change file mode bits

-R, --recursive
       change files and directories recursively

-f, --silent, --quiet
       suppress most error messages

--no-preserve-root
       do not treat `/' specially (the default)

The  format  of  a  symbolic  mode  is  [ugoa...][[+-=][perms...]...], where perms is either zero or more
letters from the set rwxXst, or a single letter from the set ugo.  Multiple symbolic modes can be  given,
separated by commas.

Change the mode of each FILE to MODE.