Remote Login Services
There may come a time when you need to log into your Mac from another machine or log into another Mac (or Unix system) from your machine. For this, Mac OS X offers remote login services such as the Secure Shell, Telnet, and the remote shell.
The Secure Shell
The Secure Shell (
SSH), is a protocol for using
key-based encryption to allow secure communication between machines.
As its name suggests, it is most commonly used for interactive
sessions with shells on remote machines, so that you can use the
ssh command as described in
“Remote Logins” in Chapter 8.
Mac OS X ships with the OpenSSH (http://www.openssh.com) client and server
software. This includes the
ssh command, which
you use to open SSH connections to other machines, and the
sshd daemon program, which you run to allow
other machines to SSH into your Mac.
As with FTP (see Section 12.5), running an SSH service (the
sshd daemon) on Mac OS X is easy: just activate
the Remote Login checkbox in the Sharing pane.
OS X versions prior to 10.1.0 shipped with
telnetd, a daemon that runs the Telnet protocol,
as its default remote login server. Telnet is a decades-old method
for getting a virtual terminal on a remote machine through a network.
However, it’s inherently insecure, because all its
transmissions are cleartext, lacking any sort of encryption, and hence easily readable by malevolent entities monitoring the traffic that enters and leaves your network. Use of Telnet has, in recent years, fallen ...