If you ever need to restart the secure shell (ssh) service on Linux, you need to restart the sshd daemon. Here is how to do it on different Linux distributions.
Debian / Ubuntu
CentOS / Fedora / Redhat / RHEL
If you know some other distribution that makes it any different, let us know please.
Note: Consider that if you do it remotely, you will not be signed out, unless of course there is something wrong with the configuration and the sshd daemon would not start again, so be careful.