Linux+ Guide to Linux Certification, Third Edition Chapter 4
Linux Filesystem Management Slide 2 Objectives Find files and
directories on the filesystem Understand and create linked files
Explain the function of the Filesystem Hierarchy Standard Use
standard Linux commands to manage files and directories Linux+
Guide to Linux Certification, 3e2 Slide 3 3 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 The Filesystem Hierarchy Standard Filesystem
Hierarchy Standard (FHS): standard set of directories for Linux and
UNIX systems Standard file and subdirectory contents Simplifies the
task of finding specific files Gives Linux software developers
ability to locate files on any Linux system Create
non-distributionspecific software Linux+ Guide to Linux
Certification, 3e4 Slide 5 5 The Filesystem Hierarchy Standard
(continued) Table 4-1: Linux directories defined by the Filesystem
Hierarchy Standard Slide 6 Linux+ Guide to Linux Certification, 3e6
The Filesystem Hierarchy Standard (continued) Table 4-1
(continued): Linux directories defined by the Filesystem Hierarchy
Standard Slide 7 Linux+ Guide to Linux Certification, 3e7 Managing
Files and Directories mkdir command: creates new directories
Arguments specify directorys absolute or relative pathname mv
command: moves files Minimum of two arguments: Source
file/directory (may specify multiple sources) Target file/directory
Pathnames can be absolute or relative For multiple files, can use
wildcards in pathname Also used to rename files or directories
Slide 8 Linux+ Guide to Linux Certification, 3e8 Managing Files and
Directories (continued) cp command: copies files Same arguments as
the mv command Also used to make copies of files Recursive:
referring to itself and its own contents Recursive copy command
copies the directory and all subdirectories and contents Recursive
search includes all subdirectories in a directory and their
contents Use r option Slide 9 Linux+ Guide to Linux Certification,
3e9 Managing Files and Directories (continued) Interactive mode:
Prompts user before overwriting files i option f option (force):
Overrides interactive mode rm command: Removes files Arguments are
a list of files Can use wildcards Interactive mode by default Use
-f option to override Slide 10 Linux+ Guide to Linux Certification,
3e10 Managing Files and Directories (continued) rmdir command:
removes directories Arguments are a list of files Can use wildcards
Interactive mode by default Use -f option to override Cannot be
used to remove directory full of files To delete directory and all
its contents (subdirectories and files), use rm r command Slide 11
Linux+ Guide to Linux Certification, 3e11 Managing Files and
Directories (continued) Table 4-2: Common Linux file management
commands Slide 12 Linux+ Guide to Linux Certification, 3e12 Finding
Files locate command: Search for files on system Receives full or
partial filename as argument Uses premade indexed database of all
files on system To update the database use updatedb command
Information returned may not fit on screen Use with more or less
commands Slide 13 Linux+ Guide to Linux Certification, 3e13 Finding
Files (continued) find command: recursively search for files
starting from a specified directory Slower than locate command, but
more versatile Format: find -criteria e.g., find /root name project
If using wildcard metacharacters, ensure that they are interpreted
by the find command Place wildcards in quotation marks To reduce
search time, specify subdirectory to be searched Slide 14 Linux+
Guide to Linux Certification, 3e14 Finding Files (continued) Table
4-3: Common criteria used with the find command Slide 15 Linux+
Guide to Linux Certification, 3e15 Finding Files (continued) Table
4-3 (continued): Common criteria used with the find command Slide
16 Linux+ Guide to Linux Certification, 3e16 Finding Files
(continued) PATH variable: lists directories on system where
executable files are located Allows executable files to be run
without specifying absolute or relative path which command: search
for an executable file Searches the PATH variable If the file is
not found, lists the directories that were searched Slide 17 Linux+
Guide to Linux Certification, 3e17 Linking Files Symbolic link: one
file is a pointer or shortcut to another Hard link: two files share
the same data Slide 18 Linux+ Guide to Linux Certification, 3e18
Linking Files (continued) Filesystem has three main structural
sections: Superblock: Contains general information about the
filesystem e.g., number of inodes and data blocks, size of each
data block The inode table: consists of several inodes, each of
which describes a file or directory Unique inode number, file size,
data block locations, last date modified, permissions, and
ownership Data blocks: Data making up contents of a file Slide 19
Linux+ Guide to Linux Certification, 3e19 Linking Files (continued)
Hard linked files share the same inode and inode number Must reside
on the same filesystem To remove hard linked files, delete one of
the linked files Reduces the link count for the file Slide 20
Linux+ Guide to Linux Certification, 3e20 Linking Files (continued)
Figure 4-1: The structure of hard linked files Slide 21 Linux+
Guide to Linux Certification, 3e21 Linking Files (continued)
Symbolic linked files do not share the same inode and inode number
with their target file Symbolic linked file is a pointer to the
target file Data blocks in the linked file contain only a pathname
for the target file Linked file and target file have different
sizes Editing symbolic linked file actually edits the target file
If the target file is deleted, symbolic link serves no function
Slide 22 Linux+ Guide to Linux Certification, 3e22 Linking Files
(continued) Figure 4-2: The structure of symbolically linked files
Slide 23 Linux+ Guide to Linux Certification, 3e23 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 Arguments can be
relative or absolute pathnames Slide 24 Linux+ Guide to Linux
Certification, 3e24 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 25 Linux+ Guide to
Linux Certification, 3e25 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 whoami command: view current user name groups
command: view group memberships and primary group touch command:
create an empty file Slide 26 Linux+ Guide to Linux Certification,
3e26 File and Directory Ownership (continued) chown (change owner)
command: change ownership of a file or directory Two arguments: New
owner File to change Can use R option for contents of directory
chgrp (change group) command: change group owner of a file or
directory Same arguments and options as for chown command Slide 27
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 Linux+
Guide to Linux Certification, 3e27 Slide 28 Linux+ Guide to Linux
Certification, 3e28 Interpreting the Mode Figure 4-3: The structure
of a mode Slide 29 Linux+ Guide to Linux Certification, 3e29
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 Permissions are not additive Slide 30 Linux+ Guide to Linux
Certification, 3e30 Interpreting Permissions Table 4-4: Linux
permissions Slide 31 Linux+ Guide to Linux Certification, 3e31
Changing Permissions chmod (change mode) command: change mode
(permissions) of files or directories Two arguments at minimum
Criteria used to change permissions Filenames to change Permissions
stored in a files or a directorys inode as binary powers of two
Slide 32 Linux+ Guide to Linux Certification, 3e32 Changing
Permissions (continued) Table 4-5: Criteria used within the chmod
command Slide 33 Linux+ Guide to Linux Certification, 3e33 Changing
Permissions (continued) Figure 4-4: Numeric representation of the
mode Slide 34 Linux+ Guide to Linux Certification, 3e34 Changing
Permissions (continued) Table 4-6: Numeric representations of the
permissions in a mode Slide 35 Linux+ Guide to Linux Certification,
3e35 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 36 Linux+ Guide to
Linux Certification, 3e36 Default Permissions (continued) Figure
4-5: Performing a umask 022 calculation Slide 37 Linux+ Guide to
Linux Certification, 3e37 Default Permissions (continued) Figure
4-6: Performing a umask 007 calculation Slide 38 Linux+ Guide to
Linux Certification, 3e38 Special Permissions Three more optional
special permissions for files and directories SUID (Set User ID)
SGID (Set Group ID) Sticky bit Slide 39 Linux+ Guide to Linux
Certification, 3e39 Defining Special Permissions SUID If set on a
file, user who executes the file becomes owner of the file during
execution e.g., ping command No functionality when set on a
directory Only applicable to binary compiled programs Cannot be
used on shell scripts Slide 40 Linux+ Guide to Linux Certification,
3e40 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 files group owner
is set to be the directorys group owner and not the users primary
group Slide 41 Linux+ Guide to Linux Certification, 3e41 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 his/her own files when given write
permissions in a directory Slide 42 Linux+ Guide to Linux
Certification, 3e42 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 Indicating letter in the mode will be
capitalized Add special permissions via chmod command Add an extra
digit at front of permissions argument Slide 43 Linux+ Guide to
Linux Certification, 3e43 Setting Special Permissions (continued)
Figure 4-7: Representing special permissions in the mode Slide 44
Linux+ Guide to Linux Certification, 3e44 Setting Special
Permissions (continued) Figure 4-8: Representing special
permissions in the absence of the execute permissions Slide 45
Linux+ Guide to Linux Certification, 3e45 Setting Special
Permissions (continued) Figure 4-9: Numeric representation of
regular and special permissions Slide 46 Summary The Linux
directory tree obeys the FHS Allows system files to be located in
standard directories Many file management commands exist Can find
files using different commands locate: search preindexed database
which: search PATH variable find: search for file based on criteria
Linux+ Guide to Linux Certification, 3e46 Slide 47 Linux+ Guide to
Linux Certification, 3e47 Summary (continued) Files can be created
as pointers to another file or as a linked duplicate of another
file Called symbolic and hard links, respectively Each file and
directory has an owner and a group owner Owner can change
permissions and grant ownership Permissions can be set on the owner
of a file, members of the group of the file, and everyone on the
system (other) Slide 48 Linux+ Guide to Linux Certification, 3e48
Summary (continued) Three regular file and directory permissions
(read, write, execute) and three special file and directory
permissions (SUID, SGID, sticky bit) Permissions can be changed
using chmod New files and directories receive default permissions
from the system The root user has all permissions to all files and
directories on the Linux filesystem Root user can change the
ownership of any file or directory on the Linux filesystem
