On a server where :

• The forum is located at : /home/web/forum/www/
• The open_basedir is defined to : /home/web/forum/

The $phpbb_filesystem->resolve_path() function will try to resolve symlinks on each part of the path, like this:

• /home
• /home/web
• /home/web/forum
• /home/web/forum/www

In this case, the first two parts are outside of the open_basedir, and will trigger the following warnings:

[phpBB Debug] PHP Warning: in file [ROOT]/phpbb/filesystem/filesystem.php on line 838: is_link(): open_basedir restriction in effect. File(/home) is not within the allowed path(s): (/home/web/forum/:/tmp/:/usr/share/php/:/usr/share/pear/)

[phpBB Debug] PHP Warning: in file [ROOT]/phpbb/filesystem/filesystem.php on line 875: is_dir(): open_basedir restriction in effect. File(/home/) is not within the allowed path(s): (/home/web/forum/:/tmp/:/usr/share/php/:/usr/share/pear/)

[phpBB Debug] PHP Warning: in file [ROOT]/phpbb/filesystem/filesystem.php on line 880: is_file(): open_basedir restriction in effect. File(/home) is not within the allowed path(s): (/home/web/forum/:/tmp/:/usr/share/php/:/usr/share/pear/)

Even if this issue can be mitigated when you are on your own server (by changing or disabling the open_basedir restriction, considering that unix permissions are sufficient), this should be fixed on phpBB, because the open_basedir is used as an additional security measure by a lot of hosting providers using shared servers.