Difference between revisions of "Introduction to Linux in HPC/Users and permissions"

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Introduction to Linux in HPC/Users and permissions
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</quiz>
 
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{{Warning|mode=info|text= '''no tips in this section'''}}
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{{Warning|mode=warn|text= '''no warnings in this section'''}}
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=== Exercises in Terminal (slide 89) === <!--T:5--> 
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1. Create an empty file, make it read-only, make it executable.
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  {| role="presentation" class="wikitable mw-collapsible mw-collapsed"
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    | <strong>Answer:</strong>
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    |-
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    |
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      Create an empty file: touch file.txt.
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      make it read-only: chmod a-w file.txt; chmod a-x file.txt; chmod a+r file.txt.
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      make it executable: chmod a+x file.txt.
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      Explanation: The touch command can be used to create an empty file. In this example it is file.txt.
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          chmod a-w file.txt; chmod a-x file.txt; chmod a+r file.txt means to execute the three commands subsequently.
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          chmod a-w file.txt removes the write permission for all users.
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          chmod a-x file.txt removes the executable permission for all users.
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          chmod a+r file.txt adds the read permission for all users.
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          chmod a+x file.txt makes file.txt executable for all users.
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    |}
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2. Start a process (e.g. sleep 10m)
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  {| role="presentation" class="wikitable mw-collapsible mw-collapsed"
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    | <strong>Answer:</strong>
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    |-
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    |
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      Use a second console to look at it in top.
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      Kill it.
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      Hint:
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        To kill the started process (e.g. sleep 10m):
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        1. Go to the terminal that started the process.
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        2. Press Ctrl-C to kill it.
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    |}
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3. Start a process, bring it into background/foreground.
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  {| role="presentation" class="wikitable mw-collapsible mw-collapsed"
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    | <strong>Hint:</strong>
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    |-
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    |
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      To bring a process to background:
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        Press Ctrl-Z (pause the process).
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        Type bg (bring it to background).
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      To bring a process to foreground:
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        Type fg (bring it to foreground).
 +
    |}

Revision as of 18:25, 1 October 2020

Video

Linux Introduction Slides 67 - 88 (22 pages)


Slide Layout

   page 1: 
       Linux is a multi-user system.
       A user is logged in with an account and certain permissions.
   page 2: 
       Each file and directory has certain permissions.
       root has top permissions.
       Normal users may belong to multiple groups.
   page 3: 
       Read permission
       Write permission
       Execute permission for i) file and ii) directory
   page 4 - 12: 
       Example of ls -l (animation)
   page 13 - 16: 
       Permissions for user, group and other (animation)
   page 17: 
       chown to modify owner/group
       chmod to modify permission
   page 18: 
       Process is an instance of a program
       top and pstree
       Each process has permissions of that user.
       Each process has a unique ID (PID).
   page 19: 
       Start command in background command &.
       Ctrl-Z and bg
       fg brings a job to foreground.
   page 20 - 21: 
       Example of top (animation)
   page 22: 
       Single-letter commands for top


Quiz

Which command can prevent other users not in your group from writing to input.dat?

chmod u-w input.dat
chmod o-w input.dat
chmod g-w input.dat


Info:  no tips in this section


Warning:  no warnings in this section


Exercises in Terminal (slide 89)

1. Create an empty file, make it read-only, make it executable.

2. Start a process (e.g. sleep 10m)

3. Start a process, bring it into background/foreground.
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