Git: Fix push failure due to large files

Github Enterprise does not allow large files to be pushed to the repositories. As a result, any push committed with a large file will fail. If you redo the push, the git client will throw error, even after deleting the large file. This is because the large file will exist in the git history. The git history should be modified in order for the push to go through.

This is done using the git filter-branch command.

git filter-branch --index-filter 'git rm -r --cached --ignore-unmatch ' HEAD

There is another awesome faster tool to do the same:

https://rtyley.github.io/bfg-repo-cleaner/

Prevent hyperlink click behavior using jQuery

Often web devs (you and me), put an anchor tag and write a custom function for its onclick event. The href field will get assigned with a "#" and you are happy to see your function getting called on every click of the hyperlink. So far so good.

It will be a little later that you notice a jerk when you click on the hyperlink, which puts your page scrolled back to the top. This is a kind of an undesired behavior which you do not want to see.

Well, the solution is simple. Just add preventDefault() call at the start of the onclick handler.  The sample code below shows an example.

<a href="#" id="link">Click here</a>
.
.
.
$("#link").click(function(param){
param.preventDefault();
//do stuff
});

Latex tip: Place tables and figures to the end of the file

You may often need to put all your figures and tables to the end of the file. You may use the endfloat package. Just use this line of code, and all your tables and figures will move to the end of the file.

\usepackage[nomarkers]{endfloat}

Latex tip: Best way to resize tables to fit in page

Shrinking tables to fit page size is a cumbersome task of any Latex user. The best way to resize tables is to use the adjustbox package.

The code below will resize the table to page width.

\usepackage{adjustbox}
.
.
.
\begin{table}[ht]
\centering
\begin{adjustbox}{width=1\textwidth}
\small
\begin{tabular}{|l|l|l|}
\hline
1 & 2 & 3
\hline
\end{tabular}
\end{adjustbox}
\caption{Test Table}
\end{table}

The above code will shrink the table to page width. The downside of this method is that the text may become less readable.

Fork Bomb Detector

Fork bomb is a denial of service attack on the operating system wherein a process continually replicates itself to deplete available resources, causing resource starvation and slow down or system crash. The current Linux kernel sets a limit to the maximum process id in the limits.conf system file
to prevent from such attacks. This would lead to denial of fork calls even to legitimate processes. This kernel functionality moves a step forward to identify a fork bomb by calculating the time between two fork calls along with enforcing a threshold.

Solution

The solution approach involves developing a loadable kernel module(LKM) that hooks the fork system call in order to examine if the system call is from a fork bomb. This can be found out if the fork call is from a process with process id larger than a predefined system threshold or if the time elapsed after process creation of the child processes is less than a predetermined period. If the call is made by a potential fork bomb, the process is not allowed to execute the fork system call and notifying the user about the event.

The module once loaded is expected to intercept all fork calls and detect if there is a fork bomb spawning processes. If it detects unusual forking by any process, the process will not be allowed to complete the fork call. The action taken will be logged in syslog.

The project is hosted in GitHub.


Fork

Why do you want to type sudo apt-get install always when you can make it short to sagi or magi?

As normal unix users, we frequently use the mundane sudo apt-get install, sudo apt-get upgrade, sudo apt-get remove etc. commands. As busy developers, we often need to initialize, commit git repos. Why don't we abbreviate these commands?

We can easily alias these commands in our bash_rc file and save our precious time for an extra movie for the day :)

In Ubuntu, add your alias to the ~/.bash_aliases file in the below format:

alias abbreviation="Command"

Example: alias sagi = "sudo apt-get install"

Now, I just need to type in $ sagi terminator to install terminator :)

If your OS flavor is not Ubuntu, just make the changes in ~/.bashrc and enjoy your extra hours for a good nap or movie.

Fix for Failed to fetch http://dl.google.com/linux/chrome/deb/dists/stable/Release Unable to find expected entry 'main/binary-i386/Packages' in Release file (Wrong sources.list entry or malformed file)

The error is because the repos try to fetch the 32 bit version of chrome which Google has stopped the support. The solution is to fetch the 64-bit version.

Just execute these two lines and the error is gone. Voila!

sudo sed -i -e 's/deb http/deb [arch=amd64] http/' "/etc/apt/sources.list.d/google-chrome.list"

sudo sed -i -e 's/deb http/deb [arch=amd64] http/' "/opt/google/chrome/cron/google-chrome"

Chinese Remainder Theorem

Chinese Reminder Theorem is a handy mathematical technique to solve a system of congruences.
The snippet simulates the theorem.

View Gist

Nmap

In this post we’ll get familiarized with Nmap, network mapping tool. It helps to perform a port scan of hosts in a network and to identify the services provided by them. In short, it is a security scanner.

The software provides a number of features for probing computer networks, including host discovery and service and operating system detection. These features are extensible by scripts that provide more advanced service detection, vulnerability detection, and other features. Nmap is also capable of adapting to network conditions including latency and congestion during a scan. Nmap is an opensource tool primarily made for linux systems, released under the GPLv2 license, and is under development and refinement by its user community.

There are a wide array of uses for Nmap. Afew of them are:

• Auditing the security of a device or firewall by identifying the network connections which can be made to, or through it.
• Identifying open ports on a target host in preparation for auditing.
• Network inventory, network mapping, maintenance and asset management.
• Auditing the security of a network by identifying new servers.
• Generating traffic to hosts on a network.
• Find and exploit vulnerabilities in a network.

---

• Getting Nmap
  In linux distributions, Nmap can be installed from the terminal.  In Ubuntu, you may install using sudo apt get-install nmap
  I have seen GUI version of the tool in Ubuntu Software Center, but I prefer the terminal version. Give it a try if you like.
• Run
  

  

  An example run of Nmap

  Nmap is run as a command from the terminal with appropriate switches to obtain the desired outcome. You may refer nmap man pages for the complete list of available switches. As an example, here are a few commands:
• Save and View Scan Report
  Scan report can be redirected to a text file for later use. This is done using the –oN switch. The command is nmap -p --oN

Wireshark

Wireshark is an open source, free network packet analyzer. It captures packets in real time and lists them in a user friendly GUI with options to color code, filter and much more. It is a defacto GUI tool to monitor network traffic and can be considered astcpdump with GUI front end and integrated sorting and filtering options. If you find it interesting to read on its history, the wikipedia page should be helpful.

We’ll just look into a few of it’s aspects and capabilities now.

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• Getting Wireshark
  As mentioned earlier, it’s a free open source tool. So you can freely download and install on your system from its official download page and is available for windows, Mac OS X and Linux distributions. On Ubuntu, you can install it from the command line:
  sudo apt-get install wireshark

• Run
  
  Run Wireshark with root provileges. This is important!
  gksudo wireshark

• Wireshark Window

  

  Wireshark Window

  Upon starting wireshark as su, the main window displays the interface list. The interface list displays the available network interfaces in the system, with options to start the capture. Capture options dialog will help you to specify various options to follow during packet capture.

  

  Capture Options Window

• Capture Window

  

  Capture Window

  The Capture Window as shown above displays the captured packets in real time. You can inspect each packet’s content, by choosing the appropriate packet from the packet list, in the packet details and packet bytes sections. Packets can be color coded for each protocol, filtered according to various filtering parameters and sorted on various fields.
• Start Packet Capture
  
  To start packet capture for a desired interface, you can select that interface and simply click on the start button. The Capture Window will appear showing real time captured list of packets.
• Apply Filter
  
  You can use the filtering option to filter and display captured packets according to some criteria. Appropriate filtering options can be specified into the filter box in the filter tool bar. An example criteria can be to display packets send from a particular ip(say 10.20.30.40). The suitable filtering option here will be
  ip.src == 10.20.30.40
• Save and Load Capture Data
  
  The captured packets can be saved as a capture file on to the disk for later use. Save the capture with a desired file name as a .pcapng file. Wireshark also allows to save the capture file in other packet capture file formats like pcap, libpcap, Microsoft NetMon formats.
• Crack passwords
  
  Thus, with Wireshark you can inspect the network packets. This obviously means you can open it up in the packet byte section and read them. What more do you need to read a submitted form fields? Or more specifically passwords? Try creating a localhost website with a password field and capture the packets transferred during form submit. You can easily find the submitted form fields in one of the captured packets. Now that you have succeeded to steal passwords why don’t you try it out for somebody’s facebook or gmail password? To start with, steal your own facebook password. Capture the packets and inspect them. What do you see? Yeah, that’s all about https.