Friday, June 16, 2017

Cryptocurrency and Cryptoasset Whitepapers

Here are some quick links to the Blockchain white papers (marketing materials in some cases!) of some popular cryptocurrencies (altcoins) and cryptoassets(tokens). Hope reading these papers help you cut through the ICO marketing fog and understand the underlying technological merits and demerits.

Last updated : 16-June-2017

ethereum - ETH

bitcoin - BTC

ripple - XRP

zcash - ZEC

bitshares - BTS

dash - DASH

nxt - NXT

stratis - STRAT

nem - XEM

siacoin - SC

factom - FCT

stellar - STR

golem - GNT

monero - XMR

lisk - LSK

syscoin - SYS

steem - STEEM

augur - REP

cryptonite - XCN

bat - BAT

blackcoin - BLK

creditbit - CRB

zcoin - XZC

maidsafecoin - MAID

primecoin - XPM

gridcoin - GRC

reddcoin - RDD

peercoin - PPC

bytecoin - BCN

gnosis - GNO

decred - DCR

aragon - ANT

iconomi - ICN

antshares - ANS

emercoin - EMC

Tuesday, February 9, 2016

How to install the Perl module Data::Dumper on Linux - RHEL, CentOS or Amazon AMI?

Below is an error message that could get thrown while installing any Bitnami package (say Bitnami Mediawiki package) on a Linux

Error: Error running /opt/app_name/mysql/scripts/ 
/opt/app_name/mysql ****: FATAL ERROR: please install the following 
Perl modules before executing scripts/mysql_install_db:


The error states that you have install the Perl Module Data::Dumper. Run the below command :
yum install "perl(Data::Dumper)"

Follow through the rest of the instructions on the command line to complete the installation. 

Sunday, February 7, 2016

How to hide or remove the View History tab on Mediawiki

Below are the steps to remove/disable/hide the View History tab on Mediawiki. This works as of early 2016 on Mediawiki 1.26x. Hope it helps!
  1. Login to your apps/mediawiki/htdocs directory. This is the directory which contains the LocalSettings.php file.
  2. Edit the LocalSettings.php file (open in text editor).  Add (append) the following lines
#====Begin : code to hide/remove View Source tab from Mediawiki====
function efAddSkinStyles(OutputPage &$out, Skin &$skin) {
    if(!$skin->getUser()->isLoggedIn()) {
        if ($skin->getSkinName() == 'vector') {
            $out->addInlineStyle('#ca-history { display:none; }');
    } else {
        if ($skin->getSkinName() == 'vector') {
            $out->addInlineStyle('#ca-view { display:none; }');

    return true;

$wgHooks['BeforePageDisplay'][] = 'efAddSkinStyles'; 
#====End of code====

Saturday, July 11, 2015

H1B things to do or checklist once you land in the USA

If you are an H1B worker, you will have to do certain important or useful things once you land in the USA for the first time. Some are mandatory and some are purely for convenience. One thing to remember : in the USA you will have to do it all by yourself. Do not expect your employer to "help" you in doing things (eg: opening a bank account).

So here we go :

1) Immigration Check and i-94 update
* This step is optional, but good to do (because I had some Lastname trouble)
* Just when your plane lands on the airport, you will have to stand in the line for immigration check.
* When doing immigration check, the officer will update your i-94 entry in their database. (simply put, the i-94 database is what the USCIS uses to record your entry and exit details).
* If you have two names in your Surname (in other words, if you have a space character in your surname), there could be some update issues.
* In this case, better check with your immigration officer if your passport names and i-94 names are an exact match.
* After few hours or 1 day, check your i-94 entry on this link :
* First, ensure that your latest entry is updated. Second, ensure that the details match with your passport entries (Firstname, Lastname, entry date, expiry date).

2) Open a bank checking account
* You will have to open a basic "checking" account for salary deposits. This is one of the easiest things to do once you land in the US.
* Bank of America (BoFA) is the most popular bank, but Chase and PNC are also equally good.
* For a basic checking account in BoFA, you will only need to show your Passport and another ID such as your home country's Driving license. If you don't have a driving license, they may accept your Employee ID badge (better to check this with the bank).
* BoFA or any other bank will give all you the following right way : temporary debit card, few check leaves, and a direct deposit form.
* Also check the  Apply for a Credit Card section below. It is convenient and useful to have a credit card.

3) Apply for SSN
* SSN is the national ID in the US. You will need this to get your salary credited, apply for driver's license or to claim insurance. Apply for SSN in the first week itself.
* To apply for an SSN, all you will need is your passport and a printout of your i-94 page.
* Identify your nearest SSN office. Go to that office. Take a token for "new SSN". Wait for your turn, and then hand it over to the officer (Tip : Go early in the morning to avoid queues and waiting time).

4) Apply for Driver's License
* In most states (barring big cities), you will need a car for even buying groceries. To buy a car, you will first need a Driver's license.
* To obtain a Driver's License, first you must be eligible by scoring 6 points in the documents check.
* Your passport will give you 4 points, 1 point for SSN and 1 point for a bank debit card.  So usually you will clear the 6-point verification once you have the SSN and the bank account.
* Next, you will have to clear the written test and the on-the-road test. Learn all the traffic signs, and rules. Make sure to take all the tests(repeatedly) from these websites:

5) Apply for a Credit Card
* Having a credit card in the US is kind of useful because it will help you maintain your "credit score" (better credit score = more trust)
* Getting a credit card is a bit difficult for first timers. You will have to go for something called "secured credit card".
* Another option is : BoFA has tie ups with some popular companies (only the bank staff can tell you which companies are eligible). If you are an employee of these companies, chances are you will get a credit card easily.  May be they will give you low initial credit limit (say $2000), but good enough to get started with your credit history.

Wednesday, May 27, 2015

Setup WordPress On Amazon EC2 : Installation steps with Linux commands cheat sheet

This is a real quick guide to setup WordPress On Amazon EC2. It is a direct result of following a Youtube tutorial on the same subject by a guy named Avishai Sam Bitton, who is the Marketing Director at Imonomy & Founder of Go Social.

The Youtube tutorial by itself was great. In 10 minutes, Avishai shows you how to go from creating a Linux instance to the WordPress admin page. It is done on the Amazon Linux AMI (not Ubuntu or RHEL). The only missing thing is the Linux commands cheat sheet (copy-paste-able) which I will cover in the following paragraphs. I will try to provide maximum information in minimal words.

Here is the actual video and what follows is my notes on the same :

To setup a WordPress blog on the Amazon EC2 infrastructure, you need to know and do the following as a prerequisite:
  • Have Putty and PuttyGen installed (or ready for use)
  • Have basic understanding of Linux concepts and commands. Know how to use putty, and optionally understand security concepts.
  • You should have created an Amazon AWS account. A credit card signup is required even though the basic Linux instance (micro instance) is free for 12-months.
Once you're ok with the above, follow these steps.

Part A

  1. Login to the Amazon AWS console.
  2. Select :  EC2  - Virtual servers in the cloud.
  3. Under Create Instance, click on Launch Instance.
  4. Select Amazon AMI Linux - 64 bit
  5. Check settings. Maintain defaults. Keep clicking next - until you reach the Configure Security Group section.
  6. Click Add Rule twice : 
    • One for the HTTP (port 80) 
    • another for the HTTPS (port 443). 
    • Also add a third one and select Custom TCP port. Enter port 8080 (if your apache or nginx server runs on this port)
    • The SSH rule is already added with port 22.
  7. Click Review and Launch. Click Launch. This opens a dialog to create a new key pair. 
  8. Create a new key pair. Download the pem file to your local folder.
  9. Now click Launch Instance (wait for 5 mins for startup)
  10. In the meantime, convert the pem file to ppk file
    • Windows :  PuttyGen tool, go to Menu->Convert->Import->Save file with ppk extension to your local drive.
    • If you are on Mac, no need to convert. You can use the pem file to login directly using the generated Elastic IP address (steps given below).

Part B

  1. The instance which you launched couple of steps back should now be running(green tick mark)
  2. On the Left pane -> click Elastic IPs -> Allocate New Address -> Yes,Allocate
  3. Right click on the allocated Elastic IP -> Associate Address -> running instance (some 10-character code). Click Associate.
  4. Go to EC2 Dashboard -> Running Instances. Check the Public IP and Elastic IP (both should be same).
  5. Copy the IP address. Open Putty and copy the IP address (say into putty's Host.
  6. Go to SSH->Auth, browse open the converted ppk file. Go back to Session and click Open. Putty's black screen should open up.
    • Windows  : Login as : ec2-user
    • Mac : 
      ssh -i keyfile.pem ec2-user@

Part C - The Linux Commands (aka Cheat Sheet)

Once you've logged in as the ec2-user, type in the below commands one after another.
Note: In all the "install" commands, press "y" if the shell asks for install confirmation.
sudo yum updateUpdates all software patches on the instance.
sudo suSwitching to root user
yum install httpdInstalls Apache server
service httpd startStarts Apache server
yum install php php-mysqlInstalls PHP
yum install mysql-serverInstalls MySQL
service mysqld startStarts MySQL server
mysqladmin -uroot create myblogmyblog will the name of the database in this example)
mysql_secure_installationFollow these steps:
* Enter current password for root: just press enter key
* Set root password? : Y (enter password twice)
* Remove Anonymous Users? : Y
* Disallow root login remotely: Y
* Remove test database and access to it? : Y
* Reload privileges table now? : Y
cd /var/www/htmlGo to this directory
wget the latest version of Wordpress
tar -xzvf latest.tar.gzExtract Wordpress
mv wordpress myblogRename the the blog to myblog
cd myblogGo to the myblog directory
mv wp-config-sample.php wp-config.phpRename the php config file.
vi wp-config.phpEdit the wp-config.php file with the given information :
* define('DB_NAME', 'myblog')
* define('DB_USER', 'root')
* define('DB_PASSWORD', 'yourpassword')
* press escape key
* :wq! (to save and exit)
service httpd restartRestarts Apache server

Now, open your browser, and enter : http://IPAddress/myblog  (in our case,
Your Wordpress blog's Admin installation page should be ready for configuration.
If your web server is running on port 8080, then use the url :

Saturday, May 23, 2015

How to find lines not containing (matching) a string in Notepad++

 In Notepad++, you might have a requirement to find or replace lines which do NOT match a particular string.
Lets say you have the following lines in your text file - and you would like to the find lines NOT containing the string "USA"

Apple - USA
Airbus - France
Google -USA
SAP - Germany

For this, you will have to use the Notepad++ Regex find option

Here's how:
  • Press Ctrl + F to pop open the Find dialog box
  • Select the Regular Expression radio button
  • Type in the find box : ^(?!.*USA).*$ 
  • Now find or replace.
Here are couple of awesome books to understand more about Regular expressions :

Here's a screenshot of my notepad++ screen.


Thursday, May 14, 2015

The best book for website user experience UX design

One of the best books for web developers / designers is Steve Krug's Don't Make Me Think