CHMOD Calculator – calculate Linux file permissions online

Each digit is the sum of read (4), write (2), and execute (1). The first digit applies to the Owner, the second to the Group, and the third to Others. So 755 means the Owner can read, write, and execute (7), while Group and Others can read and execute (5): rwxr-xr-x in symbolic notation. The CHMOD Calculator starts with this value and explains the permissions for each class in a sentence.

777 (rwxrwxrwx) gives every user on the system full read, write, and execute permissions. In most cases, this is unsafe: on a web server, it is often enough to let users modify files at will. For web directories, 755 is usually appropriate for directories and 644 for files; 777 is only justifiable in clearly defined exceptional cases.

Use ls -l. The permission string appears at the start of each line, such as -rwxr-xr-x for a file or drwxr-xr-x for a directory. Paste it into the calculator’s reverse input field: the file type character at the beginning is ignored, and you get the octal value with an explanation for each class. The field also accepts 3- or 4-digit octal values and 9-character symbolic notation.

600 (rw-------) is common for the private key, and 700 (rwx------) for the ~/.ssh directory. This gives only the Owner access. If the permissions are too open, SSH will usually reject the key. To set this in the calculator, clear all checkboxes for Group and Others.

For a file: r = read contents, w = modify contents, x = execute file (e.g., a script). For a directory: r = list files, w = create, delete, or rename files, x = enter the directory or open files within it.

These are three special permissions, represented by a fourth digit at the beginning (such as 4755). setuid (4) makes a program run with its owner’s permissions instead of those of the user running it. For directories, setgid (2) makes newly created files automatically inherit the same group. The sticky bit (1) prevents users from deleting other users’ files in shared writable directories (such as /tmp). In the calculator, you set them under “Special bits.” In symbolic notation, they appear as s or S (Owner, Group) and t or T (Others); uppercase means execute permission is absent at that position.

Use the -R flag, such as chmod -R 755 /pfad/zum/ordner. Enable “Recursive (-R)” in the chmod command generator. This sets permissions on the directory itself and all files and subdirectories inside it. Be careful: -R gives files and directories the same permissions. Scripts often need to be executable, while regular files usually do not. For directories containing both, set permissions selectively rather than recursively.

chmod changes who can do what (read, write, and execute permissions). chown changes who owns the file (Owner and/or Group). The two commands are often used together but work independently. The CHMOD Calculator generates chmod commands only.