Linux+ Guide to Linux Certification, Second Edition Chapter 5 Linux Filesystem Management.

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  • Slide 1
  • Linux+ Guide to Linux Certification, Second Edition Chapter 5 Linux Filesystem Management
  • Slide 2
  • Linux+ Guide to Linux Certification, 2e2 Objectives Explain the function of the Filesystem Hierarchy Standard Use standard Linux commands to manage files and directories Find files and directories on the filesystem Understand and create linked files
  • Slide 3
  • Linux+ Guide to Linux Certification, 2e3 Objectives (continued) Modify file and directory ownership Define and change Linux file and directory permissions Identify the default permissions created on files and directories Apply special file and directory permissions
  • Slide 4
  • Linux+ Guide to Linux Certification, 2e4 The Filesystem Hierarchy Standard Filesystem Hierarchy Standard (FHS): Standard set of directories for Linux and UNIX systems File and subdirectory contents Gives Linux software developers ability to locate files on any Linux system Create non-distributionspecific software
  • Slide 5
  • Linux+ Guide to Linux Certification, 2e5 The Filesystem Hierarchy Standard (continued) Table 5-1: Linux directories defined by FHS
  • Slide 6
  • Linux+ Guide to Linux Certification, 2e6 The Filesystem Hierarchy Standard (continued) Table 5-1 (continued): Linux directories defined by FHS
  • Slide 7
  • Linux+ Guide to Linux Certification, 2e7 Managing Files and Directories mkdir command: Creates new directories Arguments specify directorys absolute or relative pathname mv command: Moves files Two arguments minimum: Source file/directory (may specify multiple sources) Target file/directory Also used to rename files
  • Slide 8
  • Linux+ Guide to Linux Certification, 2e8 Managing Files and Directories (continued) cp command: Copies files Same arguments as mv command Recursive: Referring to itself and its own contents Recursive search includes all subdirectories in a directory and their contents r option
  • Slide 9
  • Linux+ Guide to Linux Certification, 2e9 Managing Files and Directories (continued) interactive mode: Prompts user before overwriting files i option f option: Overrides interactive mode rm command: Removes files Arguments are a list of files rmdir command: Removes directories r and f options are helpful
  • Slide 10
  • Linux+ Guide to Linux Certification, 2e10 Managing Files and Directories (continued) Table 5-2: Common Linux file management commands
  • Slide 11
  • Linux+ Guide to Linux Certification, 2e11 Finding Files locate command: Search for files on system Shortcut to the slocate command Information returned may not fit on screen Use with more or less commands Uses indexed database of all files on system Find command: Recursively search for files starting from a specified directory
  • Slide 12
  • Linux+ Guide to Linux Certification, 2e12 Finding Files (continued) Table 5-3: Common criteria used with find command
  • Slide 13
  • Linux+ Guide to Linux Certification, 2e13 Finding Files (continued) Table 5-3 (continued): Common criteria used with find command
  • Slide 14
  • Linux+ Guide to Linux Certification, 2e14 Finding Files (continued) which command: Search for an executable file Searches the PATH variable PATH variable: Lists directories on system where executable files are located Allows executable files to be run without specifying absolute or relative path
  • Slide 15
  • Linux+ Guide to Linux Certification, 2e15 Linking Files Symbolic link: One file is a pointer or shortcut to another Hard link: Two files share the same data
  • Slide 16
  • Linux+ Guide to Linux Certification, 2e16 Linking Files (continued) Filesystem has three main structural sections: Superblock: Contains general information about the filesystem e.g., number of inodes and data blocks Inode: Describes a file or directory Unique inode number, file size, data block locations, last date modified, permissions, and ownership Inode table: Consists of several inodes Data blocks: Data making up contents of a file
  • Slide 17
  • Linux+ Guide to Linux Certification, 2e17 Linking Files (continued) Figure 5-1: The structure of hard linked files
  • Slide 18
  • Linux+ Guide to Linux Certification, 2e18 Linking Files (continued) ln (link) command: Create hard and symbolic links Two arguments: Existing file to link Target file to create as a link to existing file Use s option to create symbolic link Hard linked files share two inodes Data blocks in symbolically linked files contain pathname to target file
  • Slide 19
  • Linux+ Guide to Linux Certification, 2e19 Linking Files (continued) Figure 5-2: The structure of symbolically linked files
  • Slide 20
  • Linux+ Guide to Linux Certification, 2e20 File and Directory Permissions All users must login with a username and password Users identified by username and group memberships Access to resources depends on username and group membership Must have required permissions
  • Slide 21
  • Linux+ Guide to Linux Certification, 2e21 File and Directory Ownership Primary group: Users default group During file creation, files owner and group owner set to users username and primary group Same for directory creation touch command: Create an empty file
  • Slide 22
  • Linux+ Guide to Linux Certification, 2e22 File and Directory Ownership (continued) chown (change owner) command: Change ownership of a file or directory chgrp (change group) command: Change group owner of a file or directory
  • Slide 23
  • Linux+ Guide to Linux Certification, 2e23 Managing File and Directory Permissions Mode: Inode Section that stores permissions Three sections, based on the user(s) that receive the permission: User permissions: Owner Group permissions: Group owner Other permissions: Everyone on system Three regular permissions may be assigned to each user: Read Write Execute
  • Slide 24
  • Linux+ Guide to Linux Certification, 2e24 Interpreting the Mode Figure 5-3: The structure of a mode
  • Slide 25
  • Linux+ Guide to Linux Certification, 2e25 Interpreting the Mode (continued) User: Refers to owner of a file or directory Owner: Refers to users with ability to change permissions on a file or directory Other: Refers to all users on system Shell scripts: Text files containing instructions for the shell to execute
  • Slide 26
  • Linux+ Guide to Linux Certification, 2e26 Interpreting Permissions Table 5-4: Linux permissions
  • Slide 27
  • Linux+ Guide to Linux Certification, 2e27 Changing Permissions chmod (change mode) command: Change mode (permissions) of files or directories Permissions stored in a files or a directorys inode as binary powers of two
  • Slide 28
  • Linux+ Guide to Linux Certification, 2e28 Changing Permissions (continued) Table 5-5: Criteria used within the chmod command
  • Slide 29
  • Linux+ Guide to Linux Certification, 2e29 Changing Permissions (continued) Figure 5-4: Numeric representation of the mode
  • Slide 30
  • Linux+ Guide to Linux Certification, 2e30 Changing Permissions (continued) Table 5-6: Numeric representations of the permissions in a mode
  • Slide 31
  • Linux+ Guide to Linux Certification, 2e31 Default Permissions New files given rw-rw-rw- permissions by default umask: Takes away permissions on new files and directories umask command: Displays the umask Changing the umask Use a new umask as an argument to the umask command
  • Slide 32
  • Linux+ Guide to Linux Certification, 2e32 Default Permissions (continued) Figure 5-5: Performing a umask 022 calculation
  • Slide 33
  • Linux+ Guide to Linux Certification, 2e33 Default Permissions (continued) Figure 5-6: Performing a umask 007 calculation
  • Slide 34
  • Linux+ Guide to Linux Certification, 2e34 Special Permissions SUID (Set User ID) SGID (Set Group ID) Sticky bit
  • Slide 35
  • Linux+ Guide to Linux Certification, 2e35 Defining Special Permissions SUID If set on a file, user who executes the file becomes owner of the file during execution No functionality when set on a directory Only applicable to binary compiled programs
  • Slide 36
  • Linux+ Guide to Linux Certification, 2e36 Defining Special Permissions (continued) SGID Applicable to files and directories If set on a file, user who executes the file becomes member of the files group during execution If a user creates a file in a directory with SGID set, the directorys group owner is changed to match the files group owner
  • Slide 37
  • Linux+ Guide to Linux Certification, 2e37 Defining Special Permissions (continued) Sticky bit Previously used to lock files in memory Currently only applicable to directories Ensures that a user can only delete files his/her own files
  • Slide 38
  • Linux+ Guide to Linux Certification, 2e38 Setting Special Permissions Special permissions require execute Mask the execute permission when displayed by the ls l command May be set even if file or directory does not have execute permission Via chmod command Add an extra digit at front of permissions argument
  • Slide 39
  • Linux+ Guide to Linux Certification, 2e39 Setting Special Permissions (continued) Figure 5-7: Representing special permissions in the mode
  • Slide 40
  • Linux+ Guide to Linux Certification, 2e40 Setting Special Permissions (continued) Figure 5-8: Representing special permissions in the absence of the execute permissions
  • Slide 41
  • Linux+ Guide to Linux Certification, 2e41 Setting Special Permissions (continued) Figure 5-9: Numeric representation of regular and special permissions

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