Archive for the ‘Computers’ category

Distraction Free Writing mode Themes for WordPress



Distraction Free Writing mode Themes is a WordPress plugin I’ve been working for the past couple of weeks – it provides themes/color schemes for for Distraction Free Writing mode in WordPress. You can use one of the built-in themes or write your own with CSS.

As someone who uses a dark color scheme for programming I didn’t like the default color scheme in WordPress (black text on white background).

The plugin has six themes in total. The default theme is based on Monokai:


Plugin page at

Screenshots of the different themes available:

How CloudFlare client-side DDOS detection works


I was looking through Hacker News today, and upon clicking one of the links a screen popped up, pictured below:


This is interesting. What kind of technique does CloudFlare employ to detect potential DDOS attacks inside the browser?

The answer turned out to be simple – let’s dive in.

The page consists of two parts, a form:

<form id="ChallengeForm" action="" method="POST">
<input type="hidden" name="act" value="jschl"/>
<input type="hidden" name="jschl_vc" value="afc458a1300ed9eb1a853d757eadd306"/>
<input type="hidden" id="jschl_answer" name="jschl_answer"/>

And a small piece of JavaScript:


The form has a unique hidden value (jschl_vc) and an empty hidden value (jschl_answer).

The Javascript snippet calculates a mathematical challenge – in our case 9+50*1, which it inserts into jschl_answer and submits the form.

The jschl_vc form field uniquely identifies the challenge to CloudFlare, so that the backend knows what the answer should be. If jschl_answer is interpreted as being the correct result, a cookie called cf_clearance is created with a unique id that identifies the user as having verified the challenge.

In summary

The Cloudflare page checks whether the user has JavaScript enabled.

This looks like a really effective technique against primitive DDOS floods, which issue simple GET requests to a server.

Below are links to the full source of the page:


Ultimate guide to setting up the LAMP stack on CentOS 6 (Apache, PHP, MySQL)


Brace for awesome!

This is a tutorial that covers the entire process of setting up CentOS 6 and installing/configuring Apache, PHP, MySQL, SELinux and iptables, as well as securing the server. This tutorial will give you a base setup for running static as well as dynamic web sites using PHP and MySQL. This tutorial suits VPS or other low-memory configuration as well as dedicated servers.


This tutorial assumes basic knowledge of shell/console usage and knowledge of one text editor.

You need a freshly installed CentOS 6 installation to proceed (Minimal installation is recommended) Once you’re in a root shell, start reading below!

Step 1 – Choose a text editor

Nano is very simple to use and has on-screen help at all times.

Vim is a good editor, but has a slightly steeper learning curve. Here is a good tutorial.

If you find it hard to choose, install and try them both by installing thei via Yum, the CentOS package manager!

yum install vim nano

Since this is your first installation using Yum you may be prompted about importing a GPG key. Enter Y followed by the Enter key to accept.

Step 2 – Configure your network

Attempt to ping an external server, such as google:

ping -c 4

If you receive a response, skip the rest of this section as you have connectivity. If it fails, keep reading.

Not having connectivity is most often due to the lack of a DHCP server running on the network to issue an IP to your server. If that is the case, you need to configure the IP manually.

Here is a useful step-by-step tutorial for setting up static IP address on CentOS 6.

Step 3 – Update your system

After a fresh CentOS 6 install, run:

yum update

Select all updates and let it complete, now run:

cat /etc/*release*

You should see your CentOS version, at the time of writing this, that version is:
CentOS release 6.4 (Final)

Step 4 – Configure (or disable) SELinux

I usually disable SELinux as it makes for some cryptic errors when running the LAMP stack. If you would like to have a go at running SELinux enabled with LAMP, here is a good article to get you started.

To disable SELinux:

vim /etc/selinux/config

Change the SELINUX= line to disabled, like so:


Now reboot your machine

shutdown -r now

Step 5 – Add the EPEL repo

EPEL is an extra software repository with a lot of useful software that is not in the base repo. We will need it later, so let’s add it to our CentOS install! Go to this page to get the most up to date EPEL version. Copy the link from the text epel-release-6-x.noarch and use it in the command below:

rpm -Uvh

Depending on the version of CentOS installed, you might need to change x86_64 to i386 in the URL to the repo.

Step 6 – Install Apache, MySQL and PHP

Issue the command:

yum install mysql mysql-server mysql-devel httpd php-common php-gd php-mcrypt php-pear php-pecl-memcache php-mysql php-xml php php-mcrypt php-mbstring php-devel gcc pcre-devel

Enable Apache and MySQL on startup

chkconfig httpd on
chkconfig mysqld on

Start Apache and MySQL

service httpd start
service mysqld start

After starting mysqld, you will receive a prompt to change your MySQL root user password. The dialogue will read…

To do so, start the server, then issue the following commands:

Two commands will be presented to you, run them both. You will need to use your server name in the second command, as the help prompt instructs you. The base commands are:

/usr/bin/mysqladmin -u root password 'new-password'
/usr/bin/mysqladmin -u root -h your-hostname password 'new-password'

Your web server should now be reachable via http://<your-server-ip&gt; in a web browser. If you have started Apache but the server is not visible, you probably need to configure iptables.

Step 7 – Configure iptables

Load up the iptables config file

vim /etc/sysconfig/iptables

Below the :OUTPUT ACCEPT [0:0] line, add

-A INPUT -m state --state NEW -p tcp --dport 80 -j ACCEPT

If you are going to be changing your SSH port (see separate section below), now is a suitable step to allow connections to the new SSH port.

If we are changing SSH to port 4711, this line should also be added:

-A INPUT -m state --state NEW -m tcp -p tcp --dport 4711 -j ACCEPT

Step 8 – Change SSH port

Changing your SSH port makes it harder for hackers to find information about your server via port scanning. To change the port (in our case to 4711), open the sshd config file:

vim /etc/ssh/sshd_config

Search for the line “#Port 22”, change it to:

Port 4711

(Note the removal of the hash sign.)

Make sure you have added the iptables rules for your new port! (See section above.)

Restart sshd by issuing:

service sshd restart

If you are currently on a SSH console, log out and log back on to your server using the new port.

Step 9 – Install extra “nice-to-have” packages if desired

This section is optional, go to Step 10 to continue if you don’t want any extra packages.

Good replacement for top.

yum install htop

curl and wget
Simplifies file retrieval from the command line. You should install at least one of these. They are often included in your CentOS installation.

yum install curl wget

This package allows you to unzip files

yum install unzip

Manuals for commands. Sometimes not included in minimal installations.

yum install man

Step 10 – Reboot!

Now is a great time to reboot, issue the command

shutdown -r now

If your server is not accessible with SSH/HTTP after reboot, there might be something amiss with the iptables settings.

Step 11 – Install phpmyadmin

phpMyAdmin is a powerful tool for manipulating MySQL databases, let’s install it!

cd /var/www/html
mv phpMyAdmin-3.5.6-english phpmyadmin
rm -f

Now you can browse to:

Add blowfish_secret for security

cd phpmyadmin

Add a secret key to $cfg[‘blowfish_secret’] so it looks like below:

$cfg['blowfish_secret'] = 'your-secret-key';

According to this site, your password may contain up to 46 characters.

It’s also a good idea to protect phpMyAdmin behind another layer, HTTP authentication.

You can find out how to do that in this excellent tutorial.

Step 12 – Add extra users

useradd username
passwd username

Allow your new user to sudo
sudo allows a user to temporarily take on the role as root.

vim /etc/sudoers

Note: If you are getting a blank text file (not found) in this step, install sudo with
yum install sudo

Find the line:

root    ALL=(ALL)       ALL

Under this line, add a new one to allow your newly created user to use sudo:

username ALL=(ALL)       ALL

Save the file (it’s read-only, so you need to force the write using :wq! in Vim)

Step 13 – Configure Apache

Let’s make some sane modifications to the Apache configuration to improve default behaviour and lower the memory consumption. I am configuring this for a 512MB server, if you have more memory you may retain these values at their original settings or adjust them differently.

vim /etc/httpd/conf/httpd.conf

Allow for .htaccess overrides

Search for the AllowOverride directive in the configuration file.

Change the instances of:

AllowOverride None


AllowOverride All

You will also need to uncomment the general AllowOverride declaration by removing the hashtag (#) in front of it.

Before (commented out):

# AllowOverride All

After (Correct version):

AllowOverride All

Change the amount of workers spawned

Find the IfModule prefork.c directive and change according to the example below.

<IfModule prefork.c>
 StartServers       8
 MinSpareServers    5
 MaxSpareServers   20
 ServerLimit      256
 MaxClients       256
 MaxRequestsPerChild  4000

This reduces the memory footprint of Apache, in exchange for slower responses under heavy load.

Enabling KeepAlive

Change the KeepAlive directive from Off to On.

Enabling KeepAlive improves the speed at which pages load, but may make your server crash under heavy load. See this blog post for some interesting etails.

Step 14 – Configure PHP

Let’s edit the PHP configuration file:

vim /etc/php.ini

Increase the maximum upload file size

I like to set this pretty high, as you can limit the upload filesize in a PHP script should you need it.

upload_max_filesize = 128M

You will also need to change the post_max_size restriction:

post_max_size = 128M

Increase the memory limit of PHP

This limit controls the maximum amount of memory a single script is allowed to use. The default (128M) is sensible, but you can increase it if you have a good amount of memory.

memory_limit = 256M

Increase the maximum execution and input time

The default maximum script execution time is a measly 30 seconds. You can easily bump this to 300 seconds.

max_execution_time = 300

The default maximum time to wait for POST and GET data is 60 seconds. File uploads are counted into this, so it is desirable to increase this to avoid errors when uploading large files.

max_input_time = 300

Enable the short_open_tag directive, to support shorthand syntax such as <?=$var?>. Here’s how to enable it:

short_open_tag = On

Now we can restart httpd and the changes will be active

service httpd restart

Install opcode cache

Speed up your PHP applications by installing the Alternative PHP Cache (APC).

First we need to install some dependencies, then we will compile APC using PECL.

yum install make
pecl channel-update
pecl install apc-3.1.13

Press enter multiple times when prompted to select options (this will pick the defaults.).
Add the APC extension to the PHP configuration:

vim /etc/php.ini

Under the line [PHP] add:

Adjust size of cache:

vim /etc/php.d/apc.ini

We are setting the cache to use 256MB:


(The file apc.ini does not exist at this point, simply write your changes and APC will pick up on it.)

Restart Apache and we’re done!

service httpd restart

Optional: APC comes with a small web-based control panel. It’s included in the installation but you need to copy it to your web root to use it:

cp /usr/share/pear/apc.php /var/www/html

Now you can navigate to /apc.php on your server to see the cache stats.

Step 15 – Configure MySQL

Save your default password for mysqldump

To run mysqldump in a cron job (read more about cron jobs in Step 17), you need to set a username and password to the MySQL configuration file.

Open up the file:

vim /etc/my.cnf

Add the following lines at the bottom of it:

 user = mysql-user
 password = your-password

It is not advisable to use the root user here, instead, you may use an account with global read privileges.

(Optional) Disable InnoDB

If you want to use save memory (about 60-100 MB) and don’t need InnoDB tables, you may disable them by editing the MySQL configuration file.

vim /etc/my.cnf

Under the [mysqld] directive, add the following line:


Step 16 – Add virtual hosts to Apache

Virtual hosts allow multiple web sites to be served from a single Apache installation.

The virtual hosts can be added to the end of the Apache configuration file.

Here is an example configuration with two web hosts:

NameVirtualHost *:80

<VirtualHost *:80>
DocumentRoot "/var/www/html"

<VirtualHost *:80>
DocumentRoot "/var/www/html/"

Step 17 – Set up cron jobs

Setting up cron jobs is useful for scheduling tasks. For this we’re going to install CRON and Crontab.

yum install crontabs
chkconfig crond on

To see the local user crontab issue:

crontab -e

Here is a great resource for learning how to manipulate the crontab file.

Remember that the scheduled commands are run as the user whos crontab they are in. For cron jobs that require elevated privileges, using the root crontab or changing file permissions may be necessary.

Setting up a cron job to backup all mysql databases

First start editing the crontab:

crontab -e

Now add a new line, which will run our command:

0 0 * * * mysqldump --all-databases > /root/sqldump.sql

This simple command will back up all databases to the file /root/sqldump.sql at midnight every day.
Note: This requires you to set a [mysqldump] user, as advised in Step 15.

You’re done!

Congratulations on setting up CentOS 6 with LAMP. The section below contains useful commands and other tweaks you can perform.

Test disk speed

Disk speed indicative of performance, different tests test different things, different on virtual environments (such as OpenVZ and KVM) and dedi, some tests might be better for some of them.

dd if=/dev/zero of=test bs=64k count=16k conv=fdatasync

How to judge your result (note that this is only accurate for the exact test above)

  • 0-25 MB/s -> Garbage
  • 25-70 MB/s -> Acceptable
  • 70-120 MB/s -> Good
  • >120 MB/s -> Excellent

Miscellaneous: Quick reference of useful commands

Check disk usage

df -h

Disable or enable iptables

chkconfig iptables on/off

Dump all your MySQL databases to a file (suitable for backup, in crontab or similar)

In Step 15 we saved our MySQL username and password in the MySQL configuration file /etc/my.cnf

Now we can use mysqldump without a password. To dump all databases into a file, issue:

mysqldump --all-databases > /root/sqldump.sql

Listing services that automatically run at startup, and their runlevels

chkconfig --list

Miscellaneous: Setting appropriate file permissions for PHP sites

We’d like for Apache to have as little access to the files it serves as possible. This limits the effects PHP and Apache exploits.

To accomplish this, let’s run an example with a fictional site residing in the folder:


To secure this site we are going to put up the following restrictions:

  • Files can only be read
  • Directories can only be read and executed (this is required for PHP to work)
  • Apache is the owner of all files

To do this, we invoke:

chown -R apache:apache /var/www/html/yoursite
chmod -R 400 /var/www/html/yoursite
chmod -R a+X /var/www/html/yoursite


That’s it for this tutorial! I appreciate any feedback you might have, so if something is unclear or can be improved, feel free to leave a comment!

Sources and additional information

Micro templates for rapid web design prototyping and development in PHP


When you are developing a new web site, it’s common to start by writing a static HTML version that will later be converted to a theme in the CMS of your choice. It takes away the mental overhead of adhering to theming standards and lets you focus on the client-side technologies (HTML, CSS and JavaScript) unhindered.

When working on an early static version of a site, I often find that I do miss simple templating, especially for listings (be it news posts, sidebar banners or anything that needs to be “filled up” to make the page look as it would in production) – So I set out to look for a clean, simple and minimal way to introduce templating into static projects, using PHP.

I found this post on micro templates by Brad Touesnard that perfectly suited my needs, but felt that it was missing some polish and examples for people to fully utilize it. I wrote a couple of examples for common tasks such as displaying lists and nesting templates, and released it as a library that you can use in your projects to enable faster prototyping and development.

Live demo

Click to see a live running demo.


Click to download the latest version, with examples.


Click to see the Bitbucket repository


Download php-microtemplate and put it on a php-enabled server, navigate to the php-microtemplate folder in your browser and look at the examples.

If you want to use it from scratch, just include microtemplate.php at the top of any php file:


Add an empty templates folder, so the directory structure looks like this:

Now you can use the t() function to display templates (which are just PHP files) from your templates/ folder, for example this snipped will display the content of  templates/header.php:


You may optionally pass a second parameter that will send a variable or array to the template (to be used as $v inside the template), and a third optional variable that can set the folder path where the function will look for templates, which is useful if you prefer a nested directory structure for your templates.


Short tags (short_open_tag) need to be enabled in your php.ini

Common use snippets for Widget Logic


Widget Logic is a WordPress plugin that that gives every widget an extra control field called “Widget logic” that lets you control the pages that the widget will appear on. The text field lets you use WP’s Conditional Tags, or any general PHP code.

I’ve been using Widget Logic in my WordPress projects for a while now – it’s clean, versatile and I highly recommend it.

Below are some snippets that you will likely find useful when you are building a new site.

Show widget only on specific pages or posts

This example displays the widget only on the page that has the slug example-page


This is my favourite way of specifying widgets for certain pages, as it works in a similar fashion to how you configure blocks for specific paths in Drupal.

This example displays the widget on pages with ID 1 and 5.


is_page() is very flexible and can take id’s, page names, slugs and even arrays with multiple values – see the documentation.

But what about blog posts and attachments?

Use is_single()  instead – see the documentation.

Here is an example that display the widget when the user is visiting a post with the title “About this blog”

is_single('About this blog')

Show widget everywhere except a specific page or post.

This is the inverse of the previous examples, so the first example would be:


Note the exclamation point, which inverts the logic.

The second example would be:


Show widget only on front page

Handy for front page-specific summary widgets, calendars, introductions etc.


Show widget only for a specific post type

An easy way to display widgets for certain post types.


Some common post types

  • page
  • post
  • attachment

Show widget based on a WPML language

If you are running a site using the WordPress Multilingual Plugin (WPML) you can use this snippet to only show a widget when the user is viewing the page in a certain language (English in this case)


There are more useful constants and functions available in the WPML manual.

Combining multiple rules

It’s easy to combine multiple rules with regular PHP logic. This example will display the widget only when the user is viewing a site in Swedish (WPML) and is on the pages with ID 1 or 5:

(ICL_LANGUAGE_CODE == 'sv') && is_page(array(1,5))

Don’t forget you can also use the || (or) operator!

More useful tags

I recommend reading the WordPress documentation on Conditional Tags to customize Widget Logic for your exact needs.


Do you have a useful snippets for Widget Logic? Feel free to post it in the comments!