What Is a Chmod Calculator?
A chmod calculator converts Unix/Linux file permission strings into their numeric (octal) equivalents and vice versa. The chmod command sets read, write, and execute permissions for the file owner, group, and other users. This tool lets you enter numeric values for each permission category and instantly see the resulting octal code and symbolic notation, eliminating manual binary-to-octal math.
How to Use This Chmod Calculator
- Enter a number from 0 to 7 for each of the three fields: Owner, Group, and Other.
- Click “Calculate” to see the numeric code, symbolic notation, and the chmod command.
- The result shows the permission breakdown for each category (read, write, execute).
Key Concepts
Each permission digit is the sum of read (4), write (2), and execute (1). For example, 7 means rwx (4+2+1), 5 means r-x (4+1), and 0 means no permissions. Common values include 755 for executable scripts and directories, 644 for regular files, and 600 for private configuration files. The special setuid, setgid, and sticky bits add a fourth leading digit when needed.
Permission = Owner(rwx) × 64 + Group(rwx) × 8 + Others(rwx)
Frequently Asked Questions
What does chmod 755 mean?
Chmod 755 gives the owner full read, write, and execute permissions (7), while the group and all other users get read and execute only (5). This is the standard permission for web server directories and executable scripts.
When should I use chmod 644?
Use 644 for regular files that should be readable by everyone but writable only by the owner. It is the typical default for HTML, CSS, image files, and most configuration files served on the web.
What is the sticky bit?
The sticky bit (octal 1000, shown as “t” in the others-execute position) prevents users from deleting files they do not own within a shared directory. The /tmp directory on most Linux systems uses permission 1777 for this reason.