Introduction to Linux in HPC/Users and permissions

HPC.NRW
Other HPC Courses
1.	Gprof Tutorial
2.	OpenMP in Small Bites
Introduction to Linux in HPC
1.	Background and History
2.	The Command Line
3.	Directory structure
4.	Files
5.	Text display and search
6.	Users and permissions
7.	Processes
8.	The vim text editor
9.	Shell scripting
10.	Environment variables
11.	System configuration
12.	SSH Connections
13.	SSH: Graphics and File Transfer
14.	Various tips

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

Exercises in Terminal (slide 89)

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

Answer:

     Create an empty file: touch file.txt.
     make it read-only: chmod a-w file.txt; chmod a-x file.txt; chmod a+r file.txt.
     make it executable: chmod a+x file.txt.

     Explanation: The touch command can be used to create an empty file. In this example it is file.txt.
          chmod a-w file.txt; chmod a-x file.txt; chmod a+r file.txt means to execute the three commands subsequently. 
          chmod a-w file.txt removes the write permission for all users. 
          chmod a-x file.txt removes the executable permission for all users.
          chmod a+r file.txt adds the read permission for all users.
          chmod a+x file.txt makes file.txt executable for all users.

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

Answer:

     Use a second console to look at it in top.
     Kill it.
     Hint:
        To kill the started process (e.g. sleep 10m): 
        1. Go to the terminal that started the process.
        2. Press Ctrl-C to kill it.

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

Hint:

     To bring a process to background:
        Press Ctrl-Z (pause the process).
        Type bg (bring it to background).
     To bring a process to foreground:
        Type fg (bring it to foreground).

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