Chapter 21. OpenSSH
OpenSSH is a free, open source implementation of the SSH
SHell) protocols. It replaces
rlogin, rsh, and
rcp with secure, encrypted network connectivity tools.
OpenSSH supports versions 1.3, 1.5, and 2 of the SSH protocol. Since
OpenSSH version 2.9, the default protocol is version 2, which uses RSA
keys as the default.
If you use OpenSSH tools, you are enhancing the security of your
machine. All communications using OpenSSH tools, including passwords,
are encrypted. Telnet and ftp use
plain text passwords and send all information unencrypted. The
information can be intercepted, the passwords can be retrieved, and your
system could be compromised by an unauthorized person logging in to your
system using one of the intercepted passwords. The OpenSSH set of
utilities should be used whenever possible to avoid these security
Another reason to use OpenSSH is that it automatically forwards the
DISPLAY variable to the client machine.
In other words, if you are running the X Window System on your local
machine, and you log in to a remote machine using the
ssh command, when you run a program on the remote
machine that requires X, it will be displayed on your local machine.
This feature is convenient if you prefer graphical system administration tools
but do not always have physical access to your server.