SSH

SSH: 

 The Secure Shell Protocol is a cryptographic network protocol for operating network services securely over an unsecured network. Its most notable applications are remote login and command-line execution. SSH applications are based on a client–server architecture, connecting an SSH client instance with an SSH server. 

SSH connection: 
ssh -p 22 oracle@IP

SSH connection problem with "Host key verification failed..." error

"Host key verification failed" means that the host key of the remote host was changed.

SSH stores the host keys of the remote hosts in ~/.ssh/known_hosts. You can either edit that text file manually and remove the old key (you can see the line number in the error message), or use

ssh-keygen -R hostname

From man page:

-R hostname

Removes all keys belonging to hostname from a known_hosts file. This option is useful to delete hashed hosts .