Typically, octal permissions are specified with three or four numbers, in these positions:

1234

Each position indicates a different type of access:

• In position 1 are the bits that set permission for set-user-ID on access, set-group-ID on access, or the sticky bit. Specifying this position is optional.
• In position 2 are the bits that set permissions for the owner of the file. Specifying this position is required.
• In position 3 are the bits that set permissions for the group that the owner belongs to. Specifying this position is required.
• In position 4 are the bits that set permissions for others. Specifying this position is required.