Chmod Calculator — Linux Permissions

chmod 755 is one of those commands people type from memory without being sure what it does. Tick the boxes, or type a mode in any notation, and this shows what it means in plain words, along with the exact command to run.

It starts on 755, which reads “The owner can read, write, run. The group can read, run.” The presets cover the modes you meet most: 644 for ordinary files, 600 for an SSH key, 400 for a .pem file and 1777 for a shared folder like /tmp.

How to Use the Permission Grid

1. Tick read, write and execute for owner, group and others, or pick a preset.
2. Or type into Octal, or paste a line from ls -l such as drwxr-xr-x. Everything else follows.
3. Choose File or Folder, because the same bits mean different things: on a folder, execute means enter.
4. Add a Path and copy the octal or symbolic command. Paths with spaces are quoted for you.

Two extras are easy to miss. Apply a symbolic change shows what g+w,o-rwx would do to the current mode before you run it. The umask box answers why new files come out as they do: a umask of 022 gives 644 for files and 755 for folders.

The Method: How Octal Digits Add Up

Read is 4, write is 2 and execute is 1, and each digit adds them up for one class. So 7 is 4+2+1, all three, and 5 is 4+1, read and execute, which makes 755 rwxr-xr-x. A fourth digit in front sets the special bits: setuid is 4, setgid is 2 and sticky is 1, so 1777 is rwxrwxrwt. A capital S or T in ls output means the special bit is on but execute is off. These conversions were checked against the real chmod and stat commands for all 4,096 modes.

Edge Cases: Recursive Modes and Folders

chmod -R 755 makes every file executable, so when Recursive is on, the tool offers a pair of find commands that treat folders and files separately. On a folder, GNU chmod 755 leaves an existing setgid or setuid bit in place; use the five-digit 00755 to clear them. In a symbolic change with no u, g, o or a, such as +x, a real shell applies your umask, while this tool assumes 0. Mistakes show a message such as “"u+z" isn’t a valid mode clause. Try u+x, g-w or a=r.” Permissions behave differently on Windows drives and some network shares. Nothing here touches a real file: it only writes the command.