Default Permissions

System calls to create new files and directories have default or base permissions:

• Directories: (octal) 0777 or rwxrwxrwx.
• Files: (octal) 0666 or rw-rw-rw-.

The first octal digit is for special permissions. The next three are for user, group and others.

Before creating the file or directory, the base permissions are compared to a mask that will "mask out" permission bits to determine the final permissions for the object being created.

The calculation to determine the final permissions is to take the binary of the base permissions and perform a logical AND operation on the ones complement representation of the binary umask.

umask

Display or set file creation mask.

The usual umask is 0022, which results in 0755 for directories, and 0644 for regular files.

  0  0  2  2         0  7  7  7         0  6  6  6
000000010010       000111111111       000110110110
111111111111       111111101101       111111101101
------------       ------------       ------------
111111101101       000111101101       000110100100
                     0  7  5  5         0  6  4  4