Chmod Calculator - Unix File Permissions

How the Chmod Calculator Works

1. 01Toggle read (r), write (w), and execute (x) permissions for owner, group, and others
2. 02See the numeric (e.g., 755) and symbolic (e.g., rwxr-xr-x) notation update in real time
3. 03Or enter a numeric value to see which permissions it represents
4. 04Copy the chmod command ready to paste in your terminal

Unix File Permissions Explained

Unix permissions control who can read, write, and execute files. The three-digit number represents owner, group, and others - each digit is a sum of read (4), write (2), and execute (1). Common values: 755 (owner full, others read+execute) for scripts, 644 (owner read+write, others read-only) for files, and 600 (owner only) for private keys. Wrong permissions are a frequent cause of 'Permission denied' errors and security vulnerabilities.

When to Use the Chmod Calculator

Use this calculator when you need to set or verify Unix file permissions. Common situations include fixing 'Permission denied' errors on Linux servers, configuring web server file permissions, setting up deployment scripts, securing sensitive files like SSH keys and config files, and understanding permissions shown by 'ls -la' output.

Common Use Cases

• —Fixing 'Permission denied' errors on Linux web servers and deployment scripts
• —Setting correct permissions for SSH keys (600) and web server files (644/755) Number Base Converter - Binary, Hex & More
• —Understanding 'ls -la' output when debugging file access issues on remote servers
• —Configuring file upload directories with appropriate write permissions

Expert Tips

• ✻Follow the principle of least privilege: give only the minimum permissions needed for the file's purpose
• ✻For web servers, directories need execute permission (755) to allow traversal, even if the files inside only need 644
• ✻Use 'chmod -R' with caution - recursive permission changes can break things if you set files and directories to the same permissions

Frequently Asked Questions

What does chmod 755 mean?→

755 means: owner can read, write, and execute (7 = 4+2+1); group can read and execute (5 = 4+1); others can read and execute (5 = 4+1). In symbolic notation: rwxr-xr-x. This is the standard permission for executable scripts and directories on web servers.

When should I use chmod 644 vs 755?→

Use 644 (rw-r--r--) for regular files: the owner can read and write, everyone else can only read. Use 755 (rwxr-xr-x) for executable files and directories: the owner has full access, everyone else can read and execute (enter directories). Never use 777 in production - it gives everyone full access.

What is the difference between numeric and symbolic notation?→

Numeric notation (e.g., 755) uses three octal digits where each digit is a sum of read (4), write (2), and execute (1). Symbolic notation (e.g., rwxr-xr-x) shows each permission as a letter or dash. Both represent the same thing - use whichever you find more readable.

Why do SSH keys require specific permissions?→

SSH requires private keys to have permissions 600 (owner read/write only) or 400 (owner read only). If permissions are more open, SSH refuses to use the key because others could potentially read your private key. This is a security feature, not a bug.