Chmod Calculator

- May 10, 2025
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Calculate and understand Unix/Linux file permissions with this chmod calculator. You can set permissions using symbolic notation, octal (numeric) values, or the interactive permission selector.

Permission Calculator

Read
Write
Execute
Owner
Group
Others
Special Permissions

Common Presets

Permission Results

chmod Command
chmod 755 filename
Octal Value
755
Symbolic Notation
u=rwx,g=rx,o=rx
Binary Representation
111 101 101

Permission Visualisation

-
rwx
r-x
r-x

Explanation

Example Usage

chmod 755 file.txt
chmod -R 755 directory/

About Unix File Permissions

Unix-like operating systems use a file permission model that controls how files and directories can be accessed. Each file has three sets of permissions (for the owner, group, and others) with three permission types (read, write, and execute).

Permission Types
  • Read (r): Permission to read the file contents or list directory contents.
  • Write (w): Permission to modify the file or create/delete files in a directory.
  • Execute (x): Permission to run the file as a programme or access files within a directory.
Special Permissions
  • SUID (Set User ID): When set on an executable file, it runs with the permissions of the file owner.
  • SGID (Set Group ID): When set on an executable file, it runs with the permissions of the file group. When set on a directory, new files inherit the directory's group.
  • Sticky Bit: When set on a directory, files can only be deleted by the file owner, directory owner, or root.
Notation Methods
  • Symbolic Notation: Uses letters and symbols (e.g., u=rwx,g=rx,o=r)
  • Octal/Numeric Notation: Uses 3 or 4 digits (e.g., 755 or 4755)
  • Binary Representation: Each permission represents a bit (e.g., 111 101 101)
Common Permission Sets
  • 755 (rwxr-xr-x): Owner can read, write, and execute. Group and others can read and execute. Common for programmes and directories.
  • 644 (rw-r--r--): Owner can read and write. Group and others can only read. Common for regular files.
  • 777 (rwxrwxrwx): Everyone can read, write, and execute. Generally not recommended for security reasons.
  • 700 (rwx------): Only the owner can read, write, and execute. No permissions for group or others.

Understanding File Permissions with the Chmod Calculator

File permissions are essential in Unix and Linux systems. They control who can read, write, or execute files. With the Chmod Calculator, you can easily set and calculate these permissions. This tool helps you understand how different settings affect access to your files and directories. Whether you're a beginner or an experienced user, this calculator makes managing permissions less complicated.

How to Use the Chmod Calculator

The Chmod Calculator offers various ways to set permissions. You can use a visual grid to select permissions, input symbolic notation, or enter numerical values. Each method gives you flexibility based on your comfort level with file permissions. This ensures that you can choose the approach that works best for you.

Exploring Permission Types

  • Read (r): Allows you to view file contents or list directory contents.
  • Write (w): Grants permission to modify the file or make changes in a directory.
  • Execute (x): Lets you run the file or access files within a directory.

Understanding these types helps you decide which permissions to set for different users—like the owner, group, and others.

Special Permissions Explained

Besides standard permissions, there are special ones that can be set using the Chmod Calculator. These include:

  • SUID: When set, a file runs with the permissions of its owner.
  • SGID: Similar to SUID but applies to groups; can also affect new files in a directory.
  • Sticky Bit: Limits file deletion in a directory to the owner or root user.

These special permissions add another layer of control over file access and security.

Using Symbolic and Numeric Notation

The calculator allows you to enter permissions using symbolic notation (like u=rwx,g=rx) or numeric values (like 755). This flexibility is great for users who are familiar with either method. Whichever you choose, the calculator will provide the equivalent settings. It showcases how to mix and match methods for convenience.

Common Permission Presets

For quick access, the Chmod Calculator includes common preset permissions. Here are a few examples:

  • 755: Standard permissions for directories, allowing full access for the owner and read/execute for others.
  • 644: Default for files, giving read/write permissions to the owner and read permissions to everyone else.
  • 700: Private settings, only letting the owner have access.

This feature simplifies the process of applying common permission settings without needing to remember specific values.

Visualising File Permissions

The visual representation of permissions helps you see how your settings apply. You can view the read, write, and execute permissions for the owner, group, and others at a glance. This immediate feedback lets you confirm that you've set the correct permissions before applying them to a file or directory.

Learning More About Unix Permissions

The Chmod Calculator is not just about calculations; it also educates users on Unix file permissions. From understanding basic permission types to the implications of special settings, the calculator provides clear explanations. This makes it an excellent resource for those wanting to grasp file permissions better.