php 上传图片，一直提示Warning: move_uploaded_file(.upload/en.jpg): failed to open stream

运行以下代码，浏览器提示
Upload: en.jpg
Type: image/jpeg
Size: 54.5830078125 Kb
Temp file: /tmp/phpk0nLl5
Warning: move_uploaded_file(.upload/en.jpg): failed to open stream: No such file or directory in /var/www/html/bbs/upload_file.php on line 24 Warning: move_uploaded_file(): Unable to move '/tmp/phpk0nLl5' to '.upload/en.jpg' in /var/www/html/bbs/upload_file.php on line 24 Stored in: upload/en.jpg

求教，该怎样解决？？？我的代码运行在linux上



<form action="upload_file.php" method="post" enctype="multipart/form-data">
<label for="file">Filename:</label>
<input type="file" name="file" id="file" />
<br/>
<input type="submit" name="submit" value="submit"/>
</form>


upload_file.php:


<?php
if ((($_FILES["file"]["type"] == "image/gif")
|| ($_FILES["file"]["type"] == "image/jpeg")
|| ($_FILES["file"]["type"] == "image/pjpeg")))
{
if ($_FILES["file"]["error"] > 0)
{
echo "Return Code: " . $_FILES["file"]["error"] . "<br />";
}
else
{
echo "Upload: " . $_FILES["file"]["name"] . "<br />";
echo "Type: " . $_FILES["file"]["type"] . "<br />";
echo "Size: " . ($_FILES["file"]["size"] / 1024) . " Kb<br />";
echo "Temp file: " . $_FILES["file"]["tmp_name"] . "<br />";

if (file_exists("upload/" . $_FILES["file"]["name"]))
{
echo $_FILES["file"]["name"] . " already exists. ";
}
else
{
move_uploaded_file($_FILES["file"]["tmp_name"],
"upload/" . $_FILES["file"]["name"]);
echo "Stored in: " . "upload/" . $_FILES["file"]["name"];
}
}
}
else
{
echo "Invalid file";
}
?>