How could I disable the annoyed beeping tone caused by Citrix client?

You have to make changes to Putty-generated RSA public key in order to remotely access Linux server over SSH protocol.

You cannot append or insert Putty-based RSA key to authorized_keys file of OpenSSH. A little bit of changes is necessary to authenticate with OpenSSH server using the Putty-generated RSA Public-key.

There is a trick to install public key generated by Puttygen into OpenSSH server. Otherwise, Putty will fail to authenticate with OpenSSH server with rejection message that says “Server refused our key”.

Is there a proper way to exit from telnet login prompt other than forcibly kill the telnet client process?

If you insist, this is the way to enable remotely login Linux server via telnet protocol with root user privilege.

What happen if you telnet clients unable to remote access Linux server, with an error message that says “Name or service not known: illegal seek”.