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→INVESTIGATION 2: FILE PERMISSIONS
''Why Study IT Professionals that Use Data Representation?:''
* ''Network Specialists'': Building Large Networks via Sub-netting
* ''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
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''Decimal Numbers''
The '''decimal''' numbering system consists of digits consisting of numbers ranging from '''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.
''Binary Numbers''
The '''binary''' numbering system consists of digits containing the numbers ranging from '''0''' or to '''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).
''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 ranging from '''0 to 7''' and ranging from '''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.
'''NOTE:''' In this course, we cannot create groups or assign users to groups in the '''Matrix''' server.<br>Instead, you will learn how to those tasks when or if you take a Unix/Linux administration course.<br>On the other hand, you can change which '''user''', '''same group members''' or '''other group members'''<br>can access or NOT access a directory or regular file.<br><br>
[[Image:directory-permissions.png|thumb|right|350px|Permissions of a '''directory''' that contain subdirectories and regular files.]]
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 a that directory.
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 directories and regular files, >you would use the '''chmod''' command.
'''Perform the Following Steps:'''
# Let's convert the following ''8-bit'' binary number '''10111110''' to a '''decimal ''' number.<br><br><span style="color:blue;">'''NOTE:''' It is important to learn and '''memorize''' the '''correct techniques''' 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 on a sheet of paper.<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, retry the method and check to see what you did wrong.<br><br>
'''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>
# 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>
