chmod (): Operation not permitted in PHP script. How to fix it

chmod (): Operation not permitted in PHP script.
A PHP script, if the new registered user uploads the file, mkdir (the user name of the new folder), chmod (the folder under the upload, 0777).
Result hint error chmod (): Operation not permitted a line in the PHP script
SSH view the permission to upload the file, if not chmod, the default is 0644. And I want to make the file into 0777 permissions, because the user after uploading if not satisfied, but also can be modified.

That's probably the PHP script.

if ($_post[' file ']) {
mkdir () file_put_content () chmod () mysql_query ()
}
------to solve the idea----------------------
Setup is chmod a+x.

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