Question

For example, I can do rsync --delete --archive --links --perms --etc source_dir final_dir and I know which options I’m using. What if I do just rsync source_dir final_dir? What are the defaults?

Answer 1

From manpage:

Rsync finds files that need to be transferred using a “quick check” algorithm (by default) that looks for files that have changed in size or in last-modified time. Any changes in the other preserved attributes (as requested by options) are made on the destination file directly when the quick check indicates that the file’s data does not need to be updated.

Howewer, when you just call rsync 1/ 2/ w/o any options (such as -a), nothing happens