because each service might require special commands.
After all the system scripts have been run, your system is configured, and all
the necessary system services have been started. If you are using a runlevel
other than 5, the final act of the init process is to launch the user shell
—bash, tcsh, zsh, or any of the many other command shells available.
The shell launches, and you see a login prompt on the screen.
Controlling Services at Boot with Administrative
Tools
You can configure what services run at startup with Startup Applications
Preferences (shown in Figure 15.1). Here Ubuntu lists all the services that you
can have automatically start at boot time. Checked programs are enabled by
default, but you can uncheck the ones you don’t want. It is not recommended
that you disable services randomly “to make things go faster.” Some services
might be vital for the continuing operation of your computer, such as the
graphical login manager and the system communication bus.
FIGURE 15.1 You can enable and disable Ubuntu’s boot services by toggling
the check boxes in the Startup Applications Preferences dialog.
Changing Runlevels
After making changes to system services and runlevels, you can use the
telinit command to change runlevels on-the-fly on a running Ubuntu
system. Changing runlevels this way enables system administrators to alter
selected parts of a running system to make changes to the services or to put
into effect changes that have already been made (such as reassignment of