How to Compress, Uncompress to .gz, .bz2?

Tar (tape archive) does not compress files. They are used for grouping all files in a folder so that it can be transferred across locations. In order to compress the files, you need to use zip, gzip or bzip2 utilities.

gzip, bzip2 are file compression utilities and gunzip, bunzip2 are file uncompression utilities.

bzip2 compresses files to a smaller size compared to gzip, but it takes longer to compress the files. Bzip2 uses Burrows-Wheeler block sorting text compression algorithm (with Huffman coding) and gzip uses Lempel-Ziv coding. so, a file compressed with one utility cannot be uncompressed with the other utility.
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Ubuntu: Where to find Apache Error log?

Location where the Apache error log entries can be found in Ubuntu

user@server:~# less /var/log/apache2/error.log


SSL Error: Revocation information for the security certificate for this site is not available.

SSL Error: Revocation information for the security certificate for this site is not available. Do you want to proceed?

i) Install the root CA under Trusted Certificate Authority or,
ii) Add an exception to the browser filter not to check certificate revocation or,
iii) Programatically handle the SSL stream when request is made from the server


Choosing version control system (VCS): Git vs Subversion


– Distributed repository system (adaptive work flow models)
– Source control taxonomy: DAG storage
– URI to git directory is where the repository is stored and it always has branches and tags
– Repository root folder contains a .git directory which maintains file history
– Scalability
– Faster, Efficient branching and merging
– License: Copyleft

Subversion (SVN)

– Centralized repository system
– Source control taxonomy: Delta storage
– URI to a subversion depository most commonly adopts /trunks, /branches and /tags directories
– Each folder maintains a .svn directory to store the file history
– Not efficient in scaling
– Not efficient in branching and merging
– License: Copyfree


PDF Split and Merge (pdfsam)

PDF Split and Merge (pdfsam) – an elegant tool that establishes the tasks stated in the name of the product.

pdfsam is distributed under GPL license and requires Java Virtual Machine 1.4.2 or higher.

This tools helps you in splitting PDF documents into individual pages, merge many pages into a single document, extract odd/even pages and many other features in its basic version.

To learn more about this tool or to download a copy of it visit


HTTP-Header: User-agent modification

When a browser makes a request to the server, it sends information such as its operating system name, version in addition to the type of the browser from which the request originates in the header variable “user-agent”.

Depending on the request made, server responds back with specific details which can range from browser specific css layout to calling certain javascriptsfor certain browsers.

Changing the user-agent also helps us in understanding how spider-agents or bots will see the pages that we build. It also helps us design applications that will mimic a request as originating from a mobile phone and helps us in viewing the behavior of the application in different mobile clients.

To read more about HTTP-Headers check ietf


LogMeIn, Hamachi: Create VPN in minutes

Managed or Unmanaged networks? Create a VPN in minutes with this software which is available FREE of cost for non-commercial use.

Setting up a Virtual Private Networks is as easy as clicking through the buttons. Check out this product at LogMeIn


WebScarab for web application test

WebScarab is a testing tool used for analysing application data that is passed between browsers and servers. It can be used to review and modify data at either end by intercepting data originating from http and https layers. This tool can also be used as a bandwidth simulator (slow/fast network), in session id analysis, spidering url’s, parameter analysis and for many other testing schemes.

WebScarab is developed as an open source tool by The Open Web Application Security Project (OWASP) and can be downloaded from OWASP website


GUID: Meaning and its application

GUID stands for “Global Unique Identifier” and is a term usually referring to Microsoft’s implementation of unique identity number (in a distributed environment) that it generates to identify different entities such documents, COM’s, DLL’s, interfaces, records, and other objects. It is also known as UUID – Universal Unique Identifier interchangeably.

GUID implemenation is a 128 bit (16 byte) value consisting of sets of hexadecimal digits separated by hyphens. As the total number of unique keys is large the probability of two numbers being the same is very small.

The AutoNumber datatype in MS-Access and the Identity datatype in SQL Server is a GUID implementation.
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Firefox: Developer Friendly Browsing Tool

Firefox is one of the best tool available for web developers which equips the developer with code testing and debugging capabilities.

There are many useful firefox options and extensions that comes in handy during software development life cycle and in this article we will be listing few of useful plugins that we commonly use.

To find information related to the page that is getting displayed on the browser click Tools > Page info. This will give you permission settings of a page, security identity of the page, feed url and other page specific information like page content-type, encoding, meta tags used, cookie permission settings etc.

Web Developer extension
Added as a toolbar in firefox, this extension gives CSS related information, page information, outlines page elements, tab index, gives topographic information and many such details.
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