Zend OpCache

The Zend OpCache provides faster PHP execution through opcode caching and optimization. It improves PHP performance by storing precompiled script bytecode in the shared memory.

Installing Zend OPCache on PHP 5.3 or 5.4

1. Login to SSH on your server

2. Type the following commands:

#cd /usr/local/src

#wget http://pecl.php.net/get/ZendOpcache

# to get the latest (master) build do the following instead:

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Icinga2 for CentOS7

Icinga is a fork of Nagios monitoring system. There are lots of changes and upgrades compared to Nagios, especially in version 2. The main visible difference is UI which is built on ext js. Other significant differences are in hosts and services definitions. Icinga2 designed to monitor large complex environments.

Pre-requisites

We need to make sure to install a LAMP stack and epel repository on the CentOS7 server for other dependency application which will support icinga2 . Icinga2 will collect the service information based on the monitoring plugins, so we need to install nagios plugins. Also, we should install IDO modules for MySQL which will use for Icinga2 Web interface and other web interfaces. Then set up MySQL database (create icinga DB and import Icinga 2 IDO schema into the database).  Web interfaces and other icinga addons are able to send commands to Icinga2 through the external command pipe, for that we need to set up external command pipe.

Setup Icinga Web 2 Interface

  • Navigate your browser to http://localhost/icingaweb2/setup or http://IP-Address/icingaweb2/setup or http://Domain-Name/icingaweb2/setup which will launch Icinga Web 2 setup wizard and past the Generate Authenticate token, then hit Next button to move forward.

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The extra second in June 30, 2015 – The Leap Second !

The International Earth Rotation & Reference Systems Service (IERS) has mentioned that an extra second is to be added to Coordinated Universal Time (UTC) at 23:59:59 on 30 June 2015 and this is to make sure the alignment of astronomical and atomic time.

Coordinated Universal Time, UTC is one of the basic time conventions used by most of the world’s local time zones. This UTC time convention has been derived from a bunch of atomic clocks that are distributed across several countries globally.

The rotation of our earth is not so constant and it changes a bit over time and in-turn it decreases the mean rotation speed slowly. This is the exact cause behind leap seconds that gets added up to the UTC time scale, as they adjust the process of the UTC time itself to scale the real earth rotation.

This 1 second adjustment have hardly affected the normal human lives till now. But high performance timekeeping is most important for scientific and economic computing because even a second interruption may become stunningly important in these technologies. This scenario was last observed in 2012 when a second was added to the world time. Websites like Foursquare, Reddit, LinkedIn suffered glitches as the extra second got added because their system clocks were unable to figure out the sudden change.

In fact, on June 30, 2015 when the clock stuck 23:59:60, this will cause problems to many scientific and economic computing systems which are not programmed for this additional time. As conventional computing systems depend on precise time by using the Network Time Protocol (NTP) to be in match with the world’s atomic clocks, issues are expected, as many systems are not programmed for this extra leap second.

The International Earth Rotation and Reference System Service (IERS) in Paris, France observes the time between earth’s rotation and the atomic time. When the difference between the two approaches 0.9 seconds, they order a leap second to be added worldwide.

The workaround for this in our Linux machines is to reboot the server before the leap second period and then execute “date -s now” command in the server so as to update the leap second in the server.

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