How to fix Sierra not remembering SSH keys. As described in detail on https://openradar.appspot.com/27348363, macOS/OS X till Yosemite used to remember SSH keys added by command ssh-add -K . Unfortunately this way no longer works and command ssh-add -K in macOS Sierra no longer saves SSH keys in OS's keychain. As Apple Developer stated: "That’s expected. We re-aligned our behavior with the mainstream OpenSSH in this area."

How to set up SSH. Elementary beyond compare but overlooked.