chmod Calculator

chmod Calculator turns Linux and macOS file permissions into something you can see. Tick read, write and execute for the owner, the group and everyone else, and the octal number (755), the letter form (rwxr-xr-x) and a ready-to-paste chmod command update together. It works the other way too: type 0644, paste a whole column from ls -l such as drwxr-sr-x, or type a change like g+w, and the boxes follow.

Most calculators stop at the nine basic boxes. This one also handles the three special bits — setuid, setgid and sticky — including the capital S and T that ls shows when the execute bit underneath is off. Every result comes with a plain-English line for each class of user, worded for files or for folders, because “execute” on a folder means “can open it”, not “can run it”. Risky choices such as 777, world-writable folders without the sticky bit, or setuid on a writable file get a clear warning.

There is a umask helper for working out what permissions new files and folders will get, and ten common presets with a note on when to use each. Nothing leaves your browser.

1. Tick the boxes under Read, Write and Execute for Owner, Group and Others, or tap one of the “Common permissions”.
2. Or type straight into “Octal” (755, 0644, 4755) or “Symbolic” (rwxr-xr-x, or a full ls -l string like drwxr-xr-x).
3. To change what is there, type into “Or type a chmod change”, for example u+x or go-w.
4. Enter your file or folder name, tick “It’s a folder” if it is one, and “Everything inside too (-R)” to apply it recursively.
5. Press the copy button next to the Numeric or Symbolic command and paste it into your terminal.

• Two-way sync between the tick boxes, octal (3 or 4 digits, with or without a leading 0) and symbolic letters.
• Setuid, setgid and sticky bits, with s, S, t and T shown exactly as ls -l prints them.
• Pastes a full ls -l permission column and detects whether it is a folder from the leading d.
• Applies chmod symbolic changes: u, g, o, a with +, − and =, letters r w x X s t, copying (g=u) and several clauses at once.
• Numeric and symbolic chmod commands, with -R for folders and safe quoting of names with spaces.
• Plain-English meaning for each class of user, worded differently for files and folders.
• Warnings for 777, world-writable files and folders, setuid with write access and settings that do nothing.
• umask helper showing default permissions for new files and new folders, plus ten common presets.

• For a website, 755 for folders and 644 for files is the usual safe pair. Avoid 777, even “just to test”.
• SSH refuses private keys that others can read. Use 600 for the key file and 700 for the ~/.ssh folder.
• chmod -R 644 on a folder also removes execute from the folders inside, so nobody can open them. Add a capital-X change such as a+X when you want folders openable but files not runnable.
• Only the file’s owner or root can change its permissions, so you may need sudo in front of the command.
• umask is subtracted bit by bit, not as decimal maths: a umask of 022 turns 666 into 644 and 777 into 755.