6.1. Linux Security6.1.1. The /etc/passwd file6.1.2. The /etc/shadow file6.1.3. Adding a new user6.1.4. Removing a user6.1.5. Modifying a user6.1.5.1. usermod6.1.5.2. passwd and chpasswd6.1.5.3. chsh, chfn, and chage6.2. Using Linux Groups6.2.1. The /etc/group file6.2.2. Creating new groups6.2.3. Modifying groups6.3. Decoding File Permissions6.3.1. Using file permission symbols6.3.2. Default file permissions6.4. Changing Security Settings6.4.1. Changing permissions6.4.2. Changing ownership6.5. Sharing Files6.6. Summary