1. Exploring the UNIX File System and File Security
Understanding Files and Directories

2. Understanding the UNIX File System
A file is the basic component for data storage
UNIX considers everything it interacts with a file
A file system is UNIX’s way of organizing files on mass storage (disk) devices
A physical file system is a section of the hard disk that has been formatted to hold files
The file system is organized in a hierarchical structure similar to an inverted tree

4. Understanding the Standard Tree Structure
The structure starts at the root level
Root is the name of the file at this basic level and it is denoted by the slash character (/)
A directory is a file that can contain other files and directories
A subdirectory is a directory within a directory
The subdirectory is considered the child of the parent directory

5. Using UNIX Partitions
The section of the disk that holds a file system is called a partition
When installing UNIX, one of the first tasks is deciding how to partition a storage device, or hard disk
Hard disks may have many partitions
UNIX partitions are given names
Like hda1 and hda2

6. Using UNIX Partitions Storage devices are called peripheral devices
Peripheral devices connect to the computer through electronic interfaces
IDE - Integrated Drive Electronics
SCSI - Small Computer System Interface

7. Exploring the Root File System
UNIX must mount a file system before any programs can access files on it
To mount a file system is to connect it to the directory tree structure
The root file system is mounted by the kernel when the system starts

8. Exploring the Root File System
The root directory contains sub-directories that contain files:
/bin contains binaries, or executables needed to start the system and perform system tasks
/boot contains files needed by the bootstrap loader as well as kernel images
/dev contains system device reference files

10. Exploring the Root File System
Root subdirectories continued:
/etc contains configuration files that the system uses when the computer starts
/lib contains kernel modules, security information, and the shared library images
/mnt contains mount points for temporary mounts by the system administrator
/proc is a virtual file system allocated in memory only

11. Exploring the Root File System
Root subdirectories continued:
/root is the home directory of the root user, or the system administrator
/sbin contains essential network programs used only by the system administrator
/tmp is a temporary place to store data during processing cycles
/var contains subdirectories which have sizes that often change, such as error logs

12. Understanding Paths and Pathnames
To specify a file or directory, use its pathname, which follows the branches of the file system to the desired file
A forward slash (/) separates each directory name
The UNIX command prompt may indicate your location within the file system
Use the UNIX pwd command to display the current path name

13. Navigating the File System
To navigate the UNIX directory structure, use the cd (change directory) command
UNIX refers to a path as either:
Absolute - begins at the root level and lists all subdirectories to the destination file
Relative - begins at your current working directory and proceeds from there

14. Listing Directory Contents
The ls (list) command displays a directory’s contents, including files and subdirectories

15. Listing Directory Contents
The system normally uses hidden files to keep configuration information and for other purposes

16. Managing Directories and Files
mkdir (make directory) command
Create a new directory
rmdir (make directory) command
Delete an empty directory
cp (copy) command
Copy files from one director to another
rm (remove) command
Delete files

17. Setting File Permissions

18. Setting File Permissions
Owner has read w
Owner has write x
Owner has execute
Group has read -
Group does not have write
Group has execute
Others have read
Others do not have write
Others have execute

19. Setting File Permissions for Security
chmod command
To set file permissions
Settings are read (r), write (w), execute (x)
The three types of users are owners, groups, and others
Setting permissions to directories
Use the execute (x) to grant access