Chmod Calculator — Unix File Permissions
Calculate Unix file permissions visually. Convert between symbolic and numeric (octal) notation. Free tool for developers and sysadmins.
| Read | Write | Execute | |
|---|---|---|---|
| Owner | |||
| Group | |||
| Others |
755
rwxr-xr-x
Chmod Calculator — Unix File Permission Calculator
Calculate Unix file permissions by toggling read, write, and execute flags for owner, group, and others. Convert between numeric notation (like 755) and symbolic notation (like rwxr-xr-x) instantly. Generates the complete chmod command ready to paste into your terminal.
Unix permissions use a three-digit octal number where each digit represents a user class (owner, group, others). Each digit is the sum of read (4), write (2), and execute (1). The calculator maps interactive checkbox toggles to both numeric and symbolic representations in real time.
Linux server administrators set permissions on web server files and directories. Developers fix 'Permission denied' errors by adjusting file permissions. DevOps engineers configure deployment scripts with correct execution permissions. Security auditors review file permissions to identify overly permissive settings.
Follow the principle of least privilege: give only the minimum permissions needed. Web files typically need 644 (owner read/write, others read-only). Scripts need 755 (owner full, others read/execute). Private keys must be 600 (owner only). Never use 777 in production — it gives everyone full access.
While the chmod command itself is straightforward, remembering what each number means is the challenge. This calculator eliminates memorization by providing a visual interface. For understanding the octal number system behind permissions, see our Number Base Converter which explains base-8 notation.
How the Chmod Calculator Works
- Toggle read (r), write (w), and execute (x) permissions for owner, group, and others
- See the numeric (e.g., 755) and symbolic (e.g., rwxr-xr-x) notation update in real time
- Or enter a numeric value to see which permissions it represents
- Copy 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
- 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.
- 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.
- 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.
- 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.
What does chmod 755 mean?▾
When should I use chmod 644 vs 755?▾
What is the difference between numeric and symbolic notation?▾
Why do SSH keys require specific permissions?▾
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