According to what I read online and in the Man pages, I should also be able to do something like this (where Fred is Admin account):
sudo -u Fred lsThat should ask for Fred's password then execute ls with Fred's privileges.
Except it doesn't. It runs against my non-admin account and fails. As though it were ignoring the -u flag. Instead I have to run
su Fredto execute as Fred, then run sudo.
I can't find anyone else who complains about this, so I assume I'm doing something wrong.
Note to test this you have to run from a non-admin account.
Update 8/23/2016: I can't get sudo to work at all in El Capitan for a non-admin users. Says: "error retrieving current directory: getcwd: cannot access parent directories: Permission denied."