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Finding Prime Numbers

April 22, 2016 – 2:09 pm

I have no intention of competing with GIMPS. To me this is a fun scripting exercise that may produce useful results beyond this initial application. Our goal is to take a bunch of integers and …

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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 »

Nohup Without Nohup.out

July 13, 2016 – 12:55 am

This is a common question: how can I run nohup without creating the annoying nohup.out ? And the common answer is: you can’t. But this is not exactly true. Read the full story »

Socket Statistics ss Command

July 11, 2016 – 8:10 pm

This is a small collection of useful ss (written by Alexey Kuznetsov of the Russian Nuclear Research Institute) syntax examples that go beyond the basics covered by other sources. Here’s one I use often: it shows established connections to …

Filesystem Synchronization with Freehold

July 8, 2016 – 2:43 am

Whenever an application description begins with phrases like “runs on anything” and “is easy to setup”, attribute such bravado to the author’s lack of experience outside his development sandbox. Freehold comes as a tarball for “any Linux” …

Osync and DiffTree

July 8, 2016 – 1:49 am
filing cabinet files

Think of osync as a kind of rsync that is more suited for making backups. While rsync certainly has more options, osync takes a lot of the complexity out of writing a backup script with a few options that are …

Improving Your Scripts with ShellCheck

July 7, 2016 – 8:42 pm

Unlike most other popular scripting languages, Bash has few style-checking utilities. The best one, I think, is ShellCheck – a very cool and useful utility that can greatly  enhance robustness of your scripts. Like that time …

Increasing Entropy Pool in Linux

June 28, 2016 – 9:48 pm

The pool of random numbers in Linux is derived primarily from user interaction (keystrokes and mouse movement). A server does not have such a source and the random pool may start running low, especially during …

Fixing NIC Name in Cloned VMWare Linux Machines

June 28, 2016 – 12:32 pm
network switch

A suspected bug with certain versions of VMware ESX causes cloned Linux VMs to obtain a sequentially-number NIC. For example, if the parent VM had eth0, the clone will have eth1, and the clone of …

Better ‘date’ Functionality in Solaris

June 28, 2016 – 8:53 am

The Solaris date command does not have many of the useful features of its GNU equivalent. A workaround is to use Tcl. This requires tclsh to be installed (which tclsh). You can implement this workaround as …

Create NFS share from QNAP CLI

June 13, 2016 – 2:21 pm

In this example we create the “test” NFS share on a QNAP NAS from CLI and export it to client_ip_01 and client_ip_02. Things to keep in mind: this only creates an NFS share – not …

Speed Up Shell Loops Using Arrays

June 7, 2016 – 9:02 am

Just a quick note on addressing a common issue of running redundant commands when using shell loops. Let’s say you needed to get a count of network connections to an Oracle database server for each connection …

Kodi Volume Control Stops Working

May 22, 2016 – 1:01 am

All of a sudden, when using the remote (either radio or IR), Kodi sound controls stop responding. The volume level does not change and the mute button doesn’t work. These are possible symptoms of an …

VMWare VMDK Locked Error

May 21, 2016 – 10:27 pm

So, being a Unix admin on-call for the week, I just spent half of my Saturday fixing a dead Windows VM. Very annoying. The best I can tell, the issue occurred during the snapshot operation. …

Decrypting Mac Disk

May 20, 2016 – 11:41 am

It is generally a good idea to use full-disk encryption, especially on a laptop. However, this becomes bothersome if you are trying to re-partition your disk, say, to make the system dual-boot. Here’s a quick …

Useful Bash One-Liners

May 2, 2016 – 8:43 am

Here’s a  loosely-organized pile ‘o shell quickies I kept googling now and then and finally decided to write ’em down.

Monitoring NetBackup Daemons

April 27, 2016 – 9:25 pm
tape dlt backup

Here’s an example of a script you can use to monitor NetBackup server daemons in a Linux environment. The main difficulty with keeping track of these services is that there are so many of them. …

Using JTR to Crack Office Documents

April 22, 2016 – 5:35 pm
Macro computer screen shot with binary code and password tex, great concept for computer, technology  and online security.

John the Ripper is a free multi-platform password-cracking software. This article is not intended to be a comprehensive guide to jtr, rather a quick how-to. Starting with version 1.7.9, jumbo patch 6, jtr supports password …

Counting Beer Calories

February 24, 2016 – 10:58 pm

Calories in beer come mainly from alcohol, unfermented sugar, and residual yeast. You’ve heard of the beer belly, but there’s nothing special about beer calories. A bottle of Heineken (150 calories) won’t make you any …

Monitoring Application Network Connections

February 11, 2016 – 3:12 pm
network switch

A Java application on one of my servers has been causing problems by opening up too many network connections and now closing them quickly enough. I needed to be notified when the number of connections …

Run Cron Jobs at Arbitrary Intervals

January 27, 2016 – 10:24 am
time clock watch

Current versions of cron support sophisticated syntax making creating weird schedules a breeze. With older versions of cron you normally had to schedule multiple jobs to fill every time slot in a complex schedule. The …

Diff on Output of Remote Commands

January 25, 2016 – 1:47 pm

Let’s say you run the same command on two remote servers and you want to compare the output. Here’s a quick example:

Show NIC Bandwidth Utilization

January 15, 2016 – 12:43 am
network switch

Just a quick script that will measure bandwidth utilization in KB/s for all NICs on your server over the specified period of time. You can call the script with an optional time wait parameter in seconds.

Find + Rsync + Xargs

December 22, 2015 – 11:09 am

Just some quick syntax for running multiple rsync threads in parallel using find and xargs. In many cases (especially if NFS is involved)  this can greatly speed up the copy operation.

Taking Linux Temperature

December 14, 2015 – 12:21 am

Just some notes on setting up temperature monitoring and alerting on CentOS/RHEL running on HP ProLiant. The first step is to install lm_sensors: