Chmod Calculator

Calculate Unix file permissions with interactive checkboxes, octal, and symbolic notation

Features

Bidirectional sync: octal (e.g. 755) ↔ symbolic (e.g. rwxr-xr-x)
3-digit and 4-digit octal modes — special bits (SUID, SGID, sticky) supported via the optional 4th digit
Per-bit checkboxes for owner / group / others + separate toggles for SUID, SGID, sticky
`chmod` command preview (octal form) and `chmod u=…,g=…,o=…` symbolic form
Runs entirely in your browser

How to use

Toggle the read, write, and execute checkboxes for each user group.
Or type an octal value (e.g., 755) in the input field.
Or click a common preset button.
Copy the generated chmod command to use in your terminal.

Tips & Best Practices

4-digit octal: the first digit is SUID (4) + SGID (2) + sticky (1). Common combinations: 4755 (suid binary), 2755 (sgid binary), 1777 (sticky directory like /tmp).
Sticky bit on a directory means only the owner can delete files inside, even with write permission (think /tmp).
SUID on an executable runs as the file owner — security-sensitive; use sparingly.
Symbolic output replaces `x` with `s` for SUID/SGID and `t` for sticky; uppercase letters (S, T) indicate the special bit is set but execute is OFF.
For typical web-app files, 644 (regular files) and 755 (directories / scripts) cover most cases.

FAQ

What does chmod 755 mean?

755 means the owner can read, write, and execute (7), while group and others can only read and execute (5). This is the standard permission for directories and executable scripts.

What does chmod 644 mean?

644 means the owner can read and write (6), while group and others can only read (4). This is the standard permission for regular files.

What is the difference between octal and symbolic notation?

Octal uses numbers (e.g., 755) while symbolic uses letters (e.g., rwxr-xr-x). Both achieve the same result — octal is more concise for setting absolute permissions, while symbolic notation (chmod u+x) is more readable when you only want to add or remove specific bits.

What does chmod 777 do and why is it dangerous?

777 grants read, write, and execute permissions to the owner, group, and everyone else on the system. Using it in production allows any user or compromised process to modify or execute your files, which is a serious security risk — use 644 or 755 instead and adjust ownership with chown.

What are the special permission bits (setuid, setgid, sticky)?

The fourth digit in a 4-digit octal mode like 4755 sets special bits: setuid (4) makes a binary run as the file owner, setgid (2) inherits the group on new files inside a directory, and the sticky bit (1) — common on /tmp — prevents users from deleting other users' files. They appear as s, s, and t in symbolic notation.

How do I apply chmod recursively to a directory?

Use chmod -R 755 /path/to/dir to apply permissions to a directory and everything inside it. To set different modes for files vs directories, combine find with chmod — e.g., find . -type d -exec chmod 755 {} + and find . -type f -exec chmod 644 {} +.

Why doesn't chmod work on my file?

On Linux, only the file owner or root can change permissions — use sudo if you do not own the file. On Windows-mounted drives (NTFS, FAT32) and some network shares, Unix-style permissions are not enforced because the underlying filesystem does not support them.

Is the chmod calculator safe to use?

Yes, this calculator runs 100% in your browser — no permission values, file names, or commands are sent to any server. You can use it offline once the page loads, making it safe even for sensitive infrastructure work.

chmod Commands