Linux is a multi-user system, so every file needs rules about who can read it, change it, or run it. This module explains how those rules work and how to control them.
It starts with reading permissions in the output of
ls -l: the owner, group, and other classes and the
r, w, and x bits. From there you'll learn to
change permissions with chmod using both symbolic and
numeric modes, then to change ownership with chown and
chgrp. It closes with default and special permissions:
umask, the setuid and setgid bits, and the sticky bit.
Avoid the shortcut of chmod 777, because it fixes the error by removing the
protection. When you can explain why a file is or isn't accessible, continue on to
Text Processing & Pipes.
Read the output of ls -l and learn what the read, write, and execute bits mean for the owner, the group, and everyone else.
Set permissions using symbolic mode (u+x, go-w) and numeric mode (755, 644), and learn how to choose sensible values.
See who owns a file, change its owner and group with chown and chgrp, and learn why some changes need sudo.
Understand where the default permissions of new files come from, and what the special bits do on programs and shared directories such as /tmp.