Here is a simple steps to install JSON for PHP in *nix server. The sample command below are running under Centos OS.

yum update "*php*"

Make sure you have install PHP Pear.
yum install php-pear

and The pecl command can then be found at /usr/bin/pecl

Then, we can start install PHP JSON.
pecl install json
cd /etc/php.d/
echo “” >> json.ini
service httpd restart

If you are using JQuery with JSON, take a look at this JQuery Json Library. Easy to use and simple.