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[ws001]
XSERVER	= XF86_SVGA
X_MOUSE_PROTOCOL		= “Microsoft”
X_MOUSE_DEVICE		= “/dev/ttyS1”
X_MOUSE_RESOLUTION = 50
X_MOUSE_BUTTONS		= 3
X_MOUSE_BAUD		= 1200
[ws002]
XSERVER	= XF86_Mach64
[ws003]
XSERVER	= XF86_SVGA
X_COLOR_DEPTH		= 24
USE_XFS	= N
[ws004]
UI_MODE	= CHAR

These parameters are used to create a basic configuration that allows the creation of terminals. These terminals may be GUI-based and can be configured to perform all the tasks required by the clients.

Monitoring remote connections

4.11 Use network commands to connect to and manage remote systems (e.g., telnet, ftp, ssh, netstat, transfer files, redirect Xwindow)

FTP, HTTP, TELNET, and ssh create remote connections to a system. They allow you to be able to login and use the remote machine as if you were sitting physically at the console.

Telnet

Telnet is a terminal emulation program for clients running on TCP/IP networks. It connects you to a terminal on another machine. This connection allows you to enter commands on that machine as if you were at the actual physical console. To connect to a host called server1, you would enter the command:

telnet server1

You should then receive a login prompt from where you can log into the system and start entering commands. To exit out of the telnet command, you simply have to logout, or use the quit command.

FTP

FTP (File Transfer Protocol) is a protocol that is part of the TCP/IP suite. It allows you to connect to a remote host and transfer files to or from the remote host. For example, to connect to a host called server1, you would enter the command:

Chapter 10 Linux Terminals and Shells 339

ftp server1

This command will connect you to the FTP server process on server1, which will prompt you with a login. Once logged into the system, you can use the cd and ls commands to traverse and examine the directories on the system. Retrieving files from the remote host is accomplished by the get command. Uploading a file to the host is accomplished by using the put command.

SSH

SSH (secure shell) is similar to telnet, in that you use it to connect to a remote machine, but in this case, the communications and authentication are encrypted to prevent someone from listening in to the session.

X remote login

The X Windows system allows for remote X logins to other hosts, and also allows the ability of a client to run an X Windows session on another machine. For example, if you need to start an X login with server1, you would use the command:

X -query server1

You can also redirect your own display to a remote host, as long as the appropriate permissions are in place. For example, your client (client1) wants to open up an X Window on server that is from your client machine. First, the server has to give you permissions to do this:

xhost + client1

Now, you have to use the DISPLAY command to export your display:

DISPLAY=server1:0 xterm &

This command starts xterm in background mode (&), so you will not interfere with the main X session that is running on the server.

Netstat

The connections from these services, such as telnet, ssh, and ftp, may require detection by an administrator, so that any unauthorized attempts at logging in can be seen and logged. One of the most common tools used to perform this task is netstat. The netstat command provides information similar to the following:

[user@dhcppc1 user]$ netstat
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address							Foreign Address	State
tcp	0	0	192.168.0.7:telnet			192.168.0.8:blackjack ESTABLISHED
tcp	0	20 192.168.0.7:ssh				192.168.0.6:1137 ESTABLISHED
Active UNIX domain sockets (w/o servers)
Proto RefCnt Flags				Type	State		I-Node Path
unix 8		[ ]	DGRAM		10679 /dev/log

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unix 2	[ ]	DGRAM	16916
unix 3	[ ]	STREAM	CONNECTED	16330	/tmp/.X11-unix/X0
unix 3	[ ]	STREAM	CONNECTED	16329
unix 3	[ ]	STREAM	CONNECTED	16321	/tmp/.font-unix/fs-1
unix 3	[ ]	STREAM	CONNECTED	16320
unix 3	[ ]	STREAM	CONNECTED	16322	/tmp/.X11-unix/X0
unix 3	[ ]	STREAM	CONNECTED	16317
unix 2	[ ]	DGRAM	15166
unix 2	[ ]	DGRAM	14346
unix 2	[ ]	DGRAM	11463
unix 2	[ ]	DGRAM	10704
unix 2	[ ]	DGRAM	10691
unix 2	[ ]	STREAM	CONNECTED	10101

This output shows some of the current active UNIX domain sockets and remote hosts. In this example, the remote hosts use TELNET and ssh to connect to the system. Netstat is a powerful tool that uses the options shown in Table 10-1.

	Table 10-1
	Netstat Options
Option	Description
No Options	By default, netstat displays a list of open sockets.
-a --all	Shows both listening and non-listening sockets.
-A --protocol=family	Specifies the address families for which connections are to be
	shown.
-c --continuous	Causes netstat to print the selected information every second
	continuously.
-C	Prints the routing information from the route cache.
-e --extend	Displays additional information.
-F	Prints routing information from the FIB.
-g --groups	Displays multicast group membership information for IPv4 and
	IPv6.
-I --interface=iface	Displays a table of all network interfaces, or the specified iface.
-l --listening	Shows only listening sockets.
-M --masquerade	Displays a list of masqueraded connections.
-n --numeric	Shows numerical addresses instead of trying to determine
	symbolic host, port, or user names.
--numeric-hosts	Shows numerical host addresses but does not affect the
	resolution of port or user names.