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
434

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