Understanding Linux File Permissions and Numeric Representation
Introduction to Linux File Permissions
Linux file permissions regulate access to files and directories, ensuring security and control over who can read, write, or execute them. Understanding both symbolic and numeric representation of permissions is essential for managing files effectively.
Symbolic Representation
In symbolic representation, permissions are represented by three characters: r (read), w (write), and x (execute).
rwxindicates read, write, and execute permissions.rw-indicates read and write permissions, but no execute permission.r--indicates read-only permission.
It's important to note that a directory requires the execute x permission to be able to access it.
Numeric Representation
Numeric representation simplifies permissions by assigning a numeric value to each permission:
| Permission | Numeric Value |
|---|---|
| Read (r) | 4 |
| Write (w) | 2 |
| Execute (x) | 1 |
To calculate the numeric representation for a set of permissions, add up the values for each permission type. For example:
- Read and write:
4 (read)+2 (write)=6 - Read, write, and execute:
4 (read)+2 (write)+1 (execute)=7
User, Group, and Others Permissions
Each file or directory has three sets of permission numbers corresponding to user, group, and others.
For example setting the following would equate to a 775 or rwxr-xr-x for the files full permissions.
- User Permissions:
7represents read, write, and execute (rwx). - Group Permissions:
5represents read and execute (r-x). - Other Permissions:
5represents read and execute (r-x).
Command Examples
Let's see some examples:
This command sets myfile.txt to 7 (user) 5 (group) 5 (others) or rwxr-xr-x:
1user@machine:~$ chmod 755 myfile.txt
This command sets myfile.txt to 6 (user) 4 (group) 4 (others) or rw-r--r--:
1user@machine:~$ chmod 644 myfile.txt
Conclusion
Understanding both symbolic and numeric representations of Linux file permissions is crucial for effective file management. By mastering these concepts, users can accurately set permissions to control access to files and directories, ensuring security and privacy on Linux systems.