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Recover Crontabs from Log

February 27, 2017 – 12:15 am

Some time ago I was using PDSH to update root crontab on a bunch of servers and ran into what looked like a PDSH-specific bug. The same command that worked just fine when executed locally or …

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Networking

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

Applications

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

Data

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

Monitoring

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 »

Install Webmin on CentOS and Redhat

February 27, 2017 – 2:10 pm
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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.

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Sun T-Series ILOM and Solaris 11 Network Configuration

February 20, 2017 – 11:16 am
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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 googling …

Monitoring DNS Queries

January 27, 2017 – 7:20 am
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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
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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
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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
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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
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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
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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
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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
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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 …

Installing Alternative Java Versions on RHEL/CentOS

October 26, 2016 – 2:23 pm
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Below is shorthand for installing alternative versions of Java on your RHEL/CentOS system. This may come in useful for the purposes of testing.

Loan Payment Calculator in Bash

October 13, 2016 – 5:53 pm
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Just a little bit of fun with Bash: a loan payment calculator. Nothing fancy here. Maybe I’ll add the amortization schedule to it later…

Installing NetData on RHEL/CentOS

October 13, 2016 – 5:50 pm
overloaded

NetData is a real-time system monitor great for visualizing performance data. Instances of netdata run independently on monitored systems. The results can be accessed remotely and grouped into a single dashboard view, making this tool highly scalable. …

BIND DNS Query Frequency Analysis

September 6, 2016 – 1:30 pm
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The little script (dns_qpm2) below will look through your BIND query logs and calculate average query-per-minute rate for the given clients.e Nothing fancy, but can be useful in identifying the heavy-hitters.

Using YUM to Sync Packages with Master Server

August 21, 2016 – 10:40 pm
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I just built a new CentOS box and needed to make sure it had all the same packages installed as one of my other servers. So, before this gets lost in the shell history, here’s …

Nohup Without Nohup.out

July 13, 2016 – 12:55 am
shell

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.

Socket Statistics ss Command

July 11, 2016 – 8:10 pm
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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
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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
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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
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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 …