Updated: 2015-11-27 02:00 EST

1 Due Date and DeliverablesIndexup to index

Do not print this assignment on paper!

WARNING: Some inattentive students upload Assignment #10 into the Assignment #09 upload area. Don’t make that mistake! Be exact.

2 Purpose of this AssignmentIndexup to index

Do not print this assignment on paper! On paper, you cannot follow any of the hyperlink URLs that lead you to hints and course notes relevant to answering a question.

This assignment is based on your weekly Class Notes.

  1. Working with tar archives from Package Management
  2. Working with Processes and Jobs
  3. Working with System Log Files
  4. Using the Crontab and At Job Schedulers (cron and at)
  5. Sending EMail and Reading EMail on the CLS.
  6. Writing a Shell Script.

Remember to READ ALL THE WORDS to work effectively and not waste time.

3 Introduction and OverviewIndexup to index

This is an overview of how you are expected to complete this assignment. Read all the words before you start working.

For full marks, follow these directions exactly.

  1. Complete the Tasks listed below, in order, and don’t skip steps.
  2. Verify your own work before running the Checking Program.
  3. Run the Checking Program at the end of the task to help you find errors.
  4. Submit the output of the Checking Program to Blackboard before the due date, following the directions given below.
  5. READ ALL THE WORDS to work effectively and not waste time.

3.1 Notes on checking your workIndexup to index

  1. 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. 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!
  2. 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.
  3. You can modify your work and check it with the Checking Program as often as you like before you submit your final mark. You can submit your mark as many times as you like before the due date.

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.

3.2 Save your workIndexup to index

You will create file system structure in your HOME directory on the CLS, with various directories, files, and links. When you are finished the tasks, leave these files, directories, and links in place as part of your deliverables on the CLS. Do not delete any assignment work until after the term is over! Assignments may be re-marked at any time; you must have your term work available right until term end.

3.3 The Source DirectoryIndexup to index

All references to the Source Directory below are to the CLS directory ~idallen/cst8207/15f/assignment10/ 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.

3.4 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.

4 TasksIndexup to index

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

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 assignments very difficult.

  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. Base Directory: Make the CLS directory named ~/CST8207-15F/Assignments/assignment10 in which you will create the files and scripts resulting from the following tasks. (You do not have to create any directories that you have already created in a previous assignment.) Spelling and capitalization must be exactly as shown:

check

  1. Create the check symbolic link needed to run the Checking Program, as described in the section Checking Program below.

This assignment10 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.

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

4.2 Part A – Disk Usage, tar Archive and ListingIndexup to index

You need to know Disk Usage and Package Management to do this task.

  1. Make your Base Directory your current directory and do not change directories for this task. All recorded pathnames must be relative to the Base Directory.

maze10

abcd0001

  1. In the current directory (the Base Directory), create a directory named maze10. Without changing directories, create a symbolic link in that maze10 directory that is the name of your 8-character CLS userid. The symlink should point to the absolute path of the maze directory that is in the Assignment #03 Source Directory. The symbolic link will have a size of exactly 43 characters (the absolute path of the maze directory), e.g. for userid abcd0001 the symlink long listing would start like this:

    lrwxrwxrwx 1 abcd0001 abcd0001 43 Mar 22 12:03 maze10/abcd0001 -> 

    The rest of the symlink is the absolute path of the maze directory.

    You probably have it right if ls maze10/abcd0001 shows about 2600 (non-hidden) pathnames from the maze.

  2. Display the sum total of disk blocks in the hidden maze10/abcd0001/.0 sub-directory inside the maze. Do not change directories to do this!
    • Use your own symlink and userid in the name, not abcd0001
    • The number of blocks printed should be larger than 6900.
    • The relative pathname beside the number should include your symlink name exactly as given above.
    • You will need this exact relative pathname in the next questions.
    • If you get the wrong pathname, re-read the first sentence of Item #1, above about changing directories.

mazeblocks.txt

  1. Put the above one-line of output (the number of disk blocks) into a new file mazeblocks.txt in the maze10 directory.
    • The file will be one line long, containing two words: a number larger than 6900 and a relative pathname containing two slashes.

YYYYMMDD.tar.gz

  1. Create a gzip-style compressed tar archive in the maze10 directory containing the contents of the .0 directory from above. Use the relative pathname from above as the source of the files to archive. Name the new archive YYYYMMDD.tar.gz (no spaces) under maze10, where YYYYMMDD is the numeric year-month-day date of the final exam in this course.
    • The gzip-style compressed archive will be approximately 25,000 bytes.
    • All the pathnames in the tar archive file must be relative paths with maze10/abcd0001/.0/ at the beginning of every name.

YYYYMMDD.tar.bz2

  1. Create a bzip2-style compressed tar archive in the maze10 directory of the same .0 directory from above. Use the same name as for the gzip archive, but use the file extension .bz2 instead of the .gz extension.
    • Use the correct options to generate the bzip2-style compressed archive, and also use the correct output name.
    • The bzip2-style compressed archive will be approximately 8300 bytes. If it’s larger than that, you didn’t use the right options to create it.
  2. Look up the option to ls that gives just “the allocated size of each file, in blocks” and use that option (and only that option) to display the size and name of the two tar archives you just created in the maze10 directory.
    • A GLOB pattern will be helpful to generate the two archive pathnames in the maze10 directory as arguments to ls.
    • The output will be one line long, four words, with each tar archive name preceded by its size in blocks.

mazeblocks.txt

  1. Append the output of the above command line (the sizes and relative pathnames) to the disk blocks file you created earlier. The file will now be three lines (six words) long.
    • Note how the output of ls changes to separate lines when output is to a file instead of directly to your screen. This is one of the few commands that does this.
    • Look at the three lines in the disk blocks file and note how the compressed tar archives are much smaller (fewer disk blocks) than the original disk space used.
    • Note how the newer bzip2 compression algorithm is much better at compressing this file (fewer disk blocks) than the older gzip algorithm.
    Hint: Go back and re-read the first step in this task if you don’t have the right pathnames in your output.

tar_table.txt

  1. Generate a verbose listing of your gzip-style tar archive file, showing the contents of the archive including all the owners and date/time stamps, but don’t display it directly on your screen since it’s over 1,700 lines long. (Generate the verbose listing and verify that it outputs over 1,700 lines by counting them.)

    Once you know you can generate the verbose listing, save just the first five and last five lines of the verbose listing into file tar_table.txt under maze10 directory. The file word count will be 10 61 786 and the first line and last line should look like this (where abcd0001 is replaced by your userid):

    drwxr-xr-x idallen/idallen   0 2014-10-25 03:16 maze10/abcd0001/.0/
    -rw-r--r-- idallen/idallen 156 2014-10-25 03:16 maze10/abcd0001/.0/jawo0006*txt

    Hints: You will need to use one command pipeline to generate the first five lines into the output file, and then use a second command pipeline to generate the last five lines and append them to the output file to make a total of ten lines in the file. If the checking program says you have unprintable characters in your file, you have not used the right command to generate a verbose listing of a tar file; re-read the notes on how to use tar given at the top of this Part A section.

  2. The bzip2 compression algorithm is better than the gzip compression algorithm; bzip2 produces smaller compressed files. Answer this question:

    True or False: Because bzip2 is smaller than gzip, generating the verbose table of contents of the bzip2-style tar archive file will produce fewer lines than the table of contents of the gzip-style archive.

    Append your one-word answer true or false to the tar_table.txt file. (The file will now contain 11 lines.) (The checking program will not check this answer. Your instructor will check the answer and mark it after you hand in your assignment.)

Run the Checking Program on the CLS to verify your work so far.

If you have errors, go back and re-read the first step in this task.

4.3 Part B – Process ListingIndexup to index

You need to know Processes and Jobs to do this task.

psbsd.txt

  1. Place a full list of all processes for all users, BSD format, all users, text user name (not numeric UID), full wide listing (not truncated at all), into file psbsd.txt in your Base Directory. It should be at least 105 lines and 9KB. The top header line and one of the very long lines will be a dhclient line similar to this (use a text-searching command to find it in the output):

    USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
    root      4078  0.0  0.0   7264   388 ?        Ss   Nov11   0:00 dhclient3 -e IF_METRIC=9999 -pf /var/run/dhclient.eth0.pid -lf /var/lib/dhcp/dhclient.eth0.leases -1 eth0

psunix.txt

  1. Place a full list of all processes for all users, UNIX (System V) format, text user name (not numeric UID), full wide listing (not truncated at all), into file psunix.txt in your Base Directory. It should be at least 105 lines and 7KB. The top header line and one of the very long lines will be a dhclient line similar to this (use a text-searching command to find it in the output):

    UID        PID  PPID  C STIME TTY          TIME CMD
    root      4078     1  0 Nov11 ?        00:00:00 dhclient3 -e IF_METRIC=9999 -pf /var/run/dhclient.eth0.pid -lf /var/lib/dhcp/dhclient.eth0.leases -1 eth0

mine.txt

  1. Pick off the first line (the header line) of the psbsd.txt file and put the one line into file mine.txt. (1 11 73 mine.txt)
    • There is a command that can do this easily.
    • Make sure you pick the header line from the right file.
  2. Find all lines in psbsd.txt that contain your userid anywhere in the line and append those lines to the mine.txt file. (Some of the lines in this file may be very long.)

4.4 Part C – System Log FilesIndexup to index

You need to know System Log Files to do this task.

syslog.txt

  1. What is the actual name of the syslog program on the CLS? Search for and extract the one line from each file psbsd.txt and psunix.txt that contains this name and redirect the results (two lines, one from each file) into file syslog.txt. (The result will be 2 lines and 21 words.)

authlog.txt

  1. The system authentication log file is named auth.log in the system log directory. Generate an ls long listing showing inode number of this file using the full absolute pathname, and put the results of the ls (the output of ls) into file authlog.txt. (The output of the ls command should be one line, starting with a number, showing the permissions, owner, group, etc.)

    (Optional: You may find it convenient to set a shell variable to this absolute pathname, so that you can use the short variable name rather than the long absolute pathname in the rest of these exercises. Or, you could make a short symbolic link to this file.)

me.txt

  1. Use one command name (no arguments) to put a list (one line) of your numeric UID, your userid, your numeric GID, your group name, and your additional group names into the file me.txt. The result will be 1 (long) line, 3 words. See Permissions for the command to use to do this. Do not edit the output of the command.

myperms.txt

  1. Look at the contents of the me.txt and authlog.txt files. Note that your account is in a group that matches the group of the system auth.log file, giving you group permissions on this file. Using a text editor, put the matching group name, the symbolic group permissions (three characters), and the octal group permissions (one digit), onto three lines in file myperms.txt. (The result will be 3 lines, 3 words, 10 characters. Do you remember why a file containing seven alphanumeric characters on three lines is counted as a 10-character file on Linux? Review Line End Differences.)

authhead.txt

  1. The system auth.log file contains (November 2015) over 1,119,704 lines. Use a command to extract just the first line (one line) from the head of this file and redirect that one line into new file authhead.txt. (The result will be 1 line 14 words 110 chars.) The time and date at the start of this line is when this copy of the log file was started.

failedpass.txt

  1. If you count the number of lines in the system auth.log containing the exact text string Failed password, the count is more than 6,959 lines (November 2015). Of those lines (the lines containing that exact text string), extract just lines 100 through 110 (inclusive) and put only those lines into file failedpass.txt. The word count for the file will be 11 170 1291. Every line should contain the exact text string somewhere.

Run the Checking Program on the CLS to verify your work so far.

4.5 Part D – CrontabIndexup to index

You need to know Crontab and At Job Schedulers to do this task. Re-read the Notes on checking your work before you continue.

crontab.txt

  1. Create a personal crontab entry that uses a command with one pathname argument to update the access and modify times on file crontab.txt in your Base Directory (not in your HOME directory) every minute of every day. Use the shortest relative pathname to your crontab.txt file. Do not use an absolute pathname. Verify that the time of the file changes every minute.

    Hints: If it doesn’t work, read your Linux EMail for EMail messages from the Cron daemon showing possible errors. See Reading EMail for help. The single working crontab line should be seven words: five for the date/time, a command name, and a relative file name.

crontab1.txt

  1. List your personal crontab that you just created (one entry, with perhaps some comment lines) and redirect the output into file crontab1.txt in your Base Directory. This crontab entry should run every minute.

  2. Delete your personal crontab (the one that runs every minute).

crontab.txt

  1. Create a personal crontab entry that redirects the current date and time into the same file crontab.txt at The Crontab Time. Also use a relative pathname, not an absolute pathname.

crontab2.txt

  1. List your personal crontab (one entry, with perhaps some comment lines) and redirect the output into file crontab2.txt. Do not delete this personal crontab entry; leave it for marking. Make sure your displayed cron job is scheduled at The Crontab Time.

Run the Checking Program on the CLS to verify your work so far.

Re-read the Notes on checking your work if you are trying to check your work in the middle of a task instead of at the end of a task.

4.6 Part E – At Job ReminderIndexup to index

You need to know Crontab and At Job Schedulers to do this task.

  1. Create an at job that prints the list of users on the system, one per line, at The Crontab Time in the year 2016. You can use any of several commands to show the list of users one per line; see the List of Commands You Should Know.

    Hints: You need to get the order of the date correct on the at command line; see the Crontab and At Job Schedulers course notes or RTFM to find out how to specify both a time and a date for an at job. No pipes are needed for this at job; it’s just one command name.

  2. Display your list of at jobs to confirm the correct scheduling date and time in 2016.

  3. Create an at job that runs the command that prints the log messages in the kernel ring buffer. Schedule the job at The Crontab Time in the year 2016. (See the List of Commands You Should Know.)

    Hints: You need to get the order of the date correct on the at command line; see the Crontab and At Job Schedulers course notes or RTFM to find out how to specify both a time and a date for an at job. No pipes are needed for this at job; it’s just one command name that displays the in-memory kernel log buffer.

  4. Create an at job that echoes the five words of text CST8207 Final Exam 8am Saturday as a mail message to your Algonquin Live EMail account at 1 PM on the day before your final exam in this course. The EMail message sent at 1pm must have the exact message text above and the exact subject line (also five words, but different): CST8207 Final Exam 8am Tomorrow

    Hints: A pipe will be needed to connect the one-line output of echo with the standard input of the mail program. See Sending EMail for help in sending EMail with a subject line. Did you use the exact words given to you for the message and Subject texts?

  5. Check the queue of at jobs and make sure the scheduled times are correct for all three jobs.

  6. Delete just the (first) at job that shows the list of users.

atjob.txt

  1. Display both your queued at jobs and redirect the output into file atjob.txt. You will only have two jobs – two lines. If you have more than two lines, delete the other jobs.

  2. Leave these two jobs queued on the CLS for marking.

Run the Checking Program on the CLS to verify your work so far.

4.7 Part F – Shell ScriptIndexup to index

You need to know Shell Scripts to do this task.

partA.sh

  1. Write an executable Bourne shell script that does all the work done in Part A of this assignment. Create and use the output directory maze99 (in the current directory) instead of the original directory maze10. Do not change directories inside the script.

    1. The first three lines of the executable script file should be the three lines of the Standard Script Header.
    2. Make the file editable and executable for only the owner (you). Group and others can read the file but not write or execute it. Hint: Review Permissions.
    3. The script should recursively and silently remove any existing maze99 from the current directory at the start of the script. (You used a command to do this silent recursive removal in almost every new Lab section of every Worksheet.)
    4. Create a new directory named maze99 in the current directory.
    5. Run sufficient commands to create the symlink and four files from Part A, inside the new maze99 directory.
    6. Do not change directories inside your script file.
    7. Use the new maze99 directory for all output.

Hint: Having already done Part A, your bash shell history already contains all the command lines you need for your script. All you need to do is adapt each command line to use the maze99 directory instead of the original directory. My solution script contained three lines of Standard Script Header followed by ten command lines to create the directory, the symlink, and the four files from Part A.

Run the Checking Program on the CLS to verify your work so far.

4.8 Part G – Personal bin directoryIndexup to index

You need to know Shell Scripts, Search Path, Start-Up Files, and Symbolic Links to do this task.

bin

  1. Create your own personal bin directory in which to keep your own personal Linux commands. Use the exact name bin and create it in your HOME directory.

  2. Append your bin directory path to the end (tail) of your search PATH. Do this at login time in your shell start-up file so that it applies to all shells.

    Hints: Review Search Path, Start-Up Files, and Working with your search PATH in Assignment #07 HTML.

partA

  1. Create a relative symlink named partA in your bin directory. The symlink should point to (have a target of) your partA.sh script file.

    Hints: Review Symbolic Links. The relative symlink target from the bin directory to your script will contain four slashes.

  2. Make sure that you can now type your new command name partA at your shell to execute your partA.sh shell script.

Run the Checking Program on the CLS to verify your work so far.

4.9 When you are doneIndexup to index

That is all the tasks you need to do.

Read your CLS Linux EMail and remove any messages that may be waiting. See Reading EMail for help.

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.

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.

check

  1. There is a Checking Program named assignment10check 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/cst8207/15f/assignment10/assignment10check | less

    Create a symbolic link named check in your Base Directory that links to the Checking Program in the Source Directory, as you did in a previous assignment. Use the symlink to check your work:

    $ ./check | less
  2. 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 assignment10.txt in your Base Directory on the CLS, like this:

    $ ./check >assignment10.txt
    $ less assignment10.txt
    • Use standard output redirection with that exact assignment10.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 assignment10.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.
    • 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 assignment10.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 find the current assignment.
    3. Under Assignments, click on the underlined assignment10 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 assignment10.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 assignment10.txt file for upload. Do not attach any other file names.
    5. After you have attached the assignment10.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 assignment10.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.

    Use only Attach File on the Upload Assignment page. Do not enter any text into the Text Submission or Comments boxes on Blackboard; I do not read them. Use only the Attach File 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.

  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. 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.)

    You will also see the Review Submission History page any time you already have an assignment attempt uploaded and you click on the underlined assignment10 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!

6 Appendix I: The Crontab TimeIndexup to index

This section shows you how to calculate your personal Crontab Time for use in your cron and at jobs. You need to know your nine-digit student number and how to calculate the arithmetic modulus of a number.

  1. Take your 9-digit student number and remove the first three digits (probably 040), leaving six digits. Use these last six digits as follows:
  2. Take the first two of those six digits as a number, modulo 12, and then add 1, giving a number between 1 and 12. This is your month number.
  3. Take the next (middle) two of those six digits as a number, modulo 24, giving a number between 0 and 23. This is your hour number.
  4. Take the last two of those six digits as a number, modulo 60, giving a number between 0 and 59. This is your minute number.
  5. Take the same last two of those six digits as a number, modulo 28, and then add 1, giving a number between 1 and 28. This is your day-of-the-month number.

For example, if your nine-digit student number were 123456789:

  1. Remove the first three digits 123, leaving the last six digits 45 67 89
  2. Using the first two digits 45, the month would be (45 mod 12) + 1 = 10 (October)
  3. Using the next two digits 67, the hour would be 67 mod 24 = 19 (7pm)
  4. Using the last two digits 89, the minute would be 89 mod 60 = 29
  5. Using the last two digits 89, the day of the month would be (89 mod 28) + 1 = 6

The Crontab Time for student number 123456789 is October 6 at 19h29 (7:29pm).

Exercise: Show that The Crontab Time for student number 987654321 is

  1. last six digits = 65 43 21
  2. month = 6 (June)
  3. hour = 19 (7pm)
  4. minute = 21
  5. day of month = 22

which is June 22 at 19h21 (7:21pm).

Author: 
| Ian! D. Allen  -  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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