Sorting and comparing in vi / vim / vimdiff

I regularly use vimdiff to compare files on a local server with a remote server via SFTP. I keep forgetting how to get VI to refesh the view when one of the files has changed on the filesysem. It’s simply done with
When comparing, if the order of lines in the file doesn’t matter and you think that they are similar except for the order, you can also use the built-in command:
to sort the lines. Mark the lines you want to sort first with visual marking mode (V) and then apply the sort.