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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 …

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Articles in Monitoring

Measure DNS Server Performance

March 25, 2019 – 4:04 pm
Tangled FX 2.1.2 (Jan 10, 2019 at 6:31:40 PM)
B & W Etching preset

This is not an entirely proper way to benchmark a DNS server, but, in a pinch, it should give you some idea of its responsiveness and stability.

Automating Web Page Screenshots

January 9, 2019 – 4:22 pm
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Automatic Web page screenshots are commonly used for various monitoring tasks, such as detecting copyright infringement, website defacement, and other legal and security matters. Automatic screenshotting can also be a useful tool for researchers, developers, and journalists. There are free and open-source tools out there that can help you automate the task of creating Web page screenshots.

Automating Web Page Screenshots

July 13, 2018 – 2:25 pm
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Automatic Web page screenshots are commonly used for various monitoring tasks, such as detecting copyright infringement, website defacement, and other legal and security matters. Automatic screenshotting can also be a useful tool for researchers, developers, …

CLI System Monitoring Tools

November 12, 2017 – 12:24 pm
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The multitude of sophisticated centralized monitoring tools available these days excel at one thing: telling you what happened while you’ve been sleeping. But what if you’re awake and need to know what’s going on right …

Watching VSFTP

November 8, 2016 – 10:56 pm
servers_006

I have an FTPS server running VSFTP and below is collection of commands useful for monitoring activity and analyzing the logs.

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. …

Atop Script with Scheduling and Logging

August 3, 2016 – 7:35 pm
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When something is going down on a server, the first thing most sysadmins will run is the venerable top utility. This happens automatically: if you suspect the server is being sluggish, your fingers just type top without you …

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 …

Log Event Time Distribution (Part II)

November 11, 2015 – 2:30 am
time clock watch

Earlier I discussed a way to visualize frequency and distribution of messages in log files. Here’s a script to help you with that. Currently, the script works with two time formats: the one used in …

Upping the Soft nproc Limit

October 5, 2015 – 11:12 am
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This is just a quick note to myself about increasing the “soft nproc” value. On one of the RHEL 6 Tomcat servers I got the following error when trying to “su – tomcat”:

Reduce SNMPd Logging Level

September 8, 2015 – 11:01 am
overloaded_0003

By default, (on RHEL/CentOS, at least) snmpd will log all connection attempts, which can turn your /var/log/messages into a giant mess, looking something like this…

Collectl & Colplot Sytem Performance Analysis Tools

August 26, 2015 – 11:17 am
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It is not often that I run into Unix performance analysis tool that, a), I haven’t seen before and, b), is worth my attention. Collectl is both. It is a very useful combination of iostat, …

Dealing with Runaway Processes

July 14, 2015 – 10:46 pm
shell_003

There is no official definition of a “runaway process”. Generally, it is a process that ignores its scheduled priority. It can also be a process that enters an infinite loop. Or it can be a process …

Multi-Cluster Ganglia Configuration

June 17, 2015 – 11:28 am
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I’ve discussed Ganglia configuration and RHEL/CentOS installation in the past. The usual structure is where every node belongs to one cluster. Recently I ran into a requirement to have nodes assigned to more than one cluster. …

Observium Agent Installation on Pidora

April 13, 2015 – 11:50 am
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Just some quick notes on installing Observium agent on Raspberry Pi running Pidora. Pretty much the same process applies to any Fedora-like flavor.

Using Pflogsumm Postfix Log Analyzer

December 4, 2014 – 12:29 am
postfix_logo

Pflogsumm is an oldie but a goodie. It’s a Perl script that sifts through your Postfix server maillog and provides you with a neat summary of events and some statistics. This information can be useful …

Visualizing Apache Logs with Logstalgia

December 4, 2014 – 12:01 am
Visualization

The Logstalgia is a cool graphical utility for visualizing the Apache access_log files. The practical value of Logstalgia is debatable, but it’s entertainment value is not in question. The managers and NOC operators can stare …

openlava Quick Test

February 22, 2013 – 12:46 pm
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After years working with PBS and LSF, ran into Jeff Layton’s “Share the Load” review of openlava resource manager in the Feb 2013 issue of the Admin Magazine and nostalgia took over. So I built …

Filesystem Performance Testing Using dd

February 5, 2013 – 3:35 pm
Shell Script

Below is a simple script to test filesystem read/write performance using dd with varying blocksize parameter. This can be useful for testing local filesystems as well as network-mounted filesystems. The end result will be a …

Simple Host Monitoring with SSH

September 23, 2011 – 12:10 am
shell

Sometimes you just need something very simple to monitor a server or an application on a temporary basis. A basic ping monitor is fine, but it will only tell you if a server is responding on the network. It will not tell you if there is some other problem on the system. The script below relies on passwordless SSH setup to periodically log into the monitored nodes and check on their health by executing a local or remote script.

Changing Process CPU Affinity on Linux

September 13, 2011 – 4:58 pm
cpu

A common real-life scenario: on a multi-CPU system Oracle processed have taken over and the system has ground to a crawl. The average system load is in double-digits and even logging in takes several minutes. The possible root causes for the problem can range from inefficient SQL queries (the common problem) to insufficient system resources. But at this point you just need to make the system a bit more responsive, so you can start troubleshooting.

Load-Testing HPC Linux Clusters with “stress”

April 28, 2011 – 8:43 pm

The “stress” is a simple-to-use load generator for POSIX systems that I found very useful for stress-testing HPC clusters. The current version of the application is 1.0.4 and it was easy to compile and install. Stress can create configurable system load for CPU, memory, I/O, and disks. In the example below we ran “stress” on a SLES 11 HPC cluster with HP CMU 4.2 installed.