Two useful links comparing CentOS 6.X's - SysV-Init vs CentOS 7.X - SystemD - init systems

In CentOS 6.8, the init system that brings up all the services (link autoexec files in Windows) was called SysV- Init. This has been the foundation for ages as long I’ve been using CentOS. But in the latest release of CentOS (CentOS 7+) the init engine has been moved to a more favorable engine labeled SystemD. SystemD is the init engine behind Ubuntu, Fedora, Red Hat and CentOS. So the standardization is good for the Linux community but moving from CentOS 6.

Tiny storage device writes information atom-by-atom

Memory that writes atom-by-atom. Approx. 500TB per square inch. Entire library of Congress archives can be stored in .1mm square inches. Write speed measured in minutes. Not yet ready for prime time but promising future. http://www.bbc.co.uk/news/science-environment-36824902

WaitUntilPortOpens() - How to wait until process A runs and binds to a port before spawning process B?

Sometimes we have situations where you need to wait until one application is loaded that may bind to a certain port before kicking off a second application that may depend on that port. This process is typically described as “Wait-Until-Port-Opens” (or it could be the reverse - where you want to wait until a port closes). Here are some use-cases for this method or script: You have a Java web application (Jetty, Tomcat, WildFly, etc) that listens on port 8080 and you want your Nginx or Apache HTTPd server to start as a proxy-server once that back-end web server is bound to port 8080.

bash script to generate config or property file from a template file containing variables

Sometimes we have configuration or properties file (as templates) such as httpd.conf or server.conf where we want to dynamically replace $variables with values before writing the output to a new file. Example: # httpd.conf.tmpl SetHandler server-status Order deny,allow Deny from all Allow from $MONITOR_IP We want to develop an install script in Bash such that it reads the httpd.conf.tmpl and replaces the $STATUS_URI and $MONITOR_IP with appropriate values (either passed in as script arguments or coded in the bash script) and then write out the resulting output to a new file such as /tmp/httpd.

Bizarre fourth state of water discovered

Bizarre fourth state of water discovered Scientists at the Oak Ridge National Lab (ORNL) have discovered that when (water) put under extreme pressure in small spaces, the life-giving liquid can exhibit a strange fourth state known as "tunneling". Quantum tunneling means that a particle, or in this case a molecule, can overcome a barrier and be on both sides of it at once – or anywhere in between. Think of rolling a ball down one side of a hill and up another.

Article: The spherical genius of the Hüttlin Kugelmotor

The spherical genius of the Hüttlin Kugelmotor Electrical motors are an energy-efficient method for driving vehicles but battery technology is simply not going to advance quickly enough for all-electric vehicles to be a practical reality for most uses anytime soon. The near and mid-term future is undoubtedly a combination of compact combustion engine generators charging dense battery packs that drive electric motors - the "range extender" option. After nearly twenty years of development another “range extender” candidate is going through final testing and it is a work of elegant genius - Dr.

Appeals Court Hands Obama Administration Major Win In Net Neutrality Case

Appeals Court Hands Obama Administration Major Win In Net Neutrality Case The Obama administration’s rules prevent internet service providers from charging content producers for faster or more reliable service, a practice known as “paid prioritization.” The rules also ban blocking and purposefully slowing the traffic of lawful services, and apply to both mobile and fixed broadband service. Today’s ruling is a victory for consumers and innovators who deserve unfettered access to the entire web, and it ensures the internet remains a platform for unparalleled innovation, free expression and economic growth

Two static website generators explored - Hugo & Jekyll

Today I had to quickly assemble a wiki/blog website for our family temple back in India. At first, I considered doing my traditional option to leverage Wordpress (this blog MyThinkPond.com uses Wordpress). Then I thought of all the complexities of setting up a MySQL database, creating and registering the site with WP Jetpack, etc. I wanted something quick, easy to maintain and something that I can hand over to someone else for maintaining.

Egyptian History as we know today

Much of the Egyptian/Nubian history and culture we know today was a result of colonization by the European empires. In their thirst for expansion, they colonized much of the known world. In India, the Dutch, the Portuguese then the British all came under the name of colonization and expansion. They came in search of new trade-routes to the orient and as history has it, the interests of trade slowly turned into colonization and expansion of the empire.

merging bash ssh session history

You may have observed once in a while that when you SSH onto a server and you try to look up a command you ran earlier (maybe the previous day) in the “history” output but you do not see it. This is because of how a SSH session works! Each time you ssh into a server, it leverages a set of TTY screens to maintain an individual history for that session.

CentOS 7 - How to open ports in firewalld?

Prior to CentOS 7, “iptables” and “shorewall” were the two options avaiable. Since CentOS-7, the default firewall tool is “firewalld”. Here is a short-guide on how to open two ports in the firewalld application: firewall-cmd --get-active-zones # Lets open Jetty Web Server port firewall-cmd --zone=public --add-port=8080/tcp --permanent # Lets open some other port 4242 for TCP firewall-cmd --zone=public --add-port=4242/tcp --permanent # Commit changes firewall-cmd --reload firewall-cmd --list-all Cheers.

How to configure OpenTSDB (or any process) as a systemd service in CentOS 7?

CentOS 7 uses Systemd for managing services (prior to CentOS 7 it was using upstart-init.d to manage the services). Step-1: Create CentOS 7 Service file: vim /usr/lib/systemd/system/opentsdb.service [Unit] Description=OpenTSDB Service After=network.target hbase.service [Service] Type=forking PrivateTmp=yes ExecStart=/usr/share/opentsdb/etc/init.d/opentsdb start ExecStop=/usr/share/opentsdb/etc/init.d/opentsdb stop Restart=on-abort [Install] WantedBy=multi-user.target Step-2: Let’s test the start and stop of this new OpenTSDB service $ sudo systemctl start opentsdb # If it starts up good, you should see the website when you goto http://<servername>:4242/ ps -leaf | grep "tsdb" # shows you something similar then you can add it as a service to auto-start sudo systemctl enable opentsdb Step-3: (optional) Reboot node and make sure that the service starts up accordingly after a reboot.

Fixing vim editor for dark backgrounds so comments are not dark blue

Here is a simple command that can fix your vim editor for dark backgrounds so that your comments are not showing up in dark blue (unreadable). Example screenshot: The temporary fix is to run the following command in the vim editor: :set background=dark instead of :set background=light The permanent fix for this is to add the command inside $HOME/.vimrc file set background=dark Please note that when you’re adding the property into the .

Kairosdb - Cassandra - localhost:9160 - connection refused

If you install the latest KariosDB and Cassandra, when you try starting KariosDB pointing to the Cassandra storage, you will see the following exception: 03-14|14:24:42.331 [main] ERROR [HConnectionManager.java:71] - Could not start connection pool for host localhost(127.0.0.1):9160 03-14|14:24:42.331 [main] INFO [CassandraHostRetryService.java:68] - Host detected as down was added to retry queue: localhost(127.0.0.1):9160 03-14|14:24:42.332 [Hector.me.prettyprint.cassandra.connection.CassandraHostRetryService-1] DEBUG [HThriftClient.java:152] - Creating a new thrift connection to localhost(127.0.0.1):9160 03-14|14:24:42.334 [Hector.me.prettyprint.cassandra.connection.CassandraHostRetryService-1] DEBUG [HThriftClient.java:183] - Unable to open transport to localhost(127.

Go lang - Revel Web Framework - .gitignore file starter sample

For those of you trying to create a new Go Language - Revel Web Framework based project, here is a sample .gitignore file. But before I provide you with the information, we need to discuss the project structure. If you visit the Revel site here, you will see their organization structure of a Revel project. In my case, their my_gocode/ folder is much deeper in what I store in my BitBucket account (or GitHub for that matter).