To understand how we can control filesystem permissions, we'll need first to review exactly what permissions are, and how they are set. Documentation of this subject from a Linux perspective is available at
http://www.faqs.org/docs/linux_intro/sect_03_04.html. Our discussion here is not intended to be a Unix or Linux tutorial; we focus exclusively on the subject of permissions, and leave it to you to fill in any gaps.
Let's imagine a sample user
timb, whose Unix-style directory listing (displayed with the command
ls -l) might look like this:
drwxr-xr-x 2 timb www 68 20 Nov 15:04 images -rw-r--r-- 1 timb www 545 20 Nov 15:04 index.php lrwxrwxrwx 1 timb www 4 9 Nov 22:57 lib -> /usr/lib/php -rw-r--r-- 1 ...