Hi!
It is sourcing back to the wordpress core, from file wp-includes/class-phpass.php, from line 68. Here is the context, starting with line 68:
if ( @is_readable('/dev/urandom') &&
($fh = @fopen('/dev/urandom', 'rb'))) {
$output = fread($fh, $count);
fclose($fh);
}
It’s the core random bytes generator function. This error should be surpressed as it’s called with the “@” prefix: @is_readable(‘/dev/urandom’)
as far as I can see.
Make sure to have the error reporting disabled for surpressed error messages.
Alternatively you can ask the the WordPress core development support forums for further explanations and guides on how to get rid of this error message, if that article does not help.