Under Mac OS X, there are several ways to configure and control the startup process. The most straightforward way is to use the Startup Disk pane of the System Preferences application to select a startup volume. There are other ways you can control system startup as well, such as selecting a startup volume during the startup process, starting up in the single-user mode, and starting up in the verbose mode.
The Startup Disk pane of the System Preferences application enables you to select a startup volume. Open the pane to see a list of the valid startup volumes on your machine. Select the volume from which you want to start up and click Restart. You are prompted to confirm this action by clicking the Restart button. Your selection is saved and your Mac restarts from that volume.
Under Mac OS X, you can select the startup volume by holding down the Option key while the machine is starting up. When you do, you see a window that displays each of the valid startup volumes on your machine. The currently selected startup volume is highlighted. You can select a startup volume by clicking it and pressing Return (you can also click the right-facing arrow icon to select the startup volume).
You can refresh the list of valid startup volumes by clicking the circular arrow button.
The Console mode starts up your Mac in a Unix-like environment. In this environment, you can run Unix commands outside of Mac OS X. This can be useful in a couple of situations, mostly related to troubleshooting problems.
Console mode is also called single-user mode.
To start up in Console mode, hold down -S while the machine is starting up. Many system messages appear and report on how the startup process is proceeding. When the startup is complete, you see a date and time message, and near that you see the localhost Unix prompt.
During the startup process, you are likely to see some information that doesn't make a lot of sense to you unless you are fluent in Unix and the arcane system messages you see. You will also probably see some odd error messages, but typically I wouldn't worry about them too much. However, if you have particular problems you are trying to solve, some of these messages might provide valuable clues for you.
One of the more useful things you can do is to run the Unix disk-repair function, which is fsck. At the prompt, type
and press Return. The utility checks the disk on which Mac OS X is installed. Any problems it finds is reported and repaired (if possible).
If the startup disk is Journaled, type /sbin/fsck -yf to force the utility to run.
You can use many other Unix commands at this prompt, just as if you were using the Terminal application from inside Mac OS X.
To learn more about using Unix commands, see Chapter 9, "Unix: Working with the Command Line," p. 243.
To resume the startup process in Mac OS X, type the command reboot and press Return. Additional, even more arcane Unix messages appear and then the normal Mac OS X startup process continues. When that process is complete, you end up at the Login window or directly in the Mac OS X desktop, depending on how your Login preferences are configured.
If you hold down -V while your Mac is starting up, you start up in the verbose mode. In this mode, you see all sorts of system messages while the machine starts up. The difference between verbose mode and single-user mode is that the verbose mode is not interactive. All you can do is view the system messages; you can't control what happens. Many of the messages you see will probably be incomprehensible, but some are not (particularly messages about specific system processes starting up). This mode is likely to be useful to you only in troubleshooting. And even then, the single-user mode is probably more useful because it gives you some control over what is happening.
Table 8.2 lists various startup options and their keyboard shortcuts.
How to Select It
Prevent automatic login
Hold the left Shift key and mouse button down when you see the progress bar during the startup process.
Close open Finder windows
Hold down the Shift key.
Start up from a computer connected via
Press T during startup.
FireWire in Target Disk Mode
Eject a CD during the startup process
Hold down the mouse button.
Prevent startup items from opening
Hold down the Shift key.