- Click the checkboxes in the permission grid to assign Read (r), Write (w), and Execute (x) rights for the Owner, Group, and Public classes.
- Alternatively, type an octal number (e.g., 755) directly into the Octal input field to automatically update the visual grid.
- You can also enter a symbolic notation (e.g., rwxr-xr-x) into the Symbolic field to sync the permissions.
- Copy the resulting numeric value or symbolic string to use alongside the chmod command in your Unix or Linux terminal.
CHMOD Calculator
CHMOD Calculator tool on AzWebTools.
Result
Fill inputs and click run.
How to Use This Tool
Learn More About CHMOD Calculator
Understanding Linux File Permissions
In Unix-like operating systems, chmod (change mode) is the command used to change the access permissions of file system objects (files and directories). Permissions are divided into three distinct user classes:
- Owner (User): The specific user account that owns the file.
- Group: Other users who are members of the file's assigned user group.
- Public (Others): Everyone else with access to the system.
Read, Write, and Execute
Each class can be assigned three specific permissions, each represented by a number:
- Read (r) - 4: Permission to read the file's contents or list a directory's contents.
- Write (w) - 2: Permission to modify the file or add/remove files within a directory.
- Execute (x) - 1: Permission to run the file as a program or traverse a directory to access its contents.
Octal Representation
The octal permission format is a three-digit number where each digit represents the sum of the permissions for the Owner, Group, and Public respectively. For example, the common permission 755 is calculated as follows:
- Owner (7): 4 (read) + 2 (write) + 1 (execute)
- Group (5): 4 (read) + 1 (execute)
- Public (5): 4 (read) + 1 (execute)
The Origin of CHMOD
The chmod command first appeared in AT&T UNIX Version 1 in 1971. It was introduced to allow administrators and users to assign file access rights using a succinct numeric or symbolic notation. This foundational security model remains a core component of modern Linux, macOS, and Unix-like operating systems today.
The chmod command has been the standard utility for managing Unix file permissions since its introduction in 1971.
- Introduced
- 1971
- Operating System
- Unix Version 1
- Purpose
- File access control
Examples
Standard Executable (755)
Runtime-verified example for chmod-calculator
Input
{"octal":"755","symbolic":"rwxr-xr-x"}Output
{
"octal": "755",
"symbolic": "rwxr-xr-x"
}Standard File (644)
Runtime-verified example for chmod-calculator
Input
{"octal":"644","symbolic":"rw-r--r--"}Output
{
"octal": "644",
"symbolic": "rw-r--r--"
}Strict Private (600)
Runtime-verified example for chmod-calculator
Input
{"octal":"600","symbolic":"rw-------"}Output
{
"octal": "600",
"symbolic": "rw-------"
}Full Access (777)
Runtime-verified example for chmod-calculator
Input
{"octal":"777","symbolic":"rwxrwxrwx"}Output
{
"octal": "777",
"symbolic": "rwxrwxrwx"
}Use Cases
- Securing web server files (e.g., setting 644 for standard files, 755 for directories).
- Configuring SSH key permissions to meet strict security requirements (e.g., 400 or 600 for private keys).
- Granting script execution rights securely for deployment automation (e.g., +x or 700).
- Performing general Linux system administration, security auditing, and access troubleshooting.