Controlling Services at Boot with the YaST Runlevel Editor

YaST provides a startlingly easy way for system administrators to manage which services run at boot. The YaST Runlevel Editor module is easy to understand and gives you important information about each service. The start/stop process is nothing more than a mouse click.

How wonderful, you're thinking. A nice change. Experienced system administrators may cringe a little, though. It is so easy to destroy your system. The help text to the left of the Runlevel Editor, shown in Figure 22.8, offers a relatively calm warning: The runlevel editor is an expert tool. Only change settings if you know what you are doing, otherwise your system might not function properly afterwards.

Figure 22.8. The YaST Runlevel Editor makes it incredibly easy to turn services on and off. Great care must be taken so that you do not disrupt your system's functioning.

That's fine as far as it goes. The Caution box coming up next may be closer to the point.

Caution

You can render your system unbootable if you do not take particular care when starting new services, and especially when stopping existing services.

Using the Runlevel Editor in Expert Mode is potentially more dangerous. Don't change the runlevel for a service without very good reason.

Always review the changes you made before closing the Runlevel Editor. They will not take effect until you reboot your computer, so you can prevent catastrophic errors if necessary.

Using the Runlevel Editor

When you open the Runlevel Editor module from the YaST System page, a list of all available services appears. The second column tells you whether this service currently is loaded at boot, and the third column offers a brief description of each service. Click a service, such as freshclam in Figure 22.9, and see a more detailed description in the bottom pane.

Figure 22.9. The Runlevel Editor Expert Mode lets you start and stop services, set different runlevels for individual services, and set the default runlevel on boot.

To start a service when you next boot your system, select it from the list and click Enable. To turn a service off, select it and click Disable. Review your changes and click Finish to confirm them. Reboot your computer to force the changes.

Expert Mode

Click the Expert Mode button to display the additional options (see Figure 22.9). The first thing you may notice are the boot scripts and other services listed here. When in Expert Mode, you really need to know what you're doing, and you get much less hand holding as far as descriptions of each service.

In Expert Mode, you can do the following:

• Change the default runlevel on boot.

• Identify which service can run on each runlevel, from boot to shutdown and everything in between.

• Start, Stop, or Restart any service without rebooting.

• Enable all services on boot.

As in Simple Mode, the editing process is straightforward. Use the drop-down menu to select the default runlevel. Select a service to make changes. Click the Start/Stop/Refresh menu to act on a service now: Start a service not currently running, Stop a running service, or Refresh (stop, if necessary, then start) a service.

Use the check boxes near the bottom of the screen to change the runlevel of a selected service. B runs a service at boot. S runs a service at shutdown.

Notice that when you change from Simple Mode to Expert Mode, the second column changes from Enabled to Running. This lets you use the Start/Stop/Refresh menu. The Set/Reset menu lets you Enable or Disable individual services and adds a third option: Enable All Services.

Make your changes, review them carefully, and then click Finish to confirm your changes.