Introduction to the Linux EXT4 Filesystem

This article is now available here, on this site.

The EXT filesystem has been the default filesystem for many Linux distributions for many years. EXT2 was the first filesystem I encountered when I first started with Linux 20 years ago. It is robust and works well in almost every mainstream application environment. The EXT4 filesystem is the latest incarnation of this line of filesystems and brings even more speed and reliability to the table.

My latest article at is an Introduction to the Linux EXT4 filesystem. It covers the history of Minix, the EXT predecessor, as well as the evolution of EXT to where it is today.

Testing hardware for Linux compatibility using a Live USB stick

Ever go into a store that sells computers and try to pick out a computer that will work with Linux? Short of reading a review that mentions Linux compatibility or finding a compatibility list – most of which are completely out of date – there is little real information out there on hardware compatibility with Linux.

That is not to say that compatibility is a major problem these days because it certainly is not. Most computers will work just fine with Linux, but there are some bits of hardware that may still cause problems. Laptops tend to be more proprietary than desktop workstations, so testing them before you purchase is more of a necessity because they tend to use less compatible devices.

My latest article on is about Testing Linux hardware compatibility with USB sticks. It shows you one method for creating a bootable Live USB stick that you can use to test computers in a retail store. My article gives you my experiences along with those of another intrepid tester here in Raleigh, NC, and some tips for in-store testing.


My second article in the DNS series on – Build your own DNS name server on Linux

My latest article Build your own DNS name server on Linux, has been posted on This is the second article in my series on DNS name services.

Published yesterday, April 6, Introduction to the Domain Name System (DNS), talks about how name services work on both the client and server side, and lists some of the more common DNS records and their uses.

You may also be interested in some of my other articles about networking. The following list of articles are posted here, and may also be posted on

The following articles are currently posted only on as of April 7, 2017.

My latest article on – Introduction to the Domain Name System (DNS)

My latest article, Introduction to the Domain Name System (DNS), has been posted on This article talks about how name services work on both the client and server side, and lists some of the more common DNS records and their uses.

You may also be interested in some of my other articles about networking. The following list of articles are posted here, and may also be posted on

The following articles are currently posted only on as of April 6, 2017.

Problems with JetPack 4.8

If you are using WordPress and have JetPack installed, do not under any circumstances install JetPack 4.8 at this time. JetPack 4.8 causes significant problems. It apparently prevents loading of all plugins and prevents the site from working.

I reverted back to JetPack 4.7.1 which resolved the problem.

I will post an update to this story when there is a fix available.


New Look

In the previous few days I have transferred the DNS registration of this site to Google Domains and changed the name and URL for the site. So I think it only fitting that I also change the look of the site with a new WordPress theme.

I also wanted to ensure that some of the wider code, system listings, tables, and graphics on various pages of this web site have enough page width to show up completely; that had been a problem and now seems to be resolved with this new theme.

Please contact me if there are still issues with some listings – or if you just want to comment on the new theme.

Name and URL change

Please note that the address of the DataBook web site has changed to:

There are a couple reasons for this, but the primary one is that I like the name better. The old name does not reflect the true character of this web site.

The old URL will get you here for a while longer, but once you are here and click on any DataBook link the new URL will be used. Be sure to change your bookmarks.

Unixmen: Five lesser known tools

I just read an interesting article on about some useful tools that are not widely known. All are interesting, and some are CLI while others are for a GUI environment.

I particularly like two of the CLI tools, iptraf to monitor TCP/IP traffic on your computer, and lsblk to list information about all block devices attached to a computer; that would usually be disk drives of all types. I particularly like the tree view that lsblk displays of not just the drives, but also the partitions on the drives.

Note that iptraf is now iptraf-ng in some distributions.

The following output displays the list of disk drives, including DVD-ROM and USB drives, as well as the hard drives and their partitions.

Typical output from the lsblk command.

Typical output from the lsblk -a command. In this case several different disk types are shown.

The information provided by the lsblk -a command as shown above contains data about hard drives and removable USB hard drives.  It also shows removable CD-DVD/ROM drives, sr0 and sr1. Disks sda, sdb, and sdc are all three regular hard drives. The sdd and sde devices are attached USB removable drives.

The man page contains detailed assistance for getting the most out of this command.

See the article for more information about the other tools.


My PiWall

If you have not heard of the Raspberry Pi yet – or just Pi or rPi for short – you really should learn about it. Soon!

Kids learning computers

The Raspberry Pi is a very small computer that was designed to help children learn about computers and how they work. Although it can be used as a platform for kids to learn programming skills, it can also be used to learn about robotics, remote sensing, and almost anything a computer can be used for. Because of its low price and small form factor, the Pi is also extending the ways in which computers are being used.

Raspberry Pi Model 3B

Raspberry Pi Model 3B

One of the amazing things about the Pi is its $35US price tag. Of course by the time you add a small case,, keyboard, mouse, and display, the cost is a bit more, but $35 is very low for just the computer itself. This provides access to computers for low-income students and the schools they attend in a way never before possible.

Grown-up uses

But the Raspberry Pi can be used for much more than that. Many of us hackers have found important real-world uses for our Pi computers.

I personally have two Raspberry Pi’s performing firewall duties for my network. These Pi’s replace two much larger and more expensive computers that used to perform the same functions. They do this easily and quietly, running day after day to protect my network. And sometimes I have hundreds of individual attacks on my network in a single day so it is an important function.

You can read the details of how I set up my Raspberry Pi firewall at

Cluster Failures

No, “cluster failures” is not a euphemism for a problem encountered in the military service and widely known to be caused by officers with clusters on their shoulders. Nor does this page relate to failures of computing clusters.

This is about failures of independent computer systems and other devices that occur very close together in time. In some cases, the failures may also be of similar type such as a series hard drive or motherboard failures.

And recently I really have had a cluster of problems, some with computers and some not. Actually a cluster of clusters.

I have been repairing things for about sixty years. I started with TV’s, ours and our friends’ and neighbors’. Then I worked at a couple now defunct audio stores. I went on to fixing unit record equipment and computers for IBM. And when personal computers started hitting the streets, I started fixing those as well, both hardware and software.

Cluster failures are a real thing. When working at the audio stores, there would be days or weeks when the most common things people brought in for repair were receivers. And they were frequently similar failures such as the power output stage, or the IF stage. Other days it would be turntables with broken belts or component tuners that would not tune.

When I worked for IBM, there was one week when I fixed three punched card readers with nearly identical feed failures. And later, when working at the IBM PC National Support Center, there were days when most of the calls I fielded were memory (RAM) problems.

Sure, randomness abounds in the universe, including the failures of electronic and electromechanical devices. But sometimes that randomness expresses itself in clusters of failures.

The Church Cluster

It all began on Wednesday, September 9, when the server at my church began failing; really crashing hard. The computer we use as a firewall was also failing with intermittent crashes. In addition, one of the office computers froze up and the telephone system began failing.

It took a couple days for this to this play out and repair the computers. I don’t do the phone system, someone else does that.

The server, a donated Dell, was clearly having hard drive problems. There were specific errors on the console pointing to one of the hard drives. Murphy rules and there were no errors recorded in the logs, because the failing hard drive was where the logs were kept. So because I was not on site and the errors were displayed on the console, the person who rebooted for me could not read the errors as the display had timed out into power saving mode and pressing keys on the keyboard did not wake it.

In addition, the computer we use for a firewall was locked up so I rebooted it.

I took the server home to rebuild and by the next day had mostly completed that task, but not without discovering serious hardware issues. One of the hard drives had failed catastrophically. That was easy enough to fix. But in attempting to install a new operating system on the replacement hard drive, it became obvious that there were other problems as well. The motherboard was failing as well and it was impossible to boot or even to get through the BIOS POST. So I installed the spare Dell motherboard we kept on hand for just this event, and was able to proceed.

I was able to restore the data for our web site and email servers from the good and well-tested backups I designed. I was also able to restore the data for  the DHCP and name service (BIND) servers.

However, soon after I returned home with the server that I needed to rebuild, a different computer, the firewall began locking up more frequently. The office staff were still able to get out to the Internet so long as that firewall was working, but our web site and email was down because that is all housed on our server. Without the firewall, all external access was gone.

The next day, Thursday, I returned to the church and installed the rebuilt server, which worked fine.

However, after installing the server, the firewall started failing so frequently that I could not leave the premises before it would do so again. I made a quick trip back home to obtain a spare computer that had been given to me and had been used as a firewall itself. I installed it at the church, made a couple simple configuration changes, and the replacement firewall was up and running.

The Home Cluster

While all of that was going on at the church, my home network was also embroiled in a cluster of problems.

First, my own server started failing. One of the four 1GB memory DIMMs had failed. One of my workstations had a motherboard failure, and another system developed a defective power supply. A fan then failed on my server, and a video adapter failed on a different workstation. And, oh yes, a hard drive failed on my own workstation. And then a hard drive failed on my server.

And don’t get me started on my refrigerator and car.

What’s it all about, Alfie?

All of this took place within the space of a week, both at church and home. So it was a very trying week.

But what does it mean?

Well, as much as we like to assign meaning to things, there really is none. Things fail. Most of the time they work for years without a problem. Sometimes the failures are spread out evenly over time, or suddenly many things seem to fail at once.

So, sometimes when you get something fixed one day and it fails with another problem the next, that is just the randomness of the universe in which we live.

And now, weeks after the events described, all is well with the computers at church, at home, with my computers, car and fridge — until the next time.