Red Hat System Administration I

Log in as student on your desktopX machine.

ssh to your serverX machine. Accept the host key if asked. The host key is recorded on our local machine to identify the remote machine. The ssh command will fail to execute properly if the remote ssh host appears to have a different key than the recorded host key. The host key records are stored in the known_hosts file in the .ssh directory in the user's home directory on the local system.

[student@desktopX ~]$ ssh student@serverX
The authenticity of host 'serverX (172.25.X.11)' can't be established. 
ECDSA key fingerprint is 47:bf:82:cd:fa:68:06:ee:d8:83:03:1a:bb:29:14:a3.
Are you sure you want to continue connecting (yes/no)? yes
student@serverX's password: student

Run the w command. The output of the w clearly indicates we have logged in as user student from desktopX.

[student@serverX ~]$ w -f
11:01:23 up 1 day, 19:10, 1 user, load average: 0,0,0
USER    TTY   FROM       LOGIN@ IDLE  JCPU  PCPU  WHAT
student pts/1 desktopX 11:01  0.00s 0.12s 0.09s w

Execute the exit command to terminate the secure shell connection.

[student@serverX ~]$ exit
[student@desktopX ~]$ 

This time, ssh to your serverX machine as user root.

[student@desktopX ~]$ ssh root@serverX
root@serverX's password: redhat
[root@serverX ~]# 

Run the w command again. This time, the output of the w shows the active connection to the root user account from desktopX.

[root@serverX ~]# w -f
11:01:23 up 1 day, 19:10, 1 user, load average: 0,0,0
USER    TTY   FROM       LOGIN@ IDLE  JCPU  PCPU 
root    pts/2 desktopX 11:09  0.00s 0.13s 0.08s w

Run the exit to terminate the secure shell connection.

[root@serverX ~]# exit
[student@desktopX ~]$ 

There are different reasons why a remote host might have legitimately changed its host key. One common reason is when the remote machine is replaced because of hardware failure, or reinstalled. Usually, it is advisable to only remove the key entry for the particular host in the known_hosts. In this case, there is only one host entry in the known_hosts, so it can be removed completely. Remove the known_hosts file for the user student.

[student@desktopX ~]$ rm ~/.ssh/known_hosts

ssh to serverX as root again. Accept the key, log in, and then exit the session.

[student@desktopX ~]$ ssh root@serverX
The authenticity of host 'serverX (::1)' can't be established.
ECDSA key fingerprint is 47:bf:82:cd:fa:68:06:ee:d8:83:03:1a:bb:29:14:a3.
Are you sure you want to continue connecting (yes/no)? yes
root@serverX's password: redhat
[root@serverX ~]# exit
[student@desktopX ~]$ 

Use ssh non-interactively to run the hostname command on serverX as root.

[student@desktopX ~]$ ssh root@serverX hostname
root@serverX's password: redhat
serverX.example.com