Maintaining Your System Configuration

SUSE LINUX Enterprise Server (SLES) maintains information about your system's configuration in the directory /etc/sysconfig. The files and directories present in this location dictate the behavior of the various hardware and software components that make up your server.

When the time comes to reconfigure your server, the files in /etc/sysconfig have to be updated to reflect the change in resources. A proper understanding of the mechanisms involved in making such modification is necessary to allow you to quickly diagnose any difficulties that arise.

SuSEconfig

It is possible to maintain your system manually by editing files residing under /etc/sysconfig and then alerting the system's services of the changes by running SuSEconfig. However, this approach is not recommended unless you have in-depth knowledge of the service you are maintaining and the syntax of its configuration files.

The same configuration files are often required for a number of services. Conversely, one service may depend on multiple configuration files in numerous distinct directories. Making manual changes to one service may have negative effects on others. If you choose to edit the configuration files, make sure to store backup copies first in case of an emergency.

The changes to the static setup files will not affect the functioning of the system until after their services have been restarted. The SUSEconfig utility is invoked to implement the changes.

WARNING

Manual editing of some files is required to gain access to certain advanced configuration features because they are not accessible using the GUI tools. For this reason, you may decide that you would like to maintain some configuration files manually.

It is important that you allow yourself a method for rolling back changes. Making a pre-edit snapshot, or backup copy, of the file you want to change is crucial. In the event of unexpected behavior, the offending configuration file can be quickly replaced without having to rely on the previous days' backups. Depending on the significance of the change, the previous backup media might not be accessible!

Being paranoid is an integral part of system management. Having a quick restore point will save hours of frustration and downtime. Trading a little bit of disk space for peace of mind is a good investment at any time.

SUSEconfig is located in /sbin. This high-level utility invokes the necessary secondary scripts to implement configuration parameters defined in /etc/sysconfig. These scripts, located in the /sbin/conf directory, are named Suseconfig.subsystem-name. Each SuSEconfig script manages one of the subsystems currently installed on the server.

A drawback with SuSEconfig is that it is not the master of all the configuration files found in /etc/sysconfig. SuSEconfig does not handle a number of configuration files, notably the ones containing your machine's IP address and volume information.

Limitations in the scope of the SuSEconfig utility, coupled with the intricate nature of modifying multiple files in multiple directories for a single change, make the manual reconfiguration of servers a daunting task. Though servers have been maintained this way for quite some time, a more consistent and efficient automated tool offered with SLES is YaST.

YaST (Yet another Setup Tool)

YaST, as its name implies, is a setup tool for configuring SUSE systems. This utility has been built to present a more intuitive GUI-based environment for maintaining system configuration files. YaST also organizes information drawn from multiple files in different directories into a simple, consistent presentation. This allows you to concentrate on the changes you are trying to make and removes the underlying complexities. Whenever possible, YaST leverages the SuSEconfig utility to manage subsystems.

The YaST configuration tool is accessible through two separate GUI interfaces. The Qt interface is present under the X Windows System, whereas the other uses ncurses and allows a GUI interface in a terminal environment. Both implementations allow you access to the full functionality of the application.

YAST INTERFACES

Both YaST interfaces can be invoked from a terminal session. In an X Windows System terminal session, you invoke the Qt version of YaST by typing yast2 at the command line. Navigation within yast2 is done with the mouse. In non-X terminal sessions, you invoke YaST by simply typing yast. The ncurses version of YaST is navigated using the arrow keys as well as Alt-letter combinations, where the letter required is highlighted within the keyword for each menu option.

You might wonder why both interfaces were created. The simple answer is that for a number of server environments, the X Windows System interface is simply not required. Keep in mind that it is imperative to run only the applications required to support a server's tasking. Additional applications can potentially contain vulnerabilities that could compromise the environment.

Also, running these additional applications requires system resources. If the X Windows System interface is not used, the resources it and its associated routines consume would be better dedicated to the server's applications.

On most servers, it is considered prudent not to install the X Windows System or run the server at runlevel 3. On such systems, the ncurses version of YaST allows you to quickly reconfigure the machine with minimal impact on system resources.

You can see the initial YaST menu for both interfaces in Figures 2.1 and 2.2. The main menu for the YaST tool subdivides maintenance into the following main categories:

• Software This section allows you to control what modules are installed on your system, the location of the installation media, as well as how you keep the applications and services up to date. From this selection, you can configure User Mode Linux (UML) as well as your YaST Online Update Server.

• Hardware This section allows you to maintain the different hardware components of your system. Menu options found here cover your server's controller cards for video, sound, and disk. You also can use this section to define peripheral devices such as printers and joysticks.

• System This section of YaST covers your system configuration. It allows you to fine-tune how your system will behave through startup, disk volume, and power management.

• Network Devices This section defines how your server interacts with the outside world. Included in this submenu are server-network interfaces as well as service/appliance connections such as FAX and answering machines.

• Network Services In this section, you maintain the applications that define your server's tasking. You should find configuration options that allow you to customize the services your machine offers. Included are the modules you installed in the Software menu option earlier in this list.

• Security and Users This section allows you to define your password policies, users, groups, your server's internal firewall settings, and the way your server will manage its certificates.

• Misc This catch-all option allows you to view your startup and systems logs in a GUI environment. You can also use this section to define your server as a source server for installations.

Figure 2.1. The ncurses YaST main menu.

Figure 2.2. The X Windows System's YaST main menu.

The YaST tool provides command-line shortcuts for accessing the configuration options of the various modules. As an example, you can access the firewall configuration screen by starting YaST, selecting the Security and Users menu, and then selecting the Firewall option. Alternatively, you can go directly to the firewall configuration routines by invoking YaST with the "firewall" command-line parameter. The man pages for yast2 discusses the -list option, which, when invoked, reveals a list of the shortcuts to the different submenu options. Though at first navigating from the main YaST screen will be more comfortable, quickly accessing what is required directly will become second nature.

NOTE

You can find the man page documents for the non-X terminal version of YaST under the yast2 man pages.

SuSEconfig and YaST are tools bundled with SLES that help you configure and maintain your server. Together, the utilities provide a consistent approach and reduce the chances of a forgotten step when multiple changes are required. Now that you have a basic understanding of the YaST tool, it is time to apply this knowledge to everyday system management.