Key differences between Understanding and Learning (Memorization)

Many Educational Institutes, even today, do not focus on understanding. Their tests can be easily passed with memorization. This weakens the foundation of the students and adversely affects his future performance in professional engagements. Let’s look at the key differences between understanding and memorization and why understanding should be the priority for all students.

Memorization is simple. We all know that by repeated reading of any subject matter we can remember it by heart and be able to regurgitate (repeat information without analyzing or comprehending it) on demand, even matching similar sounding questions with the answer you have learned. And that is pretty much all you need to get through in most school systems and even most colleges.

Understanding, on the other hand, is knowing the underlying ideas and concepts so well that you can then explain them in your own words, even if you do not remember any of the terminology used. It allows you to develop insights that comes from inductive or deductive reasoning on the concepts.

You know you have understood something well when you can apply it to real life situations and clearly explain it to a layman with ease.

With understanding your can identify the similarities and differences between similar sounding ideas on your own.

Understanding is the key to advancing knowledge and discovering new knowledge.

Understanding is what is useful in real life, learning alone takes us nowhere.

Today computers can store much more facts than you will ever learn and can regurgitate it faster, even for complex queries (like Google). Instead of focusing your energies on memorization, which is anyways a losing and pointless battle, why not focus on understanding the topic at hand?

You will find that when you understand any topic, you tend to remember the key words and phrases too, thereby serving both the purposes of your exams as well as much bigger purpose of excelling real life and profession.

How to Easily Configure WiFi in Raspberry Pi

Any version of Raspberry Pi can be very easily configured with WiFi access. Coupled with ssh or vnc, it allows you to manage your Pi remotely. Here is the simplest way I could think of, illustrated by a screenshot and detailed below.

Once your Raspberry Pi boots up, you will get to this shiny screen. Now open a Terminal by clicking on the black square icon on top-left of the screen.Screenshot from 2017-01-04 11-29-18

This opens a Terminal where you type in:

sudo leafpad /etc/network/interfaces

This opens up a notepad-like editor. Make three changes to the text as shown in the highlighted section:

  1. Change manual to dhcp in the line starting with “iface wlan0”
  2. Replace wifi_id with the Wireless Access ID / SSID
  3. Replace password with your actual password for Wireless Access

Now save it (Ctrl-S) like notepad and exit it. The terminal should still remain open.

Now either reboot the Pi or restart the network with the following command on Terminal (don’t forget to press <Enter> after you typed):

sudo service networking restart

Wait for a few minutes for the WiFi to come up. On latest Raspbian with PIXEL, you can verify by seeing the two blue arrows in opposite direction, as can be seen from the screenshot.

Steps to secure and protect your Skype account from Hacking

Skype accounts are being hacked since at least August last year. Breached Skype accounts are used to send thousands of spam messages before they’re locked by Microsoft. The owners then have to regain access and that is when most find out about it. Skype has fallen victim to similar attacks before, and hackers were able to spoof messages on the system in 2015 after using lists of stolen usernames and passwords to gain access to accounts.

Problem

This wave of attack appears to be growing in size, and Skype users who opted for Microsoft’s two-factor security are also vulnerable. Microsoft offers the ability to link a Skype and Microsoft Account together to make sign-in and security easier. It turns out that Microsoft keeps your original Skype account password separate so that it can still be used to access the service with a Skype username. If that password isn’t secure then hackers can use it to gain access to your Skype account, bypassing any two-factor authentication provided by Microsoft. Essentially Microsoft has left a backdoor open to their vaunted two-factor security! It can be safely assumed that the new wave of attack is dictionary based and Skype / Microsoft allows unlimited login tries at some entry point.

Solution

The solution, in brief, is to switch to Microsoft’s two-factor security and then disable access by old method.

1. Update your Skype account to a Microsoft account:

  • Go to https://account.microsoft.com, if you’re already signed in, sign out.
  • Enter your Skype name and password when prompted and then select
  • Sign in.
  • If your Skype account is not updated already, you will be notified to update your account.
  • Select Next to continue.
  • You will be asked to add an email to your account, and verify that email.
  • Congrats, your Skype account is also a Microsoft account.

2. Ensure that your Accounts are fully merged:

  • Go to https://account.microsoft.com, if you’re already signed in, sign out.
  • Enter your Skype name, not your Microsoft Account email address, and use your Skype password to sign-in
  • If you’ve linked your Microsoft Account previously, you’ll be prompted to sign-in and merge the accounts to create a Skype alias

3. Disable Skype alias:

Once the two accounts are properly merged, Microsoft creates a Skype alias to let you keep signing in with a Skype username. Disable it under the aliases preferences, to ensure complete protection.

Maximum number of Files in a Directory

Different file systems in different Operating Systems has different limitations in the number of files that can be in a directory as determined by the underlying architecture.. Here is an overview of maximum of number of files that you can have in a directory and associated problems, if any, like performance.

FAT32

  • Maximum number of files: 268,173,300
  • Maximum number of files per directory: 216 – 1 (65,535)
  • Maximum file size: 2 GiB – 1 without LFS, 4 GiB – 1 with

NTFS

  • Maximum number of files: 232 – 1 (4,294,967,295)
  • Maximum file size
    • Implementation: 244 – 26 bytes (16 TiB – 64 KiB)
    • Theoretical: 264 – 26 bytes (16 EiB – 64 KiB)
  • Maximum volume size
    • Implementation: 232 – 1 clusters (256 TiB – 64 KiB)
    • Theoretical: 264 – 1 clusters

ext2

  • Maximum number of files: 1018
  • Maximum number of files per directory: ~1.3 × 1020 (performance issues past 10,000)
  • Maximum file size
    • 16 GiB (block size of 1 KiB)
    • 256 GiB (block size of 2 KiB)
    • 2 TiB (block size of 4 KiB)
    • 2 TiB (block size of 8 KiB)
  • Maximum volume size
    • 4 TiB (block size of 1 KiB)
    • 8 TiB (block size of 2 KiB)
    • 16 TiB (block size of 4 KiB)
    • 32 TiB (block size of 8 KiB)

ext3

  • Maximum number of files: minimum (volume Size / 213, number of Blocks)
  • Maximum file size: same as ext2
  • Maximum volume size: same as ext2

ext4

  • Maximum number of files: 232 – 1 (4,294,967,295)
  • Maximum number of files per directory: unlimited
  • Maximum file size: 244 – 1 bytes (16 TiB – 1)
  • Maximum volume size: 248 – 1 bytes (256 TiB – 1)

Possible causes & solutions for MongoDB not running

Is your MongoDB properly running? A simple way to check it would be with:

service mongod status

On my CentOS 5.x it gave:

mongod dead but subsys locked

There are two possible causes I could find. First is related to disk space. If you do not have enough space for dbpath (database directory) then you may get this message.

To solve it you can add following to the config file provided when running mongod --config mongod.conf

For MongoDB 3.x (latest version)

storage:
   mmapv1:
      smallFiles: true

For version 2.6+

storage:
   smallFiles: true

For version 2.4 and less

smallfiles = true

Then just execute mongod to accept your config file (here it assumes that location of the config is /etc/mongodb.conf):

mongod -f /etc/mongodb.conf

Documentation for smallfiles parameter:

Set to true to modify MongoDB to use a smaller default data file size. 
Specifically, smallfiles reduces the initial size for data files and
limits them to 512 megabytes. The smallfiles setting also reduces the
size of each journal files from 1 gigabyte to 128 megabytes.
Alternatively you can run mongod with --smallfiles parameter like:
mongod --smallfiles

On my machine the problem was different. It was expecting a directory /var/lib/mongod with proper permissions, which was not there. The solution is simple:

sudo mkdir /var/lib/mongod
sudo chown -R mongod /var/lib/mongod

However how did I find out about the problem(s) in the first place. Again the solution is very simple. I looked in the log file:

vi /var/log/mongodb/mongodb.log

Always start with the log file.

Finally you can verify that your system is running properly with:

sudo service mongod status

After fixing it gave:

mongod (pid 26194) is running...

Now that’s solved, let’s get back to mongodb coding..

Ubuntu: How to Change Host name and Propagate to DHCP Server

How to change Hostname on Ubuntu

First find your current host name by typing:

hostname

Open /etc/hostname and change the host name specified there to the new host name.

sudo vi /etc/hostname

Now open /etc/hosts and locate the old host name in the file and change it to the new host name.

sudo vi /etc/hosts

Now restart hostname with:

sudo service hostname restart

How to propagate Hostname Change to DHCP Server and other machines

The chosen host name should be propagated to the DHCP server so that any other computer can refer to this computer by your new chosen hostname. To do that run the following commands:

sudo dhcclient -r ; sudo dhclient

Now you should be able to access this machine by its newly chosen host name from any other machine in the same network and served the same DHCP server.

An exception would be if a machine is configured statically or not configured to use the name server associated with this dhcp server.

Most routers today comes with DHCP server and an associated Name Server which can be configured as shown above.

Suggestions for Raspberry Pi Demo & Tutorial for Engineering Students

Next week I am giving a demo of Raspberry Pi and a Tutorial to Engineering students, primarily from Electronics & Computer Science department. I am collecting suggestions on what to show them in this seminar. Currently I have thought about the following items

  • How to use Raspberry Pi to create a mini FM Radio Station as a cool example to get them hooked on Pi
  • How to write simple Java Programs with built-in IDE to show the capability of Pi

What else do you think I should show and tell?

Safest way to Update and Upgrade Raspbian Wheezy (Raspberry Pi OS)

There are plethora of instructions on the web to update and upgrade Raspbian and they work too, under normal conditions. However as Raspberry Pi is increasingly being used for Mission Critical tasks, it is important to adopt a procedure which won’t leave you with broken packages or worst, a un-bootable Operating System with your data on it. The following is a simple procedure, with explanations which will make sure that your Pi remains working.

First let’s update and upgrade the Pi with a single line command, run from terminal:

sudo apt-get update -y && sudo apt-get upgrade -y && echo success

This will update and upgrade your Pi and if successful will print success at the end.

Now reboot the Pi with:

sudo reboot

Normally Pi would reboot properly 99% of the time. If it refuses to boot then you can select the old kernel while booting to get back an usable version of Raspbian OS.

After this only two more steps remain. First is to dist-upgrade the Raspbian OS:

sudo apt-get dist-upgrade -y && sudo apt-get autoremove -y && echo success

You  may wonder why I didn’t do it the very first time. While dist-upgrade is better than plain upgrade as it can intelligently install packages based on dependency, upgrade retains the older kernel and gives you a way to back out safely, unlike dist-upgrade. The procedure outlined above protects your OS from cases where the upgrade is broken for any reason.

Now all that is left is to reboot again to make sure everything is OK.:

sudo reboot

You may notice that I didn’t ask you to rpi-update, an instruction you will find at many places online. This is because you do not need rpi-update, the necessary firmware updates are already installed when you upgraded Raspbian. In fact, and I speak from experience, rpi-update can break your running system. Let’s leave that bleeding edge to who really needs it. If you are reading this article, then it can safely be said you don’t.

I used sudo apt-get autoremove to remove any extra packages.

The && before echo success makes sure success is printed only when the previous command succeeds.

Disk space is premium in SD Card. So it may not be out of place to check for available disk space before running update, upgrade or dist-upgrade:

df -h

To save some space clean up the downloaded debian archives with:

sudo apt-get clean

Now you understand why automating Raspbian updates / upgrades is a bad idea, unless you want to use the Raspberry pi only for testing purposes.

Advanced Note on why rpi-update was not suggested:

It’s current Raspberry Pi practice not to use this [ rpi-update ] unless you REALLY need it as it can bring in a non-working kernel (i.e. the latest bleeding edge version, which is not guaranteed to work).

My thoughts are that it is not actually required once you have done the apt-get update/upgrade cycle.

James, Raspberry Pi Foundation (Trading)

How to remove Squeak and Scratch from Raspberry Pi: Raspbian Jessie and Wheezy Distro

Raspbian Jessie and Wheezy distribution includes Squeak and Scratch. While these can be helpful educational tools for students which provides a gentle introduction to programming, it doesn’t have much use for others. The following instructions will remove both Squeak and Scratch from your Raspberry Pi (Raspbian distribution). It saves 92.7 MB and 1.15 MB respectively in Jessie and another 10.2 MB with subsequent autoremove, so over 100 MB space saved.

root@puma:/home/pi# apt-get remove --purge scratch*
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Note, selecting 'nuscratch' for regex 'scratch*'
Note, selecting 'squeak-plugins-scratch-dbg' for regex 'scratch*'
Note, selecting 'squeak-plugins-scratch' for regex 'scratch*'
Note, selecting 'python3-pifacedigital-scratch-handler' for regex 'scratch*'
Note, selecting 'libdirectory-scratch-perl' for regex 'scratch*'
Note, selecting 'libdirectory-scratch-structured-perl' for regex 'scratch*'
Note, selecting 'scratch' for regex 'scratch*'
Package 'libdirectory-scratch-perl' is not installed, so not removed
Package 'libdirectory-scratch-structured-perl' is not installed, so not removed
Package 'squeak-plugins-scratch-dbg' is not installed, so not removed
The following packages were automatically installed and are no longer required:
  fonts-roboto gtk2-engines-clearlookspix liblightdm-gobject-1-0
  libxfce4ui-1-0 libxfce4util-bin libxfce4util-common libxfce4util6
  libxfconf-0-2 lightdm-gtk-greeter pimixer pipanel squeak-vm wiringpi
  xfce-keyboard-shortcuts xfconf
Use 'apt-get autoremove' to remove them.
The following packages will be REMOVED:
  nuscratch* python3-pifacedigital-scratch-handler* scratch*
  squeak-plugins-scratch*
0 upgraded, 0 newly installed, 4 to remove and 1 not upgraded.
After this operation, 92.7 MB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 136309 files and directories currently installed.)
Removing nuscratch (20160115) ...
Removing 'diversion of /usr/bin/scratch to /usr/bin/scratch.old by nuscratch'
Removing 'diversion of /usr/bin/squeak to /usr/bin/squeak.old by nuscratch'
Removing 'diversion of /usr/share/scratch/locale/ja_HIRA.po to /usr/share/scratch/locale/ja_HIRA.po.old by nuscratch'
Removing 'diversion of /usr/share/scratch/locale/ja.po to /usr/share/scratch/locale/ja.po.old by nuscratch'
Purging configuration files for nuscratch (20160115) ...
Removing python3-pifacedigital-scratch-handler (2.0.5-1) ...
Purging configuration files for python3-pifacedigital-scratch-handler (2.0.5-1) ...
Removing scratch (1.4.0.6~dfsg1-5) ...
Purging configuration files for scratch (1.4.0.6~dfsg1-5) ...
Removing squeak-plugins-scratch (1.4.0.2~svn.r83-2) ...
Processing triggers for hicolor-icon-theme (0.13-1) ...
Processing triggers for man-db (2.7.0.2-5) ...
Processing triggers for gnome-menus (3.13.3-6) ...
Processing triggers for desktop-file-utils (0.22-1) ...
Processing triggers for mime-support (3.58) ...
Processing triggers for shared-mime-info (1.3-1) ...
root@puma:/home/pi# apt-get remove --purge squeak*
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Note, selecting 'squeak-plugins-scratch-dbg' for regex 'squeak*'
Note, selecting 'squeak-vm' for regex 'squeak*'Mathematica
Note, selecting 'squeak-plugins-scratch' for regex 'squeak*'
Package 'squeak-plugins-scratch' is not installed, so not removed
Package 'squeak-plugins-scratch-dbg' is not iAfter this operation, 1,151 kB disk space will be freed.nstalled, so not removed
The following packages were automatically installed and are no longer required:And 
  fonts-roboto gtk2-engines-clearlookspix liblightdm-gobject-1-0
  libxfce4ui-1-0 libxfce4util-bin libxfce4util-common libxfce4util6
  libxfconf-0-2 lightdm-gtk-greeter pimixer pipanel wiringpi
  xfce-keyboard-shortcuts xfconf
Use 'apt-get autoremove' to remove them.
The following packages will be REMOVED:
  squeak-vm*
0 upgraded, 0 newly installed, 1 to remove and 1 not upgraded.
After this operation, 1,151 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 135057 files and directories currently installed.)
Removing squeak-vm (1:4.10.2.2614-1.1+b1) ...
Processing triggers for shared-mime-info (1.3-1) ...
Processing triggers for gnome-menus (3.13.3-6) ...
Processing triggers for desktop-file-utils (0.22-1) ...
Processing triggers for mime-support (3.58) ...
Processing triggers for gnome-icon-theme (3.12.0-1) ...
Processing triggers for man-db (2.7.0.2-5) ...

Don’t forget to run clean and autoremove:

apt-get clean

How to remove Wolfram Language and Mathematica from Raspberry Pi: Raspbian Jessie and Wheezy distro

Raspbian Jessie and Wheezy distribution includes Wolfram Language and Mathematica. While this can be helpful for students, it doesn’t have much use for others. The following instructions will remove both Wolfram and Mathematica from your Raspberry Pi (Raspbian distribution). It saves 658MB in Jessie.

sudo apt-get remove wolfram-engine
Reading package lists... Done
Building dependency tree 
Reading state information... Done
The following packages will be REMOVED:
 wolfram-engine
0 upgraded, 0 newly installed, 1 to remove and 59 not upgraded.
After this operation, 658 MB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 150191 files and directories currently installed.)
Removing wolfram-engine (10.3.1+2016012407) ...
Processing triggers for man-db (2.7.0.2-5) ...
Processing triggers for gnome-menus (3.13.3-6) ...
Processing triggers for desktop-file-utils (0.22-1) ...
Processing triggers for mime-support (3.58) ...
Processing triggers for shared-mime-info (1.3-1) ...
Processing triggers for hicolor-icon-theme (0.13-1) ...

Then there is one final step:

sudo rm /usr/share/raspi-ui-overrides/applications/wolfram-language.desktop /usr/share/raspi-ui-overrides/applications/wolfram-mathematica.desktop

And you are done!

PS. You can read more about these free (not for commercial use) packages here.