Users and Permissions
Introduction to Linux in HPC/Users and permissionsJump to navigation Jump to search
|Title:||Introduction to Linux in HPC|
|Topic Area:||HPC Platforms|
|1. Background and History|
|2. The Command Line|
|3. Linux Directory Structure|
|5. Text display and search|
|6. Users and permissions|
|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|
This tutorial covers the concept of users (and groups) in the multi-user operating system Linux. It will also explain the various permissions that a file or directory can have, how to determine and change them. As an example, it will show how to make a Python script executable by the user.
Who can change the permissions of a file?
How is the top-level admin (or superuser) called in Linux?
Which one of the following is not a file permission?
Who can change the owner or group of a file?
Which command can prevent other users not in your group from writing to input.dat?
Exercises in Terminal (slide 89)
1. List your home-directory, so that you can see users and permissions. Pick a file of your choice and explain 1) whom it belongs, 2) to which group it belongs and 3) what permissions all other users have for this file.
List your home-directory: ls -l $HOME or ll ~ The owner of a file can be found in the middle, right to the first small number. The group follows to the right of the owner. The permissions for other users are in the third rwx-grouping, i.e., left to the first small number. If these permission state e.g., "r--", then the file is readable from everyone else, but neither writeable nor executable.
2. Create an empty file, make it read-only, make it executable.
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.