The OAuth extension requires both PEAR (which enables you to install the package) and libpcre3-dev, which enables the OAuth package to be compiled. To install the packages and confirm that OAuth is enabled, enter the following commands in the order shown: apt-get install php-pear apt-get install libpcre3-dev pecl install oauth If the following displays, you must edit your php.ini file to find the OAuth library: configuration option “php_ini” is not set to php.ini location You should add “extension=oauth.so” to php.ini Open php.ini in a text editor (location in /etc/php5/apache2/) and add the following anywhere in php.ini: [OAuth] extension=oauth.so Save your changes to php.ini and restart the Apache web server. Now check again if that OAuth is Installed Successfully. http://ralph.soika.com/magento-rest-api/