Chmod Calculator

chmod ("change mode") is the Linux and macOS command that sets the permissions of a file or directory - who can read, write, and execute it. You reach for it constantly: making a script runnable, locking down an SSH private key, or fixing a "Permission denied" error on a web server.

This calculator turns the permission checkboxes into the precise numeric and symbolic command, so you never have to guess whether you want 644 or 755.

Every file has three permission groups - Owner (the user who owns it), Group (members of the file's group), and Others (everyone else). Each group can be granted any combination of three permissions, and each permission has a numeric value:

• Read (r) = 4
• Write (w) = 2
• Execute (x) = 1

Add the values for each group to get its digit. Read + write + execute is 4 + 2 + 1 = 7; read + execute is 4 + 1 = 5. Do that for owner, group, and others and you get the familiar three-digit number, like 755.

The same permissions can be written two ways. Octal uses the digits above - 755. Symbolic spells out each group as nine characters - rwxr-xr-x - which is exactly what you see in the output of ls -l. A dash means the permission is not granted.

chmod accepts both. chmod 755 file and chmod u=rwx,g=rx,o=rx file do the same thing. The calculator above shows both forms live as you toggle permissions.

A fourth, leading digit controls three special bits. setuid (4) runs an executable as its owner, setgid (2) runs it as its group (or makes new files in a directory inherit the group), and the sticky bit (1) stops users from deleting each other's files in a shared directory like /tmp.

Toggle them in the calculator and the octal value gains a leading digit - for example 1755 for a sticky directory, or 4755 for a setuid binary.

1. Tick the read, write, and execute boxes for owner, group, and others.
2. Or click a preset (644 for files, 755 for scripts, 600 for SSH keys) to set them all at once.
3. Need a special bit? Toggle setuid, setgid, or sticky.
4. Watch the octal and symbolic values update live, or type an octal value to work backwards.
5. Add an optional file path and the recursive flag, then copy the ready-to-run command.