Exploring UNIX File System & Security

1. Chapter Two Exploring the UNIX File System and File Security

2. Lesson A Understanding Files and Directories

3. Objectives • Discuss and explain the UNIX file system • Define a UNIX file system partition • Use the mount command to mount a file system

4. Objectives (cont.) • Discuss relative and absolute path addressing • Diagram the UNIX file system hierarchy • Navigate the file system

5. Understanding the UNIXFile 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

7. 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

8. 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 • LINUX uses hda1 and hda2

9. 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

11. 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

12. 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

14. 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

15. 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

16. Using the Mount Command • Users can access mounted file systems which they have permission to access • Additional file systems can be mounted at any time using the mount command • To ensure system security, only the root user uses the mount command

17. Understanding Pathsand 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

19. 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

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

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

22. Lesson B Working with Files, Directories, and Security

23. Objectives • Create new directories to store files • Copy files from one directory to another • Set file permissions for other user access to directory and files

24. 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

25. Setting File Permissions

26. Setting File Permissions

27. Setting File Permissionsfor 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

28. Chapter Summary • In UNIX, a file is the basic component for data storage and UNIX considers everything a file • A file system is the UNIX system’s way of organizing files on mass storage devices and each file is referenced using a correct and unique pathname • The standard tree structure starts with the root (/) directory • The section of the mass storage device (or disk) that holds a file system is a partition

29. Chapter Summary • A path serves as as a map to access any file on the system • You may customize your command prompt to display the current working directory name, the current date and time, and several other items • The ls command displays the names of files and directories contained in a directory • Wildcard characters (i.e. *, ?) can be used in a command such as ls and take the place of other characters in a file name

30. Chapter Summary • Use the mkdir command to create a new directory, as long as you own the parent • Use the chmod command to set permissions such as read (r), write (w), execute (x) for files that you own • Use the cp command to copy a source file to a destination file and directory