Unable to open Roundcube Webmail with error 500: Class 'PDO' not found

Symptoms

• Roundcube Webmail failed to open with 500 error in browser.

• The following error appears  in /var/log/plesk-roundcube/errors :

  PHP Fatal error: Class 'PDO' not found in /usr/share/psa-roundcube/program/lib/Roundcube/rcube_db_mysql.php on line 144
  

• Listing of system php modules does not show pdo_sqlite module:

  # php -m | grep -i pdo 
  #

• There is a custom value for extension_dir directive:

  # php -i | grep extension_dir
  extension_dir => ./ => ./

Cause

System PHP misconfiguration.

Resolution

1. Log in to Plesk server via SSH

2. Comment out extension_dir directive in the /etc/psa-webmail/roundcube/php.ini and /etc/php.ini files, e.g.:

   # grep extension /etc/psa-webmail/roundcube/php.ini
   ;extension_dir = "./"

   So, the value for extension_dir directive should look as follows:

   # php -i | grep extension_dir
   extension_dir => /usr/lib64/php/modules => /usr/lib64/php/modules

3. Turn on the pdo, pdo_mysql and pdo_sqlite extensions under Home > Tools & Settings > PHP Settings > %php_version% by OS vendor FastCGI application

4. Make sure that modules were activated using the following command:
   

   # php -m | grep -i pdo PDO pdo_mysql pdo_sqlite