Exploring the UNIX/Linux File Systems and File Security

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Chapter 2

• Exploring the UNIX/Linux File Systems and File
  Security

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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

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Objectives (continued)

• Navigate the file system
• Create and remove directories
• Copy and delete files
• Configure file permissions

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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)

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Understanding UNIX/LinuxFile Systems (continued)
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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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Listing Directory Contents

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

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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

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Creating and Removing 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 directory to another
• rm (remove) command
• Delete files

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Configuring File Permissions for Security
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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
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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

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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

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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