Module 07 : Navigating the Filesystem

Exam Objective
2.3 Using Directories and Listing Files
Objective Description
Navigation of home and system directories and listing files in various locations.

Introduction

Introduction

  • In Linux, everything is stored in files.
  • Files are used to store data such as text, graphics, and programs.
  • Directories are a type of file used to store other files.
  • Directories are used to provide a hierarchical organization structure.

Directory Structure

Directory Structure

  • On a Windows system, the top level of the directory structure is called My Computer.
  • The Linux directory structure, called a filesystem, also has a top level called the root directory (symbolized by the slash / character).
  • To view the contents of the root directory, use the ls command with the / character as the argument:
  • Notice that there are many directories with descriptive names including /boot, which contains files to boot the computer.

Home Directory

  • On most Linux distributions there is a directory called home under the root / directory.
  • Under this /home directory there is a directory for each user on the system.
  • When a user opens a shell, they should automatically be placed in their home directory.
    • The user has the full control to create and delete additional files and directories in their home directory.
    • Most other directories in a Linux filesystem are protected with file permissions.
  • The home directory has a special symbol used to represent it, the tilde ~ character.
  • The directory name is the same as the name of the user.
  • So, a user named sysadmin would have a home directory called  /home/sysadmin:

Current Directory

  • The pwd (print working directory) command can be used to determine where the user is currently located within the filesystem.
  • The pwd command prints the working directory, which is the current location of the user within the filesystem.   pwd [OPTIONS]

Changing Directories

  • When a user opens a shell, they typically begin in their home directory.
  • To navigate the filesystem, use the cd (change directory) command.
  • To move from the home directory into the Documents directory use the directory name as an argument to the cd command:
  • After changing directories, the new location can also be confirmed in the new prompt, again shown in blue.
  • When used with no arguments, the cd command will take the user to their home directory.
  • If the user tries to change to a directory that does not exist, the command returns an error message:

Paths

Paths

  • A path is a list of directories separated by the / character.
  • There are two types of paths: absolute and relative.
  • For example, /home/sysadmin is a path to the home directory:

Absolute Paths

  • Absolute paths allow the user to specify the exact location of a directory.
  • Absolute paths always starts at the root directory, and therefore it always begins with the / character.
  • The path /home/sysadmin is an absolute path; it tells the system to:
    • Begin at the root / directory  >  move into the home directory  >  then into the sysadmin directory
  • If the path /home/sysadmin is used as an argument to the cd command, it moves the user into the home directory for the sysadmin user.

Relative Paths

  • A relative path gives directions to a file relative to the current location in the filesystem
  • The user must currently be in a directory that contains objects in the path

Paths – Shortcuts: The .. Characters

  • Two period .. characters always represents one directory higher relative to the current directory, sometimes referred to as the parent directory.
  • For example, to move from the Art directory back to the School directory:
  • The double dot can also be used in longer paths as well:
  • The single period . character always represents the current directory.
  • For the cd this shortcut is not very useful, but it comes in handy for commands covered in subsequent sections.

Listing Files in a Directory

  • The ls (list) command is one of the most powerful tools for navigating the filesystem.
  • The ls command is used to display the contents of a directory and can provide detailed information about the files.
  • When used with no options or arguments, the ls command lists the files in the current directory:
  • The ls command can also be used to list the contents of any directory in the filesystem, provide the path to the directory as an argument.

Listing Hidden Files

  • A hidden file is any file (or directory) that begins with a dot . character.
  • The ls command omits hidden files by default.
  • To display all files, including hidden files, use the -a option to the ls command:
  • Most of the hidden files are customization files, designed to customize how Linux, your shell or programs work. ○For example, the .bashrc file in the home directory customizes features of the shell

Long Display Listing

  • Each file has details associated with it called metadata, this can include information such as the size, ownership, or timestamps.
  • Use the -l option to the ls command to view this information.
  • For example, below, a listing of the /var/log directory:
  • In the output above, each line describes metadata about a single file.
  • The following describes each of the fields of data in the output of the ls -l  command:
    • File Type:
  • Permissions:
  • The next nine characters demonstrate the permissions of the file.
    • Permissions indicate how certain users can access a file.
  • Hard Link Count:
  • This number indicates how many hard links point to this file.
  • User Owner:
    • Every file is owned by a user account. 
    • This is important because the owner has the rights to set permissions on a file. 
  • Group Owner:
    • Indicates which group owns this file, this is important because any member of this group has a set of permissions on the file.
  • File Size:
    • Size of files in bytes.
  • Timestamp:
    • Indicates when a file’s contents were last modified.
  • File Name:
    • The name of the file or directory.

Human Readable Sizes

  • The -l option to the ls command displays file sizes in bytes. 
  • For text files, a byte is 1 character so small files are easy to read, but for larger files, it is hard to comprehend how large the file is:
  • The file size is hard to determine in bytes. Is 1561400 a large file or small?
  • To present the file size in a more human readable size, like megabytes or gigabytes, add the -h option (with the -l option) to the ls command:

Listing Directories

  • When the command ls -d is used, it refers to the current directory, and not the contents within it.  
  • The . represents the current directory.
  • The ls -l command lists the contents of the directory:
  • To use the ls -d command in a meaningful way requires the addition of the -l option:

Recursive Listing

  • Recursive listing is when you want to display all of the files in a directory as well as all of the files in all subdirectories under a directory.  
  • To perform a recursive listing, use the -R option to the ls command:
  • Note that in the example above, the files in the /etc/ppp directory were listed first and the files in the /etc/ppp/peers directory were listed after.

Sort a Listing

  • By default, the -ls command sorts files alphabetically by file name.
  • Sometimes it may be useful to sort files using different criteria.
  • To sort files by size, we can use the -S option (capital letter s).
  • While the -S option works by itself, it is most useful when used with the -l option so the file sizes are visible:
  • It may also be useful to use the -h option to display human-readable file sizes:
  • The -t option sorts files based on the time they were modified:
  • For more detailed modification time information you can use the –full-time option to display the complete timestamp (including hours, minutes, seconds):
  • It is possible to perform a reverse sort by using the -r option. It can be used alone, or combined with either the -S or -t options:
Gambar 7.1 Navigating the Filesystem

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