Chapter Two

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Chapter Two

• Exploring the UNIX File System and File Security

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Lesson A

• Understanding Files and Directories

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Objectives

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

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Objectives (cont.)

• Discuss relative and absolute path addressing
• Diagram the UNIX file system hierarchy
• Navigate the file system

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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 UNIXs 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

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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 (/)
• 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

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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

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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

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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

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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

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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

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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

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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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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

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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

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Listing Directory Contents

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

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Listing Directory Contents

• The system normally uses hidden files to keep
  configuration information and for other purposes

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Lesson B

• Working with Files, Directories, and Security

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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

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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

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Setting File Permissions
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Setting File Permissions
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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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

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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 systems 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

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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

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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

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