June 23, 2015

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

Filed under: General Topics,Server Tweaking — Bella @ 12:10 am

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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May 22, 2015

VENOM – QEMU vulnerability – CVE-2015-3456

Filed under: Miscellaneous,Server Security — Bella @ 1:23 am

VENOM vulnerability also known as QEMU exploit is the most recent vulnerability reported on May 13, 2015 and it is discovered by Jason Geffner while performing a security review of virtual machine hypervisors.

VENOM stands for “Virtualized Environment Neglected Operations Manipulation”.

This venom exploits QEMU, an open source machine emulator. The venom CVE-2015-3456 vulnerability resides in the virtual floppy drive code (FDC) used by the virtualization platforms. If it gets exploited, it allows an attacker to gain full control of the operating system hosting them and as well as on the other guest VMs running on the same host machine.

This is an Image

Failure to mitigate this issue, this exploited virtual machine escape could open access to the host system and all other VMs running on that host, potentially giving elevated access to the host’s local network and adjacent systems running on the network.

Generally, to eliminate the possibility of exploitation, proceed with the following.

To install the updates using the yum package manager, execute the command given below.

yum update

To update the QEMU package and its dependencies alone, execute the command given below.

yum update qemu-kvm

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May 20, 2015

Unable to fork: Cannot allocate memory

Filed under: Linux Basics,Server Tweaking — Bella @ 9:29 pm

Issue :

Receiving the below error while login to a container from OpenVZ node :

#vzctl enter 10524

Unable to fork: Cannot allocate memory

where ‘10524’ is the id of the container you are trying to login to. (more…)

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May 12, 2015

Load Balancing via Round Robin DNS

Filed under: General Topics,Linux Basics,Miscellaneous — Bella @ 9:24 pm

Round robin is a balancing mechanism used by the DNS servers which is usually used for sharing the network load and managing the load of geographically distributed Web servers. The DNS server that uses the round robin mechanism will provide alternates for each client request.

Concept :-

Suppose, you have a domain name and three identical home pages hosted on three servers with three different IP addresses. By using Round Robin DNS, when one user accesses the home page, the request will be sent to the first IP address. The second user who accesses the home page will be sent to the next IP address, and the third user will be sent to the third IP address.
In each case, once the IP address is used out or taken, then that particular IP address will goes to the end of the list. Therefore, the fourth user will be sent to the first IP address, and so on. Thus, we can distribute the load across several servers with identical configuration. (more…)

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April 25, 2015

Switching PHP versions : An overlook

Filed under: General Topics,Miscellaneous,Technical Articles — Bella @ 11:45 pm

PHP: Hypertext Preprocessor has been involving in all of its dynamics in the recent years. In recent times it has involved included and engulfed many of the recent development and api that has been introduced to the computer world especially web developing.

Switching to higher version of PHP is always good but before proceeding the switch we recommend to test the code in the new version and be well satisfied on the code execution.

In this doc we will be taking an overlook on the changes and precaution one should take if your are switching from a lower PHP version to higher PHP version, as below :

Migrating from PHP 5.5.x to PHP 5.6.x
Migrating from PHP 5.4.x to PHP 5.5.x
Migrating from PHP 5.3.x to PHP 5.4.x
Migrating from PHP 5.2.x to PHP 5.3.x
===== (more…)

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