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Exploring the UNIX/Linux File Systems and File Security

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Title: Exploring the UNIX/Linux File Systems and File Security


1
Guide To UNIX Using Linux Third Edition
  • Chapter 2
  • Exploring the UNIX/Linux File Systems and File
    Security

2
Objectives
  • Discuss UNIX/Linux file systems
  • Explain partitions and inodes
  • Understand the elements of the root hierarchy
  • Use the mount command
  • Explain and use paths, pathnames, and prompts

3
Objectives (continued)
  • Navigate the file system
  • Create and remove directories
  • Copy and delete files
  • Configure file permissions

4
Understanding UNIX/LinuxFile Systems
  • File basic component for data storage
  • UNIX/Linux considers everything to be a file
  • A file system is UNIX/Linuxs way of organizing
    files on mass storage 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 (inverted tree)

5
Understanding UNIX/LinuxFile Systems (continued)
6
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 (/)
  • Directory file that can contain other files and
    directories
  • Subdirectory directory within a directory
  • The subdirectory is considered the child of the
    parent directory

7
Using UNIX/Linux Partitions
  • The section of the disk that holds a file system
    is called a partition
  • When installing UNIX/Linux, one of the first
    tasks is deciding how to partition a storage
    device, or hard disk
  • Hard disks may have many partitions
  • UNIX/Linux partitions are given names
  • LINUX uses hda1 and hda2

8
Using UNIX/Linux Partitions (continued)
  • Storage devices are called peripheral devices
  • Peripheral devices connect to the computer
    through electronic interfaces
  • IDE Integrated Drive Electronics
  • SCSI Small Computer System Interface

9
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10
Setting Up Hard Disk Partitions
  • Partitioning your hard disk provides organized
    space for file systems
  • At least 3 partitions (root, swap, /boot) often
    recommended
  • Root partition holds root file system directory
    (/), size depends on installation but often
    ranges between 1.2 to 5 GB

11
Setting Up Hard Disk Partitions (continued)
  • Swap partition acts as a memory extension, often
    has same size as RAM, enables virtual memory
  • /boot partition used to store os files comprising
    kernel, relatively small
  • Other often used partitions include /usr, /home,
    /var

12
Using Inodes
  • Inodes are associated with directories and files
    in ufs and ext file systems
  • An inode contains the name, general information,
    and location information (a pointer) for a file
    or directory
  • A superblock contains information about about
    block layout on a specific partition

13
Exploring the Root Hierarchy
  • UNIX/Linux 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

14
Exploring the Root Hierarchy (continued)
  • 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

15
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16
Exploring the Root File Hierarchy (continued)
  • 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

17
Exploring the Root File Hierarchy (continued)
  • 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

18
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

19
Using Paths, Pathnames, and Prompts
  • 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/Linux command prompt may indicate your
    location within the file system
  • Use the UNIX/Linux pwd command to display the
    current path name

20
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21
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22
Navigating the File System
  • To navigate the UNIX/Linux directory structure,
    use the cd (change directory) command
  • UNIX/Linux 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

23
Using Dot and Dot Dot Addressing Techniques
  • UNIX/Linux interpret a single dot (.) to mean the
    current working directory
  • Two dots (..) mean the parent directory
  • cd .. moves you up a level in the directory
    structure

24
Listing Directory Contents
  • The ls (list) command displays a directorys
    contents, including files and subdirectories

25
Using Wildcards
  • A wildcard is a special character that is used as
    a placeholder
  • The wildcard represents any group of characters
    in a file name
  • The ? wildcard represents a single character in a
    file name
  • The wildcard represents a single character in
    a file name but only searches for the characters
    within the square brackets

26
Creating and Removing Directories and Files
  • mkdir (make directory) command
  • Create a new directory
  • rmdir (remove directory) command
  • Delete an empty directory
  • Delete non empty directory use rm -r
  • cp (copy) command
  • Copy files from one directory to another
  • rm (remove) command
  • Delete files

27
Configuring File Permissions for Security
28
Configuring File Permissions for Security
(continued)
File Permissions File Permissions
r Owner has read
w Owner has write
x Owner has execute
r Group has read
- Group does not have write
x Group has execute
r Others have read
- Others do not have write
x Others have execute
29
Configuring File Permissions for Security
(continued)
  • 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

30
Chapter Summary
  • In UNIX/Linux, a file is the basic component for
    data storage and UNIX and Linux consider
    everything a file
  • A file system is UNIX/Linuxs way of organizing
    files on mass storage devices and each file is
    referenced using a correct and unique pathname
  • The section of the mass storage device that holds
    a file system is a partition

31
Chapter Summary (continued)
  • You can 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
  • Use the chmod command to set permissions such as
    read (r), write (w), execute (x) for files that
    you own
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