An Introduction to Unix Permissions
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 ...Get Pro PHP Security: From Application Security Principles to the Implementation of XSS Defenses, Second Edition now with the O’Reilly learning platform.
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