LPI Linux Certification in a Nutshell, 2nd Edition

Objective 4: Secure Shell (SSH)

SSH, also known as Secure Shell, is an encrypting version of the old rsh/rlogin/rcp suite. The primary use for SSH is encrypted shell sessions to remote hosts, but it can also be used to copy files and to tunnel other protocols.

SSH is a server/client protocol offering sshd as the server and the ssh command as the client. The client connects to the server, they establish an encrypted session, and then the server demands authentication before finally logging in the client. For file copying in the manner of RCP, the secure replacement is the scp command.

In addition to simple login sessions and file copying, SSH can also provide transparent port forwarding, and as an extension of this, X authentication and forwarding. When you have an SSH session , you can start an X client on the remote machine, and the X Window System protocol will travel encrypted over your connection and display on your local machine without the need for settings such as DISPLAY=foo:0 or the xhost or xauth commands.

The implementation of SSH generally used on Linux systems is OpenSSH.

Installation and Configuration

OpenSSH may or may not be installed on your system by default. When it is installed, it generates a host key for your machine. This key will serve to authenticate your host in subsequent SSH sessions. Then you will typically want to create SSH authentication keys for your own personal account, as well as the root account. After that, you as the administrator should ...