Understanding Administrative Access

When you are the administrator, of course you will need a method of accessing and administering a system without having to be in the location of your server. Besides accessing, you might also want to know who else is accessing your system at the same time. Aside of "who," you might also want to know how they are accessing.

So the first thing is once your system is up and running from a fresh installation... you have to be able to identify your console. Consoles are extremely significant as they are the way you manage your server. If you don't know how consoles work in linux or how to access them, it will make your life miserable as an admin working with linux.

Physical Console, Virtual Consoles, and PseudoTerminals

When you think of the physical console, you should be looking at things you can touch... your mouse, your keyboard, your monitor. These are inputs to a console. The monitor itself is only an output device... not really the console. What you may see is some of the console messages that have been mapped to display in your virtual console. However, the console may be remote, the console may be hooked up to a console server that connects to serial-only ports to access servers directly. The point is, that the console is just your entry to give commands to your linux kernel to perform tasks.

Your physical consoles can be recognized in your /dev directories as either tty0 or fb0. The significance between the two applicable  physical console device is within the architecture of the operating system. With the 32-bit version, you will use a /dev/tty0 console. 64-bit Editions will use /dev/fb0. For both of your virtual consols When you boot a linux system and the physical console devices are detected, they will default to those physical devices. Init will send information to /dev/console and the output you see on the screen is the output being fed to /dev/console directly. That is why you see all diagnostic information when you boot your linux server/desktop. This is controlled by the kernel and the parameters within the kernel with a console = parameter.

The virtual consoles: tty#, fb#, ttyS#, xvc#; all virtual consoles that are part of the linux operating system. The console xvc# wasn't mentioned but this is a serial simulated console for Xen Paravirtualized machines. You have several applications that are automatically configured in a Red Hat® Enterprise Linux® or Fedora Linux. The progarm used for the text based logins and virtual consoles is called mingetty. Mingetty is short for Minimal Getty, getty is used to fetch the virtual consoles. Prefdm is a program used to start a display-managed X Session. However, mingetty has no support for serial consoles. Agetty, or alternative linux getty, is the serial supported terminal console that is represented as ttyS#. If you didn't already know the acronyms... "TeleTYpe, FrameBuffer, TeleTYpe Serial, Xen Virtualized Console.

X Server

The X Window server, also referred to as X11 is the base for the GUI in most linux distributions. Including Red Hat® or Fedora® Linux. As far as maintenance to the X server system, it is maintained by the X Consortium @ http://www.x.org. XOrg is simply a project that makes X available for all different types of hardware. In almost every case, you will find the XOrg configuration files in /etc/X11/ directory path (xorg.conf).

Some tools used to onfigure or initialize X are prefdm, startx, and system-config-display.make an entire page just about X Server all daybut I will let you do your own research for this. One tip, if your X server doesn't automatically configure, you can execute the system-config-display --reconfig command.

SSH

In short, ssh is a replacement for telnet,  rcp, rlogin, and ftp. In almost all cases, you will be using SSH version 2 or higher. SSH if ever used anymore... is susceptible to man-in-the-middle attacks, which means that a rougue system can intercept and transmit credentials to authenticate themselves to your server with your credentials. This is just review from the beginners section. but if you are going for the Red Hat certifications, it's necessary knowledge.

Using SSH has many advantages, one of my personal favorite is the automatic redirection of X displays. Now in order to do that, X, as described above, is a server just like other services. On a single system, it's a local client and server. X Server can be directed to face a client remotely for applications that do not have command line support or text-user interface.

Examples:

[bob@station0014 ~]$ ssh -X server24
Last login: Wed Oct 27 14:22:09 2010
[bob@server24 ~]$ firefox

A window will pop up on your screen to display Firefox, note the header on Firefox. It should display as follows:
WebPage Title - Mozilla Firefox (on server24.itjournal.com)
So you get the idea with the (on server.domain.com) displayed on any window you have open. if you have your firewall at default configuration because it will tunnel and compress X through ssh session. Who says you can't use command line to modify a server. Try this with system-config tools and make life easier on yourself. You do not have to be on the system you're configuring if you can SSH to it. See the networking page in the Beginners Menu to setup SSH to isolate passwords and passphrases to a single-signon to gnome.