No images, content, or theme after site migration from dev server to nginx on ubuntu
Try to give more information about the files/directories.  What user/group owns the files?  You should also make sure you know what user nginx is running on.  Try these commands for debugging:

ls -l for printing details about file permissions and ownership

ps -ef to check running processes to see if any user stands out (like www-data or www, figure out which user nginx uses)

Files in sites/default/files should be rw- permissions, and directories in sites/default/files should be rwx permissions.  rw- is 6 and rwx is 7.

The file:
-rw-r--r--  1 ubuntu www-data     468 Dec 10 15:59 test.php is owned by the ubuntu user and the www-data group. The ubuntu user can access the file with read/write, and the www-data can only read the file.  If this file were in sites/default/files it would be a problem, because the webserver wouldn't have rights to remove it.