14.4. OpenSSH Clients

To connect to an OpenSSH server from a client machine, you must have the openssh-clients and openssh packages installed (see Section 8.2.4, “Installing Packages” for more information on how to install new packages in Red Hat Enterprise Linux).

14.4.1. Using the ssh Utility

The ssh utility allows you to log in to a remote machine and execute commands there. It is a secure replacement for the rlogin, rsh, and telnet programs.
Similarly to the telnet command, log in to a remote machine by using the following command:
ssh hostname
For example, to log in to a remote machine named penguin.example.com, type the following at a shell prompt:
~]$ ssh penguin.example.com
This will log you in with the same user name you are using on the local machine. If you want to specify a different user name, use a command in the following form:
ssh username@hostname
For example, to log in to penguin.example.com as john, type:
~]$ ssh john@penguin.example.com
The first time you initiate a connection, you will be presented with a message similar to this:
The authenticity of host 'penguin.example.com' can't be established.
RSA key fingerprint is 94:68:3a:3a:bc:f3:9a:9b:01:5d:b3:07:38:e2:11:0c.
Are you sure you want to continue connecting (yes/no)?
Type yes to confirm. You will see a notice that the server has been added to the list of known hosts, and a prompt asking for your password:
Warning: Permanently added 'penguin.example.com' (RSA) to the list of known hosts.
john@penguin.example.com's password:

Important

Update the host key of an SSH server if the key changes. The client notifies the user that the connection cannot proceed until the server's host key is deleted from the ~/.ssh/known_hosts file. Contact the system administrator of the SSH server to verify the server is not compromised, then remove the line with the name of the remote machine at the beginning.
After entering the password, you will be provided with a shell prompt for the remote machine.
Alternatively, the ssh program can be used to execute a command on the remote machine without logging in to a shell prompt:
ssh [username@]hostname command
For example, the /etc/redhat-release file provides information about the Red Hat Enterprise Linux version. To view the contents of this file on penguin.example.com, type:
~]$ ssh john@penguin.example.com cat /etc/redhat-release
john@penguin.example.com's password:
Red Hat Enterprise Linux Server release 6.2 (Santiago)
After you enter the correct password, the user name will be displayed, and you will return to your local shell prompt.