Moodle and Big Blue Button

MOODLE is one of the best Learning Management system and BigBlueButton is the best Virtual classroom software. How they are related to each other. If you want to have a virtual classroom session with your students, here is the step for that

  1. A teacher can create a login with and you can use MOODLE right from there. the free version of offers 200 mb of storage space with 50 users. the advantage is its comes with Big Blue Button also wherein BBB shares their cloud space for the Virtual classroom session.

2. If you want to know more about BBB (Big Blue Button) , please refer the following slide


Using Index of in Google Search

If you want to download a movie directly using Google without bothering the torrent. As torrent is blocked in most of the countries, here is a tip to download anything from google directly.

Open and input the following text (without quotes)

+”index of” “MovieName”  Year

Example +”index of” “Kung Fu Panda” 2016

Here is the output

Index of


Here is the second link from the above image is clicked.

Download Movie
Download Movie

From one of the four links, the movie can be downloaded easily.

Enabling Telnet and SSH in Mac OS X

Enable Telnet

This post shows how to enable Telnet and SSH in Mac OS X.

To Enable Telnet, issue the following command (Open the Terminal and issue)

$] sudo launchctl load -w /System/Library/LaunchDaemons/telnet.plist

This will enable Telnet, and to check its working, try this

$] telnet localhost

To disable Telnet, issue the following command

$] sudo launchctl unload -w /System/Library/LaunchDaemons/telnet.plist

Enable SSH

To enable SSH, in the Mac OS X,

Open System Preferences -> Sharing -> Remote Login (Put the Tick Mark)


Once enabled, these machines can be connected remotely using their IP Addresses. Both these things works only when the port 22 and 23 are unblocked by the firewall

To check Telnet is working or not

$] telnet localhost

supply the username and password (you are connected..)

Virtual Host in Bitnami Lampstack

IF you have a website that runs with an IP address and you decide to move it to a domain, then here is the clear step.  Also this post will be helpful to you if you are running a same website by two different IP Address (One in campus and another outside the campus)


Your IP Address (Example): (Internal IP)

Your IP Address (Example): (External IP)

You want to move it to: (instead of

Step 1:

Open the file /opt/lampstack-5.5.31-0/apache/conf/bitnami/bitnami.conf

In the above file, Change these lines  (The bold lines are the changed ones)

<VirtualHost _default_:80>
DocumentRoot “/opt/lampstack-5.5.31-0/apache2/htdocs/site”
<Directory “/opt/lampstack-5.5.31-0/apache2/htdocs”>
Options Indexes FollowSymLinks
AllowOverride All
<IfVersion < 2.3 >
Order allow,deny
Allow from all
<IfVersion >= 2.3 >
Require all granted


<VirtualHost _default_:80>
DocumentRoot “/opt/lampstack-5.5.31-0/apache2/htdocs/site
<Directory “/opt/lampstack-5.5.31-0/apache2/htdocs”>
Options Indexes FollowSymLinks
AllowOverride All
<IfVersion < 2.3 >
Order allow,deny
Allow from all
<IfVersion >= 2.3 >
Require all granted

Step 2: (Optional)

Open the file using sudo, /etc/hosts and include your IP with the domain name

GNU nano 2.2.6 File: /etc/hosts localhost administrator
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

Once done, restart apache server or the bitnami server by issuing this command

$/opt/lampstack-5.5.31-0] ./ctlscript restart 

And now check in the browser, you have done…..

If you manage apache server manually (Other than using bitnami lampstack), then you can edit the httpd-vhosts.conf file with the above steps.


Realtek audio Hanging in Bootcamp–solved

If you own a MacBook Air or MacBook Pro, then some of you may experience this problem when you install windows 7 or 8.x or 10.

Realtek Audio will hang and the installation will never complete

A small workaround. Whenever it hangs, open the task manager (ctl + alt + delete) and click “more tasks” and End the task “Realtek setup 32bit”. Once the task ended, the installation will continue as usual and bootcamp installs successfully.

Merge VOB files in Linux

Assuming that you have purchased a DVD of a movie and trying to copy it to the hard disk. It is annoying to see individual vob files like VTS_01_1.vob, etc.  If there are multiple vob files, you can merge in to a single file using the cat command in linux/Unix/Mac OS

It is easy to handle and in no time, the conversion can happen.

Here is the command

$] cat VTS_01_1.vob VTS_01_2.vob > FullMovie.vob

the above command concatenate two vob files and merge it into a file called FullMovie.vob

This method had advantages whenever you like to see the movie with subtitles. Assuming that the subtitle is downloaded and you cannot see the full movie with sub title running for all the individual VOB files. So in that context, this method is very helpful.

Refer the images shows the conversion.

Merge Vob files
merge VOB files
merge VOB files
merge VOB files

Ubuntu Drivers for Macbook and Macmini

\nstalling Linux along with windows within Macbook or Macmini is quite time consuming and cumbersome. If you get all the three OS installed, Windows has a support from Apple BootCamp but Linux it has to be customized our own way. Here is a small help that can help you to install the Linux drivers for Mac Machines (The system under test is Mac Mini Late 2012) model.

OS Tested: Yosemite, Windows 8.1, Linux Mint 17.2

For installing all the the three OS as mentioned above, please refer the following link

Once installed, all the three OS, Open Linux Mint and check for Internet  (Drivers were absent or not installed, so it is necessary to install the drivers)

Now a days getting a ethernet based network is so tough and one cannot rely on it.

So, the preferred method can be USB tethering or 3G or 2G networks. USB tethering does well as you are already connected with a wifi network in your phone and that can be inserted in the usb port of mac mini. Ubuntu or linux mint detects the internet through the USB tethering mode.

Linux Mint detects that and thats it the network is in place. Open the terminal and give the command

$ sudo apt-get update

Once done, press command key and search for driver or device (You will get a option like Device Drivers) and open it with super user (The system asks for the password of super user). Refer the picture given below.

Mint in Mac

It shows the broadcom driver and have to be installed. Select the driver and apply changes and its done. Will take sometime to download the driver and Thats it!!!. The installation is done.

NS-2.35 (ns2) installation in various Linux distros

Linux Mint
There are so many flavors of linux and so many distros. Installing a particular software in each one of these linux needs knowledge on the package management and other basic settings related to the software source.
NS2 also has similar issues when it is installed on different platforms or distributions.
This post will let you know how to install ns-2.35 in various distributions.

Most of the posts of the following are linked with


  • Use always the Long Term Support (LTS) operating systems, if you are using Ubuntu or Linux Mint. Ex. Ubuntu 12.04, 14.04. These LTS has a support of upto 5 years. Ubuntu 12.04 has support of upto 2017 and 14.04 has the support of upto 2019.
  • If you are a beginner, better to use Ubuntu or Linux Mint , which is a user friendly Linux OS.
  • Linux Mint is doing well these days, so everyone can prefer Linux Mint as the OS, as it comes with all the audio, video codecs, support for all development and it uses the synaptic package manager of Ubuntu, so whatever support you get in Ubuntu, you can get it in Linux Mint also.
  • If you have worked with Red Hat Linux or Red Hat Enterprise Linux, then you may try Fedora as one option.
mint ns2
Linux Mint NS2 

To install in Ubuntu 11.04 and later (Also Linux Mint 14, 15, 16, 17 any of the versions.), you can refer the following link

ubuntu ns2
Ubuntu ns2

To install in Fedora 18, follow this link

To install in Fedora 19,`

fedora ns2
Fedora ns2

To install in Fedora 20,

For any other queries related to ns2, you can refer the

Pradeep Kumar TS

How to take Screenshot in OS X (Mac)

There are different methods for taking a screenshot in windows and Linux OS. But macintosh machines with  OS X has an inbuilt mechanism where in one can take a screenshot.
Depending on the keyboard used, the keystrokes may vary.

Screenshot of entire screen
If you are using Apple Keyboard the combination is Command+Shift+3 keys together pressed and released. Once the keys are released, the screenshot will be stored in the desktop itself.
If you are using Conventional Keyboard for Macs (Ex: For Mac mini, etc), the key combination is

Window  Key+Shift+3 
(See the screenshot below)

Screenshot in Mac (OS X)
Screenshot in Mac (OS X)

Screenshot of a particular Area
To take the screenshot of a particular area, then you can use Command+shift+4 keys pressed and released. Once released, you will get a + symbol with x and y location. Simply drag the area you want to take a screenshot and release it. Thats it!!!. See the screenshot taken using this method.

screenshot in mac using Command+shift+4
Screenshot in mac before taking a Command+shift+4

Also, there are other methods like storing the image to a clipboard and later can be used inside the document processing applications.  Also there is a provision for storing the screenshot files in an user specified location rather than on the Desktop.

If you want to record your screen, Mac OS X has the method using Quick Time player. There may not be any need for desktop recording application, the quick time player will do that. But if you need a complete customization pack, then you may think of any such app.

Pradeep Kumar TS

How to open Ports in CentOS

CentOS is the most preferred alternative OS for RHEL. Those who cannot afford to purchase the support license of RHEL, they can use CentOS that comes with almost similar to RHEL.

This post tells you about the usage of CentOS when web servers are installed and accessed from remote machines.

CentOS is a Server based OS and most of the ports are closed by default and you need to open it for access from outside (remote).
For ex. if wordpress is installed in CentOS with a hostname  which is very well accessed within the server. When the same is tried from outside like (, then it will not get accessed.
The problem is the closure of ports in CentOS. So you need to open it and save it to iptables, here are the commands that will help you to do that.


Port number : 80 is used here

$prompt] ifconfig (find out which interface uses the assigned ip, eth1, eth0, etc)
$prompt] iptables –line -vnL
(See which line the input has to be accepted and in my case it is 6) and give the following command
$prompt] iptables -I INPUT 6 -i eth1 -p tcp –dport 80 -m state –state NEW,ESTABLISHED -j ACCEPT
$prompt] service iptables save (Save and restart the IP Tables)
$prompt] service iptables restart

Thats all!!!! I solved this problem, when I installed MOODLE in my Blade server with Cent OS installed.

Pradeep Kumar TS

Simple Screen Recorder for Linux

Recording the screen in Linux OS is always a tedious task, as either the video/audio malfunctions or support may not be there. There is a tools called simple screen recorder for Linux.
Its a very simple tool that is recorded and processed in no time. For example, if you record an 1 hour video, the processing may take another 20 to 50 minutes. But this software does the “On the fly recording and processing”
This software has a straight forward interface and its incomparable to other softwares in the market.
  • Its faster than VLC
  • It never takes more amount of RAM like VLC do.
  • Its multithreaded, if you have more than one core, then the processing happens at all the cores.
  • it can do live streaming also, but it is under experimental setting.
  • it supports many different codecs.
Here is the simple screenshot.
Simple Screen Recorder
Simple Screen Recorder
A 42 minute video is recorded using this software and it takes just 42minute only. no extra time for processing. Please see the youtube video attached below.
See the above video taken using SSR and its about SSR. To download this software follow this URL
For any doubts, just ping me throught the comment form

Pradeep Kumar TS

time command in Linux

The time command is linux is very much useful if you want to know the time information while running a program or a process.
The time command usage is as follows

prompt $] time <commandname>
prompt $] time ls
The output will be
real 0m0.002s
user 0m0.004s
sys 0m0.000s

If you want to see the detailed system parameters occupied during a program or process, then the command will be
prompt$] TIMEFORMAT=”” time -v <commandname>
See the screenshot given below

The output of the above command is
Desktop  Documents  Downloads  examples.desktop  Music Pictures  Public  Templates  Videos
Command being timed: “ls”
User time (seconds): 0.00
System time (seconds): 0.00
Percent of CPU this job got: 400%
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.00
Average shared text size (kbytes): 0
Average unshared data size (kbytes): 0
Average stack size (kbytes): 0
Average total size (kbytes): 0
Maximum resident set size (kbytes): 3600
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 0
Minor (reclaiming a frame) page faults: 286
Voluntary context switches: 1
Involuntary context switches: 0
Swaps: 0
File system inputs: 0
File system outputs: 0
Socket messages sent: 0
Socket messages received: 0
Signals delivered: 0
Page size (bytes): 4096
Exit status: 0

Similarly, if a C or C++ program is compiled and linked to a file called helloc (the creation of helloc is given below)
prompt $] gcc -o helloc hello.c 
prompt $] g++ -o helloc 
if you want to execute this command 
prompt $] TIMEFORMAT=”” time -v ./helloc
The time command will show you the memory page faults, context swtiching, swap memory used and other system parameters, etc.
If you have any added input for this command, let you write in the comment section.

Pradeep Kumar TS

Display the Product name and System Vendor name in Linux

This post will help you to find out the

  • Product Name
  • System Vendor Name
This will help you to find the suitable device drivers if any.
The following is the command to find the System Vendor (in my case it is Hewlett Packard)
prompt $] cat /sys/class/dmi/id/sys_vendor
Here is the command to find the product name
prompt $] cat /sys/class/dmi/id/product_name
Printing the System Vendor and Product Name
cat is the command to concatenate the files and print it to the standard output

Pradeep Kumar TS

nohup command in Linux/Unix

Often you come across a situation where you try to open a machine remotely using ssh and try to start a server or a run a command indefinitely.

But once you close the ssh session, your session also terminates and the background process also terminates. So here is a solution.

To open ssh remotely,

prompt $] ssh username@machinename
Ex: ssh root@
Ex: ssh 
prompt $] ssh -X username @machinename 
Ex. ssh -X root@ 

(this -X indicates the remote session can be opened in X window (GUI) mode)

Assume we need to start a httpd server in the remote machine.
we can issue the command like this

prompt$] nohup command 
if any error or log information may be stored in the nohup.out file. if you want to redirect to a file use the redirected symbol (1>  indicates standard output and 2> indicates standard Error). Specify the filenames for the output. Here is the typical nohup command to start the httpd server.

prompt $] nohup  /etc/init.d/httpd start  1> file.out 2> file.err & 
nohup is the command simply tells “no hangup”. This will send the output to non-tty.
The above command will start the httpd server and any error or output will be written on to the files file.err and file.out respectively (The & indicates the background process that closes the current terminal and prompts for further inputs).

nohup in Linux

This command I learnt when i try to deploy Sage math libraries in a IBM Blade Server. We were really struggling to run the notebook in sagemath library. But finally accomplished using the nohup command.

The alternative to nohup is crontab or cronjob can be used.

Pradeep Kumar TS

Command Based Youtube downloader for Linux (youtube-dl)

Downloading videos to local machine is always a challenge as the streaming sites keep on updating their policies in blocking the videos.
But there is a tool that is available in the command line (Terminal based) on Linux Operating Systems.
That is youtube-dl, this is a python based code and can be executed in linux OS without any hassles.

youtube-dl in windows or Mac OS can be achieved by installing python interpreter and try it.

for installing in linux, the command is
$prompt] sudo yum install youtube-dl (in redhat or centos or fedora)
$prompt] sudo apt-get install youtube-dl (ubuntu or linux mint)
See the image for downloading in Fedora 20

Youtube-dl in Fedora 20

In ubuntu, you can update the sudo package before installing the youtube-dl.
sudo apt-get update

To download videos 
$prompt] youtube-dl

the above command will download the video in the best possible format. See the image below.
The video downloaded is of the format webm (Its a Web Movie format from Google for optimized view in web browsers)


To view all formats, use the following command,
$prompt] youtube-dl -F
Setting language
D980jXvyKUY: Downloading webpage
D980jXvyKUY: Downloading video info webpage
D980jXvyKUY: Extracting video information
[info] Available formats for D980jXvyKUY:
format code extension resolution  note
139         m4a       audio only  DASH audio , audio@ 48k (worst)
140         m4a       audio only  DASH audio , audio@128k
160         mp4       192p        DASH video
133         mp4       240p        DASH video
17          3gp       176×144
36          3gp       320×240
5           flv       400×240
18          mp4       640×360     

43          webm      640×360     (best)

The above is output and to download the corresponding video format, then here is the command
$prompt] youtube-dl -f 18
The above command will download the file in the mp4 format as specified in the option obtained in the previous command.

if you need any help on the commands, you can use the following command 
$prompt] youtube-dl –help

Often, youtube-dl is updated, it can be easily updated as given below,
$prompt] sudo youtube-dl -U

Also now youtube-dl supports various other video streaming sites also, to name a few,,, etc.

If you are behind the proxy, type the command in the terminal  
export http_proxy= 
or copy the above line in /etc/profile.d/ (this will be set for all the users of the computer, also need root password)

Download and Enjoy!!!

Pradeep Kumar TS