How to install ionCube Loaders on Linux server?
which protected by ionCube to be executed.

I will help you to install ionCube Loaders:

The following guide requires root access, be careful with anything you do while you are logged in as root.

Installing ionCube Loaders on Linux servers/VPSs

1. Download and uncompress the latest Loaders from ionCube. Perform the following:
Change directory:

cd /usr/local/
Download the Loaders from ionCube

wget http://downloads2.ioncube.com/loader_downloads/ioncube_loaders_lin_x86.tar.gz
Uncompress the Loaders.

tar zxvf ioncube_loaders_lin_x86.tar.gz
2. Find out the PHP version.

php -v
You'll see something like this:

[root@server ~]# php -v
PHP 5.1.6 (cli) (built: Jul 16 2008 19:53:00)
Copyright (c) 1997-2006 The PHP Group
[root@server ~]#
5.1.6 is the PHP version, take note of it.
Your result might be different than mine.

3. Find out the location of php.ini

php -i | grep php.ini
You will see something like this:

root@server [~]# php -i | grep php.ini
Configuration File (php.ini) Path => /usr/local/lib
Loaded Configuration File => /usr/local/lib/php.ini
root@server [~]#
The location of php.ini file varies on different system.

4. Open php.ini file

nano /usr/local/lib/php.ini
5. Find out if there is Zend Optimizer installed. Hit Ctrl + W on your keyboard, type:

zend_extension
Then hit Enter

6a. If you see something like this:

zend_extension_manager.optimizer=/usr/local/Zend/lib/Optimizer-3.3.3
zend_extension_manager.optimizer_ts=/usr/local/Zend/lib/Optimizer_TS-3.3.3
It means Zend Optimizer installed on your server/VPS.
Remember, ionCube must be loaded before Zend Optimizer. So, we'll add the ionCube Loaders line before Zend Optimizer.

ionCube Loader line:

zend_extension=/usr/local/ioncube/ioncube_loader_lin_5.1.so
I'm using ioncube_loader_lin_5.1.so because my PHP version is 5.1.x.

It will be look like this:

zend_extension=/usr/local/ioncube/ioncube_loader_lin_5.1.so
zend_extension_manager.optimizer=/usr/local/Zend/lib/Optimizer-3.3.3
zend_extension_manager.optimizer_ts=/usr/local/Zend/lib/Optimizer_TS-3.3.3
6b. If you did not get the searc result, means Zend Optimizer is not installed.
Just add the line below to the end of the php.ini file.

zend_extension=/usr/local/ioncube/ioncube_loader_lin_5.1.so
7. Save and exit nano

Ctrl + O
Ctrl + X
8. Restart Apache

/etc/init.d/httpd restart
9. Verify ionCube Loader successfully installed.

php -v
You'll see something like this:

root@server # php -v
PHP 5.1.6 (cli)
Copyright (c) 1997-2007 The PHP Group
Zend Engine v2.2.0, Copyright (c) 1998-2007 Zend Technologies
with the ionCube PHP Loader v3.1.32, Copyright (c) 2002-2007, by ionCube Ltd.
root@server #
Notice the "with the ionCube PHP Loader", its means ionCube is installed. Otherwise, its not.

Done !

Some things that worth noted:
This How To works on cPanel and Plesk servers. The only differences might be the location of your php.ini file.

If you got this error on your server/VPS somewhere during the installation:

Error: cannot restore segment prot after reloc: Permission denied
Its probably caused by the security extension SeLinux. SeLinux is active in newer Linux distributions with 2.6. kernels. SeLinux changes some system default behaviour, including the shared library loading.
This can be resolved by disabling SeLinux temporarily or permanently.

To temporarily disable SeLinux
Execute the following on your server/VPSs:

/usr/sbin/setenforce 0
To permanently disable SeLinux
Do the following:

nano /etc/sysconfig/selinux
Add the following to the file:

SELINUX=disabled
Save the file Ctrl + O and exit Ctrl + X.
You might need to restart the server for this to take effect.

More information about ionCube here.

Good luck!