30 de out de 2010

My Spambox, Create A Temporary Email Address In Firefox

My Spambox, Create A Temporary Email Address In Firefox: "

Temporary email services are great when it comes to protecting one’s privacy on the Internet. They are especially useful during website and service sign ups, considering that a lot of services sell user information or use the information to send advertisements.

But, those disposable email addresses are not suited for all purposes. It is often not a good idea for instance to use a temporary email address for signing up with a service that the user wants to use on a regular basis. Why? Think of signing up for Facebook with a temporary email service. Most services of this kind allow anyone access to all email addresses, which means that any user knowing the email address, or stumbling upon it, could access the user’s Facebook account.

This possibility depends largely on the type of temporary email service though. The Firefox add-on My-Spambox adds capabilities right to the browser’s status bar to create a temporary email address.

my spambox

It seems to use the temporary email service jetable for this. What it does is the following. The user enters an email address in the first field of the configuration window. This is the email address the temporary email address gets forwarded to.

My-Spambox creates the temporary email address then and the user can use it for the next twelve hours. After that the link is removed and the forwarding of email messages is no longer working.

The generated email address is automatically copied to the clipboard. There is however no history or log to access it again if needed. If the user loses the temporary email address there is no way to get it back, which should not be a huge problem on the other hand considering that a new one can be created right away.

My-Spambox is a Firefox add-on for all Firefox versions from 1.5 to the latest Firefox 4 nightly builds.

© Martin for gHacks Technology News, 2010. | Permalink | Add to del.icio.us, digg, facebook, reddit, twitter
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Restore the Windows Boot Loader After an Ubuntu Update

Restore the Windows Boot Loader After an Ubuntu Update: "
Will your computer not boot into Windows after installing an update on your dual-boot or Wubi Ubuntu install? Here’s how you can get your Windows boot loader back so you can easily get back to work in either OS.
We’ve mentioned before how Wubi is a great way to run Ubuntu on your Windows PC or netbook, and in general it works great. However, sometimes your system may receive updates to GRUB, and if you choose the wrong option, the next time you reboot your computer you may find that it think there’s only Ubuntu and no Windows installed on your computer.

Or, perhaps, even more ominously, you boot your computer to see that it thinks it has no operating system.


Often, there’s no need to panic. If you recently received an Ubuntu update, or somehow managed to mess up or remove your boot loader, it’s quick and easy to get it back using familiar Windows tools. Here’s how.

Reinstall Your Windows Boot Loader From the Windows DVD

To get back into Windows, you’ll need to reinstall your Windows boot loader. Thankfully this isn’t as difficult or time consuming as reinstalling Windows, but it will require your Windows DVD. Boot your computer from the DVD, and if it doesn’t automatically offer to let you boot from the disk, you may need to change your boot settings in the BIOS. You can usually access by pressing the F2, F10, or Delete key on the initial boot screen, depending on your computer.


Save the changes and reboot your computer from the Windows DVD. After a few moments, you should see the install setup screen. Select your preferred language, then click Next.


Your install disk is designed to install Windows on your computer, but also contains tools to help repair your existing Windows install. On the bottom left of the Install window, click the Repair your computer link to get started repairing your current install of Windows.


System Recovery will automatically start scanning to see if there’s an existing Windows install with something it can easily fix automatically. You may have to wait a few minutes while it scans your computer.


If your only problem is the boot loader, often it will automatically detect the problem and offer to fix it. If so, simply click Repair and restart, and your computer should be booted back into Windows as normal within minutes.


Reinstall Your Boot Loader Manually From the Windows DVD

Alternately, if it doesn’t automatically detect anything to fix, you’ll have to choose your own recovery options. Click the bullet option on the top then click Next to use recovery tools to fix Windows.


Now, select Command Prompt from the available recovery tools.


In the command prompt window, enter the following to repair your boot loader:

bootrec /rebuildbcd

After a few moments, it should detect your Windows installation and ask if you want to add it to the boot loader. Enter Y to add it, then exit the command prompt and reboot your computer when you’re finished.


Moments later, you should see your standard Windows login screen as normal, and all of your files and programs should be fine and ready to use.


As you may notice, the option to boot into Ubuntu will no longer show up in your boot menu, and your computer will act like you only have Windows installed. To get your Wubi Ubuntu or full Ubuntu install accessable from the boot loader again, you’ll need to restore it as well. The easiest way is to Add Wubi Back to the Bootloader With EasyBCD. Once you’ve done that, you should be back in business, ready to use Windows or Ubuntu as you need.

29 de out de 2010

The Linux credit card -- with Tux on the front and everything

The Linux credit card -- with Tux on the front and everything: "
Filed under: ,
I couldn't make this up if I tried: The Linux Foundation is now offering a platinum rewards Visa credit card. There is no annual fee, a low introductory APR -- in fact, it's a normal credit card with Tux on the front.

Every purchase you make with the Linux credit card will kick back a percentage to the Linux Foundation. The Foundation also gets $50 for every activation! In the words of the Foundation, this card is for 'those who want to support the Linux Foundation's activities while expressing their commitment to Linux. The Linux credit card is an easy way for anyone to contribute to the growth of Linux and identify themselves as supporters of the community by carrying Tux in their pocket.'

Unfortunately it's for U.S citizens only, otherwise I'd sign up right now! If you're going to rack up credit, why not do it in a way that benefits the most important software movement of the last 20 years? Why don't more charities have credit cards...?

[via Hacker News]
The Linux credit card -- with Tux on the front and everything originally appeared on Download Squad on Fri, 29 Oct 2010 06:37:00 EST. Please see our terms for use of feeds.
Read | Permalink | Email this | Comments


Prisão de homem na Rússia faz circulação mundial de SPAM cair 20%

Prisão de homem na Rússia faz circulação mundial de SPAM cair 20%: "
Provavelmente você não percebeu, mas a empresa que administra sua conta de e-mail sim: depois que a Rússia prendeu Igor A. Gúsev, 31 anos, um dos maiores spammers da atualidade (para não dizer o maior), a circulação de SPAM caiu cerca de 20% em todo o mundo.

De acordo com a polícia de Moscou, Gúsev é o principal nome por trás de uma rede que pagava a outros spammers para a emissão de mensagens indesejadas, especialmente sobre medicamentos falsificados comercializados por uma empresa chamada Depsmedia. Esse esquema pode ter gerado um faturamento de nada menos que 120 milhões de dólares nos últimos três anos e meio.

A rede de Gúsev foi desativada repentinamente no dia 27 de setembro (2010) e, nesta semana, sua residência foi invadida pelas autoridades russas, operação que resultou na apreensão de computadores, unidades de armazenamento de dados e até remédios. Com a desativação da rede e, consequentemente, com a diminuição dos pagamentos, os spammers “terceirizados” deixaram de enviar cerca de 50 milhões de mensagens por dia.

As autoridades russas também investigam se Gúsev está por trás de uma rede de propagação de malwares que tem o intuito de utilizar computadores contaminados como “escravos” para a emissão de SPAM.

De acordo com a Associação Russa de Comunicação Eletrônica, a prática de SPAM causou prejuízos de aproximadamente 466 milhões de dólares em 2009 só no país.

Referências: ABC.es, RT.
Notícias relacionadas:
  1. Débito Direto Autorizado (DDA) faz uso de boletos bancários cair 10%
  2. Brasil é o 2º país em número de computadores “zumbis”, aponta a Microsoft


How to Crash Any Version of Internet Explorer with Simple HTML

How to Crash Any Version of Internet Explorer with Simple HTML: "

We’ve already shown you why so many geeks hate Internet Explorer, and since it’s almost Halloween we figured we’d show you something really scary—how to crash any version of Internet Explorer with nothing more than HTML and CSS.

Note: we’re really not trying to bash on Internet Explorer—in fact, the latest beta version is really quite nice, but we figured we’d have some fun with this bug, and maybe somebody at Microsoft will fix this problem before the final release.

How to Crash Internet Explorer with HTML

Simply open up notepad or another text editor, paste in the following, and save it as SomeFilename.html.

<style type="text/css">
#a {
margin:0 10px 10px;

#b {

<title>IE Crasher</title>
<div id="a">
<form id="b">
<input type="text" name="test"/>
</td><td width="1"></td></tr></table>

It should end up looking something like this:


Then open it up in Internet Explorer, and BOOM! IE is dead.

Note: hilariously, when I originally put this HTML code into the article, it actually crashed Windows Live Writer repeatedly. Finally had to login to WordPress and remove the code from there in order to be able to even open up the post again.

Where Does This Work?

We’ve tested this out, and it seems to crash just about every single version of IE, from IE6 even up to the latest Internet Explorer 9 platform preview that was released earlier today.



It’s at this point that we should point out that we didn’t figure this out—in fact, there’s a web site that you can visit that will crash IE, and we got the source code from that site.


Please share this link responsibly.

28 de out de 2010

Statistics show European Microsoft Windows browser ballot screen to be useless

Statistics show European Microsoft Windows browser ballot screen to be useless: "

Filed under:

Browser ballot screen numbers

The browser ballot screen that Windows users in the EU have started to see since March, which was supposed to lessen the monopolistic stronghold that Internet Explorer has on browser market share, has proved to be quite useless. New data shows that the differences in browser use trends between the EU and the world from January to October are within the error margin. This is despite Opera's past claims that the browser ballot screen at one point made downloads of its browser in the EU skyrocket.

Let's take a look at the numbers (seen in the table above). IE use dropped 5.25% in Europe between January and October, and 5.92% worldwide. Firefox market share went down 1.23% in Europe and 0.14% worldwide. Chrome jumped 6.4% in Europe and 6.24% worldwide. Safari went up 0.05% in Europe and 0.8% worldwide. And so on.

Now that we've established that the browser ballot screen has done nothing to shift browser choice in Europe compared to the rest of the world, let's look at the numbers another way. IE kept dropping, which is to be expected, but Firefox market share went down too, interestingly. Chrome seems to emerge as the overall winner in the race to gain market share this year, regardless of whether you look at the numbers for Europe, North America or the whole world. Its growth percentage varies, but is still the strongest in all cases.

The stats used are from the StatCounter website.

Statistics show European Microsoft Windows browser ballot screen to be useless originally appeared on Download Squad on Wed, 27 Oct 2010 16:00:00 EST. Please see our terms for use of feeds.


Free OCR Software for Windows

Free OCR Software for Windows: "


arrow Windows Windows only arrow

I’ve never been a huge fan of Optical Character Recognition (OCR) applications because of how they have a hard time reproducing the original document that is being used as the source. Sometimes, however, the formatting may not be as important as just trying to avoid retyping a few dozen pages that you only have in a printed form.

If you’re in that situation I’d definitely recommend checking out FreeOCR. It’s not the most extravagant OCR program I’ve seen, but it’s both free and really simple to use. Since it is capable of directly tying into most scanners I’d say that even a novice computer user could figure out how to use this.

You don’t have to use a scanner though. FreeOCR can also be used to open a PDF file or an image (including most common image types and TIFFs). I tested out the accuracy by printing a snippet from one of our articles, and then scanning it back in. The results I got were really good, but as of right now it can’t really recognize paragraphs. That falls under the formatting issues many OCR apps have since it puts a line break at the end of each line that it sees in the source. In the Text menu you’ll find an option to remove all of the line breaks, which is what I did in the screenshot above, and then manually put the line breaks in where I knew they needed to be. It’s not optimal, but it could sure beat having to retype a huge document.

Something to note is that they are currently running a private Beta test of FreeOCR version 4. This version, once released, will have even better accuracy and some kind of page analysis. It’s definitely worth keeping an eye on this project.

FreeOCR Homepage (Windows only; Freeware)

Copyright © 2010 CyberNet | CyberNet Forum | Learn Firefox
Free OCR Software for Windows

Related Posts:


CIO Essentials for Cloud Computing

CIO Essentials for Cloud Computing: "Cloud computing is changing everything we ever believed about information technology (IT). By essentially renting Web-based applications instead of purchasing software and servers, businesses are beginning to understand the implications of cloud computing for virtually on-demand scalability and reduced infrastructure and complexity as well as saving money. And that's just the beginning. IT professionals and decision-makers had better be ready for the next generation of cloud computing.

View this ZDNet Webcast to learn more about the fast-changing implications of the most important technology since the Internet and what it means for both business and IT leaders:

Find out how cloud computing will continue to profoundly impact the way that software is purchased and consumed and what it means in terms of issues such as service, security, storage, and compliance
Learn why cloud computing is completely re-shaping our thinking of the data center and what it means for the future of IT support and management
Discover what you need to know about the different types of cloud computing providers and the important roles that they will soon most likely play in your business

This Webcast, CIO Essentials for Cloud Computing 3.0, will help get business and IT decision-makers up-to-speed fast on what's happening today and -- perhaps more importantly -- what's happening next in cloud computing.

View It Today!

Note: This premium editorial content is underwritten by Google. The registration information you provide will be shared with this sponsor."

27 de out de 2010

10 ways for road warriors to avoid snags and snafus

10 ways for road warriors to avoid snags and snafus: "

From small aggravations to huge headaches, a lot can go wrong when you hit the road. Veteran globetrotter Brien Posey offers some advice that will help you stay productive when you travel.

Between consulting gigs, technology conferences, and vacationing in exotic places, I travel more than just about anybody I know. So I have a lot of practical experience with working while on the road. Over the years, I have adopted numerous techniques that help me stay productive while I am traveling, and I want to share some of those tips with you.

Note: This article is also available as a PDF download.

1: Bring your own power strip

If someone were to ask me my number one tip for road warriors, I would tell them to always bring their own power strip. Over the years, I have found that some hotels are severely lacking when it comes to electrical outlets. Having my own power strip allows me to power my laptop and charge my cell phone (and other devices) even when there is a shortage of outlets.

There are other reasons for bringing a power strip as well. I recently stayed in one hotel in which the shape of the available outlets prevented plugging in any device that had a transformer built into the plug. Had I not brought my own power strip, I would not have been able to charge my cell phone.

I also like having a power strip because it can double as an extension cord. I once stayed in a hotel in which there were plenty of outlets around the desk area. The problem was that I wanted to watch a movie on my laptop while I was in bed. Had I not had a power strip, there is no way my laptop’s power cord would have reached the outlet.

2: Use a Wi-Fi locator

Even if a hotel claims to have Wi-Fi throughout, there are always some areas with weak signals. I like to bring a Wi-Fi locator with me when I travel. That way, if I have trouble getting a signal, I can check to see whether there is another area close by where there is a signal before I go through the trouble of moving my laptop.

3: Use a personal firewall

Public Wi-Fi networks, such as those found in hotels, are almost always insecure. There is a very real danger of someone using the Wi-Fi connection to infiltrate your computer. Make sure that your computer is equipped with some sort of firewall to prevent this from happening. Windows has a built-in firewall, but there are a number of techniques that a hacker (or a Trojan) can use to disable it. So I tend to feel safer using a third-party firewall.

4: Have a Plan B for getting your work done

Since most hotels offer Wi-Fi connectivity, you might assume that you can use their Internet connection to take care of any necessary work. While this assumption may have been true at one time, it is becoming much more common for hotels to filter Internet traffic.

Much of the traffic filtering does not affect business users. For example, many hotels block access to services such as Netflix and Hulu in an effort to force patrons to purchase pay-per-view movies. However, I have stayed in a couple of hotels that blocked VPN access. I can only assume that this is the hotel’s way of trying to conserve Internet bandwidth.

The lesson here is that you can’t necessarily depend on the hotel’s Internet service to provide access to the resources you need, so you should have a backup plan in place. That plan may involve going to a coffee shop and using its Internet connection, or it might involve using your cellular provider’s mobile data service.

5: Bring Ethernet cable

As strange as it might sound, I always bring an Ethernet cable with me when I travel. I have stayed in several hotels that provided both Wi-Fi and wired Internet access. Wired access tends to be faster and is less susceptible to packet sniffing.

6: Physically secure your laptop

When I travel, I typically use my laptop only at night. The rest of the time, it is in my hotel room unattended. Since laptops are stolen so frequently, I try to physically secure my laptop however I can.

If I have a rental car with me, I will usually lock my laptop in the trunk. Some might consider this risky, but the car keys are under my direct control and nobody should have access to the trunk of my car except me. (I never use valets.) The same can’t be said for a hotel room. You never know when the housekeeper or the maintenance crew will come into your room.

Sometimes, I have no choice but to leave my laptop in a hotel room. If I’m traveling with my netbook, I will lock it in the safe in my room, but my full size laptop is too big to fit in a safe. So if I’m traveling with my larger laptop, I will usually lock it in my suitcase and put the suitcase in a closet. It doesn’t ensure complete security, but at least would-be thieves will have to use some effort. They can’t just pick my computer up off the desk and walk off with it.

7: Don’t forget the AC adapter

At the risk of making myself look like an idiot, I have to tell you to be careful not to leave your laptop’s AC adapter at home. Several years ago, I covered a Las Vegas trade show for TechRepublic. Upon my arrival in Las Vegas, I realized that I had left my laptop’s power cord behind. Unfortunately, I couldn’t find a place to buy a new power cord and there was nobody at home who could overnight my power cord to me. Since I had a job to do, I had no choice but to purchase another laptop. As you can see, leaving my power cord at home proved to be an expensive mistake.

8: Choose voltage regulators carefully

If you’re going to be traveling out of the country, you will need a voltage regulator for your electronics. But beware: Not all voltage regulators are the same. Some of the European voltage regulators are nothing more than adapters. They do not actually decrease the voltage. If you plug your laptop into such an adapter, you will cook your laptop unless it has a 110 / 220 power supply.

Other voltage regulators will convert the voltage to standard 110, but may be unsuitable for use with electronics. When I traveled to Europe for the first time, I bought such a voltage regulator only to discover that it was suitable only for use with hair dryers, electric shavers, and that sort of thing. The instructions specifically said that it was not suitable for use with personal electronics.

9: Make your own backups

Many road warriors store data locally on their laptops. The problem is that the data is vulnerable to loss until it has been copied to the corporate network. Therefore, I would advise anyone who keeps data on their laptop to make their own backups.

When I travel, I bring along either some USB flash drives or an external hard drive (depending on what I am working on) and back up data to it. After making a backup, I store the backup media in a separate bag from my laptop. That way, if my laptop is stolen or damaged, I still have a backup of my data.

10: Invest in a travel kit

One last bit of advice I would give to anyone who travels frequently is to invest in a laptop travel kit. A variety of such kits are on the market, but the one I use has all of the essentials you might need when you travel. For example, it contains a three-prong adapter (in case I stay someplace with two-prong outlets), a spare flash drive, a wireless mouse, a USB-powered keyboard light, a retractable Ethernet cable, a retractable modem cable, and the list goes on.

More tips?

Have you ever run into problems trying to stay productive while on the road? What other suggestions would you add to this list?


Use Robocopy's multi-threaded feature to quickly backup your data in Windows 7

Use Robocopy's multi-threaded feature to quickly backup your data in Windows 7: "
Soon after Windows Vista came out, I discovered that Microsoft had updated the venerable Robocopy with a bunch of extra features and made it a regular part of the Windows operating system. Of course, when Windows 7 came out I immediately examined the newest version of Robocopy and discovered that Microsoft had again updated Robocopy with a single, but very powerful new feature - the ability to perform a multi-threaded copy option. More specifically, with multi-threaded capabilities Robocopy can now simultaneously copy multiple files in parallel, which will result in very fast backup operations.

In this edition of the Windows Desktop Report, I’ll show you how to take advantage of Robocopy’s features to create an exact mirrored duplicate of all the pertinent data files in your user profile folder (C:\Users\YourName). As I do, I’ll show you how to use the new multi-threaded copy feature.

This blog post is also available in the PDF format in a TechRepublic Download.

Why use Robocopy?

If you’re a conscientious about the safety of your data, chances are good that you are already using Windows 7’s Backup and Restore tool to create an image file of your hard disk as well as to backup your data files on a regular schedule. However, you may like to have an additional copy of your data files just to be on the safe side. While you can easily do so by copying your files and folders to an external hard drive via drag and drop, that can be a tedious operation.

Fortunately, Robocopy provides more than 80 different command line switches that will allow you to create a powerful data backup operation. To help you get a leg up, I have delved into Robocopy ’s command line switches and have developed a nice little script that you can use to create an exact mirrored duplicate of all the data files in your user profile folder (C:\Users\YourName). Let’s take a closer look.

Constructing the command line

For my example, I’m going to back up the data file contents of my user profile folder, C:\Users\Greg Shultz, to a folder named TheBackup on an external hard disk which is assigned drive letter G. (You’ll of course substitute the names and paths with your own.) As such, my command will begin with:

Robocopy “C:\Users\Greg Shultz” “G:\TheBackup”

Now, I want to backup every folder in the source, even any empty folders, as they may be place holders for future data. I also don’t want to have files on the backup that I deleted from my hard disk. While I can use the /S and /PURGE switches to accomplish my goal, I can use the /MIR switch to accomplish both of these tasks with one switch. As such, my command is now:

Robocopy “C:\Users\Greg Shultz” “G:\TheBackup” /MIR

The C:\Users\Greg Shultz folder contains several hidden, system files and folders that I don’t want or need to backup. For example, I don’t need to back up the NTUSER.DAT file nor do I need to backup the contents of the AppData folder. In addition, the C:\Users\Greg Shultz folder contains a host of junction points that I don’t need to back up.

Windows 7 uses junction points to link various operating system folders to the user profile folder. For example, the Cookies folder and the SendTo folder are linked to the user profile folder via junction points.

I’ll use the /XA:SH switch to exclude the hidden, system files and I can use the /XD AppData to exclude the entire AppData folder. I’ll then use the /XJD to exclude all of the junction points. As such, my command is now:

Robocopy “C:\Users\Greg Shultz” “G:\TheBackup” /MIR /XA:SH /XD AppData /XJD

One of Robocopy’s most useful features comes into play when it encounters a file that is in use. When it does, Robocopy will stop and wait for that file to be closed so that it can continue with the copy operation. It will retry to copy the file every 30 seconds. The default number of retries is 1 million (no joke!). As this will most like prevent the backup operation from ever completing, you should reset it to a reasonable number.

To change the number of retries, you’ll use the /R switch and to change the wait time between retries you’ll use the /W switch. I chose 5 retries with a 15 second wait time. That way after a reasonable number of retries and wait period, Robocopy will move on. As such, my command is now:

Robocopy “C:\Users\Greg Shultz” “G:\TheBackup” /MIR /XA:SH /XD AppData /XJD /R:5 /W:15

At this point, I am ready to add the new multi-threaded switch: /MT[:n], where n is a number from 1 to 128 and indicates the number of threads to be used. Keep in mind that n is optional and that by default, the /MT switch will use 8 threads. I’ll use 32 threads in my example, as I found it to be a good starting point. (Note that the multi-threaded option is not compatible with the /IPG and /EFSRAW switches.) At this point, my command is now:

Robocopy “C:\Users\Greg Shultz” “G:\TheBackup” /MIR /XA:SH /XD AppData /XJD /R:5 /W:15 /MT:32

Like all command line tools, Robocopy keeps you apprised of the status of operation right in the Command Prompt window. However, chances are that you’ll want to customize and record that feedback in a log file. I like to have the whole picture, so I’ll use the /V switch. However, I really don’t need to know the percentage progress of each file copy, so I’ll use the /NP switch. To create my log file, I’ll use the /LOG switch, which will overwrite the existing log file each time. Now, my command is:

Robocopy “C:\Users\Greg Shultz” “G:\TheBackup” /MIR /XA:SH /XD AppData /XJD /R:5 /W:15 /MT:32 /V /NP /LOG:Backup.log

Creating and using your script

Now that you know how the script works and the necessary switches, you can launch Notepad, type the command, and save the file as RobocopyBackup.cmd. To make sure that the script and open log file doesn’t interfere with the backup, I created a folder in the root directory called BackupTool (C:\BackupTool) and saved the script there.

You’ll find the log file in the same directory as the script after each backup operation. Keep in mind that while the log file is a simple text file, it can be larger than Notepad can handle. As such, you may want to use Wordpad or another word processor to open and view the log file.

Now, anytime that you want to make an extra backup you can just double-click on the RobocopyBackup.cmd to launch it. When it is done, you can examine the Backup.log file. You can also use the Task Scheduler to automatically run your RobocopyBackup.cmd on a regular basis if you want.

What’s your take?

Have you used Windows 7’s version of Robocopy? If so, what’s been your experience? Would you add any additional switches to the script that I presented? As always, if you have comments or information to share about this topic, please take a moment to drop by the TechRepublic Community Forums and let us hear from you.

Stay on top of the latest Microsoft Windows tips and tricks with TechRepublic’s Windows Desktop newsletter, delivered every Monday and Thursday. Automatically sign up today!


What is the Linux Kernel and What Does It Do?

What is the Linux Kernel and What Does It Do?: "
Image by ingridtaylar

With over 13 million lines of code, the Linux kernel is one of the largest open source projects in the world, but what is a kernel and what is it used for?

So What is the Kernel?

A kernel is the lowest level of easily replaceable software that interfaces with the hardware in your computer. It is responsible for interfacing all of your applications that are running in “user mode” down to the physical hardware, and allowing processes, known as servers, to get information from each other using inter-process communication (IPC).

Different Types of Kernels

There are, of course, different ways to build a kernel and architectural considerations when building one from scratch. In general, most kernels fall into one of three types: monolithic, microkernel, and hybrid. Linux is a monolithic kernel while OS X (XNU) and Windows 7 use hybrid kernels. Let’s take a quick tour of the three categories so we can go into more detail later.

Image by uptown popcorn

A microkernel takes the approach of only managing what it has to: CPU, memory, and IPC. Pretty much everything else in a computer can be seen as an accessory and can be handled in user mode. Microkernels have a advantage of portability because they don’t have to worry if you change your video card or even your operating system so long as the operating system still tries to access the hardware in the same way. Microkernels also have a very small footprint, for both memory and install space, and they tend to be more secure because only specific processes run in user mode which doesn’t have the high permissions as supervisor mode.


  • Portability
  • Small install footprint
  • Small memory footprint
  • Security


  • Hardware is more abstracted through drivers
  • Hardware may react slower because drivers are in user mode
  • Processes have to wait in a queue to get information
  • Processes can’t get access to other processes without waiting

Monolithic Kernel
Monolithic kernels are the opposite of microkernels because they encompass not only the CPU, memory, and IPC, but they also include things like device drivers, file system management, and system server calls. Monolithic kernels tend to be better at accessing hardware and multitasking because if a program needs to get information from memory or another process running it has a more direct line to access it and doesn’t have to wait in a queue to get things done. This however can cause problems because the more things that run in supervisor mode, the more things that can bring down your system if one doesn’t behave properly.


  • More direct access to hardware for programs
  • Easier for processes to communicate between eachother
  • If your device is supported, it should work with no additional installations
  • Processes react faster because there isn’t a queue for processor time


  • Large install footprint
  • Large memory footprint
  • Less secure because everything runs in supervisor mode

Image via schoschie on Flickr

Hybrid Kernel
Hybrid kernels have the ability to pick and choose what they want to run in user mode and what they want to run in supervisor mode. Often times things like device drivers and filesystem I/O will be run in user mode while IPC and server calls will be kept in the supervisor mode. This give the best of both worlds but often will require more work of the hardware manufacturer because all of the driver responsibility is up to them. It also can have some of the latency problems that is inherent with microkernels.


  • Developer can pick and choose what runs in user mode and what runs in supervisor mode
  • Smaller install footprint than monolithic kernel
  • More flexible than other models


  • Can suffer from same process lag as microkernel
  • Device drivers need to be managed by user (typically)

Where Are the Linux Kernel Files?


The kernel file, in Ubuntu, is stored in your /boot folder and is called vmlinuz-version. The name vmlinuz comes from the unix world where they used to call their kernels simply “unix” back in the 60’s so Linux started calling their kernel “linux” when it was first developed in the 90’s.

When virtual memory was developed for easier multitasking abilities, “vm” was put at the front of the file to show that the kernel supports virtual memory. For a while the Linux kernel was called vmlinux, but the kernel grew too large to fit in the available boot memory so the kernel image was compressed and the ending x was changed to a z to show it was compressed with zlib compression. This same compression isn’t always used, often replaced with LZMA or BZIP2, and some kernels are simply called zImage.

The version numbering will be in the format A.B.C.D where A.B will probably be 2.6, C will be your version, and D indicates your patches or fixes.

In the /boot folder there will also be other very important files called initrd.img-version, system.map-version, and config-version. The initrd file is used as a small RAM disk that extracts and executes the actual kernel file. The system.map file is used for memory management before the kernel fully loads, and the config file tells the kernel what options and modules to load at startup.

Linux Kernel Architecture

Because the Linux kernel is monolithic, it has the largest footprint and the most complexity over the other types of kernels. This was a design feature which was under quite a bit of debate in the early days of Linux and still carries some of the same design flaws that monolithic kernels are inherent to have.

One thing that the Linux kernel developers did to get around these flaws was to make kernel modules that could be loaded and unloaded at runtime, meaning you can add or remove features of your kernel on the fly. This can go beyond just adding hardware functionality to the kernel, by including modules that run server processes, like low level virtualization, but it can also allow the entire kernel to be replaced without needing to reboot your computer in some instances.

Imagine if you could upgrade to a Windows service pack without ever needing to reboot…

Kernel Modules


What if Windows had every driver available already installed and you just had to turn on the drivers you needed? That is essentially what kernel modules do for Linux. Kernel modules, also known as a loadable kernel module (LKM), are essential to keeping the kernel functioning with all of your hardware without consuming all of your available memory.

A module typically adds functionality to the base kernel for things like devices, file systems, and system calls. LKMs have the file extension .ko and are typically stored in the /lib/modules directory. Because of their modular nature you can easily customize your kernel by setting modules to load, or not load, during startup with the menuconfig command or by editing your /boot/config file, or you can load and unload modules on the fly with the modprobe command.

Third party and closed source modules are available in some distributions, like Ubuntu, and may not be installed by default because the source code for the modules is not available. The developer of the software (i.e. nVidia, ATI, among others) do not provide the source code but rather they build their own modules and compile the needed .ko files for distribution. While these modules are free as in beer, they are not free as in speech and thus are not included by some distributions because the maintainers feel it “taints” the kernel by providing non-free software.

A kernel isn’t magic, but it is completely essential to any computer running properly. The Linux kernel is different than OS X and Windows because it includes drivers at the kernel level and makes many things supported “out of the box”. Hopefully you will know a little bit more about how your software and hardware works together and what files you need to boot your computer.