9.2.2. Starting an OpenSSH Server

Note: Make Sure You Have Relevant Packages Installed

To run an OpenSSH server, you must have the openssh-server and openssh packages installed. Refer to Section 1.2.2, “Installing” for more information on how to install new packages in Red Hat Enterprise Linux.

To start the sshd daemon, type the following at a shell prompt:

~]# service sshd start

To stop the running sshd daemon, use the following command:

~]# service sshd stop

If you want the daemon to start automatically at the boot time, type:

~]# chkconfig sshd on

This will enable the service for all runlevels. For more configuration options, refer to Chapter 7, Controlling Access to Services for the detailed information on how to manage services.

Note that if you reinstall the system, a new set of identification keys will be created. As a result, clients who had connected to the system with any of the OpenSSH tools before the reinstall will see the following message:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.

To prevent this, you can backup the relevant files from the /etc/ssh/ directory (see Table 9.1, “System-wide configuration files” for a complete list), and restore them whenever you reinstall the system.