Updated: 2018-03-06 11:18 EST

1 Due Date and DeliverablesIndexup to index

Do not print this assignment on paper!

WARNING: Some inattentive students upload Assignment #8 into the Assignment #7 upload area. Don’t make that mistake! Be exact.

2 Purpose and BackgroundIndexup to index

This assignment is based on your weekly Class Notes and covers these topics:

  1. Examine how hard links work with disk usage in an easy, medium, hard, and ugly set of exercises.
  2. Create your own hard links and soft (symbolic) links.

3 How to complete this AssignmentIndexup to index

For full marks, follow these directions exactly:

  1. These tasks must be done in your account via Remote Login to the Course Linux Server.

  2. Do the tasks in order, from top to bottom. Do not skip steps. Most tasks are independent, but some depend on successful completion of a previous task.

  3. READ ALL THE WORDS in each task before you begin the task, especially all the Hints and links.

  4. Verify your own work before running the Checking Program. You won’t have a checking program at your job interview and the Checking Program is not guaranteed to check everything.

  5. Run the Checking Program at the end of the task to grade your work and help you find some of your errors. A perfect mark from the Checking Program does not mean your answers are correct.

  6. When you are done with this Assignment, submit the output of the Checking Program to Blackboard before the due date, following the directions given at the end of this Assignment.

3.1 Notes on doing assignment workIndexup to index

  1. You can use the Checking Program to check your work after you have completed each task.

    Most task sections below require you to finish the whole task section before running the Checking Program. You may not always be able to run the Checking Program successfully in the middle of a task or after every single task sub-step. The assignment tells you where you can safely check your work.

  2. You will create file system structure in your CLS home directory containing various directories and files. When you are finished the tasks, leave the files and directories in place on the CLS as part of your deliverables for your instructor to verify.

    Assignments may be re-marked at any time on the CLS; you must have your term work available on the CLS right until term end. Do not delete any assignment work until after the term is over!

  3. You can modify your work and check it with the Checking Program as often as you like before you submit your final mark to Blackboard. You can upload your marks to Blackboard as many times as you like before the due date. Partial marks are accepted.

  4. Your instructor will also mark on the due date the work you do in your account on the CLS. Leave all your work on the CLS and do not modify it after you have submitted your final mark to Blackboard.

  5. You must keep a list of command names used each week and write down what each command does, as described in the List of Commands You Should Know. Without that list to remind you what command names to use, you will find future assignments very difficult.

3.2 Searching the course notes on the CLSIndexup to index

All course notes are available on the Internet and also on the CLS. You can learn about how to read and search these CLS files using the command line on the CLS under the heading Copies of the CST8207 course notes near the bottom of the page Course Linux Server. You also learned how to search the notes in Assignment #05 HTML.

3.3 Draw File System DiagramsIndexup to index

Many students find it extremely helpful to draw a quick graph/picture of their file system directory structure on paper before attempting to answer questions about relative pathnames.

You need to be able to visualize the relative locations of names in the file system tree to answer these questions. Draw the trees on paper!

3.4 The Source DirectoryIndexup to index

All references to the Source Directory below are to the CLS directory ~idallen/cst8207/18w/assignment08/ and that name starts with a tilde character ~ followed by a user name with no intervening slash. The leading tilde indicates to the shell that the pathname starts with the HOME directory of the account idallen (seven letters).

You do not have permission to list the names of all the files in the Source Directory, but you can access any files whose names you already know.

4 TasksIndexup to index

Have you completed all the prerequisites, before attempting these tasks?

4.1 Set Up – The Base Directory on the CLSIndexup to index

  1. Do a Remote Login to the Course Linux Server (CLS) from any existing computer, using the host name appropriate for whether you are on-campus or off-campus. All work in this assignment must be done on the CLS.

  2. Create the assignment08 directory in your usual Assignments directory.

    This assignment08 directory is called the Base Directory for most pathnames in this assignment. Store your files and answers in this Base Directory, not in your HOME directory or anywhere else.

Hints: See your previous assignment for hints on doing the above.

Run the Checking Program to verify your work so far.

4.2 Four Disk Usage Exercises: easy, medium, hard, ug1yIndexup to index

You need to understand Hard Links and Disk Usage to do this task.

Read this task all the way through, especially the Hints, before you delete anything, or else you will have to start over again.

For the next task, you will need to look up the copy option that means archive that preserves hard links (as well as all the other attributes) when you copy a directory (RTFM).

My Disk Use

  1. After you have run the Checking Program at least once, you will find created for you in the Source Directory a disk usage directory named DiskUse/abcd0001 (where abcd0001 is replaced by your own userid). Copy, using the archive option, this directory into your Base Directory using the name My Disk Use. (Do not create the My Disk Use directory before you do the archive copy or else you will create an extra level of directory.)

Verification of the copy:

You will know you did the copy correctly if your personal copy of the My Disk Use directory has the same disk usage summary value (du -s) as the one in the Source Directory and there must be a sub-directory named My Disk Use/e/foo with two hard-linked file names in it.

If there are no hard links anywhere, you didn’t copy using the archive option that preserves hard links. Delete everything and re-copy.

A recursive list of pathnames under My Disk Use should count 422 names.

The My Disk Use directory should contain almost three dozen sub-directories, each of which may contain one or more files and further sub-sub-directories. (If you don’t see almost three dozen sub-directories under your copy of My Disk Use, read all the words in the Hints again, below.)

In your personal My Disk Use directory, some of the files are hard links to each other.

There are four levels of difficulty in this task, one for each of four specially-named sub-directories in your personal My Disk Use directory. Do the easy level first, followed by the medium level, followed by the hard level, followed by the ug1y level.

Read this task all the way through, especially the Hints, before you delete anything, or else you will have to start over again.

4.2.1 The easy level and the three steps A B CIndexup to index

  1. Locate the sub-directory of your personal My Disk Use directory that contains the text easy in the name. Make this your current directory and then follow steps A through C below:
  1. Under the current directory, there is a directory named foo.

  2. Reclaim all the disk space used by the files under foo by removing all the files under foo and any hard links to those files. Some of those hard links may be to files in other sub-directories under the current directory; you don’t have to scan the whole file system to find the hard links. Read the Hints carefully before you remove anything.

  3. Run the Checking Program to verify your work so far. See the Hints if you need to start over.

4.2.2 The medium levelIndexup to index

  1. Locate the sub-directory of your personal My Disk Use directory that contains the text medium in the name. Make this your current directory. Repeat the steps A through C above.

4.2.3 The hard levelIndexup to index

  1. Locate the sub-directory of your personal My Disk Use directory that contains the text hard in the name. Make this your current directory. Repeat the steps A through C above.

4.2.4 The ug1y levelIndexup to index

  1. Locate the sub-directory of your personal My Disk Use directory that contains the text ug1y in the name. (Note carefully the strange spelling, which is not the same as ugly.) Make this your current directory. Repeat the steps A through C above.

4.2.5 Hints for each level: easy, medium, hard, ug1yIndexup to index

Hints: The current directory must be set as given above for each level.

  1. Do not remove any names from foo until you also know how to find and remove all the other names for these files. Once you have removed all the files from foo, it is too late to try to find out which other names were hard links to the files in foo.

  2. One or more of the files in the foo subdirectory have more than one name. Some of those other names may be located in other subdirectories somewhere under the current level. (You don’t have to search the whole disk partition to find them.) The disk blocks for these files in foo will not be freed until you find and remove all their names. You will need to look at inode numbers to know which files in directory foo are also named in the other directories. You read about how to do this in Disk Usage.

  3. Options to ls to display hidden names and nongraphic (unprintable) characters will be needed for the harder sections (RTFM). Many names will need to be quoted to hide shell metacharacters (see Quoting).

  4. If you don’t get the right answer for a difficulty level, you can start over by re-copying all or part of your My Disk Use directory from where you originally got it in the Source Directory.

    If you make errors in this task and need to redo one of the four sections, you can remove and re-copy from the Source Directory just the sub-directory for that one section. You don’t have to remove and re-copy the whole DiskUse/abcd0001 directory, since that would lose the work you did on the other sections.

    If you do want to remove your entire personal My Disk Use directory to start over, you will need to redo all four levels. If you are smart and rename the directory instead of removing it, you can salvage from the saved directory the parts of the task you have already done successfully, so you won’t have to redo those parts.

  5. If you find that you don’t own any of the files under your My Disk Use directory, and that you have no permission to remove any files, then you didn’t copy the files correctly. Delete everything and re-read and re-do that first step.

  6. Do not remove any names from foo until you also know how to find and remove all the other names for these files. Once you have removed all the files from foo, it is too late to try to find out which other names were hard links to the files in foo.

4.4 Hard and Soft Linking exerciseIndexup to index

You need to understand Hard Links and Symbolic Links and to do this task.

linkdir1/abcd0001.txt

  1. In your Base Directory, create a sub-directory and an empty file linkdir1/abcd0001.txt (no spaces), where the text abcd0001 is replaced by your own eight-character userid in the file name. NOTE: The sub-directory name is linkdir1 (seven letters and one digit).

  2. For every unique character in your own eight-character userid, create a sub-sub-directory under linkdir1 with that single-character name.

    For example, the userid abca0151 would result in six unique sub-sub-directory names under the linkdir1 directory – one sub-sub-directory for each of the unique characters a, b, c, 0, 1, 5. Each new directory must be directly under the linkdir1 directory. (Note: You can create multiple directories with one single command line.)

    Do this for your own userid, which means you may have more or fewer sub-sub-directories, depending on the letters and digits in your own userid.

  3. Inside each of those new sub-sub-directories, create a single Hard Link to the empty file from the first step. Keep the same file name as the original for each hard link you create. Use hard links, not symbolic links.

    Continuing the above example, the abca0151 user would hard link the original empty file name abca0151.txt into each of those six new sub-sub-directories, creating six additional names for the same file. Keep the same file name as the original for each hard link.

    Check the link counts on everything to make sure that you have created links to the same file and not made copies of the file. Use hard links, not symbolic links.

  4. For every lower-case letter directory name you created, create a short, relative Symbolic Link that is its upper-case equivalent. If you created directory a, then create symlink A that points to (has a target of) a so that both ls linkdir1/a and ls linkdir1/A give identical results. (You must use symbolic links, because you cannot make hard links to directories.)

  5. In every file you have just created in this section, enter the following information, one name per line: Enter the names of the three common file system commands that are “directory only” commands that require permission only on the directory inode to work properly, and that do not require permissions on the file inode to work. The answer is three lines, one command name per line. The right answer has a word count of 3 3 9.

Hints: All the file names you created in this section should be hard links to the same file; you have very little editing to do. The three command names are all common commands that are directory operations that manipulate file names; they don’t touch the file data and don’t need any permissions on the file data. See your in-class notes for the three names I wrote on the board, or re-read the course notes about links and inodes.

Use your symbolic link ./check to run Checking Program to verify your work so far.

4.5 When you are doneIndexup to index

That is all the tasks you need to do.

Check your work a final time using the Checking Program below and save the standard output of that program into a file as described below. Submit that file (and only that one file) to Blackboard following the directions below.

Your instructor will also mark the Base Directory in your account on the due date. Leave everything there on the CLS. Do not delete anything.

When you are done, log out of the CLS before you close your laptop or close the PuTTY window, by using the shell exit command:

$ exit

5 Checking, Marking, and Submitting your WorkIndexup to index

Summary: Do some tasks, then run the Checking Program to verify your work as you go. You can run the Checking Program as often as you want. When you have the best mark, upload the single file that is the output of the Checking Program to Blackboard.

Since I also do manual marking of student assignments, your final mark may not be the same as the mark submitted using the current version of the Checking Program. I do not guarantee that any version of the Checking Program will find all the errors in your work. Complete your assignments according to the specifications, not according to the incomplete set of the mistakes detected by the Checking Program.

  1. There is a Checking Program named assignment08check in the Source Directory on the CLS. You can execute this program by typing its (long) pathname into the shell as a command name:

    $ ~idallen/cst8207/18w/assignment08/assignment08check

    You learn one way to make this path shorter in this assignment.

  2. When you are done, execute the above Checking Program as a command line on the CLS. This program will check your work, assign you a mark, and display the output on your screen.

    You may run the Checking Program as many times as you wish, allowing you to correct mistakes and get the best mark. Some task sections require you to finish the whole section before running the Checking Program at the end; you may not always be able to run the Checking Program successfully after every single task step.

  3. When you are done with this assignment, and you like the mark displayed on your screen by the Checking Program, you must redirect only the standard output of the Checking Program into the text file assignment08.txt in your Base Directory on the CLS, like this:

    $ ~idallen/cst8207/18w/assignment08/assignment08check >assignment08.txt
    $ less assignment08.txt
    • Use standard output redirection with that exact assignment08.txt file name.
    • Use that exact name. Case (upper/lower case letters) matters.
    • Be absolutely accurate, as if your marks depended on it.
    • Do not edit the output file; the format is fixed.
    • Make sure the file actually contains the output of the Checking Program!
    • The file should contain, near the bottom, a line starting with: YOUR MARK for
    • Really! MAKE SURE THE FILE HAS YOUR MARKS IN IT!
  4. Transfer the above single file assignment08.txt (containing the output from the Checking Program) from the CLS to your local computer.
    • You may want to refer to the File Transfer page for how to transfer the file.
    • Verify that the file still contains all the output from the Checking Program.
    • Do not edit or open and save this file on your local computer! Edited or damaged files will not be marked. Submit the file exactly as given.
    • The file should contain, near the bottom, a line starting with: YOUR MARK for
    • Really! MAKE SURE THE FILE YOU UPLOAD HAS YOUR MARKS IN IT!
  5. Upload the assignment08.txt file from your local computer to the correct Assignment area on Blackboard (with the exact name) before the due date:
    1. On your local computer use a web browser to log in to Blackboard and go to the Blackboard page for this course.
    2. Go to the Blackboard Assignments area for the course, in the left side-bar menu, and under there find assignment08
    3. Under Assignments, click on the underlined assignment08 link for this assignment.
      1. If this is your first upload, the Upload Assignment page will open directly; skip the next sentence.
      2. If you have already uploaded previously, the Review Submission History page will be open and you must use the Start New button at the bottom of the page to get to the Upload Assignment page.
    4. On the Upload Assignment page, scroll down and beside Attach File use Browse My Computer to find and attach your assignment08.txt file from your local computer. Make sure the assignment file has the correct name on your local computer before you attach it. Attach only your assignment08.txt file for upload. Do not attach any other file names.
    5. After you have attached the assignment08.txt file on the Upload Assignment page, scroll down to the bottom of the page and use the Submit button to actually upload your attached assignment08.txt file to Blackboard.
    6. Submit the file exactly as uploaded from the CLS.
    7. Do not submit an empty file. Do not submit any other file names. Make sure the file name on Blackboard is correct!

    Use only Attach File, Browse My Computer on the Upload Assignment page. Do not enter any text into the Write Submission or Add Comments boxes on Blackboard; I do not read them. Use only the Attach File, Browse My Computer section followed by the Submit button. If you need to comment on any assignment submission, send me EMail.

    You can revise and upload the file more than once using the Start New button on the Review Submission History page to open a new Upload Assignment page. I only look at the most recent submission.

    You must upload the file with the correct name from your local computer; you cannot correct the name as you upload it to Blackboard. Make sure the file name on Blackboard is correct!

  6. Verify that Blackboard has received your submission: After using the Submit button, you will see a page titled Review Submission History that will show all your uploaded submissions for this assignment. Each of your submissions is called an Attempt on this page. A drop-down list of all your attempts is available.
    1. Verify that your latest Attempt has the correct 16-character, lower-case file name under the SUBMISSION heading.
    2. The one file name must be the only thing under the SUBMISSION heading. Only the one file name is allowed.
    3. No COMMENTS heading should be visible on the page. Do not enter any comments when you upload an assignment.
    4. Click on the Download button to open and view the file you just uploaded. MAKE SURE THE FILE YOU JUST UPLOADED HAS YOUR MARKS IN IT!
    5. Save a screen capture of the Review Submission History page on your local computer, showing the single uploaded file name listed under SUBMISSION. If you want to claim that you uploaded the file and Blackboard lost it, you will need this screen capture to prove that you actually uploaded the file. (To date, Blackboard has never lost an uploaded file.)
    6. Make sure you have used Submit and not Save as Draft. I cannot mark draft assignments. Make sure you Submit.

    You will also see the Review Submission History page any time you already have an assignment attempt uploaded and you click on the underlined assignment08 link. You can use the Start New button on this page to re-upload your assignment as many times as you like.

    You cannot delete an assignment attempt, but you can always upload a new version. I only mark the latest version.

  7. Your instructor may also mark files in your directory in your CLS account after the due date. Leave everything there on the CLS. Do not delete any assignment work from the CLS until after the term is over!

READ ALL THE WORDS. OH PLEASE, PLEASE, PLEASE READ ALL THE WORDS!

Author: 
| Ian! D. Allen, BA, MMath  -  idallen@idallen.ca  -  Ottawa, Ontario, Canada
| Home Page: http://idallen.com/   Contact Improv: http://contactimprov.ca/
| College professor (Free/Libre GNU+Linux) at: http://teaching.idallen.com/
| Defend digital freedom:  http://eff.org/  and have fun:  http://fools.ca/

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