Chmod Calculator
Convert between symbolic (rwx) and numeric (octal) Unix file permissions interactively.
About This Tool
The Chmod Calculator is an interactive tool that helps you understand and set Unix/Linux file permissions. File permissions control who can read, write, and execute files and directories on Unix-like operating systems including Linux, macOS, and BSD. Every file has three sets of permissions: one for the owner(the user who created the file), one for the group(users in the same group), and one for others(everyone else on the system).
Each permission set contains three flags: read (r), which allows viewing the file contents or listing a directory; write (w), which allows modifying the file or creating/deleting files in a directory; and execute (x), which allows running the file as a program or entering a directory. These nine flags are represented in two common notations: symbolic (e.g., rwxr-xr-x) and numeric/octal (e.g., 755).
In octal notation, each digit represents a permission set: read = 4, write = 2, execute = 1. You sum the values you need. For example, read + execute = 5. The tool also supports special permissions: SUID (set user ID), SGID (set group ID), and the sticky bit. These are represented by a leading fourth digit in the octal notation (e.g., 1777 for the sticky bit on a world-writable directory like /tmp).
All calculations run entirely in your browser using native JavaScript. No data is sent to any server. Simply click the checkboxes or type an octal value to see the corresponding permissions instantly.
How to Use
- Use the permission grid to toggle read, write, and execute permissions for Owner, Group, and Others by clicking the checkboxes.
- Alternatively, type an octal value (e.g.,
755or1777) in the numeric input field. - Click a common permissions button to quickly set a well-known permission combination.
- Toggle SUID, SGID, or Sticky bit using the special permissions checkboxes.
- Review the symbolic notation, chmod command, and ls -l output to verify your selection.
- Click the copy button next to any value to copy it to your clipboard.
FAQ
What does chmod 755 mean?
Chmod 755 gives the file owner full read, write, and execute permissions (7 = 4+2+1), while the group and others can only read and execute (5 = 4+1). This is the most common permission for executable scripts, web server directories, and program files. In symbolic notation it is rwxr-xr-x.
What is the difference between 644 and 755?
Permission 644 (rw-r--r--) allows the owner to read and write, while group and others can only read. Permission 755 (rwxr-xr-x) adds execute permission for all three roles. Use 644 for regular files (HTML, CSS, images) and 755 for directories and executable scripts.
What are SUID, SGID, and sticky bit?
SUID (Set User ID, octal 4000): When set on an executable, it runs with the permissions of the file owner, not the user executing it. SGID (Set Group ID, octal 2000): On executables, it runs with the group permissions; on directories, new files inherit the directory's group. Sticky bit (octal 1000): On directories, only the file owner can delete or rename files, even if others have write access (commonly used on /tmp).
How do I read ls -l output?
The ls -l command shows a 10-character string. The first character is the file type (- for regular file, d for directory, l for symlink). The next nine characters are three groups of three: owner, group, and others, each showing r (read), w (write), and x (execute), or - if not set.
What permission should I use for web server files?
For most web hosting setups: directories should be 755 (owner can write, web server can read and traverse), regular files should be 644 (owner can write, web server can read), and configuration files with sensitive data should be 600 (owner-only access). Avoid 777 in production as it grants full access to everyone.
Is my data sent to any server?
No. All permission calculations are performed entirely in your browser using client-side JavaScript. No data ever leaves your machine. You can verify this by checking your browser's network tab while using the tool.
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