Hi, probably a few things to check as per the suggestions in this topic:
php - PostgreSql ‘PDOException’ with message ‘could not find driver’ - Stack Overflow
Start from the beginning - what’s different about your two environments, i.e. the old one compared to the new one? Is postgresql installed and running correctly - can you confirm this? Did you install a new version of PHP on your new Linux environment? If so, is the config .ini file different? Is the php extension for postgresql on? Output your configuration settings for PHP on each environment so you can compare the two using phpinfo():
PHP: phpinfo - Manual
There is also some further information here from PostgreSQL - but I suspect the answer lies somewhere in the above:
PostgreSQL: Linux downloads (other)
Refrain from changing too much if you know your application already works on a similar environment, the answer will be something simple - take a step back and slowly work it out.