is_dir returns false even when it is a dir?

Question

Why does is_dir() return false even if it is a dir?

returns no error

$path_mysql = '/var/lib/mysql/';
if(!is_dir($path_mysql)){
    echo 'error';
}

returns error

$path_mysql = '/var/lib/mysql/domain.com/';
if(!is_dir($path_mysql)){
    echo 'error';
}

/var/lib/mysql/domain.com/ does exsits, but is_dir() returns false!?

I can get access to the dir through both PuTTY and WinSCP

Answer 1

Possibly because it cannot check whether the /var/lib/mysql/domain.com/ exists or not, because it does not have enough rights to do that (permission problems).

Check the execute (list) permission of /var/lib/mysql/ directory for the user which runs this PHP script (probably it's www-data)