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Tutorial4: Data Representation / Numbering Conversion / File Permissions

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When '''directories''' and r'''egular files''' are created, they are assigned to an '''owner''' (typically the username which is the creator).

To ''allow'' or ''limit'' '''access''' to those files and directories, those files and directories are assigned to an 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 own those ''directories'' and ''regular files'' are referred to as '''users''', users that belong within the same group are referred to as '''same group members''', and those users that do NOT belong to a particular group are referred to as '''other group members'''.

Users that own those ''directories'' and ''regular files'' are referred to as '''users''', users that belong within the same group are referred to as '''same group members''', and those users that do NOT 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. [[Image:~~directory~~file-permissions.png|thumb|right|350px|Permissions of a '''~~directory~~regular file''' ~~that contain subdirectories and regular files~~contained within a directory.]]

File Permissions consist of '''two-layers''': '''First''', the permissions of a '''directory''' that contains regular files, and '''second''', permissions of the ''subdirectories and/or regular files'' within 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 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.

'''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.]]

'''Symbolic Method:'''

The chmod can use '''symbols''' to ''add'', ''remove'', and ''set'' rwx permissions for the '''user''', '''same group members''', and/or o'''ther group members''' for a directory or reqular file.

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

'''Octal (Absolute) Method:'''

[[Image:octal-permissions.png|thumb|right|150px|Using octal numbers to represent setting file permissions.]]

Since 1 octal digit represents 3 binary digits, one octal digit can represent the rwx 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).

~~[[Image:absolute-chart.png|thumb|left|550px|Examples of adding, removing and setting permissions using the '''chmod''' command with the '''Absolute / Octal''' method.]]~~

~~ ~~

'''NOTE:''' You can use the '''-R''' option to set permissions for directory, subdirectory and directory contents '''recursively'''.

'''Setting Permissions for Newly-Created Directories and Regular Files (umask):'''

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.

=INVESTIGATION 1: NUMBERING CONVERSIONS=

'''ATTENTION''': Depending on your ULI101 instructor, you may be required to complete this tutorial for '''marks''' in this course. Please refer to your instructor's course notes and lecture notes regarding evaluation for this course. The due date for successfully completing this tutorial (i.e. '''tutorial 4''') is by '''Friday by midnight''' next week (i.e. '''Week 5'''). If your instructor has NOT assigned marks for completing this tutorial, you can perform it for '''practice'''.

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

[[Image:file-permission-practice-1.png|right|250px|thumb|]]

In this ~~section~~investigation, you will get experience using the '''chmod''' command to '''change permissions''' for existing files and the using '''umask''' command to automatically set permissions for newly-created files.

# '''Login''' to your matrix account and issue a command to '''confirm''' you are located in your '''home''' directory.

# Issue a single Linux command to create the following directory structure displayed in the diagram to the right. '''NOTE:''' You will now run a shell script to confirm that you properly created that directory structure in your ''Matrix'' account.

# Issue the following Linux command to run a checking script: ~~bash /home/murray.saul/scripts~~~uli101/week4-check-1

# If you encounter errors, make corrections and '''re-run''' the checking script until you receive a congratulations message, then you can proceed. [[Image:file-permission-practice-2.png|right|450px|thumb|]]

# Issue Linux commands to create '''empty files''' for each of those newly created '''directories''' as shown in diagram to the right: '''NOTE:''' You will now run another shell script to confirm that you properly created those empty files within those specified directories.

# Issue the following Linux command to run a checking script: ~~bash /home/murray.saul/scripts~~~uli101/week4-check-2

# If you encounter errors, make corrections and '''re-run''' the checking script until you receive a congratulations message, then continue the remaining steps. Let's get practice '''viewing permissions''', '''changing permissions''', and automatically '''setting permissions for newly created files'''.

# Issue the following Linux commands: ls -ld ~/documents ~/clients ~/vendors ls -lR ~/documents ~/clients ~/vendors '''NOTE:''' You should see permissions already set for those newly created directories and regular files. What do these permissions mean for '''same group member''' and '''other group member''' access to those directory and regular files?

# Issue the following Linux commands: chmod 640 ~/documents/memos/memo*.txt chmod 640 ~/documents/reports/report*.txt chmod 640 ~/documents/contracts/contract*.txt

# Issue the ls -lR command for the '''~/documents''' directory to confirm that those regular file permission have changed. Let's run a checking script to make certain you correctly set permissions for those directories and files.

# Issue the following: ~~bash /home/murray.saul/scripts~~~uli101/week4-check-3

# If you encounter errors, make corrections and then re-run the checking script until you receive a congratulations message and then continue with this tutorial. Let's get some practice setting permissions to allow users to make editing changes to regular files.

# Issue the following Linux command: chmod ugo-w ~/documents/memos/memo*.txt

# To '''abort''' your editing session in '''vi''': type :q! and press '''ENTER'''. To '''abort''' your editing changes in '''nano''': type ctrl-x type n and then press '''ENTER''' when prompted to save editing changes.

# Issue the following Linux command to add write permissions for all files in the '''memos''' directory for yourself (i.e. user): chmod u+w ~/documents/memos/*

# Repeat steps to edit the file '''~/documents/memos/memo1.txt''' (as you did in ''step #20''). Were you able to edit the file and save your editing changes? # Issue a Linux command to view the contents of the '''~/documents/memos/memo1.txt''' text file that you were able to edit.

# Issue the following Linux command to view permissions for your '''home''' directory: ls -ld ~ What does execute permissions mean for same group members and other group members in terms of your '''home''' directory?

# Issue the following Linux command to create a new subdirectory: mkdir ~/shared

# Issue the following Linux command: ls -ld ~/shared2 Do the permissions for this newly created directory match the predicted permissions that you calculated in '''step #30'''?

# Issue the following Linux command to create an empty regular file called '''myfile.txt''' in the '''~/shared2''' directory: touch ~/shared2/myfile.txt

# Use the ls -l command to view the permissions for this newly created regular file. What do you notice about those permissions? Let's run a checking script to make certain you correctly set permissions for those recently-created directories and files. # Issue the following: ~uli101/week4-check-4 If you encounter errors, make corrections and then re-run the checking script until you receive a congratulations message and then continue with this tutorial.

# Logout of your Matrix account, and then log-back into your Matrix account.

# Issue the following Linux command (without arguments): umask What happened? Referring to your notes, what do you need to do to make that umask value persistent? '''WARNING''': You should be extremely aware of your permissions since you may perform '''assignments''' for other courses on your '''Matrix''' server. 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''' involving '''assignment submission'''). If students can have access to your directories and assignment files, they could '''copy''' your work and thus make yourself and other student(s) that copied your assignment work to be charged with '''academic dishonesty'''. # : After you complete the Review Questions sections to get additional practice, then work on your '''online assignment 2''' and complete the sections '''1''' and '''2''' labelled: '''Practice Using The vi Text Editor''' and '''Permissions''' respectively.

= LINUX PRACTICE QUESTIONS =

Msaul

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Tutorial4: Data Representation / Numbering Conversion / File Permissions

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