How do I restart the SSH service?

How do I stop/start ssh? I've tried

/etc/init.d/ssh restart
sudo service ssh restart
sudo restart ssh

I get errors every time.

15.04 and newer:

Use this command:

sudo systemctl restart ssh

To restart the SSH server/daemon.

Going forward with systemd starting with Ubuntu 15.04, you now use this syntax to stop, start, or restart services:

sudo systemctl <action> <service-name>

Pre 15.04:

It should be as simple as (tested on a fresh install with openssh-server)

sudo stop ssh
sudo start ssh

As it leverages upstart, this is The Best Way™ to do it, rather than using /etc/init.d/ssh, service, or invoking sshd directly. Make sure to run both commands; if you get an error on stop ssh, start ssh anyway and see what it says—the service could already be stopped.

(I would recommend stop/start over restart, unless you are trying to restart a system remotely. If ssh is already stopped, restart will not start it.)

If those commands don't work, you are probably either experiencing a bug or have tinkered too far with your system, in which case you at least know what the problem isn't.