The SSH client lets you remotely log in to systems that provide an SSH server. It’s likely that the installation procedure installed the SSH client for your use. To check whether it’s installed, issue the command:

               rpm -q openssh

If openssh is installed, the command reports its version number; otherwise, the command reports that openssh is not installed.

You can manually install the SSH client by using GnoRPM to install the following packages:

To install the SSH server, use GnoRPM to install the openssh-server package.

Once installed, the SSH server should start automatically. To check the status of the SSH server, issue the command:

               service sshd status

The command’s output should report that the server is running. If not, you can manually start the server by issuing this command:

               service sshd start

If you want to stop the SSH server, issue this command:

               service sshd stop

To verify that the SSH server is properly running, you can access it via a client on the local system by issuing the following command:

               ssh localhost

The client will attempt to log you onto the local system using your current user account and will prompt you for your password. If you supply the correct password, you should see a shell prompt, indicating that the client and server are functioning correctly. Type exit and press Enter to exit SSH.

To log on to a remote system, simply specify the hostname or IP address of the remote system in place of localhost. If you want to log in to a user account other than one named identically to the account you’re using on the local system, issue the command:

               ssh 
               userid@host

where host is the hostname or IP address of the remote host and userid is the name of the user account you want to use. For example:

# ssh [email protected]

You can use the SSH client’s scp command to transfer files to or from a remote system running an SSH server. To transfer a file to a remote system, issue a command such as this one:

               scp 
               file 
               userid @host:path

where file is the path of the file to be transferred, host is the hostname or IP address of the remote host, path is the directory to which the file should be transferred, and userid is your user account on the remote system. You can specify multiple files to be transferred if you like. For example:

# scp rhbook_rev.txt [email protected]:bmcarty/files

You can use shell metacharacters to specify a set of files to be transferred. You can also specify the -r flag, which specifies that scp should recursively copy a directory rather than a file or set of files. For example, the following command copies an entire directory to the remote system:

               scp -r Desktop [email protected]:bmcarty/files

To transfer files from a remote system, issue a command based on this pattern:

               scp 
               userid @host:file 
               path

where host is the hostname or IP address of the remote system, file is the path of the file to be transferred, path is the destination path of the file, and userid is your user account on the remote system. For example:

# scp [email protected]:/outgoing/word98temp.doc /home/bmcarty/files

This command would log in the user bmcarty to ftp.ora.com/outgoing, retrieve the word98temp.doc file, and place it in his /home/bmcarty/files directory.

SSH also provides the sftp command, which lets you transfer files in much the same way the ftp command does. The command has the following form:

               sftp 
               user@host

The command will prompt for the password associated with the specified user account. For example, to transfer files to and from the host ora.com, you could issue the following command:

               sftp [email protected]

After establishing a connection to the specified host, the sftp command presents a prompt that lets you enter commands similar to those supported by the ftp command. Use the help command to learn more about the supported commands.

To log on to your Linux system from a remote system via SSH, you must install an SSH client on the remote system. A suitable client for Windows is Simon Tatham’s PuTTY, available at http://www.chiark.greenend.org.uk/~sgtatham/putty. Simply download PuTTY to any convenient directory (the windows directory is a good choice). The program doesn’t have a setup script; you can run it by selecting Start → Run and typing putty; if the directory in which PuTTY resides is not on the execution path, you must type the drive, path, and filename. Alternatively, you can create a shortcut that spares you the trouble. Figure 12-7 shows PuTTY’s main screen.

Figure 12-7. PuTTY’s screen

To use PuTTY to connect to a host, specify the following information:

Click Open to make the connection to the specified host.

The left pane of PuTTY’s screen provides access to several configuration options, such as:

Like most Telnet or FTP clients, PuTTY lets you save configurations so you can quickly connect to often-used hosts. Use the Load, Save, and Delete buttons to manage your list of hosts and associated configurations.

SSH lets you establish a network connection that you can use as a Virtual Private Network (VPN), so called because traffic flowing over the connection is encrypted and therefore secure from eavesdroppers. This facility is known as protocol tunneling because the data that flows via the connection need not use the standard TCP/IP protocol; for example, the data might be encoded using Novell’s IPX protocol.

Configuring and troubleshooting a VPN is not a task for a Linux newbie. However, if your Linux skills are growing and you desire a challenge, see Arpad Magosanyi’s VPN HOWTO, available at http://www.linuxdoc.org/HOWTO/mini/VPN.html. Also see Virtual Private Networks, by Charlie Scott, Paul Wolfe, and Mike Erwin (O’Reilly & Associates, Inc.).