The general form of the chmod command:

   chmod options file

The options are constructed by choosing one from each of these columns, with no blank between them:

WhoOperationPermission
A combination of:
  u user (file owner)
  g group
  o others
  a all (same as ugo)
Permissions are:
  = assigned
  + added
  - subtracted
A combination of:
  r read
  w write
  x execute
or one of the following:
  u user
  g group
  o other
to copy permissions