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How to Fix “nova.compute.manager Stderr: u”qemu-img: Could not open”

All of a sudden, the Hypervisor Summary page in Horizon dashboard was not updating the usage stats of vCPUs, RAM and Local storage for one of the compute node. I see new VMs are launched on that compute node, but the stats page still showed all the vCPUs, RAM and disk were intact/not-used (though the new VMs […]

Fix HTTP 403 Forbidden, Failed to Open Stream – PHP Copy function

I wrote a simple PHP program to copy an image from a website to local directory. The copy() function will copy a file to the specified destination and it can be used to copy a file that’s stored locally and also from a remote website. But I was stuck with an error “failed to open […]

How to install LEMP on Ubuntu 14.04 LTS

LEMP is a group of open source software stack used to setup web server, database and PHP on a Linux operating system to serve dynamic web pages. LEMP stands for Linux, Nginx (pronounced as Engine X) web server, MySQL database and PHP. Another stack called LAMP (alternative to LEMP) is also available in which Nginx web […]

Write a Batch Script to Automate File Transfer Between Linux & Windows using WinSCP

Question: I have been running cron on a Linux server to take a backup of my website once in a day. But I download those backups to my local machine (which is Windows) once in a week or so. Is it possible to automate file transfer from Linux to Windows? Answer: Yes, you can. Take a look at […]

Fix FTP Passive Mode problem on OpenStack & EC2 VMs

Have you installed VSFTP in your OpenStack or Amazon EC2 VM and getting errors such as “Entering passive mode…connection failed“? If yes, then you have landed on the right page. This tutorial will help you to fix FTP passive mode problem on VMs started in OpenStack cloud middle-ware and in Amazon EC2. This error is […]

How to Allow SFTP and disallow SSH?

In this tutorial, I will explain how to configure SSH to allow SFTP and disallow SSH login access. Solution: Well, SFTP uses SSH and by default the users will able to use both SSH and SFTP. But if you ever want users to use only SFTP and disallow SSH access, then OpenSSH supports that. From OpenSSH […]

Install PHP 7 on a fresh Ubuntu VPS: [Fix] Unable to locate package PHP

Recently one of my client provided a fresh VPS and asked me to install PHP 7, Apache and MySQL. While installing PHP, I encountered the below error: root@webimage:~# apt-get install php Reading package lists… Done Building dependency tree Reading state information… Done E: Unable to locate package php Solution: By default PHP5.5 is only available […]

What is “Yes This Is A Really Long Request URL” connection attempt to your webserver?

Today, I noticed a strange connection attempt to my server requesting for a long file name – that starts as ‘/YesThisIsAReallyLongRequestURLbutWeAreDoingItOnPurpose……………….’. Below is the snapshot from the Apache error log. [Thu May 11 17:52:01 2017] [error] [client 137.226.113.7] (36)File name too long  : access to /YesThisIsAReallyLongRequestURLbutWeAreDoingItOnPurposeWeAreScanningForResearchPurposePleaseHaveALookAtTheUserAgentTHXYesThisIsAReallyLongRequestURL                   […]

COMODO SSL Certificate Installation : Nginx

COMODO SSL Certificate Installation – I installed LEMP stack for one of my client on his CentOS 7 machine and configured SSL certificate obtained from COMODO for his domain. It was working fine in desktops and mobile devices. But my client came back with an issue and said that he sees an SSL warning error […]

Call to undefined function simplexml_load_file() – PHP Error [Solved]

While working on a migration of a Joomla powered website on to a new VPS with PHP version 7.0 and Apache 2.4, encountered the an error “Call to undefined function simplexml_load_file()“. Below is the complete error. Error displaying the error page: Call to undefined function simplexml_load_file(): Call to undefined function simplexml_load_file() In this tutorial, I’ll explain […]

StartSSL Distrusted, Migrate to LetsEncrypt!

TRUST is the word that comes to our mind when we speak about Certificate Authority. StartSSL, a certificate authority that provides free SSL certificate with a validity of one year for non-commercial use. An initiative that aimed to secure the internet traffic has now lost TRUST – StartSSL distrusted! The CA lost trust well during October 2016 – below […]

Understanding Affinity/Anti-Affinity Group Policies in OpenStack Mitaka

Nova service controls where the instances are started within OpenStack cloud environment. It means, the nova-scheduler decides which hypervisor will run a particular instance and this behavior is controlled using two filters (Affinity/anti-affinity group policies) – namely, ServerGroupAntiAffinityFilter and ServerGroupAffinityFilter. The ServerGroupAffinityFilter allows a user to run group of instances on the same hypervisor/host and ServerGroupAntiAffinityFilter will ensure all […]

Ctrl+S freezes Vi Editor & Unix terminal? Here’s how you can resume it!

Working on a Unix terminal and all of a sudden the terminal freezes after pressing Ctrl+S? Well, did you see the same behavior when you were editing a file using Vi? Not a problem, this tutorial will help you to resume it back. Generally, most of the editors would allow you to save a file using […]

Delete Blank Rows in Excel – A Quick Tip!

Do you want to delete blank rows in an Excel file, the faster way? Excel generally uses the blank rows to determine data ranges, but sometimes you might want to get rid of those. For e.g., say you want to write a simple script to parse all the rows in excel file and perform some […]

How to update GPG key for MySQL APT repository on Debian/Ubuntu?

If you are getting an error “GPG error and Duplicate sources.list” while configuring MySQL repository for installing MySQL server version 5.7, then here’s how you can udpate GPG key. #apt-get update ….. W: GPG error: http://repo.mysql.com jessie InRelease: The following signatures were invalid: KEYEXPIRED 1487236823 KEYEXPIRED 1487236823 KEYEXPIRED 1487236823 W: Duplicate sources.list entry https://packages.sury.org/php/ jessie/main amd64 […]

How to Fix the_date() Returning Empty Date inside Loop in WordPress

Are you using the_date function inside the loop to display post published date? Well, you might notice the_date() returning empty date for the posts that are published on the same day. For example, if you have two posts published on the same day, then the_date function will return date for the first post and returns empty for […]

How to fix Call to undefined function apc_fetch() – PHP Fatal Error [Solved]

I have been migrating one of the Joomla website and was stuck with a “PHP fatal error Uncaught Error: Call to undefined function apc_fetch()”. If you are stuck with a similar error, then here’s how you can solve it. Before that, below is the snapshot of the error: Fatal error: Uncaught Error: Call to undefined function […]

How to Install MySQL v5.7 using apt-get on Debian 8 Jessie

This tutorial will explain how to install MySQL v5.7 on Debian 8 Jessie server. The default repositories in Debian 8 will install MySQL version up to 5.6, so if you ever want to install 5.7, then you need to setup a repository that has 5.7 RPMs. Alternatively, you can source compile MySQL 5.7, but this tutorial […]

Apache Error: Symbolic link not allowed or link target not accessible

In continuation to my tutorial on Installation of Datawrapper and possible errors with solutions, here’s another error in Apache – “Symbolic link not allowed or link target not accessible“. Below is the complete error message from Apache error_log. AH00037: Symbolic link not allowed or link target not accessible: /public_html/datawrapper/www/static/plugins/visualization-raphael-chart, referer: http://domain.com/chart/AJmIh/preview?innersvg=1&random=49981 I know it is nothing to […]

Not safe to rely on system’s timezone settings -PHP Warning

Here’s another error related to Datawrapper installation – “PHP warning:  It is not safe to rely on system’s timezone settings“. Below is the complete error message from Apache error_log file. [Thu Feb 23 13:18:15.040832 2017] [:error] PHP Warning:  phpinfo(): It is not safe to rely on the system’s timezone settings. You are *required* to use the […]