Tools
Chmod Calculator
The chmod calculator helps developers and sysadmins convert Unix file permission modes between symbolic notation (rwxr-xr--), octal values (755), and ready-to-run chmod commands. You can toggle individual read, write, and execute bits for owner, group, and others. The corresponding chmod command is generated automatically.
What is the chmod Calculator?
chmod is the Unix command used to change the access permissions of files and directories. Permissions are defined for three categories — owner, group, and others — and consist of read (r), write (w), and execute (x) bits. The chmod calculator lets you build any permission set visually using checkboxes and instantly see the octal value and the exact chmod command to apply it. This eliminates the need to mentally convert between symbolic and numeric modes.
How does it work?
Each permission bit is represented by a checkbox for read, write, and execute across owner, group, and others. Toggling a checkbox updates the octal value and symbolic string in real time. The tool also works in reverse: enter an octal like 644 or a symbolic string like rw-r--r-- and the checkboxes update accordingly. The generated chmod command can be copied directly and run in a terminal.
Typical Use Cases
- Setting correct permissions on web server files (644 for files, 755 for directories)
- Understanding what a permission string like rwxr-x--- means
- Generating chmod commands for deployment scripts
- Teaching Unix file permissions in workshops or documentation
Step-by-step Guide
- Step 1: Toggle the read, write, and execute checkboxes for owner, group, and others.
- Step 2: Observe the octal value and symbolic notation update in real time.
- Step 3: Alternatively, type an octal or symbolic value directly to set the bits.
- Step 4: Copy the generated chmod command and run it in your terminal.
Example
Input
Owner: rwx, Group: r-x, Others: r--
Output
chmod 754 filename
Tips & Notes
- For web server files, 644 (rw-r--r--) is the standard safe permission for static files.
- Never set 777 on production files — it grants write access to everyone on the system.
- Executable scripts need the execute bit set for at least the owner (e.g., 755 or 700).
Frequently Asked Questions
What does the sticky bit or setuid do?
Special bits like setuid (4), setgid (2), and sticky (1) are prepended to the octal as a fourth digit (e.g., 4755). They control privilege escalation and shared directory behavior, but are outside typical everyday use.
What is the difference between chmod 644 and chmod 755?
644 gives the owner read and write access while group and others get read-only. 755 additionally grants the execute bit to owner and read+execute to group and others — typical for directories and executables.
Chmod Calculator
Interactively calculate Unix file permissions — with octal value, symbolic notation, special bits (SUID/SGID/Sticky), and a ready-to-use chmod command.
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