3G  78% /
tmpfs                1004M   88K 1004M   1% /dev/shm
/dev/sda1             485M  144M  316M  32% /boot
//     907G  746G  115G  87% /host
In this example, we are adding the extra space by extending the existing virtual disk. If we were adding the space using an extra disk, we would follow a similar approach, but we would partition the new disk (/dev/sdb) instead. Keep this in mind when any device paths are used in this example.
Check the new space is visible from the operating system.
# fdisk /dev/sda

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
         switch off the mode (command 'c') and change display units to
         sectors (command 'u').

Command (m for help): p

Disk /dev/sda: 42.9 GB, 42949672960 bytes
255 heads, 63 sectors/track, 5221 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00076f69

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          64      512000   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              64        3917    30944256   8e  Linux LVM

Command (m for help):
Create a new partition using the remaining space on the disk. In this case, it was the 3rd partition on the disk, so the partition was created with the "n, p, 3, (return), (return)" sequence of entries.
Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
Partition number (1-4): 3
First cylinder (3917-5221, default 3917): 
Using default value 3917
Last cylinder, +cylinders or +size{K,M,G} (3917-5221, default 5221): 
Using default value 5221

Command (m for help):
Change the partition type to "Linux LVM". In this case, the sequence of entries was, "t, 3, 8e".
Command (m for help): t
Partition number (1-4): 3
Hex code (type L to list codes): 8e
Changed system type of partition 3 to 8e (Linux LVM)

Command (m for help):
Write the changes to the partition table using the "w" command.
Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.
Due to the final warning, the VM must be rebooted before you can continue.
 If we had used a new virtual disk, rather than extending the existing one, we would not have needed to reboot after the partitioning step.

Add Partition to LVM

Add the new partition to the volume group. Create a physical volume from the "/dev/sda3" partition using the pvcreate command.
# pvcreate /dev/sda3
  Physical volume "/dev/sda3" successfully created
Add the physical volume to the existing volume group. Display the volume group name using the vgdisplay command, then use the volume group name and partition name with thevgextend command.
# vgdisplay
  --- Volume group ---
  VG Name               vg_ol6112
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  3
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                2
  Open LV               2
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               29.51 GiB
  PE Size               4.00 MiB
  Total PE              7554
  Alloc PE / Size       7554 / 29.51 GiB
  Free  PE / Size       0 / 0   
  VG UUID               M3LcFJ-etHj-u7zh-I4em-4Js0-SczK-8JDj93
# vgextend vg_ol6112 /dev/sda3
  Volume group "vg_ol6112" successfully extended
Use lvdisplay command to get the root logical volume name. Use the vgdisplay command to get the free space in the volume group. Use this information in the lvextendcommand to extend the logical volume.
# lvdisplay | grep "LV Path"
  LV Path                /dev/vg_ol6112/lv_root
  LV Path                /dev/vg_ol6112/lv_swap
# vgdisplay vg_ol6112 | grep Free
  Free  PE / Size       2558 / 9.99 GiB
# lvextend --size +9.99G --resizefs /dev/vg_ol6112/lv_root
  Rounding size to boundary between physical extents: 9.99 GiB
  Extending logical volume lv_root to 35.56 GiB
  Logical volume lv_root successfully resized
resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/mapper/vg_ol6112-lv_root is mounted on /; on-line resizing required
old desc_blocks = 2, new_desc_blocks = 3
Performing an on-line resize of /dev/mapper/vg_ol6112-lv_root to 9322496 (4k) blocks.
The filesystem on /dev/mapper/vg_ol6112-lv_root is now 9322496 blocks long.

 If we had specified a size of 10G, we might have got an error message saying something like, "could not extend by 2560 extents", due to a rounding error. In the above example, the size of 9.99G was used to allow it to fit, but a better alternative would be to specify the size using extents, using one less extent than the number reported in the error, as shown below. Thanks to Julian Dyke for suggesting the extents approach.
# lvextend --extents +2559 --resizefs  /dev/vg_ol6112/lv_root
The lvextend command used the --resizefs option. If we had not used this, we would have to run the resize2fs command separately.
# resize2fs /dev/vg_ol6112/lv_root
Checking the size of the file systems reveals the root file system has grown by approximately 10G.
# df -h
Filesystem            Size  Used Avail Use% Mounted on
                       36G   19G   15G  56% /
tmpfs                1004M   88K 1004M   1% /dev/shm
/dev/sda1             485M  144M  316M  32% /boot
//     907G  746G  115G  87% /host
If you need more information about the Linux Logical Volume Manager (LVM), you can read about it here.

Resize Fixed Size Disks

The VBoxManage modifyhd command doesn't work on fixed disks, so to get around this, simply clone the existing disk to a dynamically allocated disk, then resize that.
$ VBoxManage clonehd ol6-112.vdi ol6-112-b.vdi --format VDI --variant Standard
$ VBoxManage modifyhd ol6-112-b.vdi --resize 40960

Once that is complete, use the new virtual disk for the virtual machine and perform the OS resize operations as before.

Friday, April 8, 2016

Dirk Pitt 5: Vixen 03

This book is better than the others, it has multiple storylines, and even though the end is predictable,  the plot is actually not.

Sunday, April 3, 2016

Numa 4 white death

Another adventure book with Austin Kurt investigating a company of fish farming. Quite light and enjoyable.

Wednesday, March 30, 2016

A time to kill, by John Grisham

Finished this book, that is about the trial of a black father who killed the rapists of his daughter. I must admit that I do not usually read books from this genre, but I liked it a lot.
The legal technicalities were from time to time a bit boring, but overall this is one of the best books I have read in the past few months

Thursday, March 24, 2016

Dirk Pitt 3: Ice Fire

A Dirk Pitt book without Dirk Pitt, still uncomplicated but better on the action side than the first two. An attempt has been made to explain the basic idea in a scientific way. Still enjoyable reading

Thursday, March 17, 2016

How to change hostname in centos7

Obviously you can do it manually, but there are a number of tools that can do it for you:

  1. hostnamectl command : Control the system hostname. This is recommended method.
  2. nmtui command : Control the system hostname using text user interface (TUI).
  3. nmcli command : Control the system hostname using CLI part of NetworkManager.
Tip stolen from here

Wednesday, March 16, 2016

Dirk Pitt 2: the Mediterranean caper

The second book of the series. Another James bond like book, simple but enjoyable. The hero always gets the girl

Tuesday, March 15, 2016

Zsh tricks

A useful cheat sheet for zsh

Tuesday, March 8, 2016

Dirk Pitt book 1

Light, enjoyable reading. The kind that would be ideal for a James bond like film. The plot is a bit naive and the characters rather shallow. Good for relaxation after work

Wednesday, March 2, 2016

Casual vacancy

This is an adult book from  John K Rowling. The story revolves around a small town called Pagford  and a larger city next to it called Yarvil. It is an interesting story albeit a little dramatic.

Sunday, January 31, 2016

Regulating automatic watches using audacity

Nice blog post

Sunday, January 10, 2016

Replacing watch movement

Never thought about replacing the movement of an old watch but it seems it is possible