Fix 'systemctl: command not found' Error on Linux

The error message 'systemctl: command not found' indicates that the 'systemctl' command is not available on your system.

'systemctl' is a command used to manage systemd services on Linux systems. It is typically found on distributions that utilize systemd as the init system, like Ubuntu, CentOS, and Fedora.

If you are using a distribution that does not use systemd, such as older versions of Ubuntu that used Upstart, you will need to use a different command to restart the SSH service. For instance, on Upstart-based systems, you can use the following command:

sudo service ssh restart

If you are running a different distribution or version, please provide more details about your system so that we can give you more specific instructions.