Chmod Calculator

How to Use

Toggle the permission checkboxes for owner, group, and others. The numeric (octal) and symbolic representations update instantly. You can also enter a 3-digit octal number directly.

What are Unix File Permissions?

Unix file permissions are a security mechanism that controls who can read, write, or execute a file or directory. Every file on a Unix-like system (Linux, macOS) has three permission groups: the owner (user who created the file), the group (users sharing a group identity), and others (everyone else). Each group can be granted read, write, and execute permissions independently. Permissions are represented in two formats: symbolic notation (rwxr-xr-x) which shows each permission as a letter, and octal notation (755) which uses a three-digit number. The chmod command is used to change these permissions from the command line.

Octal Notation

Unix file permissions control read (4), write (2), and execute (1) access for three groups: owner, group, and others. The octal representation is the sum of these values for each group. For example, 755 means rwx for owner, r-x for group and others.

Common Use Cases

• Server administration — set correct permissions for web server files and directories
• Deployment scripts — configure chmod commands in CI/CD pipelines to secure application files
• Security auditing — verify that sensitive files like configuration and key files are not world-readable
• Shared hosting — manage permissions when multiple users access the same server
• Shell scripts — make scripts executable with the right permission level

Common Permission Values

755 (rwxr-xr-x) — standard for executable files and directories. 644 (rw-r--r--) — standard for regular files. 700 (rwx------) — private, owner-only access. 600 (rw-------) — private files like SSH keys. 777 (rwxrwxrwx) — full access for everyone, generally insecure and should be avoided.

Privacy

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