PTR record(or pointer recored, or RDNS record) is a DNS record in a DNS zone file. It maps an ip address to a host name or a domain name. It is used by mail servers to fight spammers. It is…

How to set an environment variable in Linux? You must know how to set a variable in bash:

You can show its value using:

  However, the bash variable is not an environment variable. The different between ordinary…

I have been using CentOS on my VPS. Today I need to install CentOS 7 on my PC. The installation process was not smooth and I had to do it in text mode. The main task during the installation is…

We know that in html, an image is embedded with an img tag like <img src=”image.jpeg”/>. We put the image file name in the src attribute of the img tag. In email, however, there is no such concept as file.…

I never upgraded wordpress before because I’m afraid the upgrade may break existing functionalities of my site. So I always add the following line to wp-config.php:

AUTOMATIC_UPDATER_DISABLED will prevent wordpress site from upgrading itself automatically. The result is  when…

Nowadays, it is hard to prevent email from going to junk mail if you intend to spam. Most mail servers on the internet deploy spam detection and filtering software that use complex algorithms to detect spammers. The software can tell…

Adding a DKIM record is more complicated than adding a SPF record because it needs to create a public/private key pairs and it also needs to install a DKIM software and configure your mail server to cooperate with the DKIM…

Although adding an SPF DNS record won’t cost you 1 minute, understanding the format of SPF record is not easy. The SPF record is a TXT DNS record you can add through your domain registrar. Some registrars will name this…

I wrote a post on installing awstats on CentOS. That post actually teaches you to install awstats on CentOS 6, where you need to download the awstats package from sourceforge and install it and its dependent software manually. Today, I…

The migration arises from the need for php 7 support. I must admit I’ve been successfully fooled by the versioning of php and CentOS. My old system is CentOS6 where only php5 is supported. I mean you cannot use “yum…