Ubuntu Unleashed, Second Edition

Welcome to Caitlin

Running Ubuntu

* All access is logged *

login: paul

Password:

Last login: Sat Jul 9 12:05:41 from 10.0.0.5

[paul@caitlin ~]$

TIP

Note that the server responds with

Welcome to Caitlin, running Ubuntu, which is

a customized message. Your machine will probably respond with

Ubuntu and some

version information. This is insecure: giving away version numbers is never a smart

move. In fact, even saying

Ubuntu is questionable. Edit the issue and issue.net files

in your /etc directory to change these messages.

Running the

w command now shows you as connecting from the external IP address.

Telnet Versus SSH

Although Telnet is worth keeping around as a fail-safe, last resort option, SSH is superior

in virtually every way. Telnet is fast but also insecure. It sends all your text, including

your password, in plain text that can be read by anyone with the right tools. SSH, on the

other hand, encrypts all your communication and so is more resource-intensive but

secure—even a government security agency sniffing your packets for some reason would

still have a hard time cracking the encryption.

Andy Green, posting to the

fedora-list mailing list, summed up the Telnet situation

perfectly when he said, “As Telnet is universally acknowledged to encourage evil, the

service telnetd is not enabled by default.” It is worthwhile taking the hint: Use Telnet as a

last resort only.

Setting Up an SSH Server

If not installed already, the OpenSSH server can be installed through Synaptic by adding

the openssh-server package. If you have disabled it, you can re-enable it by selecting

System, Administration, Services and selecting the Remote Shell Server box. As you might

have gathered,

sshd is the name for the SSH server daemon.

Two different versions of SSH exist, called SSH1 and SSH2. The latter is newer, is more

secure, comes with more features, and is the default in Ubuntu. Support for SSH1 clients

is best left disabled so older clients can connect. This is set up in the

/etc/ssh/sshd_

config file on this line:

#Protocol 2,1

CHAPTER 19 Remote Access with SSH and Telnet

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