How to Hide Secret Data in image and audio files Ubuntu / Debian: Steghide

steganography is the technique used for hiding various data in different type of image and audio files with out changing the basic characteristics of file. Steghide is a utility for steganography. The color- respectivly sample-frequencies are not changed thus making the embedding resistant against first-order statistical tests.

Features include:
* Compression of embedded data
* Encryption of embedded data
* Embedding of a checksum to verify the integrity of the extraced data
* Support for JPEG, BMP, WAV and AU files

How to install steghide in Ubuntu / Debian
Open a terminal
$apt-get install steghide (or Use Synaptic Package Manager)

Basic Usage
$ steghide embed -cf picture.jpg -ef love.txt
  Enter passphrase:

  Re-Enter passphrase:

  embedding "love.txt" in "picture.jpg"... done

This command will embed the file love.txt in the cover file picture.jpg

After you have embedded your love letter love.txt data as shown above  and you can send the file picture.jpg to your lover.

Now How to extract file

$  steghide extract -sf picture.jpg
Enter passphrase:
the file "love.txt" does already exist. overwrite ? (y/n) y
wrote extracted data to "love.txt".

This will give file information

steghide info picture.jpg
"picture.jpg":
  format: jpeg
  capacity: 1.2 KB
Try to get information about embedded data ? (y/n) y
Enter passphrase:
  embedded file "love.txt":
    size: 34.0 Byte
    encrypted: rijndael-128, cbc
    compressed: yes

How to Synchronize a local directory with a remote directory using rsync in ubuntu

Most of the system administrators need to sync some of  their local folder to remote folder. You can do this with a simple command line utility rsync. This will synchronizes files and directories from one location to another , securely by using  delta encoding. It will synchronize files across the network by transferring only data that has changed.

Open a terminal

$sudo apt-get install rsync

$ rsync -r -a -v -e "ssh -l shibu" --delete 192.168.0.5:/var/www/ /home/shibu/public_hrml

$ rsync -r -a -v -e "ssh -l shibu" --delete ceattingal.ac.in:/webroot/ /local/webroot 

rsync command common options

• --delete : delete files that don't exist on sender
• -v : Verbose
• -z : compress file data
• -e "ssh options" : specify the ssh as remote shell
• -a : archive mode
• -r : recurse into directories

Script for Finding Size of All Folders in Linux

Some users will eat lot of space in the system by storing unwanted files. This bash script will help you find which folder using more space.

Open a terminal
Then cut & Paste the script

for f in * ; do if [ -d "$f" ]; then du -sh "$f" ; fi done | sort -n

How to Change Sudo Password Remembering Time in Ubuntu

When You use 'sudo' command it will ask for password in First time and will remember password for 15 minutes. It is a security hole for sensitive systems.
You can change sudo Password Remembering Time in Ubuntu .

Open a terminal and type
$ sudo visudo

In Ubuntu, visudo uses nano text editor, and what it does is edit the / etc / sudoers.tmp

Check for the line as shown below

Defaults        env_reset


Change it to

Defaults        env_reset , timestamp_timeout = X

Where X is the time that we remember the sudo password, if we put 0 (zero) that we always get the request.

Finally to save the changes, press Ctrl + X and said yes.

How to Recover Ubuntu after a Partial Upgrade

If your Ubuntu machine is nor working properly after a partial upgrade and have a have broken the system dependencies tree, You can recover it by using a  simple command that reinstalls all the installed packages and reconfigures them automatically.This will take a long time to complete.

$sudo dpkg-reconfigure -phigh -a

You can try the following command first

$ sudo apt-get install -f

How to setup Google Public DNS in Ubuntu 9.10 Karmic Koala

DNS (Domain Name Server) is basically a system to convert domain names into IP addresses. Domain names are easier to understand, memorize and write for humans while computers only use IP addresses to communicate.

In most of the  case, Internet Service Providers  providing the DNS servers to the customer. User can change it, the  reasons to switch to other DNS servers for performance, privacy and censorship. Most of the people using OpenDNS as the first alternative, But Now Google Public DNS is available and the performance is much better.

Now How to set up Google Public DNS in Ubuntu

Select System-->Preferences-->Network Connections

Select  the type of connection you have. For this example, we will use ‘Wired’.

Under ‘Wired’, highlight ‘Auto etho’ and click on ‘Edit’.

Now,  Inside 'Editing Auto etho' window, click on ‘IPv4 Settings’ tab. and select 'Automatic (DHCP) address only'

Put these nameserver addresses as your ‘DNS Servers’:8.8.8.8, 8.8.4.4

Click ‘OK’ and reboot your machine.

NOTE:

For avoiding  your settings get revoked after reboots, you may need to make the following changes via the command line:

$ sudo cp /etc/resolv.conf /etc/resolv.conf.auto
$ gksudo gedit /etc/dhcp3/dhclient.conf
# append the following line to the document
prepend domain-name-servers 8.8.8.8, 8.8.4.4;
# save and exit
$ sudo ifdown eth0 && sudo ifup eth0

Small Usb Keyboard for Gmail users - Gboard

Gboard is a small simple device for help gmail users. It is a USB device. The Gboard has 19 buttons and each corresponds with a task in Gmail. From the board, you can search, go to results, go to starred mail, compose a message, reply, reply to all, forward a message, star and archive messages, delete and mark messages as spam, flip through your messages , select messages and go right to the inbox.

Arrange Your Desktop windows with X-tile in Ubuntu / Debian

X-tile is a useful gnome applet for your panel (or optionally a standalone application) that allows you to select a number of open windows and tile them in different ways. This is especially useful for comparing products in separate web pages,or for programmers refering to documentation as they are programming.

Download .deb file from here

now double-click on deb file and install with gdebi installer.

or open a terminal and use sudo dpkg -i filename.deb
X-tail can be run by selecting
Applications-->accessories-->x-tile

Download youtube video in ubuntu / Debian using UTube Ripper

Utube Ripper is an application written in Gambas that works exclusively on Linux. It's useful to download and convert Youtube videos in a simple and efficient way. You can also  convert them into a non-flash format. You can use the "Rip audio only" option to extract audio from a YouTube video and can convert  into an MP3 format.

Download .deb file from here

now double-click on deb file and install with gdebi installer.


or open a terminal and use sudo dpkg -i filename.deb