Friday, February 3, 2017

Subdomain vs Address

Recently I heard an internet consultant refer to the address "" as a "subdomain" which led me to do a bit of research into what is causing this terminology confusion.

In my experience in IT, going back to '93-94 when companies were first getting up on the internet, the 1992 first edition of the O'Reilly book DNS & BIND was considered THE bible on DNS.  That book taught us early pioneers what a "subdomain" truly is.

So understand my surprise when Googling "address vs subdomain" today revealed that almost everyone now thinks that having a hostname other than "www" in front of your domain name is a "subdomain" - all thanks to internet hosting providers who don't even know what they are talking about.

I feel like the main character from the movie "Idiocracy" who finds himself in the far future and everyone has become...well, let's just say less than well-informed.  Next thing you know people will be handing out business cards with uppercase letters in their email addresses.

Once a few hosting providers start using one another's REdefinition of a term, the error spreads across the internet like a virus. 

Let's start with a simple English analysis of the word "subdomain"

"Sub" from Latin meaning "under" makes us interpret the word to mean "a domain that is under or subordinate to another domain" - this means that the subdomain must first be a domain and second it is subordinate to another domain in some manner.

Subdomains are traditionally used to break up a higher-level domain into smaller administrative parcels.  Let's take the domain for example, used by the state of California. is the domain
The NS records for this domain are:

It probably has several subdomains, but here are some I know of: for the Department of Motor Vehicles
The NS records for this domain are: (same as parent) for the Office of the Attorney General
The NS records for this domain are: (different)

Each of these two subdomains have www addresses:

The oag subdomain also has an ftp address:

Each subdomain also has different MX (mailserver) records, but I'm not going to publish them.

Traditionally a subdomain has NS records in its parent's zone file that specify the nameserver(s) hosting the zone files for the subdomain's records.  www and ftp are A records (A for Address) in the zone file. is a subdomain and are addresses

So it looks like the California IT department decided to host DNS for the DMV subdomain on their nameservers while letting the OAG IT department manage DNS on their own servers.  This is one of the legitimate reasons to create a subdomain in the first place - to delegate authority to another group. The OAG IT department can manage all the DNS records (addresses, aliases, mailservers, etc.) for their subdomain without going through the IT people at another office.

Chapter 9: Parenting from the 5th edition of DNS & BIND (Liu, Cricket and Albitz, Paul, O'Reilly Media Inc., 2006) lists three common reasons you would want to set up a subdomain:
  1. A need to delegate or distribute management of your domain to a number of organizations
  2. The large size of your domain; dividing it would make it easier to manage and reduce the load on your authoritative nameservers.
  3. A need to distinguish hosts' organization affiliations by including them in particular subdomains.
Now, just because a subdomain has an A record itself (in case people forget the www in front - sort of a "default" website for the domain) doesn't mean that every address is a subdomain.  While every basketball is a sphere not every sphere is a basketball.

A reasonable definition of a "subdomain" is that it meets one of the two following requirements:
  1. It has NS records - a "delegated" subdomain
  2. It has at least one record other than the A record for the subdomain itself - within the parent's zone file
Also, internet hosting providers need to stop calling address records "subdomains" - just call them what they are - if they add A records to the zone file, they are "addresses"


I was surprised I found a few authors on the internet who actually know what a subdomain is and bothered to try to educate others.
  1. Suso
  2. Mark Vogt on this blog and that blog
I'll add more links as I come across them.  The truth is out there.  Even Wikipedia isn't 100% accurate about the definition of a subdomain, and mentions some kind of "lively debate" over its definition.  But then again, a Wikipedia article is only as accurate as the last person to edit it.

Thursday, December 8, 2016

Raspberry Pi Security Camera Viewer

Most high-definition televisions have a "Picture-in-Picture" feature that is useless; if you are watching a HD input the PIP window can only display a low-resolution input such as RF or Composite SDTV.  Furthermore the sole Composite video input is often combined with the Component video input which may already be used by your older video game console. 

What's left?  I'll show you how to use your HDTV's coaxial cable TV RF input to view up to four network security cameras in the PIP window so you can keep an eye on your perimeter while watching something else.

We'll use the Raspberry Pi to automatically scan your network for up to four RTSP cameras and display them in a 1x1 or 2x2 grid through its composite video output fed to an RF modulator connected to your TV. 

In fact, if you still have unused "cable TV" coaxial cable running all over your home you can use it to send the camera grid to multiple televisions.  You just need to tune each TV to the RF modulator channel.  Just make sure your coaxial cables don't actually connect to the cable TV company!

The RF Modulator

I use a Channel Vision E Series E1200 but any RF modulator will do.  These take a composite video input and output it on an RF cable channel of your choice (usually between 2 and 13)

Using the correct A/V cable for the Raspberry Pi 3 is very important.  Please read this article on how cables that appear to be similar can have very different pinouts.

I have tested this Zune cable from Amazon and it works fine with the Raspberry Pi.

Camera configuration

This project requires that all your network security cameras support RTSP and use the same username, password and RTSP url suffix. 

I've been pretty happy with the Amcrest IP2M-842E Outdoor 1080P POE Security Camera available from Amazon in Black or White.  I'll assume you know how to make and run CAT6 cabling and know these need to be plugged into a POE switch or separate POE power injectors.

When you set these up using Amcrest's app be sure to configure them with the same username and password.  They all have the same RTSP url format:


Subtype 1 = SD
Subtype 0 = HD

Since we will be outputting SD from the Pi there's no need to use the HD streams.  Use subtype=1.

About Network Video Recorders (NVRs)

Using RTSP streams from your cameras should not prevent you from simultaneously using an NVR (such as the one made by Amcrest) to record camera video when motion is detected in predefined zones.  This project just gives purpose to the PIP feature on your TV whether you use an NVR or not.

While most NVRs can output a 2x2 (or better) grid for monitoring your cameras, I've only seen HDMI outputs on them.  That means I can't use the NVR with the PIP feature on my TV.

I suppose the alternative to this project is to either get a TV that supports HDMI on PIP or try to find an HDMI to Composite video converter.  But I'd still need an RF modulator anyhow.  And this means the NVR can be somewhere else, secured against theft.

Raspberry Pi 3 configuration

First, follow my initial configuration guide.

Install nmap, omxplayer and screen:

sudo apt-get install nmap omxplayer screen

Edit /boot/config.txt:

sudo nano /boot/config.txt

Comment out (add # in front) ALL occurrences of hdmi_force_hotplug - it may be in there more than once!
Add overscan_scale=1 and gpu_mem=128
Uncomment sdtv_mode and set it to 0
# uncomment if hdmi display is not detected and composite is being output

# uncomment for composite PAL

# NOOBS Auto-generated Settings:

# CCTV Settings
With these settings if the Pi boots up and does not detect an HDMI monitor connected it will use the composite video output.

Create /home/pi/cctv:

nano /home/pi/cctv

Type in (or copy and paste) this bash script, substituting the username and password used by your cameras:

Then grant execute permissions:

chmod +x /home/pi/cctv

Test the script by running it manually, specifying the horizontal and vertical resolution that works best for you:

./cctv 640 480

To configure the Pi to run the script on boot, add this line to /etc/rc.local before exit 0:

/home/pi/cctv 640 480

Wednesday, December 7, 2016

Raspberry Pi 3 initial configuration

Here are the steps I use when setting up a new Raspberry Pi 3.

I usually get an 8GB microSD card but depending on the project I've gone larger.  I like the SanDisk Extreme microSDHC UHS-I. 

Make sure you have the proper power supply for the Pi 3.  I believe it needs to be at least 2.5 amps. 

Download the NOOBS zip file from the Raspberry Pi .org site and unzip its contents into the microSD card from your PC.  The cards I buy are preformatted FAT32 which works fine for NOOBS.

Slip the microSD card into the Pi 3 and boot it up.  If you press the w key you can connect to your home wifi network in order to view the complete list of installation options.  You need to do this so you can select the Lite version of the Raspbian OS, which is my preference.

After the installation is completed and the Pi has rebooted, log in as user pi with password raspberry.

Change the root password to raspberry so you don't forget it (in case you need to su)

sudo passwd root

Go through the locale & internationalization options in raspi-config to set your timezone, keyboard, country, etc.

sudo raspi-config

Configure wpa_supplicant.conf so the Pi connects to your home wifi network on boot:

Setting WiFi up via the command line

Reboot the Pi:

sudo reboot

Update the Pi:

sudo apt-get update
sudo apt-get upgrade

Here's another way to change the keyboard configuration to US (the Pi defaults to a UK configuration):

sudo dpkg-reconfigure keyboard-configuration

Edit /etc/rsyslog.conf:

sudo nano /etc/rsyslog.conf

Comment out these lines at the bottom:
#       news.err;\
#       *.=debug;*.=info;\
#       *.=notice;*.=warn       |/dev/xconsole
Set the timezone of the Pi.  Run the next command from the console rather than over SSH:

sudo dpkg-reconfigure tzdata

Older Pi kernel versions defaulted power management to on which in conjunction with another setting may result in the integrated wifi interface going to sleep - most inconvenient when trying to manage the prop over wifi!

The apt-get update and upgrade steps performed above should upgrade the kernel.  You can check your kernel version by issuing the following command:

sudo uname -a

As of this writing my kernel version is 4.4.34-v7+ #930 SMP.

You can check the power save mode of the wifi interface using the following command:

sudo iw wlan0 get power_save

If it says power save mode is On then you can try adding this line to /etc/network/interfaces after the wlan0 section:

post-up iw wlan0 set power_save off

Then reboot and check the power save mode of the interface again to confirm it is now off.  If you ever see this mode change back to On try searching the internet to solutions for the power management issue and try different solutions until it is resolved.  Following the above steps resolved the issue for me. 

Friday, December 2, 2016

Manage animatronic props from a wireless tablet, Part 2

Step 2:  Install a suitable web server and server-side application framework

(continued from Part 1)

Rather than Apache I went with NGINX for the web server.  Since I want to develop the web application in Python 3, I selected Django.  In order to work with Django, NGINX needs uWSGI.  I also want to use PostgreSQL as the database.

sudo apt-get install nginx

sudo apt-get install uwsgi
sudo apt-get install python3
sudo apt-get install python3-rpi.gpio
sudo apt-get install uwsgi-plugin-python3
sudo apt-get install python3-django

sudo apt-get install postgresql
sudo apt-get install python3-psycopg2

Breakdown of our "stack":

  1. NGINX is the web server
  2. uWSGI is the interface between the web server and the web application framework
  3. Django is the web application framework
  4. Python is the application programming language
  5. PostgreSQL is the database
Throughout this article I may talk about "editing a file" and I may or may not tell you how to do this.  I prefer to use the nano editor.  The syntax is nano followed by the path & filename.  If you are not root you will need to add the sudo command in front.

NGINX configuration

Since users will connect from a tablet such as an iPad, once they connect to the Raspberry Pi in wifi access point mode we want to redirect all traffic to the application.

Since many of the bookmark URLs in Safari (such as Google, Apple, etc.) start with https we need to configure NGINX to allow https over port 443 in addition to regular http over port 80.

First we generate a self-signed SSL certificate.

You'll need to read up on how to configure an NGINX site.  Here's how I configured mine:
server {
listen 80;
listen 443 ssl;
if ($scheme = https) {return 302 http://$server_addr/prophome.html;}
server_name localhost;
ssl_certificate /etc/nginx/server.crt;
ssl_certificate_key /etc/nginx/server.key;
access_log /var/log/nginx/asp.access.log;
error_log /var/log/nginx/asp.error.log;
location / {
     root /var/www/asp;
     index prophome.html;
     error_page 404 302 http://$server_addr/prophome.html;
location /app {
     include         /etc/nginx/uwsgi_params;
     uwsgi_pass      unix:/var/uwsgi/propos.sock;
     uwsgi_param     UWSGI_SCHEME $scheme;
     uwsgi_param     SERVER_SOFTWARE nginx/$nginx_version;
The scheme and error_page lines redirect the user's browser to the application page prophome.html which is just a basic "Hello World" html file we create for initial testing. 

Eventually prophome.html will be changed to the real application page.

This makes connecting simple; the user just clicks any icon in their Safari bookmarks and does not have to remember any special URL to access the application.

uWSGI configuration

In /usr/share/nginx/propos/ create a test program:
def application(environ, start_response):
     start_response('200 OK', [('Content-Type', 'text/html')])
     return [b"<h1 style="color: blue;">Hello There!</h1>"]
The b after return[ is required in Python3. Without it you will not get a response.

In /etc/uwsgi/apps-available, create an ini file for the application.

sudo nano /etc/uwsgi/apps-available/propos.ini

The file should look like this:
module = wsgi:application
chdir = /usr/share/nginx/propos/
python-path = /usr/share/nginx/propos
socket = /var/uwsgi/propos.sock
chown-socket = www-data
chmod-socket = 666
enable-threads = true
master = true
plugins-dir = /usr/lib/uwsgi/plugins
plugin = python34,http
uid = www-data
gid = www-data
vacuum = true
die-on-term = true
manage-script-name = true
Create a symbolic link for this file in ../apps-enabled:

sudo ln -s /etc/uwsgi/apps-available/propos.ini /etc/uwsgi/apps-enabled/propos.ini

Then restart uwsgi:

sudo service uwsgi restart

Then you might as well restart NGINX:

sudo service nginx restart

NGINX communicates with uWSGI over a unix socket which is specified in both config files (/var/uwsgi/propos.sock) - you may need to create the directory and/or adjust the permissions.

If you go to http://(pi address)/app you should see the test output:

Hello There!

If you see that, uWSGI is working correctly.  We will be reconfiguring propos.ini to work with a Django project in the next section.

Django configuration

Create a new Django project.  In this example I will use /home/pi/propos.

cd /home/pi
(do not create a propos directory in /home/pi, django admin will do that for you automatically)

django-admin startproject propos

Django will create the propos directory containing and a propos subdirectory containing other .py files.

Reconfigure uWSGI to point to this Django application:

sudo nano /etc/uwsgi/apps-available/propos.ini

Edit the file to look like this:
chdir = /home/pi/propos/
module = propos.wsgi:application
socket = /var/uwsgi/propos.sock
chown-socket = www-data
chmod-socket = 666
enable-threads = true
master = true
plugins-dir = /usr/lib/uwsgi/plugins
plugin = python34,http
uid = www-data
gid = www-data
vacuum = true
die-on-term = true
manage-script-name = true
Restart uWSGI:

sudo service uwsgi restart

After the service fully restarts If you go to http://(pi address)/app you should see something like this:

If you see that then uWSGI and Django are working correctly!