Introduction to Unix (CA263) File System

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Introduction to Unix (CA263) File System

• By
• Tariq Ibn Aziz

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Objectives

• After reading this chapter and completing the
  exercises, you will be able to
• 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
• 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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UNIX File System

• Most versions of UNIX and Linux support the UNIX
  file system (ufs), which is the original native
  UNIX file system.
• ufs is a hierarchical (tree structure) file
  system that is
• expandable,
• supports large amounts of storage,
• provides excellent security, and is reliable.
• ufs supports journaling,
• if a system crashes unexpectedly, it reconstruct
  files or to roll back recent changes for minimal
  or no damage of the files.
• ufs also supports hot fixes
• by moving data automatically from damaged
  portions of disks to areas that are not damaged.

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UNIX File System

• In Linux, the native file system is called the
  extended file system (ext or ext fs), which is
  installed by default.
• ext is modeled after ufs,

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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

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Using Inodes

• The file system itself is identified by the
  superblock
• A superblock contains information about block
  layout on a specific partition
• Without the superblock, the file system cannot be
  accessed.
• For this reason, many copies of the superblock
  are written into the file system at the time the
  file system is created through partitioning and
  formatting.
• If the superblock is destroyed, you can copy one
  of the superblock copies over the original,
  damaged superblock to restore access to the file
  system.

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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, such
  as the hard disks, mice, printers, consoles,
  modems, memory, floppy disks, and CD-ROM drives.

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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
• /home is used to offer disk space for users
• /lib contains kernel modules, security
  information, and the shared library images
• /mnt contains mount points for temporary mounts
  by the system administrator. A temporary mount is
  used to mount a removable storage medium, such as
  a floppy disk or CD/DVD
• /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, for example sorting
• /usr partition houses software offered to users
• /var contains subdirectories which have sizes
  that often change, such as error logs. For
  incoming mail and printing spooling we have
  /var/spool/mail subdirectory or /var/spool/lpd
  subdirectory,

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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 the mount Command

• Suppose you want to access files on a CD-ROM for
  your organization.You or the system administrator
  can mount a CD-ROM by inserting a disk in the
  CD-ROM drive, and thenusing the following mount
  command
• mount -t iso9660 /dev/cdrom /mnt/cdrom
• This command mounts the CD on a device called
  cdrom located in the /dev directory. The actual
  mount point in UNIX/Linux is /mnt/cdrom, a
  directory that references the CD-ROM device.
  After the CD is mounted, you can access its files
  through the /mnt/ cdrom directory.

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Using the unmount Command

• system administrator unmounts them using the
  umount command before removing the storage media,
• umount /mnt/floppy
• umount /mnt/cdrom

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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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Configure Shell Prompt
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Configure Shell Prompt
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Configure Shell Prompt

• An environment variable, PS1, contains special
  formatting characters that determine your
  prompts configuration.
• variable contains \u_at_\h \W\
• Characters that begin with \ are special Bash
  shell formatting characters.

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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