During installation phpBB stops with the error:
[phpBB Debug] PHP Notice: in file /includes/functions.php on line 1041: is_dir(): open_basedir restriction in effect. File(/home/user/db/forum.db/) is not within the allowed path(s): (/srv/http/:/home/:/tmp/:/usr/share/pear/)
The reason seems to be less a wrong database server hostname but the (unforeseen) behaviour of is_dir() in PHP 5.3.2 (probably also other versions).
Let me explain the problem. If I load the following PHP script in my browser
and I do have a directory A and a file B, then the is_dir() check for B will throw the warning (which in the case of phpBB breaks the installation procedure).
It does not fail if B doesn't exist or if I remove the trailing slash from the name. Also, for a directory like A there is never a problem. And the problem only occurs, of course, if the error reporting and displaying is switched on like above.
In my case, the argument to is_dir() is the SQLite database file and phpBB has the error reporting on, so it breaks.
To me it seems that the behaviour of is_dir() is strange, because the warning makes no sense (we are always inside the restricted paths set by open_basedir) and I should file a bug report to the PHP people. Google tells me that this issue has occured already a while ago and has probably been fixed, while it now re-occurs again. But to me it would also make sense to adapt the phpBB code such that no matter which version of PHP I use the problem doesn't appear anymore. This is why I filed this bug report.
I propose to change line 1041 in file includes/functions.php from