Free Online Chmod Calculator

Each digit represents a different class of user: the first digit controls the owner (the user who created the file), the second controls the group (a set of users assigned to the file), and the third controls others (everyone else). Each digit is the sum of read (4), write (2), and execute (1) permissions.

chmod 755 gives the owner full permissions (read + write + execute = 7), while the group and others can only read and execute (4 + 1 = 5). It is the standard permission for executable files and directories that should be accessible to everyone but only writable by the owner.

chmod 644 is the standard permission for regular files such as web pages, configuration files, and data files. The owner can read and write (6), while group and others can only read (4). This prevents accidental modification by other users or web server processes.

Octal notation (e.g., 755) represents permissions as three digits in base-8. Symbolic notation (e.g., rwxr-xr-x) uses letters where r = read, w = write, x = execute, and - means the permission is not set. Both represent exactly the same information — symbolic is more human-readable, octal is more compact.

chmod 777 grants read, write, and execute permissions to everyone on the system. On a shared server or web host, this means any user or process can modify or execute your files, which is a significant security risk. Only use 777 for temporary debugging and never on production systems.

For directories, the execute (x) permission controls whether a user can enter (traverse) the directory using cd or access files within it. Without execute permission on a directory, a user cannot list or access the directory's contents even if they have read permission.