How do I restart the SSH service?

Question

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.

Answer 1

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>

Answer 2

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.

Answer 3

Command for restart ssh service is:

sudo service ssh restart

Answer 4

Since Ubuntu 15.04, Canonical no longer ships upstart by default.
Thus, the commands start, stop and restart are no longer available.

The correct method for restarting the SSH service (or any other service) now is one of the two following commands:

sudo systemctl restart ssh
sudo service ssh restart

Answer 5

First check to see if sshd is running using the following:

ps -ef | grep sshd

You should see something like:

root      1234     1  0 12:28 ?        00:00:00 /usr/sbin/sshd -D

If you do not see a line for /usr/sbin/sshd -D then sshd was either never started or has crashed, which will require further troubleshooting to find out why.

If you do see that line, next run this:

cat /var/run/sshd.pid

This should print the process id of sshd, so in this case you should see:

userid@computername:~$ cat /var/run/sshd.pid 
1234

If the contents of sshd.pid does not match the process id of the running instance of sshd then something has restarted it incorrectly. But whatever the details you find here should put you on the right track. Either it's crashing, being restarted incorrectly, or never being started in the first place.

Answer 6

I think that the Unknown instance error is because SSH is not running.

Try:

ps ax | grep sshd

To see if the SSH daemon is running or not, you should see something like:

/usr/sbin/sshd -D

In any case, just try any of these:
sudo /etc/init.d/ssh start
sudo start ssh