Featured »


Detecting Blurry Photos with ImageMagick

December 3, 2019 – 9:43 pm

Here’s a typical scenario: I go to a birthday party where everyone knows I’m a shutterbug, so I have to bring my camera. As time goes by and blood alcohol concentration rises and attention to …

Read the full story »

Unix and Linux network configuration. Multiple network interfaces. Bridged NICs. High-availability network configurations.


Reviews of latest Unix and Linux software. Helpful tips for application support admins. Automating application support.


Disk partitioning, filesystems, directories, and files. Volume management, logical volumes, HA filesystems. Backups and disaster recovery.


Distributed server monitoring. Server performance and capacity planning. Monitoring applications, network status and user activity.

Commands & Shells

Cool Unix shell commands and options. Command-line tools and application. Things every Unix sysadmin needs to know.

Commands & Shells, Featured »

Detecting Blurry Photos with ImageMagick

December 3, 2019 – 9:43 pm

Here’s a typical scenario: I go to a birthday party where everyone knows I’m a shutterbug, so I have to bring my camera. As time goes by and blood alcohol concentration rises and attention to detail declines, the photos become increasingly blurry. The trick is to take a lot of them and then, hopefully, some will come out well. But which ones?

Read the full story »

Working with iptables Logging

November 30, 2019 – 9:41 pm

Most commonly iptables is used to allow, block, or redirect connections. However, it also has a logging feature that can be very useful for network traffic analysis and system security.

Copying File Attributes Across Servers

November 29, 2019 – 9:40 pm

To make long story short, had to fix someone’s chmod -R 777 /. A late-night copy-paste fail, it would seem. Needless to say, console access is required, as SSH will not work with permissions on …

CD/DVD-to-ISO Helper Script

November 27, 2019 – 9:39 pm

I can’t recall the last time I needed to convert a CD to ISO. I have four laptops and not one even has a DVD drive. It took me a while to find an external …

Analyzing Network Performance

November 25, 2019 – 9:37 pm

Much of network performance analysis will be comparative in nature. Thus, seeing the output of multiple commands side by side can be quite useful. Bash has a useful little utility called pr and we’ll make …

Copying Data in a Restricted Environment

August 17, 2019 – 8:04 pm

Consider this not-so-hypothetical scenario: you have some data on server_a that you would like to copy to server_b. Unfortunately, these two servers cannot communicate with each other. Nor do they have access to any common …

Raising Dead Services

August 15, 2019 – 2:23 pm

I suppose you may say all of this can be just as easily done via systemd service config files. Well, yes and no. Yes, it can. And, no, not as easily. Not even close. Because …

IMDb Movie Title Parser in Bash

July 12, 2019 – 7:19 pm

This is an update to the IMDb parser I wrote years back. From time to time IMDb makes small changes to their setup that break my script. This time they decided to start blocking curl, …

Sending Windows Logs to Remote Syslog

July 6, 2019 – 11:21 am

Nothing fancy here: just a quick note on directing Windows event logs and select application logs to a remote syslog server.

Plugging iPhone’s Privacy Holes

July 3, 2019 – 11:19 am

Many recent publications , , suggest the iPhone is full of security holes threatening your privacy. The threat seems to be coming not so much from the phone’s operating system, but from the apps, …

Squeezing Video Files

June 30, 2019 – 11:16 am

All that crap I’ve been saving from YouTube, Facebook and whatnot tends to add up. As quality is not a huge concern here (not that it was very high to begin with), optimizing those video …

Finding Passwords in Logs and Shell History

June 27, 2019 – 11:15 am

Sooner or later it will happen: you type something after which you expect a password prompt then, without looking, you type the password. However, you fat-fingered the first command, and your password ended up in …

Anatomy of Internet Bullshit

June 25, 2019 – 11:12 am

Here’s an oldie from two years ago that reared its ugly head on Pocket: Starting Your Day on the Internet Is Damaging Your Brain, by Srinivas Rao. The author presents his personal opinion that reading …

Late Night Rant: College Admissions Scandal

June 23, 2019 – 11:11 am

This is America: you’re either a duper or a dupee. I’m a duper. You guys are the dupees.
— Frank Reynolds (Danny DeVito), It’s Always Sunny in Philadelphia
How will the 2019 college admissions scandal work out? …

Adding and Removing sshd instances on CentOS 7

June 20, 2019 – 11:09 am

As a follow-up to my previous post about adding sshd instances on CentOS 5 & 6, here’s a script that does the same on RHEL/CentOS 7.

Adding and Removing sshd instances on CentOS 6

April 20, 2019 – 8:24 pm

This is a process and a couple of script to allow you to setup an additional sshd service on an alternate port.

Creating a Chroot Jail for SSH Access

April 17, 2019 – 4:51 pm

Just a quick collection of notes on – rather than a definitive guide to – setting up an SSH chroot jail on RHEL 6. The same should work on RHEL 7 and unrelated flavors. For …

The Unix Oriental

April 14, 2019 – 4:16 pm

Placed quite appropriately in the “Security” category – my favorite Oriental cocktail recipe. Distinguishing it from the classic preparation, are absence of sweet vermouth and lime juice, as well as addition of just a couple …

Notes on ownCloud configuration

April 12, 2019 – 4:13 pm

The ownCloud file sharing application has been around for some time now, but somehow evaded my attention. My limited imagination makes me say “think of it us Dropbox hosted on the server in your basement”.

Encrypting Log Data During Log Rotation

April 9, 2019 – 4:12 pm

Most log files do not contain personally-identifiable information or other sensitive data. And even if they do, encryption of all personal data is not mandatory under GDPR. Still, on occasion, for testing and troubleshooting purposes …

DevOps Obfuscation

April 6, 2019 – 4:10 pm

Some years ago I’ve been reading “DevOps in Straight English” by Magnus Hedemark  and encountered the Release Frequency vs. Risk chart that supposedly illustrated the advantages of DevOps. It seemed convincing enough to not give …

Gnuplot with Bash

April 2, 2019 – 4:08 pm

OK, so both of these things have been around forever and will be around long after we’re gone. It’s worth your time to learn how to use the to together.

Multi-Dimensional Arrays in Bash

March 30, 2019 – 4:06 pm

Bash does not support multi-dimensional arrays, but there is a way to imitate this functionality, if you absolutely have to.