Learning Red Hat Enterprise Linux & Fedora, Fourth Edition

The Secure Shell

The Secure Shell (SSH) lets you connect to a system from another system via TCP/IP and obtain a shell prompt, from which you can issue commands and view output in a secure fashion. SSH works similarly to the older and possibly more familiar Telnet service, but differs in that conversations between SSH and its clients are sent in encrypted form so hackers cannot easily discover private information, including user account names and passwords.

Installing SSH

The installation procedure automatically installs an SSH client and server and associates the sshd service with runlevels 3-5. You can start, stop, and restart the sshd service and changes its associations with runlevels by using the Service Configuration Tool. The service must be running in order to respond to clients.

Tip

The SSH service has several configuration files, residing in /etc/ssh. You don’t have to modify them to get SSH running. If you’re curious about them, view the sshd manpage.

Using SSH

To verify that the SSH server is properly running, you can access it via a client on the local system by issuing the following command:

$ ssh localhost

The client will attempt to log you on to the local system using your current user account and will prompt you for your password. If you supply the correct password, you should see a shell prompt, indicating that the client and server are functioning correctly. Type exit and press Enter to exit SSH.

To log on to a remote system, simply specify the hostname or IP ...