These two days, I am building a website and deploying it on a VPS server which uses CentOS 5. I don't have cPanel or Plesk for my account, so I need to install and configure everything myself including Apache, PHP, MySQL and FTP server, also today's topic cron job. Since my website has a ranking algorithm to calculate the rankings of each link and update the ranking on database and I need to calculate the rankings every 5 minutes, so I think to use cron jobs. Here are what I have done which may help you.First we need to understand the crontab commands, it can have different options with this c...

I attended this weekend my first Ruby conference, Ruby Lugdunum in Lyon. Besides cool talks and the fun of meeting people like Nick, Blake, or Laetitia, my friend Camille & I did a surprise lightning talk about how PHP is better than Ruby. Here are the slides and a more detailed transcript:A lot of free hosts: it’s easy to find a PHP host, you just have to google “free php host” and you find a ton of free PHP/MySQL hostsBigger community: The PHP community is really huge, and it’s really easy to find a PHP developerEasy to learn: Most people in the IT field have so...

When determining which type of web server to use, the differences and technical details can be daunting. It can be a difficult task to compare web servers and make the decision on which is best for you and your project. Since Apache is currently the most popular web server, this article will discuss the differences between the Apache Web Server and Apache Tomcat, which are very different and fulfill different needs.The Apache Web Server, often just called “Apache” or “httpd”, was developed in 1995 by Robert McCool and continuous development as well as maintenance is...

PKCS12 is an active file format for storing cryptography objects as a single file. It can be used to store secret key, private key and certificate.It is a standardized format published by RSA Laboratories which means it can be used not only in Java but also in other libraries in C, C++ or C# etc. This file format is frequently used to import and export entries from or to other keystore types.Next we will explain the operations which can be performed on PKCS12 keystore.Create PKCS12 keystoreBefore storing an entry into a PKCS12 keystore, the keystore has to be loaded first. This means we have t...

There is one statement which says Giving out your email address is like starting a relationship. What happens when you want to break up?Once you gave out your email address, you may take the risk of receiving big amount of junk emails. However, when we register on some websites, we must provide our Email address to receive authentication emails. If we cannot receive the authentication email, we cannot finish the registration process. Is there any alternative way?We can use disposable email, i.e, some email address are like disposable chopsticks, we can throw them once we finish using them.Curr...

In this post, I will create a HTTPS server and HTTPS client demo which can establish HTTPS communication between a server and a client using Java. This should be very useful when we want to test our understanding about SSL communication. We will use both a detailed SSL client and a simple HttpsURLConnection as the HTTPS client.Before creating the actual HTTPS server and HTTPS client, we first need to generate the keystore and truststore to be used by the server and client. To generate the keystore, we can follow instructions at Different types of keystore in Java -- JKS. In this demo, we ...

Recently lots of Chinese found they experienced problems while trying to access Wikipedia, the world's largest and most well-known free encyclopedia. It turns out that the notorious Chinese GFW(Great Firewall) is playing the critical role here. It blocks the Chinese version of Wikipedia.The reason why the Chinese version of Wikipedia is blocked is said to be that Wikipedia has changed its default protocol from HTTP to HTTPS. This change made it difficult for the GFW to filter some sensitive information the Chinese government doesn't want their people to read. Speaking at the Leadersh...

As a system administrator or network engineer or application developer, there is a need to check whether a port on remote server is open so that you can tell whether the service under check is running or not. In this post, we would cover a few methods to check whether a remote server port is open or not on Linux.telnettelnet is the most frequently used command on both Windows and Linux to check port. The simple usage for this command is telnet [host] [port]When the port is open, the output will be like:Trying 192.168.56.160...Connected to 192.168.56.160.Escape character is '^]'.SSH-2.0-Op...