OPS705 Lab 2 (2227)

LAB PREPARATION

Purpose / Objectives of Lab 2

Understanding how to use a command line interface (CLI) is an incredibly useful skillset as application developers. It is present in all major operating systems, and is often how you will interact with tools and databases to accomplish tasks a GUI doesn't provide.

In this lab, you will practice working with the Linux command line environment inside your Azure CentOS VM to:

1. Understand the purpose of directories and directory pathnames.
2. Use common Linux commands to perform directory management tasks.
3. Understand the difference between absolute , relative and relative-to-home pathnames
4. Become productive at issuing Linux commands with the most appropriate pathname

If you encounter technical issues, please contact your professor via e-mail or in your section's Microsoft Teams group.

Minimum Requirements

Before beginning, you must have:

1. Successfully completed Lab 1
2. Attended the Week 2 class lecture
3. Read through the Week 2 slides, and have them handy as a reference for concepts
4. Your username-lnx CentOS VM in Azure
5. Your Seneca Azure login credentials
6. Your linked mobile device for 2FA

KEY CONCEPTS

Linux Directories

In Unix / Linux (as opposed to MS Windows), there are no drive letters (such as C:, or D:).

All files and directories appear under a single ancestor directory called "the root directory".

To better organize files (text, images, documents, spreadsheets, programs, etc) within your Linux system, they should be stored in directories. To further organize many files, directories may contain sub-directories.

The Linux file system is hierarchical, like other operating systems such as Windows, macOS, etc. In Linux (as opposed to Windows), there are no drive letters (such as C:, or D:). All files and directories appear under a single ancestor directory called the "root directory".

Learning how to issue Linux commands for navigating and manipulating directory and files within the the Linux filesystem are essential skills for Linux users and Linux system administrators (i.e. sysadmins).

In the Linux OS, the root directory / is the starting directory, and other child directories, grandchild directories, etc. can be created as required. This hierarchical structure resembles an "upside-down tree". There is actually a command called tree that displays a directory tree diagram!

• NOTE: To install the tree command: sudo yum install tree

Directory Pathnames

A pathname points to a file system location by following the directory tree hierarchy.

A pathname is used to specify a route to a file within the file system. A pathname points to a file system location by following the directory tree hierarchy expressed in a string of characters in which path components, separated by a delimiting character, represent each directory. The delimiting character is most commonly the slash ("/"). (Reference: [[1]])

The following table displays and defines commonly used directories (listed by directory pathname) for for ALL Linux filesystems:

Directory Pathname	Purpose
/	Root directory (ancestor to all directories)	Common directory pathnames for for ALL Linux Filesystems.
/home	Used to store all users’ home directories
/home/username/	A specific user's home directory
/bin	Common system binaries (commands)
/usr/bin	Common utilities (commands) for users.
/usr/sbin	Common utilities for system administration
/etc	System administration files (eg. passwd)
/var	Dynamic files (log and mail files)
/tmp , /var/tmp	Temporary files for programs
/dev	Device driver files (terminals, printers, etc.)

When you log into your Linux user account, you are automatically directed to your home directory. This directory is where the user can store files and create subdirectories to organize their files.

Pathname Types

There are different types of file pathnames that we can use to access a directory or text file.

For Example:

• Absolute Pathname: /home/userid/uli101/cars.txt
• Relative Pathname: uli101/cars.txt (this assumes you are in your home directory)
• Relative-to-Home Pathname: ~/uli101/cars.txt

These types of file pathnames can make it more efficient (i.e. less keystrokes for users to type) when issuing Unix and Linux commands.

Absolute Pathnames

The directory in red displays the FULL path from the root directory to the bin directory (i.e. the absolute pathname: /bin.	Directories in red display the FULL path from the root directory to the examples directory (i.e. the absolute pathname: /home/your-user-id/uli101/examples.
Directories in red display the path from the current directory location (which is xyz100) to the bin directory (i.e. the relative pathname: ../../../bin.	Directories in red display the path from the current directory location (which is uli101) to the examples directory (i.e. the relative pathname: uli101/examples or ./uli101/examples
Directories in red display the path from the home directory of the current user (which is userid) to the examples directory (i.e. the relative-to-home pathname: ~/uli101/examples.	Directories in red display the path from another user's home directory location to their notes directory (i.e. the relative-to-home pathname: ~otheruserid/uli101/notes

An absolute pathname is a path to a file or directory always beginning from the root directory (i.e. /).

This type of pathname is referred to as absolute because the pathname always begins from the root directory, regardless the location or your current directory. In other words, this type of pathname requires that you always provide the FULL pathname starting with the root directory.

Advantages of using Absolute Pathnames:

• Useful if you do not know your current directory location
• Understand the location of file within the filesystem.

Examples:

• ls /bin
• ls /home/your-user-id/uli101/examples

Relative Pathnames

A relative pathname is a path to a file or directory that begins from your current directory. This is called relative because it is used to locate a specific file relative to your current directory.

NOTE: In order to use relative pathnames, it is absolutely necessary that you know the location of your current directory!

Relative Pathname Symbols:

• . A period symbol "." represents the current directory
• .. Two consecutive period symbols ".." represents the parent directory (i.e. one level up)

Advantages of using Relative Pathnames:

• Possible shorter pathname (less typing)

Examples:

• ls ../../../bin
• ls examples
• ls ./examples

Relative-to-Home Pathnames

A relative-to-home pathname begins with the tilde character ( i.e. ~) to represent the user’s home directory.

The tilde character ~ stores the path of the user’s home directory (i.e. ~ = /home/current-user-id)

You can immediately place a username after the tilde to represent another user’s home directory (e.g. ~otheruserid = /home/otheruseid)

Examples:

• ls ~/uli101/examples
• ls ~otheruserid/uli101/notes

NOTE: Deciding which type of pathname to use depends on many factors including:

1. Knowledge of current directory
2. Knowledge of directory structure
3. Currently directory location
4. Type of file management command that is being used

INVESTIGATION 1: Creating and Managing Directories

In this investigation, you will learn how to create, navigate, list directory contents and remove directories in your user account.

Directory File Naming Rules

Before you learn how to create directories, it is important to understand what represents an appropriate directory filename.

Listed below are some common file naming rules:

• Linux characters are case-sensitive. It is recommended to be consistent (e.g. use all lowercase letters)
• Adopt a consistent directory naming scheme (this will help you to navigate within your directory structure)
• Make your directory names meaningful
• Avoid non-alphanumeric characters, as they may have a special meaning to the system that will make your work more difficult when changing to directories, etc.
• Avoid using spaces for directory names (consider periods, hyphens, and underscores instead)

Part 1: Directory Creation

Fig. 4: Tree diagram of directory structure to create in your home directory (displayed in blue text).

Creating subdirectories within your home directory makes it more efficient to save and access files on your Linux server.

A comparison would be rooms in a house. If there were no rooms, just one large room in a 3,000 square foot house, it would be "messy" and difficult to locate items. Each room in a house is used to for a specific purpose to be more productive to perform a task such as a kitchen, bedroom, bathroom, etc.

You will be creating the following directory structure within your home directory (refer to diagram on the right side (Fig. 4)).

Creating Directories

We will now create our first level of directories.

IMPORTANT: For the following commands, you will be using your Seneca username to replace the text "your-seneca-id" in a pathname.
For example, if your Seneca user ID was mkhan then you would write the pathname /home/your-seneca-id as: /home/mkhan

Perform the following steps:

1. SSH into your CentOS Linux account (Refer to Week 2 slides).
2. Issue a command to confirm that you are located in your home directory (/home/your-seneca-id): pwd
3. Issue the following Linux command: mkdir /home/your-seneca-id/uli101xx
   • NOTE: You should always confirm that you have created a directory. This can be done by issuing the ls command.
     

     Creating and confirming the creation of a directory.
4. Issue the following Linux command: ls /home/your-seneca-id/uli101xx
   • There are no contents that are contained in this newly-created directory; therefore, no contents appear. A useful option -d can be used to confirm that the actual directory has been created as opposed to viewing the contents of the directory.
5. Issue the following Linux command: ls -d /home/your-seneca-id/uli101xx
   • You should now see just the directory listed. You can also combine the -d and -l options to provide more detail regarding the newly-created directory.
6. Issue the following Linux command: ls -d -l /home/your-seneca-id/uli101xx
   • How can you confirm from the output of this command that the file uli101xx is a directory?
7. Issue the following Linux command: ls -ld /home/your-seneca-id/uli101xx
   • Is the output from this command the same was the output from the previous command?
   • If so, what does this say about how to use multiple options for Linux commands?
8. Issue the following Linux command to create the acp100xx and xyz100xx directories: mkdir /home/your-seneca-id/acp100xx /home/your-seneca-id/xyz100xx
   • NOTE: You can create multiple directories by issuing the mkdir command with multiple arguments. (Make sure there's a space between each path!)
9. Issue the following Linux command to confirm that those directories have been created: ls -ld /home/your-seneca-id/acp100xx /home/your-seneca-id/xyz100xx
   • Using a FULL pathname starting from the root directory (i.e. /) requires is a LOT of typing!
   • Since we are already located in our home directory, we don't have to start from the root directory. This is called a "relative" pathname. See the next instruction for an example.

Creating Subdirectories

We will now create the subdirectories that are contained in the uli101xx directory:

1. Move to the uli101xx directory using a relative pathname: cd uli101xx
2. Confirm that your current location is in the uli101xx directory (/home/your-seneca-id/uli101xx): pwd
3. Create the directories called notes, tutorials and samples: mkdir notes tutorials samples
4. Confirm that those directories have been created: ls

There are better ways to create the same directory structure without using the cd command.

Creating Subdirectories Without cd

Issuing the cd command prior to issuing other commands indicates to others that you are a novice or "newbie". You can actually lose marks on quizzes or tests if you issue multiple Linux commands to performed tasks that can be performed using a single Linux command with pathnames.

Here we'll show you how to create directories and subdirectories without having to move inside them.

First, return to your home directory:

1. Return to your home directory: cd
2. Confirm that you are now located in your home directory (/home/your-seneca-id): pwd

Although we will teach you how to remove directories and their contents in another investigation, let's remove the created directory structure and recreate the same directory structure using just one command using pathnames:

1. Remove all of the directories that you have created: rm -r uli101xx acp100xx xyz100xx
2. Confirm that the uli101xx, acp100xx and xyz100xx have been removed: ls
3. Issue the following single Linux command to create the entire directory structure: mkdir -p uli101xx/notes uli101xx/tutorials uli101xx/samples acp100xx xyz100xx
   • NOTE: The -p option allows "parent" directories to be automatically created first to then create their subdirectories.
4. Confirm that all of the directories have been created: ls -ld uli101xx/ uli101xx/notes uli101xx/tutorials uli101xx/samples acp100xx xyz100xx

Running a Shell Script to Check Your Work

Although you are being asked to create the directory structure, you might have made some mistakes.

For example:

• Forgetting to create a directory.
• Making syntax errors (eg. spelling or mixing up character case)
• Not creating subdirectories within specified directories.

To check for mistakes, a shell script has been created to check your work. If the checking shell script detects an error, then it will provide feedback and offer constructive feedback on how to fix that problem so you can re-run the checking shell scripts until your work is correct.

Perform the following steps:

If all check pass, then user performed task correctly and can continue.

If there is a warning, then feedback is provided to user to correct and re-run checking script.

1. Make certain that your current directory is your home directory.
2. Create a new directory called bin: mkdir bin
3. Install git: sudo yum -y install git
4. Using git, download all lab check scripts into your bin directory: git clone https://github.com/ops705/labs.git /home/your-seneca-id/bin/
5. Run the checking script for Part 1: labcheck2.1.sh
   • If you encounter errors, then view the feedback to make corrections, and then re-run the checking script.
   • If you receive a congratulations message that there are no errors, then proceed to the next part.

Part 2: Viewing Directory Contents / Copying & Moving Directories

Now that you have learned how to efficiently create your directory structure, you will now learn how to issue Linux commands to view directory contents as well as copy and move directories.

Perform the following steps:

Output of the tree command to display directory structure.	Output of the ls -R command to display directory structure.
Output of the tree command to confirm copy of uli101xx directory (and contents) to the xyz100xx directory.	Output of the tree command to confirm movement of acp100 directory directory (and contents) to the xyz100xx diredtory.

1. Issue the following Linux command: tree
   • NOTE: You should see the directory structure that you created in the previous investigation. You can also issue the tree command combined with a directory pathname to display the directory structure for a specific scope.
   • You can also use the -R option for the ls command to display all directories and subdirectories for a specified directory path (referred to as a recursive directory listing).
2. Issue the following Linux command: ls -lR
   • What directories do you see?
3. Issue the following Linux command: ls -lR uli101xx
   • Note the differences between both of these commands (i.e. using and not using a pathname).
4. You can copy and move entire directories (and their contents) to other directories. Issue the following Linux command: cp -R uli101xx xyz100xx
5. Display the directory structure of your home directory to confirm you copied the uli101xx directory: tree
6. Issue the following Linux command: mv acp100xx xyz100xx/uli101xx/tutorials
7. Display the directory structure of your home directory to confirm you moved the acp100xx directory: </code>tree</code>

Let's run a checking script to see if you moved and copied the directories correctly:

1. Make certain that your current directory is your home directory.
2. Run the checking script for Part 2: labcheck2.2.sh

If you encounter errors, make corrections and re-run the checking script until you receive a congratulations message.

Proceed to Part 3.

Part 3: Removing Directories

You will now learn how to safely remove directories and their contents.

Perform the following steps:

1. Confirm that you are located in your home directory.
2. The rmdir command is used to remove empty directories. Remove the empty directory called tutorials: rmdir uli101xx/tutorials
3. Confirm that you removed the tutorials directory.
4. Remove the empty directory called uli101xx: rmdir uli101xx
   • NOTE: You should get an error message, since the uli101xx directory is NOT empty.
5. To remove non-empty directories, you can use the rm -r option, which can travel down the directory paths and their contents: rm -r uli101xx
6. Confirm that the uli101xx directory (contained in your home directory) and its contents have been removed.
   • NOTE: To safely remove non-empty directories, you can add the -i option, which will prompt the user if they wish to remove contents as it your travel recursively down a directory to remove directories and their contents.
7. Issue the following Linux command (entering "y" when prompted): rm -ri xyz100xx
   • NOTE: You should have removed all directories that you have created.

Let's run a checking script to confirm that you have correctly removed all of those directories:

1. Make certain that your current directory is your home directory.
2. Issue the tree command to confirm that all of those recently created directories have been removed.
3. Run the checking script for Part 3: labcheck2.3.sh

If you encounter errors, make corrections and re-run the checking script until you receive a congratulations message.

Proceed to the next investigation.

INVESTIGATION 2: Absolute / Relative / Relative-to-Home Pathnames

The best way to learn about different types of file pathnames is to use them while issuing Linux commands and see which pathnames (or combination of pathnames) is the most efficient (i.e. requiring the least number of keystrokes).

In the following investigation (Parts 1-3), you will create the exact same directory structure each time, but using a different path type.

First, let's confirm:

1. Connect to your CentOS VM's CLI
2. Issue a command to confirm you are located in your home directory.

Part 1: Using Absolute Pathnames

In this investigation, you will create the blue sections of this tree diagram.

Let's create the following directory structure under your home directory by issuing the mkdir command using only absolute pathnames.

1. Issue the following Linux command to create the directory structure displayed to the right using absolute pathnames: mkdir -p /home/youruserid/tutorial3/practice/commands /home/youruserid/tutorial3/practice/examples /home/youruserid/tutorial3/notes/lesson1 /home/youruserid/tutorial3/notes/lesson2
   • NOTE: Just continue typing and let the text continue of separate lines. Remember to replace the text "youruserid" with your actual Seneca username.
2. Confirm that you properly created the directory structure: tree /home/youruserid/tutorial3
   • You should notice that using absolute pathnames with this Linux command requires a lot of typing.

Part 2: Using Relative-to-Home Pathnames

Let's remove this directory structure, and issue the same command using a relative-to-home pathname instead.

1. To remove this directory structure, issue the following Linux command (enter "y" at each prompt to remove ALL contents): rm -ri /home/youruserid/tutorial3
2. Confirm that the directory structure has been removed using the tree command.
3. Create the same directory structure using relative-to-home pathnames: mkdir -p ~/tutorial3/practice/commands ~/tutorial3/practice/examples ~/tutorial3/notes/lesson1 ~/tutorial3/notes/lesson2
   • NOTE: You usually generate the ~ character by Holding down SHIFT and press the button to the left of the number 1 above the text on your keyboard.
   • Did this command require less typing than the previous command using absolute pathnames?
4. Issue the tree command to confirm the directory structure was properly created.

Part 3: Using Relative Pathnames

Let's remove the tutorial3 directory and its contents and issue the same command using relative pathnames.

1. Issue the same command as you did in step #5 to remove the tutorial3 directory and its contents safely.
2. Issue a Linux command to confirm you removed the tutorial3 directory and its contents.
3. Create the same directory structure using relative pathnames: mkdir -p tutorial3/practice/commands tutorial3/practice/examples tutorial3/notes/lesson1 tutorial3/notes/lesson2
4. Issue a command to verify that the proper directory structure was created.

You may think that issuing Linux file management commands are better using relative or relative-to-home pathnames instead of absolute pathnames, but that is not always true.

Since the current directory location was your home directory, then it makes sense to use relative or relative-to-home pathnames. On the other hand, what if we changed the location to a different directory?

Part 4: Pathing Practice

This diagram should reflect your own directory structure before beginning Part 4. Refer to this tree diagram throughout Part 4 to help orient yourself.

When performing the next series of steps, refer to the tree diagram on the right. Learning to reference a tree diagram on a quiz, midterm or final exam can help to prevent errors and loss of marks!

Since we will be running Linux commands depending on the directory structure that you have created in Part 3, let's run a checking script to verify you created it correctly:

1. Make certain that your current directory is your home directory.
2. Issue the tree command to confirm that all of those recently created directories have been removed.
3. Download the Part 3 checking script: wget https://raw.githubusercontent.com/ops705/labs/main/labcheck2.4.sh -P /home/your-seneca-id/bin/
4. Run the checking script for Part 3: labcheck2.4.sh

If you encounter errors, make corrections and re-run the checking script until you receive a congratulations message.

Perform the following:

1. Change to the examples directory in your recently-created directory structure: cd tutorial3/practice/examples
2. Confirm you are located in the examples directory.
3. Remembering that we are located in the examples directory, issue the following Linux command using a relative pathname to display files in the /bin directory: ls ../../../../../bin
4. Now issue the following Linux command using an absolute pathname: ls /bin
   • Which type of pathname would be the best to use in this situation?
5. Let's copy the file called ls which is contained in the /bin directory to your home directory by using the cp command.
6. First, copy the ls command from the /bin directory to your home directory using absolute pathnames: cp /bin/ls /home/youruserid
7. Now let's issue the previous command using just relative pathname (remember, our current directory location is examples): cp ../../../../../bin/ls ../..
   • TIP: For relative pathnames that move up multiple parent directories such as these, it is HIGHLY RECOMMENDED to view the tree diagram and check for the correct number of .. symbols. Students commonly make mistakes and lose marks on these type of questions!
8. Let's issue the command using one absolute pathname and a relative pathname: cp /bin/ls ../..
   • What did this command do?
9. Let's issue the same command using one absolute pathname and a relative-to-home pathname: cp /bin/ls ~
   • What did this command do?
10. Let's copy the ls file from the /bin directory to your current directory (i.e. examples): cp /bin/ls .
11. Issue the following Linux command: cp /bin/ls ./ls.bk
    • What does this command do?

Let's run a checking script to make certain you performed the recently-issued commands correctly.

1. Make certain that your current directory is your home directory.
2. Issue the tree command to confirm that all of those recently created directories have been removed.
3. Download the Part 3 checking script: wget https://raw.githubusercontent.com/ops705/labs/main/labcheck2.5.sh -P /home/your-seneca-id/bin/
4. Run the checking script for Part 3: labcheck2.5.sh

If you encounter errors, make corrections and re-run the checking script until you receive a congratulations message.

Lab Submission

When complete, show your instructor the following in-class:

1. A successful run of labcheck2.1.sh
2. A successful run of labcheck2.2.sh
3. A successful run of labcheck2.3.sh
4. A successful run of labcheck2.4.sh
5. A successful run of labcheck2.5.sh

Make sure to fully stop your VMs when you're done!