How to Convert an EPUB to MOBI Format

Kindle is an e-book reader designed and developed by Many e-books you see on the Internet store their files in the EPUB file format. Kindle devices store their e-books in a MOBI file format. Unfortunately, Kindle cannot read files in the EPUB file format.

Add WiFi to the Raspberry Pi

USB WiFi Adapter

The Raspberry Pi comes with a 10/100 Ethernet Port to connect to the Internet. In most instances, this works fine. If you set up your Raspberry Pi as a Media Center, your Wi-Fi router and your A/V Receiver might not be in the same room. Running a long Ethernet cable from your Wi-Fi router in one room to your Raspberry Pi in another room does not seem like a practical solution.

Find Files in a Directory

Suppose you have several directories with several sub-directories with files in them. How do you go about finding the files you need? You may want to find the latest modified files. You may want to find files belonging to a certain group. You may want to find files under the dotfiles directories. The list goes on and on.

Search for a string in a directory of files


Suppose you have a string that you want to search in a directory. How would you do it? What if this directory contains many files and sub-directories? What if you want to search the string in a particular set of files?

Ubuntu Blank Screen on Boot

Have you ever installed Ubuntu, rebooted and then got a blank screen? It does not mean Ubuntu has crashed on you. This has happened to me on version 10 and 11 of Ubuntu. It appears Ubuntu does not have video drivers for certain video adapters such as Nvidia cards.

Send a Test Mail Using Telnet

Send a Test Mail Using Telnet

When you are having a problem sending a mail message, the first thing you want to do is test the SMTP (Simple Mail Transfer Protocol) connectivity. By default, SMTP listens on port 25. By using telnet, you can connect to port 25 on the mail server and test whether or not you can send a message. This step is done on your own workstation. If you are having a problem sending mail from a web form, run this step from the server that is storing the web form.

What is /dev/shm and What is it Used For?

What is /dev/shm and what is it used for?

/dev/shm is shared memory. It is offered in Linux as a way for memory to be accessed simultaneously by multiple programs.

shm is also known as tempfs or temporary file storage. On Linux it will appear as a mounted file system that you can access directly. Instead of writing to a permanent storage device such as your hard drive, it writes to virtual memory (i.e., it lives in RAM). Since it is memory, anything written to this file system will be removed the next time you reboot.

OSI Model Layer

The Open Systems Interconnection model (OSI model) by developed by the International Organization for Standardization (ISO) in 1984. OSI reference model is a way of sub-diving network communication and grouping them into logical layers. On each layer, an instance provides the services the instances to the layer above it and requests services to the layer below it.

Find and Replace with SED

Find and Replace with SED

The power of search and replace is prevalent all over Linux. Whether you are using a text editor or on the command line, regular expressions come in handy. When you … Read more

Fatal error: Allowed memory size of 33554432 bytes exhausted

Fatal error: Allowed memory size of 33554432 bytes exhausted

For the most part, WordPress is easy to use and you can set up your site in a few hours. This assumes everything works as expected. If things don’t work out as you have expected, then it will take some more troubleshooting to get to the root cause of the problem.

Disable SSLv2 and Weak Ciphers

Disable SSLv2 and Weak Ciphers

Are you still using Secure Socket Layer (SSL) version 2 on your web server? If so, you need to read this article. It can save your life. Okay, maybe not that dramatic but it will show you how to disable SSLv2. Why? There are vulnerabilities in this version. If you don’t disable it, your web server might get compromised. This vulnerability exists whether you are running Apache or IIS. The steps to disable it are fairly trivial. So go ahead and tr