View source for Tutorial4: Data Representation / Numbering Conversion / File Permissions

{{Admon/caution|DO NOT USE THIS VERSION OF THE LAB. This page will no longer be updated.|'''New version here:''' https://seneca-ictoer.github.io/ULI101/A-Tutorials/tutorial4<br />'''Andrew's students please go here:''' http://wiki.littlesvr.ca/wiki/OPS145_Lab_4}}
=Data Representation / Numbering Conversion / File Permissions=

===Main Objectives of this Practice Tutorial===

:* Understand how digital computers store data (i.e. data representation)

:* Define '''decimal''', '''binary''', '''octal''' and '''hexadecimal''' numbers

:* Manually perform '''numbering conversions''' between the '''decimal''', '''binary''', '''octal''' and '''hexadecimal''' numbering systems<br>(<u>without</u> the use of a computer or calculator)

:* Explain the purpose of '''file permissions'''

:* Explain how permissions work differently for '''directories''' as opposed for '''regular files'''

:* Change file '''permissions''' with the '''chmod''' command (both ''symbolic'' and ''absolute'' methods)

:* Use the '''umask''' command to automatically assign permissions for '''newly created directories''' and '''regular files'''<br><br>

===Tutorial Reference Material===

{|width="100%" cellspacing="0" cellpadding="10"

|- valign="top"

|colspan="1" style="font-size:16px;font-weight:bold;border-bottom: thin solid black;border-spacing:0px;"|Course Notes<br>

|colspan="2" style="font-size:16px;font-weight:bold;border-bottom: thin solid black;border-spacing:0px;padding-left:15px;"|Numbering Conversion / File Permissions Reference<br>

|colspan="1" style="font-size:16px;font-weight:bold;border-bottom: thin solid black;border-spacing:0px;padding-left:15px;"|YouTube Videos<br>

|- valign="top" style="padding-left:15px;"

|colspan="1" width="22%"|'''Slides:'''<ul><li>Week 4 Lecture 1 Notes:<br> [https://wiki.cdot.senecacollege.ca/uli101/slides/ULI101-4.1.pdf PDF] | [https://wiki.cdot.senecacollege.ca/uli101/slides/ULI101-4.1.pptx PPTX]</li><li>Week 4 Lecture 2 Notes:<br> [https://wiki.cdot.senecacollege.ca/uli101/slides/ULI101-4.2.pdf PDF] | [https://wiki.cdot.senecacollege.ca/uli101/slides/ULI101-4.2.pptx PPTX] <br></li></ul>


|  style="padding-left:15px;" | '''Data Representation Definitions:'''
* [https://home.adelphi.edu/~siegfried/cs170/170l1.pdf Data Representation]<br>
* [https://en.wikipedia.org/wiki/Decimal Decimal Numbers]
* [https://en.wikipedia.org/wiki/Binary_number Binary Numbers]
* [https://en.wikipedia.org/wiki/Octal Octal Numbers]
* [https://en.wikipedia.org/wiki/Hexadecimal Hexadecimal Numbers]<br>
 
|  style="padding-left:15px;"|'''File Permission Concepts:'''
* [https://www.booleanworld.com/introduction-linux-file-permissions/ Introduction to File Permissions]<br><br>
'''File Permission Commands:'''<br>
* [https://ss64.com/bash/chmod.html chmod]<br>
* [https://ss64.com/bash/umask.html umask]<br><br>

|colspan="1" style="padding-left:15px;" width="30%"|'''Instructional Videos:'''
* [https://www.youtube.com/watch?v=4nGgqLIKU9U Numbering Conversions]
* [https://www.youtube.com/watch?v=SdgiYoOi0CY File Permissions]
|}

= KEY CONCEPTS =

===Data Representation===
[[Image:binary-number1.png|right|200px|https://creativecommons.org/licenses/by-sa/3.0/ cc]]
Digital computers are '''electronic devices''' that contain a series of '''circuits''' and voltage levels that can store / represent data.

'''Binary numbers''' can represent those series of circuits with voltage levels.<br>Those binary numbers are combined in a sequence to form a '''byte'''. Bytes are used to represent numbers or characters. 


IT professionals may need to perform '''numbering conversion''' to use with<br>''programming functions'' or ''OS commands'' to perform common operations on a computer system.

''IT Professionals that Use Data Representation:''

* ''Network Specialists'': Building Large Networks via Sub-netting
* ''Programmers:'' Sending information over networks, files
* ''Web Developers:'' Setting color codes for webpage background or text  
* ''Unix/Linux System Administrators:'' Setting ''permissions'' for files and directories  
<br>

===Numbering Conversion Methods===

====<u>Method 1: Binary to Decimal</u>====

[[Image:convert-bin-decimal.png|thumb|right|350px|Performing a '''binary''' to '''decimal''' conversion.]]
When converting '''binary''' numbers to '''decimal''' numbers, perform the following steps:<br><br>
# Write down the binary number.<br>
# Starting from the '''right-side''', draw '''L''''s below the binary number moving to the left<br>(refer to diagram on right).<br>
# Starting on the ''rightmost'' "'''L'''", multiply the value (placeholder) by '''2''' to the power of zero.<br>
# Continually repeat '''step #3''' moving leftwards, increasing the power of ''2'' by '''1'''<br>(refer to diagram on right).<br>
# Add up the results to obtain the decimal value equivalent.<br><br>
'''NOTE:''' To convert ''octal'' and ''hexadecimal'' numbers to '''decimal''', replace the number <span style="color:red;font-weight:bold">2</span> <br>(in red in the diagram to the right) with <span style="color:red;font-weight:bold">8</span> (for ''octal'') or <span style="color:red;font-weight:bold">16</span> (for ''hexadecimal'').
<br><br>

==== <u>Method 2: Decimal to Binary</u> ====

[[Image:decimal-to-bin.png|thumb|right|275px|Performing a '''decimal''' to '''binary''' conversion.]]
When converting '''decimal''' numbers to '''binary''' numbers, perform the following steps:<br><br>
# Write down the '''decimal number''' to be converted.
# On the ''right-side'', write the number '''1''' and moving '''leftwards''', keep <u>doubling</u> the numbers until that number is '''greater than''' the decimal number to be converted (refer to the diagram on the right).<br>
# Starting on the left-side of those doubled numbers, compare that number with the decimal number. If that number if less than or equal to the decimal number, then write a '''1''' below and subtract that number from the decimal number to get a remainder. If the number is greater than decimal number (or remainder), then write a '''0''' below.<br><br>
# Repeat '''step #3''' (moving rightwards and comparing the number with the decimal's remainder)<br><br>'''NOTE:''' If you are converting to '''8-bit''', '''32-bit''', etc., add '''leading zeros''' if necessary.<br><br>

==== <u>Method 3: Octal to Binary / Binary to Octal</u> ====

<table align="right"><tr><td>[[Image:bin-to-octal.png|thumb|right|230px|Performing an '''binary to octal''' numbering conversion.]]</td><td>[[Image:octal-to-bin.png|thumb|right|275px|Performing an '''octal to binary''' numbering conversion.]]</td></table>

''Binary to Octal''

# '''One octal number''' represents '''3 binary numbers''', so '''starting from right-side''', group binary digits into '''groups of 3'''<br>(add leading zeros if necessary).
# Write '''(4)(2)(1)''' under <u>each</u> '''group of 3 binary numbers'''.
# Multiply the value or "placeholder" (i.e. '''0''''s and '''1''''s) by the corresponding '''(4)(2)(1)''' for each group to obtain the octal number (refer to diagram of ''binary to octal'' conversion).<br><br>

''Octal to Binary''

# '''One octal number''' represents '''3 binary numbers''', so space-out<br>the octal numbers to make space for a binary number.
# Write '''(4)(2)(1)''' under <u>each</u> octal number.
# Write '''0''''s or '''1''''s for each group of binary numbers to add up to the<br>corresponding octal number (refer to diagram of ''octal to binary'' conversion).<br><br>

==== <u>Method 4: Hexadecimal to Binary / Binary to Hexadecimal</u> ====

<table align="right"><tr><td>[[Image:bin-to-hex.png|thumb|right|275px|Performing a '''binary to hexadecimal''' conversion.]]</td><td>[[Image:hex-to-bin.png|thumb|right|350px|Performing a '''hexadecimal to binary''' conversion.]]</td></tr></table>
''Binary to Hexadecimal''

# '''One hexadecimal number''' represents '''4 binary numbers''', so starting from right-side, group binary digits into '''groups of 4''' (add leading zeros if necessary).
# Write '''(8)(4)(2)(1)''' under <u>each</u> group of 4 binary numbers.
# Multiply the values or "placeholders" (i.e. '''0''''s and '''1''''s) by the corresponding (8)(4)(2)(1) for each group to obtain the octal number.
# Convert values from '''10''' to '''15''' to '''A''' to '''F'''<br>(refer to diagram of ''binary to hexadecimal'' conversion)<br><br>

''Hexadecimal to Binary''

# '''One hexadecimal number''' represents '''4 binary numbers''',<br>so space-out the hexadecimal numbers to make space for a binary number.
# Convert letters '''A''' to '''F''' to '''10''' to 15 (refer to diagram of ''binary to hexadecimal'' conversion)
# Write '''(8)(4)(2)(1)''' under <u>each</u> hexadecimal number.
# Write '''0''''s or '''1''''s for each group of binary numbers to add up to the corresponding<br>hexadecimal number (refer to diagram of ''hexadecimal to binary'' conversion).<br><br>

==== <u>Method 5: Octal to Hexadecimal / Hexadecimal to Octal</u> ====

[[Image:octal-hex.png|thumb|right|275px|For conversions between octal and hexadecimal numbers, use binary as a '''bridge'''.]]
To convert using the method, simply use binary as a "'''bridge'''".

''Example:''

To convert octal to hexadecimal, convert octal to binary, then convert binary to hexadecimal.

To convert hexadecimal to octal, convert hexadecimal to binary, then convert binary to octal.
<br><br>

===File Permissions===

[[Image:listing-file-directory.png|thumb|right|400px|Detailed directory listing showing permissions for a '''directory'''<br>and a '''regular file'''.]]
Since Unix / Linux operating file systems allow for '''multiple user accounts'''<br>it is essential to have a system to '''share''' or '''limit''' access to directories and files contained within the file system.


When '''directories''' and r'''egular files''' are created, they are assigned to an '''owner'''<br>(typically the username which is the creator).
To ''allow'' or ''limit'' '''access''' to those<br>files and directories, those files and directories are assigned to an<br>initial '''group''' referred to as a "'''primary group'''".
[[Image:directory-permissions.png|thumb|right|350px|Permissions of a '''directory''' that contain subdirectories and regular files.]]
Users that <u>own</u> those ''directories'' and ''regular files'' are referred to as '''users''', users that belong within the <u>same group</u> are referred to as '''same group members''', and those users that do <u>NOT</u> belong to a particular group are referred to as '''other group members'''.

'''NOTE:''' In this course, we CANNOT create groups or assign users to groups in the '''Matrix''' server. Instead, you may learn how to those tasks when or if you take a Unix/Linux administration course. On the other hand, you can change which '''user''', '''same group members''' or '''other group members''' can access or NOT access a directory or regular file.<br><br>
[[Image:file-permissions.png|thumb|right|350px|Permissions of a '''regular file''' contained within a directory.]]
File Permissions consist of  '''two-layers''':<br><br>'''First''', the permissions of a '''directory''' that contains regular files, and '''second''', permissions of the ''subdirectories and/or regular files'' within that directory.


Permissions for directories have a different meaning than permissions for '''regular files'''. Refer to the diagrams to the right to see the explanation of permissions and how they differ between a directory and a regular file. 

A symbol ''dash'' "'''-'''" indicates that the permission has '''NOT''' been granted.

The permissions of '''newly-created''' directories and regular files are automatically assigned<br>via a '''user mask''' (we will discuss this shortly). In order to change permissions for<br>directories and regular files, you would use the '''chmod''' command.


'''Changing File Permissions with "chmod" command:'''
[[Image:symbolic-chart.png|thumb|right|550px|Examples of adding, removing and setting permissions using the '''chmod''' command with the '''Symbolic''' method.]]


'''<span style="font-style:italic">Symbolic Method:</span>'''

The chmod can use '''symbols''' to ''add'', ''remove'', and ''set'' <span style="font-family:courier;font-weight:bold;">rwx</span> permissions for the '''user''',<br>'''same group members''', and/or o'''ther group members''' for a directory or reqular file.
<br><br><br><br>
'''<span style="font-style:italic">Octal (Absolute) Method:</span>'''
[[Image:octal-permissions.png|thumb|right|150px|Using octal numbers to represent setting file permissions.]]
You can also use '''octal numbers''' to '''set''' permissions. This method is a short-cut and may require less typing than using the ''symbolic'' method. You can only use this method to set file permissions (as opposed to ''add'' or ''remove'' permissions.

Since 1 octal digit represents 3 binary digits, one octal digit can represent the <span style="font-family:courier;font-weight:bold;">rwx</span> permission granted or NOT granted. The permissions '''rwx''' are be in the form of 3 binary digits (1 represents the permission granted and 0 represents the permission NOT granted).

'''NOTE:''' You can use the '''-R''' option to set permissions for directory, subdirectory and directory contents '''recursively'''.
<br><br><br>
'''Setting Permissions for Newly-Created Directories and Regular Files (umask):'''

<table align="right"><tr><td>[[Image:umask-directory.png|thumb|right|150px|Setting '''umask''' for newly-created '''directories'''.]]</td><td>[[Image:umask-file.png|thumb|right|150px|Setting '''umask''' for newly-created '''regular files''']]</td></tr></table>
The '''umask''' command is used to set the permissions of newly-created directories and regular files.


Issuing the '''umask''' command without arguments will display the current umask value.
Refer to the diagrams on the right-side to set the umask value for directories and regular files.
Setting the umask value (for example umask 022) only takes effect for the current shell session unless the umask command is contained in a start-up file<br>(e.g. '''.profile''', '''.bash_profile''', or '''.bashrc''').
<br><br>

=INVESTIGATION 1: NUMBERING CONVERSIONS=

<span style="color:red;">'''ATTENTION''': This online tutorial will be required to be completed by '''Friday in week 5 by midnight''' to obtain a grade of '''2%''' towards this course</span><br><br>

For this investigation, we will NOT be logged into our Matrix account, but it is recommended to have an '''MS Word document'''<br>open to manually perform numbering conversions.

<span style="color:blue;">'''NOTE:''' It is essential that you learn how to <u>manually</u> perform numbering conversions since you will NOT be permitted to perform quizzes, midterm, or your final exam with a computer or a calculator. Learning to quickly perform manual numbering conversions will make IT professional more productive such as setting permissions, designing computer networks, or selecting complex colors when developing webpages.</span>

[[Image:calc-check.png|thumb|right|200px|Only use a calculator to check your numbering conversion '''AFTER''' you have performed the operation '''manually'''. ]]
You will now get practice performing numbering conversions.


'''Perform the Following Steps:'''

# Let's convert the following binary number '''10111110''' to a '''<u>decimal number</u>'''.<br><br><span style="color:blue;">'''NOTE:''' It is important to learn and '''memorize''' the '''correct methods''' to perform the<br>proper numbering conversion method (i.e. view '''method 1''' above (drawing the L's).</span><br><br>
# Write the manual conversion either in your MS Word document.<br><br>
# Use a '''calculator''' to check your work. In MS Windows, you can set the calculator to Programming mode<br>by making the selection to '''binary''', enter the binary number '''10111110''' and view the decimal equivalent.<br><br>Did you get the correct answer? If not, <u>retry</u> the method and check to see what you did wrong.<br><br>
# Perform a manual conversion of the '''decimal number 55''' to a '''<u>binary number</u>'''.<br>What method (displayed above) will you use? Use a calculator to check your work.<br><br>
# Perform a manual conversion of the '''octal number 461''' to a '''<u>binary number</u>'''.<br>What method (displayed above) will you use? Use a calculator to check your work.<br><br>
# Perform a manual conversion of the '''binary number 11110001''' to a '''<u>hexadecimal number</u>'''.<br>What method (displayed above) will you use? Use a calculator to check your work.<br><br>
# Perform a manual conversion of the '''hexadecimal number ABC''' to a '''<u>binary number</u>'''.<br>What method (displayed above) will you use? Use a calculator to check your work.<br><br>
# Perform a manual conversion of the '''binary number 10101111''' to an '''<u>octal number</u>'''.<br>What method (displayed above) will you use? Use a calculator to check your work.<br><br>
# Perform a manual conversion of the same '''binary number 10101111''' to a '''<u>hexadecimal number</u>'''.<br>What method (displayed above) will you use? Use a calculator to check your work.<br><br>
# Perform a manual conversion of the '''octal number 5636''' to a '''<u>hexadecimal number</u>'''.<br>What method (displayed above) will you use? Use a calculator to check your work.<br><br>
# Perform a manual conversion of the '''hexadecimal number D68''' to an '''<u>octal number</u>'''.<br>What method (displayed above) will you use? Use a calculator to check your work.<br><br>
# When you have performed all of the numbering conversions above, then you can proceed to the next INVESTIGATION.<br><br>

=INVESTIGATION 2: FILE PERMISSIONS=

[[Image:file-permission-practice-1.png|right|250px|thumb|]]
In this investigation, you will get experience using the '''chmod''' command to '''change permissions'''<br>for <u> existing</u> files and the using '''umask''' command to automatically set permissions<br>for <u>newly-created</u> files.


'''Perform the Following Steps:'''

# '''Login''' to your matrix account and issue a command to '''confirm''' you are located in your '''home''' directory.<br><br>
# Issue a single Linux command to create the following directory structure displayed in the diagram to the right.<br><br>'''NOTE:''' You will now run a shell script to confirm that you properly created that directory structure<br>in your ''Matrix'' account.<br><br>
# Issue the following Linux command to run a checking script:<br><span style="color:blue;font-weight:bold;font-family:courier;">~uli101/week4-check-1</span><br><br>
# If you encounter errors, make corrections and '''re-run''' the checking script until you<br>receive a congratulations message, then you can proceed.<br><br>[[Image:file-permission-practice-2.png|right|450px|thumb|]]
# Issue Linux commands to create '''<u>empty</u> files''' for each of those newly created '''directories''' as shown in diagram to the right:<br><br>'''NOTE:''' You will now run another shell script to confirm that you properly created those empty files within those specified directories.<br><br>
# Issue the following Linux command to run a checking script:<br><span style="color:blue;font-weight:bold;font-family:courier;">~uli101/week4-check-2</span><br><br>
# If you encounter errors, make corrections and '''re-run''' the checking script until you<br>receive a congratulations message, then continue the remaining steps.<br><br>Let's get practice '''viewing permissions''', '''changing permissions''', and <u>automatically</u> '''setting permissions for newly created files'''.<br><br>
# Issue the following Linux commands:<br><span style="color:blue;font-weight:bold;font-family:courier;">ls -ld ~/documents ~/clients ~/vendors<br>ls -lR ~/documents ~/clients ~/vendors</span><br><br>'''NOTE:''' You should see permissions already set for those newly created directories and regular files.<br>What do these permissions mean for '''same group member''' and '''other group member''' access to those directory and regular files?<br><br>
# Let's limit access to the '''clients''' and '''vendors''' directories to only yourself and same group members.<br>Issue the following Linux command:<br><span style="color:blue;font-weight:bold;font-family:courier;">chmod 750 ~/clients ~/vendors</span><br><br>
# Issue the '''ls -ld''' and '''ls -lR''' commands (as you did in ''step #8'') to confirm that the permissions for those directories have been changed.<br><br>'''NOTE:''' The '''-R''' option for the '''chmod''' command can change the file permissions <u>recursively</u> within a directory structure.<br><br>
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">chmod 750 -R ~/documents</span><br><br>
# Issue the '''ls -ld''' command to confirm the permissions for the<br>'''~/documents''', '''~/document/memos''' , '''~/documents/reports''', and '''~/documents/contracts''' directories.<br><br>
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">ls -lR ~/documents</span><br>What do you noticed happened to the permissions for the regular files contained in those directories.<br>Did those regular file permissions change?<br><br>We will now change permissions for regular text file contained in subdirectories<br>of the '''documents''' directory to: <span style="font-weight:bold;font-family:courier;">r w - r - - - - -</span><br><br>
# Issue the following Linux commands: <br><span style="color:blue;font-weight:bold;font-family:courier;">chmod 640 ~/documents/memos/memo*.txt<br>chmod 640 ~/documents/reports/report*.txt<br>chmod 640 ~/documents/contracts/contract*.txt</span><br><br>
# Issue the <span style="font-weight:bold;font-family:courier;">ls -lR</span> command for the '''~/documents''' directory to confirm that those regular file permission have changed.<br><br>Let's run a checking script to make certain you correctly set permissions for those directories and files.<br><br>
# Issue the following: <span style="color:blue;font-weight:bold;font-family:courier;">~uli101/week4-check-3</span><br><br>
# If you encounter errors, make corrections and then re-run the checking script until you receive a congratulations message<br>and then continue with this tutorial.<br><br>Let's get some practice setting permissions to allow users to make editing changes to regular files.<br><br>
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">chmod ugo-w ~/documents/memos/memo*.txt</span><br><br>
# Use the <span style="font-weight:bold;font-family:courier;">ls</span> command to verify that those regular file's permissions have changed.<br><br>
# Using the nano or vi text editor, open the regular file '''~/documents/memos/memo1.txt'''<br>and type in some text and try to save your editing changes.<br>What happened?<br><br>
# To <u>'''abort'''</u> your editing session in '''vi''': type <span style="color:blue;font-weight:bold;font-family:courier;">:q!</span> and press '''ENTER'''.<br>To <u>'''abort'''</u> your editing changes in '''nano''': type <span style="color:blue;font-weight:bold;font-family:courier;">ctrl-x</span><br>type <span style="color:blue;font-weight:bold;font-family:courier;">n</span> and then press '''ENTER''' when prompted to save editing changes.<br><br>
# Issue the following Linux command to add write permissions for all files in the '''memos''' directory<br>for yourself (i.e. user): <span style="color:blue;font-weight:bold;font-family:courier;">chmod u+w ~/documents/memos/*</span><br><br>
# Repeat steps to edit the file '''~/documents/memos/memo1.txt''' (as you did in ''step #20'').<br>Were you able to edit the file and save your editing changes?<br><br>
# Issue a Linux command to view the <u>contents</u> of the '''~/documents/memos/memo1.txt'''<br>text file that you were able to edit.<br><br>
# Issue the following Linux command to view permissions for your '''home''' directory: <span style="color:blue;font-weight:bold;font-family:courier;">ls -ld ~</span><br><br>What does execute permissions mean for same group members and other group members<br>in terms of your '''home''' directory?<br><br>
# Issue the following Linux command to create a new subdirectory: <span style="color:blue;font-weight:bold;font-family:courier;">mkdir ~/shared</span><br><br>
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">ls -ld ~/shared</span><br><br>What are the permissions for this newly-created directory?<br>Can other users access the directory pathname '''<span style="font-family:courier">~youruserid/shared</span>''' ?<br><br>
# Issue the following Linux command (without an argument): <span style="color:blue;font-weight:bold;font-family:courier;">umask</span><br><br>'''NOTE:''' You should see a '''four-digit octal''' number. Drop the leading zero on the left to obtain the '''default umask value'''.<br><br>
# Perform a '''mathematical calculation''' by taking the octal number '''777''' and <u>subtracting</u><br>the default umask value you determined in the previous step. What is the result?<br><br>
# Convert that octal number result to a '''binary''' number. What does that represent as newly created directory permissions?<br>Does that correspond to the permissions for the newly created '''~/shared''' directory?<br><br>
# Repeat the calculation (like in step #28) but with a umask setting of '''077''' to see how this new umask setting would<br>affect permissions of newly-created directories.<br><br>
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">umask 077</span><br><br>
# Issue the following Linux command (without arguments): <span style="color:blue;font-weight:bold;font-family:courier;">umask</span><br><br>NOTE: You should notice the value '''0077'''. By dropping the leading zero to the left,<br> that would provide the default '''umask value of 077'''.<br><br>
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">mkdir ~/shared2</span><br><br>
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">ls -ld ~/shared2</span><br><br>Do the permissions for this newly created directory match the predicted permissions that you calculated in '''step #30'''?<br><br>
# Issue the following Linux command to create an empty regular file called '''myfile.txt''' in the '''~/shared2''' directory:<br> <span style="color:blue;font-weight:bold;font-family:courier;">touch ~/shared2/myfile.txt</span><br><br>
# Use the <span style="font-weight:bold;font-family:courier;">ls -l</span> command to view the permissions for this newly created regular file.<br><br>What do you notice about those permissions?<br><br>Let's run a checking script to make certain you correctly set permissions for those recently-created directories and files.<br><br>
# Issue the following: <span style="color:blue;font-weight:bold;font-family:courier;">~uli101/week4-check-4</span><br><br>If you encounter errors, make corrections and then re-run the checking script until you receive a congratulations message<br>and then continue with this tutorial.<br><br>
# Logout of your Matrix account, and then log-back into your Matrix account.<br><br>
# Issue the following Linux command (without arguments): <span style="color:blue;font-weight:bold;font-family:courier;">umask</span><br><br>What happened? Referring to your notes, what do you need to do to make that umask value persistent?<br><br><span style="color:red;">'''WARNING''':<br>You should be <u>extremely</u> aware of your permissions since you may perform '''marked work''' for <u>other</u> courses on your '''Matrix''' server.<br>You should NOT set permissions to share your work with '''same group''' or '''other group''' members (unless given '''specific permissions instructions from your course professors'''). If students can have access to your directories and project files, they could '''copy''' your work and thus make yourself and other student(s) that copied your work to be charged with '''academic dishonesty'''.</span><br><br>
: Complete the Review Questions sections to get additional practice.<br><br>

= LINUX PRACTICE QUESTIONS =

The purpose of this section is to obtain extra practice to help with your quizzes, your midterm, and your final exam.

Here is a link to the MS Word Document of ALL of the questions displayed below but with extra room to answer on the document to
simulate a quiz:

https://wiki.cdot.senecacollege.ca/uli101/files/uli101_week4_practice.docx

Your instructor may take-up these questions during class. It is up to the student to attend classes in order to obtain the answers to the following questions. Your instructor will NOT provide these answers in any other form (eg. e-mail, etc).


'''Review Questions:'''

# List the number of digits for the following numbering systems:<ul><li>'''Decimal'''</li><li>'''Binary'''</li><li>'''Octal'''</li><li>'''Hexadecimal'''</li></ul><br>
# Write a simple chart to show which values are represented for letter '''A - F''' for a hexadecimal number.
# How many '''binary''' digits does 1 octal digit represent? 
# How many '''binary''' digits does 1 hexadecimal digit represent?[[Image:number-conversion-chart.png|right|450px|thumb|]]
# Use '''manual numbering conversion''' to complete the table displayed to the right.


<ol><li value="6">Write the '''chmod''' command (using the ''symbolic'' method) to set “'''pass-through'''” permissions<br>(eg. <span style="font-family:courier;font-weight:bold;">r w x - - x - - x</span>) for your '''home''' directory using an '''absolute pathname'''.<br>Write a Linux command to verify that permissions where set.<br><br><br></li><li>Perform a binary to octal numbering conversion for the permissions: '''r w x - - x - - x'''<br>Write single Linux command to set “'''pass-through'''” permissions for your '''home''' directory,<br>using the '''absolute method''' (i.e. octal numbers).<br><br></li><li>Write a single Linux command to '''add read permissions''' for '''same group members''' for the '''~/tests''' directory.<br><br></li><li>Write a single Linux command to '''remove write permissions''' for '''same group members'''<br>and '''other group members''' for the '''~/projects''' directory. Use the ''symbolic'' method.<br><br></li><li>Write a single Linux command to set the permissions for the '''~/assignments''' directory<br> to the following using the '''absolute''' method (i.e. octal numbers): '''r w x r - x - - x''' <br>Show your work to perform a '''binary''' to '''octal''' conversion.<br>Write the command below using octal numbers and using a relative-to-home pathname.<br><br></li><li>Assume that you just issued the command:<br>
<span style="font-family:courier;font-weight:bold">chmod u=rwx,go=x ~/linux/content</span><br>What would be the new permissions for the “'''content'''” directory?<br><br></li><li>Assume that you just issued the commands:<br><span style="font-family:courier;font-weight:bold;">umask 077<br>mkdir mydir<br>touch mydir/myfile.txt<br></span><br>What would be the permissions for the newly created '''directory''' and '''regular file'''?<br>(show your work)
</li></ol>



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Author:  Murray Saul

License: LGPL version 3
Link:    https://www.gnu.org/licenses/lgpl.html

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[[Category:ULI101]]