php网站后台上传不了图片

chmod 755 /path/to/upload/directory

upload_max_filesize = 2M
post_max_size = 8M

<form action="upload.php" method="post" enctype="multipart/form-data">
  <input type="file" name="fileToUpload" id="fileToUpload">
  <input type="submit" value="Upload Image" name="submit">
</form>

<?php
if ($_FILES["fileToUpload"]["error"] == UPLOAD_ERR_OK) {
    $target_dir = "uploads/";
    $target_file = $target_dir . basename($_FILES["fileToUpload"]["name"]);
    if (move_uploaded_file($_FILES["fileToUpload"]["tmp_name"], $target_file)) {
        echo "The file ". htmlspecialchars( basename( $_FILES["fileToUpload"]["name"])). " has been uploaded.";
    } else {
        echo "Sorry, there was an error uploading your file.";
    }
} else {
    echo "Error: " . $_FILES["fileToUpload"]["error"];
}
?>