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Selecting Time Ranges from Logs

July 29, 2017 – 6:00 pm

Consider a common situation: you would like to select lines from a log file that match a specific string, but only during a specific time frame. For example, my /var/log/messages contains entries from one of the …

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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.


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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 »

Plotting Log Data

August 9, 2017 – 10:13 pm

While I am on the subject of selecting time ranges from logs, a practical application presented itself. A lonely server in a far-away land with a habit of running out of memory could only be monitored via stunnel and reverse SSH. The server crashed again today and, after bringing it back to life, I looked at whatever meager data the SSH monitor collected to see if there was anything useful. Read the full story »

Croncal – the Cron Calendar

August 9, 2017 – 10:52 am
time clock watch

The croncal is a clever Perl script that reads entries in your crontab and outputs a schedule, showing the time when cron jobs will run.

Install and Configure Etckeeper

June 23, 2017 – 8:05 am

Etckeeper is a handy tool that uses git to keep track of changes to anything in /etc (or any other folder you choose). It’s very simple to use and can help you quickly identify and undo stupid …

Using IPTables to Allow Access to Private Networks

June 22, 2017 – 9:46 am

Below is a quick example of how to use iptables to allow port access for all types of private networks. In this case we’re allowing access to ports 10000 and 20000, commonly used by webmin and usermin.

Get a List of all ESX Hosts in a Datacenter

April 17, 2017 – 3:18 pm
storage barrels cluster hpc

Another simple one-liner to get a list of hostnames of all ESX servers in the vCenter. This can be useful for a number of things, specifically as input for other PowerCLI scripts.

Use PowerCLI to Change NIC Type

April 17, 2017 – 11:52 am

This is a quick PowerCLI script that reads from a list of VM names and for each VM with network adapter type “E1000” changes it to “Vmxnet3”. Nothing fancy, no reboot is needed. MAC should …

Pushing SSH Keys

March 21, 2017 – 10:54 am

This is just a quick note for me on pushing SSH keys using sshpass and xargs. The ~/hosts.txt file contains a list of remote hosts, one per line. And the ~/.passwd.txt contains your password. Make sure to chmod 400 …

Configure and Run esxcli on Red Hat

March 20, 2017 – 3:58 pm

The esxcli utility is used to interface with the vSphere and ESX hosts. It is a useful tool for getting to some basic VMWare functionality from Unix shell. It is also a pre-requisite for some of …

Wget Examples

March 1, 2017 – 9:25 pm
dump truck

This is a follow-up to my previous wget notes (1, 2, 3, 4). From time to time I find myself googling wget syntax even though I think I’ve used every option of this excellent utility over the …

Samba Flexible Character Mapping

March 1, 2017 – 6:33 pm

This is probably old news to most of you, but I just found out: Samba v 3.5+ has a new option for flexible mapping of filename characters. Unix filenames allow certain characters that Windows filename …

Install Webmin on CentOS and Redhat

February 27, 2017 – 2:10 pm

Just a quick short-hand to installing Webmin on CentOS/RHEL. The latest Webmin version comes with a cool new interface theme. You should check it out.

Managing VMs with PowerCLI

February 20, 2017 – 5:45 pm
storage barrels cluster hpc

Below is a collection of useful Power-CLI one-liners (or thereabouts) that can speed up your script-writing efforts. As everything Windows, things change often and for no obvious reason, so expect to see type is deprecated and …

Sun T-Series ILOM and Solaris 11 Network Configuration

February 20, 2017 – 11:16 am

Just some quick notes on setting up Oracle Sun T-series server ILOM and network aggregation with LACP. I don’t get to do this very often, so every time it’s a struggle to remember, with much …

Monitoring DNS Queries

January 27, 2017 – 7:20 am

Recently I’ve been decommissioning old DNS servers and those things are notoriously hard to get rid of. The problem was that the IP addresses could not be preserved. I needed to track down every incoming …

Google Search Tips

January 15, 2017 – 10:17 pm

Google has some advanced search features that few people use, which is a shame. Here are some of them. I am sure there are a few more, but these are the more useful ones.

Verify Network Port Access

December 27, 2016 – 1:06 pm

There are several tools you can use to verify access to a remote network port: nc, tcping, telnet. Unfortunately, nc from the netcat package has been replaced by the one from nmap, which lacks the -z option, making …

Rsync Time Backup

December 22, 2016 – 3:46 pm
dlt tape backup

This is a simple wrapper for the awesome rsync-time-backup script by Laurent Cozic. Through clever use of hard links rsync-time-backup greatly speeds up incremental backups and saves disk space.

Grepping for IPs

December 11, 2016 – 5:47 pm

This is a small collection of tools and examples for working with IP addresses and ranges in Bash. This post is not meant to be a complete reference, rather a practical how-to guide.

Copying a VM between VCenters

November 12, 2016 – 6:13 pm

I had a little task: clone an operational VM from one VCenter to another. Normally, for such a task I would use the Standalone Converter. Unfortunately, this time I ran into an annoying SSH key …

Agedu – Finding Old Files

November 7, 2016 – 3:35 pm
filing cabinet files

I almost never delete anything (not on purpose anyway). Having said that, sometimes I do need to find old data on a server and offload it to a NAS. Agedu has been around for ages. …

Monitoring Solr Cores

November 1, 2016 – 10:50 pm
binoculars watch security rifle gun

The Cloud tab of the Solr Web UI is convenient, but not for monitoring purposes. Just like you, I hate XML and parsing it from shell is more convoluted that it needed to be. But …

Tracking Emails in Postfix Logs

October 27, 2016 – 6:02 pm

Depending on your Postfix configuration, the same email may cycle through the postfix queue several times, changing it’s queue ID and making it difficult to track. For example, if you have Amavis configured for spam and …

Gather MX Records for a List of Domains

October 26, 2016 – 3:45 pm

This is a simple one: get a list of MX records for the given domains and output into CSV file. Really, the only interesting part of this is the use of array to temporarily store …