Chmod Calculator
Calculate Unix file permissions: convert between octal (755), symbolic (rwxr-xr-x), and individual checkboxes. Includes setuid/setgid/sticky bits.
Zero uploads. Everything runs in your browser — bitwise math only.
Octal
3 or 4 digits. Leading digit is special bits (setuid/setgid/sticky).Symbolic
9 or 10 chars. Optional leading file-type character (-, d).
Permission Matrix
| Read (r) | Write (w) | Execute (x) | |
|---|---|---|---|
| Owner | |||
| Group | |||
| Others |
Copy Commands
chmod 644 file
find . -type f -perm 644
Common Presets
Chmod Calculator Tutorial
Understanding Chmod
Unix permissions have 9 primary bits — 3 for each of owner, group, and others. Each trio is (read, write, execute).
Octal math: r=4, w=2, x=1. So rwx = 7, rw- = 6, r-x = 5. 755 = owner full, group+others read+execute.
Special Bits (the leading digit)
- 4 (setuid) — when executed, runs with the owner's UID. How
sudoandpasswdwork. - 2 (setgid) — on a dir, new files inherit the dir's group. On a binary, runs with group's privileges.
- 1 (sticky) — on a dir, only the file owner (or root) can delete their own files. That's how
/tmpis safe.
Good Defaults
- Regular file:
644(owner can edit, others read) - Script or binary:
755(owner edits, everyone can run) - Directory:
755or775 - SSH private key:
600— sshd refuses keys with looser permissions - SSH public key or authorized_keys:
644 - .env config with secrets:
600owned by the app user
Things to Avoid
chmod 777— never do this on a production server. Use proper ownership and ACLs instead.chmod -Ron a Git repo — messes up.git/hookspermissions- Setuid bit on a shell script — ignored by Linux for security