:* Identify Explain the purpose of '''which numbering system conversion method to usefile permissions''' when required to perform a numbering conversion

:* Explain the purpose of file permissions :* Explain how permissions work differently for '''directories ''' as opposed to for '''regular files.'''

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

|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://ictwiki.cdot.senecacollege.ca/~murrayuli101/slides/ULI101-4.1.pptx PPTX]</li><li>Week 4 Lecture 2 Notes:<br> [https://wiki.cdot.senecacollege.saulca/uli101/slides/ULI101-Week44.2.pdf PDF] | [https://ictwiki.cdot.senecacollege.ca/~murray.saululi101/uli101slides/ULI101-Week44.2.pptx PPTX]<br></li></ul>

| style="padding-left:15px;" | '''Data Representation Definitions:'''

| style="padding-left:15px;"|'''File Permission Concepts:'''

'''File Permission Commands:'''<br>* [httphttps://man7ss64.org/linux/man-pagescom/man1bash/chmod.1.html chmod]<br>* [httphttps://man7ss64.orgcom/linux/man-pages/man1bash/umask.1p.html umask]<br><br>

|colspan="1" style="padding-left:15px;" width="30%"|'''Instructional Videos:'''* [https://www.youtube.com/watch?v=L2zsmYaI5ww 4nGgqLIKU9U Numbering Conversions]

===Why Study 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.

<table align="right"><tr valign="top"><td>[[Image:binary-number1.png|thumb|right|220px|A series of '''binary Binary numbers''' form a '''byte''' to can represent '''numbers'''those series of circuits with voltage levels.<br>(Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])]]</td><td>[[Image:Those binary-number-2.png|thumb|right|200px|'''Bytes''' can be used numbers are combined in a sequence to also represent form a '''charactersbyte'''. It is job of a program to know if bytes Bytes are used to represent numbers or charactersrepresent numbers or characters. Learning to convert numbering systems<br>(like '''Hexadecimal to Binary''') can be used to know how a character is represented in '''binary'''. <br>(Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])]]</td></tr></table>''Data ... is any sequence of one or more symbols given meaning by specific act(s) of interpretation. Digital data is data that is represented using the binary number system of ones (1) and zeros (0)...''<br>Reference: https://en.wikipedia.org/wiki/Data_(computing)<br><br>

''Examples of Understanding IT Professionals that Use Data Representation:''

* ''C ProgrammingProgrammers:'' Sending information over networks, files* ''Web DevelopmentDevelopers:'' Setting color codes for webpage background or text * ''Allowing or Limiting Unix / Linux File AccessSystem Administrators:'' Setting ''permissions'' for files and directories <br><br> ===Decimal / Binary / Octal / Hexadecimal Numbering Systems=== [[Image:decimal-number-3.png|thumb|right|300px|The '''decimal''' numbering system .<br>(Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc] - modified by author).]]''Decimal Numbers'' The '''decimal''' numbering system consists of digits consisting of numbers '''0''' to '''9'''. The numbering system is based on '''sums of the power of 10''' which provides a framework for mathematic calculations. The fact that '''humans''' started counting on their fingers and thumbs most likely lead to the development of this numbering system. Referring to the diagram on the right, the value of each decimal digit consists of the '''value''' (''placeholder'') multiplied by the corresponding power of 10. For example, '''units''' are '''10⁰''', '''tens''' are '''10¹''', '''hundred''' are '''10²''' which move in a '''right-to-left''' direction.<br><br>[[Image:binary-number-3.png|thumb|right|200px|The '''binary''' numbering system.<br>(Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])]]''Binary Numbers'' The '''binary''' numbering system consists of digits containing the numbers '''0''' or '''1'''. The numbering system is based on '''sums of the power of 2'''. Digital computers have circuits which representing data in terms of voltage levels. Multiple circuits are used to represent data (in the form of ''binary'' numbers). Referring to the diagram on the right, the value of each decimal digit consists of the value (placeholder) multiplied by the corresponding power of 2. For example, '''2⁰''' , '''2¹''', '''2²''', etc. which move in a '''right-to-left''' direction.<br><br>''Octal / Hexadecimal Numbers''<table align="right"><tr valign="top"><td>[[Image:octal-number-2.png|thumb|right|200px|The '''octal''' numbering system.<br>(Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])]]</td><td>[[Image:hex-number-2.png|thumb|right|420px|The '''hexadecimal''' numbering system.<br>(Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])]]</td></tr></table>The '''octal''' and '''hexadecimal''' numbering systems consist of digits containing numbers '''0 to 7''' and '''0 to F''' respectively. For ''hexadecimal'' numbers, values for '''10 to 15''' are represented by the characters '''A to F''' respectively. The '''octal''' and '''hexadecimal''' numbering system are based on sums of the power of '''8''' and '''16''' respectively. Since '''1 octal digit represents 3 binary digits''' and '''1 hexadecimal digit represents 4 binary digits''', octal and hexadecimal numbers are used as '''short-cuts''' to represent binary number.<br><br>

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

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

# Starting on the rightleft-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 leftwards 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> ====

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

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

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'''.

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

Permissions for Directory files have a different meaning than permissions for regular files. Refer to A symbol ''dash'' "'''-'''" indicates that the diagrams to the right to see the explanation of permissions and how they differ between a directory and a regular filepermission has '''NOT''' been granted.

A symbol ''dash'' "'''-'''" indicates that the permission has '''NOT''' been granted.[[Image:file-permissions.png|thumb|right|350px|Permissions of a '''regular file''' contained within a directory.]]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.

The chmod can use '''symbols''' to '''add''', '''remove''', and '''set''' rwx permissions for user,<br>same group members, other group members or ALL categories: <table cellpadding="5" width="70%"><tr><th style="border-bottom: 1px solid black;text-align:left;">Command</th><th style="border-bottom: 1px solid black;text-align:left;">Description</th></tr><tr valign="top"><td width="40%"><span style="font-family:courier;font-weight:bold;">chmod ugo+x script.bashrwx</span></td><td>Add execute permissions to for the file '''script.bashuser''' so it can be run.</tr><tr valign="top"><td><span style="font-family:courier;font-weight:bold">chmod u=rwx,go=x ~</spanbr></td><td>Set "'''pass-thrusame group members'''" permissions of your , and/or o'''home''' directory for same group members and other group members to navigate to other subdirectories (that may have access / view permissions).</tr><tr valign="top"><td><span style="font-family:courier;font-weight:bold;">chmod go-w ~/shared</span></td><td>Remove write permissions for same ther group members and other group members for the directory '''~/shared'''</td></tr><tr valign="top"><td><span style="font-family:courier;font-weight:bold;">chmod for a=rx mydirectory or reqular file.</spanbr></tdbr><td>Set read and execute permissions for the directory '''myfile.txt'''</tdbr></tr></tablebr>  

[[Image:octal-permissions.png|thumb|right|150px|using Using octal numbers to represent setting file permissions.]]You can also use '''octal numbers''' to represent '''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 rwx permission granted or NOT granted. The permissions rwz would be in the form of 3 binary digits (1 represents the permission granted and 0 represents the permission NOT granted. '''NOTE:''' You can only use this method to '''set''' file permissions (as opposed to ''add'' or ''remove'' permissions). <table cellpadding="5" width="70%"><tr><th style="border-bottom: 1px solid black;text-align:left;">Command</th><th style="border-bottom: 1px solid black;text-align:left;">Description</th></tr><tr valign="top"><td width="40%"><span style="font-family:courier;font-weight:bold;">chmod 500 script.bashrwx</span></td><td>Set read and execute permission granted or NOT granted. The permissions for only the '''userrwx''' for are be in the file '''script.bash''' so it can be run.</tr><tr valign="top"><td><span style="font-family:courier;font-weight:bold">chmod 711 ~</span></td><td>Set "'''pass-thru'''" permissions form of your '''home''' directory for same group members and other group members to navigate to other subdirectories 3 binary digits (that may have access / view permissions).</tr><tr valign="top"><td><span style="font-family:courier;font-weight:bold;">chmod 750 ~/shared</span></td><td>Set full permissions for user, read and access permissions for some group members and no permissions for other group members for 1 represents the directory '''~/shared'''</td></tr><tr valign="top"><td><span style="font-family:courier;font-weight:bold;">chmod 555 myfile.txt</span></td><td>Set read permission granted and execute permissions for 0 represents the directory '''myfilepermission NOT granted).txt'''</td></tr></table>

  <table align="right"br><trbr><td>[[Image:umask-directory.png|thumb|right|200px|Setting '''umask''' for newly-created '''directories'''.]]</td><td>[[Image:umask-file.png|thumb|right|200px|Setting '''umask''' for newly-created '''regular files''']]</td></tr></tablebr>

For this investigation, we will NOT be logged into our Matrix account, but it is recommended to have sheets of paper ready 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 may make IT professional more productive such as setting permissions, designing computer networks, or selecting complex colors when developing webpages.</span>

# Let's convert the following ''8-bit'' 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 techniquesmethods''' to perform the<br>proper numbering conversion method (i.e. view the '''method 1''' above (drawing the L's).</span><br><br># Write the manual conversion on a sheet of papereither 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 an a '''8-bit <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 an a '''8-bit <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 '''8-bit 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 an a '''8-bit <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>

In this sectioninvestigation, you will get experience using the '''chmod''' and command to '''umaskchange permissions''' commands<br>to for <u> existing</u> files and the using '''set permissionsumask''' command to automatically set permissions<br>for '''directories''' and '''<u>newly-created</u> files'''.

# '''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># Make certain that your current directory is '''your home directory'''.<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;">bash /home/murray.saul/scripts~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 show 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;">bash /home/murray.saul/scripts~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 understanding '''viewing permissions''', '''changing permissions''', and <u>automatically</u> '''setting your Linux account to automatically set permissions for newly created directories and regular 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''' command 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>

# Again, use 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 want to will now change those permissions for regular text file permissions contained in subdirectories<br>of the '''documents''' directory to the following settings: <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 740 640 ~/documents/memos/memo*.txt<br>chmod 740 640 ~/documents/reports/report*.txt<br>chmod 740 640 ~/dcoumentsdocuments/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>

# 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 to press '''ENTER'''.<br>To <u>'''abort '''</u> your editing changes in '''nano, just ''': 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 previous file '''~/documents/memos/memo1.txt''' (as you did in ''step #1920'').<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. What happened?<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: <span style="color:blue;font-weight:bold;font-family:courier;">ls -l 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>

# 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.<br>What is the result?<br><br>

# Repeat '''steps #27''' and '''the calculation (like in step #28''' to see how ) 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;">ls -ld ~/shared2</span><br><br>Do the permissions for this newly created directory match the predicted permissions that you calculated in '''step #2930'''?<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>

# 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># After <span style="color:red;">'''WARNING''':<br>You should be <u>extremely</u> aware of your permissions since you complete the Review Questions sections to get additional practice, then may perform '''marked work ''' for <u>other</u> courses on your '''online assignment 2Matrix'''server.<br>and complete the sections You should NOT set permissions to share your work with '''same group''' or '''1other group''' and members (unless given '''2specific permissions instructions from your course professors''' labelled: ). If students can have access to your directories and project files, they could '''Practice Using The vi Text Editorcopy''' your work and thus make yourself and other student(s) that copied your work to be charged with '''Permissionsacademic dishonesty''' respectively.</span><br><br>: Complete the Review Questions sections to get additional practice.<br><br>

The purpose of this section is to obtain extra practice to help with your assignment #1, quizzes, your midterm, and your final ezamexam.

https://ictwiki.cdot.senecacollege.ca/~murray.saululi101/uli101files/uli101_week4_practice.docx

# How many '''binary''' digits does 1 hexadecimal digit represent?[[Image:number-conversion-chart.png|right|450px|thumb|]]