How can I know which version of Drupal is installed in my server?
From the database
Run the following query:
SELECT info FROM system WHERE type = 'module' AND name = 'node';
After, you will receive a serialized string value like:
a:10:{s:4:"name";s:4:"Node";s:11:"description";s:66:"Allows content to be submitted to the site and displayed on pages.";s:7:"package";s:15:"Core - required";s:7:"version";s:4:"6.20";s:4:"core";s:3:"6.x";s:7:"project";s:6:"drupal";s:9:"datestamp";s:10:"1292447788";s:12:"dependencies";a:0:{}s:10:"dependents";a:0:{}s:3:"php";s:5:"4.3.5";}
Then, unserialize this string. You can use the php unserialize function or any online web service such as: http://unserialize.me
You should see two array elements as below which shows the current version number:
[version] => 6.20
[core] => 6.x