chmod Calculator

Unix permissions come in three notations: octal (755), symbolic (rwxr-xr-x), and the chmod command itself. Toggle checkboxes or type either notation and the others update instantly, including setuid, setgid, and the sticky bit.

Common uses

• Figure out what chmod 644 actually grants
• Build the right mode for a deploy script or Dockerfile
• Understand ls -l output like drwxr-sr-x

Example

755

rwxr-xr-x — owner: read/write/execute · group: read/execute · others: read/execute

What does chmod 755 actually grant?

The owner gets read, write, and execute (7 = 4+2+1); group and others get read and execute (5 = 4+1). It is the standard mode for executables and directories that everyone may enter but only the owner may change.

Does this chmod calculator send my input to a server?

No. The conversion between octal, symbolic, and checkboxes is plain arithmetic done in your browser — nothing is transmitted or stored anywhere.

What is the fourth digit in a mode like 1777 or 4755?

A leading digit encodes the special bits: setuid is 4000, setgid is 2000, and the sticky bit is 1000. For example, 1777 is world-writable with the sticky bit, the mode used for /tmp so users can only delete their own files.

Why can't I cd into a directory I have read permission on?

Entering a directory requires the execute bit, not the read bit. Read lets you list the names inside; execute lets you traverse into it and access the files, which is why directories are normally 755 or 700 rather than 644.

What permissions should an SSH private key have?

600 — read and write for the owner, nothing for group or others. OpenSSH refuses to use a private key that is readable by anyone else and reports it as an 'unprotected private key file'.