Q:

How to give the recusive option (-R) to the M command (change the file mod) in emacs dired?

When i type "-R 777" I get:
file-modes-symbolic-to-number: Parse error in modes near `R 777'.

A:

Recursive operations aren't supported by dired-do-chmod.
It's easy to do this as a shell command, though:
M-! chmod -R 777 (files) RET
Alternatively, the Dired+ library provides a diredp-do-chmod-recursive command for this, bound to M-+M (and added only a few days ago, apparently, so that was a well-timed question).

