The chmod calculator converts between Unix/Linux file permission notations. Toggle checkboxes to build symbolic permissions (rwxrwxrwx) and instantly see the octal value (e.g., 755), or enter an octal number to see the symbolic breakdown. Includes common permission patterns for quick reference.
Symbolic → Octal
Octal → Symbolic
Common Patterns
How to Use the chmod Calculator
Unix file permissions control who can read, write, and execute files. Every file has three permission groups — owner, group, and others — each with independent read (r=4), write (w=2), and execute (x=1) bits. The chmod calculator makes it easy to convert between the visual checkbox representation and the numeric octal notation.
Understanding Octal Notation
Each octal digit (0-7) represents the sum of permission bits for one group. Read=4, Write=2, Execute=1. So: 7=4+2+1 (all permissions), 6=4+2 (read+write), 5=4+1 (read+execute), 4=read only, 0=no permissions. The three digits represent owner/group/others in order.
Common chmod Commands
Use chmod 755 filename to set standard executable permissions. Use chmod -R 755 directory/ to apply recursively. Use ls -la to view current permissions in symbolic format.
Security Best Practices
Use the minimum permissions necessary. Web server document roots typically use 755 for directories and 644 for files. Configuration files with secrets should use 600 (owner read/write only). Never use 777 on production — it grants write access to everyone on the system, enabling attackers who gain any user access to modify your files.
FAQ
Is this chmod calculator free?
Yes, completely free with no signup required.
What does chmod 755 mean?
chmod 755 sets: owner can read/write/execute (7=4+2+1), group can read/execute (5=4+0+1), others can read/execute (5=4+0+1). This is the standard permission for web server directories and executable scripts.
What is the difference between 755 and 644?
755 grants execute permission to all users (owner, group, others) — used for directories and executable files. 644 grants no execute permission — used for regular files like HTML, CSS, and config files that should be readable but not executable.
When should I use chmod 777?
Avoid chmod 777 on production servers. It grants read, write, and execute to everyone, creating a serious security risk. Use the minimum permissions needed: 755 for directories, 644 for files, and 700 or 600 for sensitive files.
How do I set permissions recursively?
Use 'chmod -R 755 /path/to/directory' to apply permissions recursively to all files and subdirectories. Be careful with recursive changes — they affect every file in the tree including sensitive configuration files.