Owner Permissions:
Group Permissions:
Public Permissions:
Linux file permissions are a foundational aspect of the operating system’s security model, defining who can access files and what they can do with them. Understanding and managing these permissions can sometimes be complex, which is where the Linux chmod calculator comes into play. This tool simplifies the process of calculating and applying file permissions, making it accessible to users of all skill levels.
Formula of Linux Chmod Calculator
Permissions in Linux are based on a simple numeric system that represents different access rights:
- Permissions: There are three main permissions: Read (4), Write (2), and Execute (1).
- User Classes: Permissions apply to three user classes: Owner (user who created the file), Group (users in the same group as the owner), and Others (all other users).
- Calculation: To determine the permissions for a file or directory, add the values of the desired permissions for each user class.
For example, if you want the owner to have read and write access (4 + 2 = 6) and everyone else to only read (4), the calculation would be:
- Owner: Read + Write (4 + 2) = 6
- Group: Read (4)
- Others: Read (4)
Final value: 644 (represents 6 for the owner, 4 for the group, and 4 for others)
General Terms Table
To further simplify the use of Linux permissions, here’s a table of common permission combinations and their meanings, eliminating the need for manual calculations:
| Permissions | Numeric Value | Description |
|---|---|---|
| rwxrwxrwx | 777 | Full permissions for everyone |
| rw-rw-r– | 664 | Owner and group have read and write, others read only |
| rw-r–r– | 644 | Owner has read and write, others have read only |
| rwxr-xr-x | 755 | Owner has full permissions, others have read and execute |
| r-xr-xr-x | 555 | Everyone can read and execute, but not write |
This table serves as a quick reference for the most commonly needed permission settings.
Example of Linux Chmod Calculator
Let’s consider a practical example. Suppose you have a file, document.txt, and you want to set its permissions so that the owner can read and write, the group can only read, and others have no access at all. According to our table, the numeric value for these permissions would be 640. To apply this, you would use the chmod command in Linux as follows:
chmod 640 document.txt
This command changes the permissions of document.txt to reflect the desired access rights, ensuring that the file is secure and accessible only to those who need it.
Most Common FAQs
“chmod 755” sets the permissions of a file or directory so that the owner can read, write, and execute it, while everyone else can only read and execute it. It’s a common setting for web pages and scripts that need to be publicly accessible but not editable by others.
To achieve this, you would use “chmod 644”, which sets the file permissions so that the owner can read and write the file, while the group and others can only read it.
Yes, the chmod calculator and the permission values apply to both files and directories. The primary difference is that execute permission on a directory allows users to enter it and access its contents.
