Controlling System Startup

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.

Choosing a Startup Volume with System Preferences

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 the volume you selected.

Choosing a Startup Volume During Startup

During the startup process, 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).

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You can refresh the list of valid startup volumes by clicking the circular arrow button.

Starting Up in Single-User Mode

The single-user 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.

NOTE

Single-user mode is also called Console mode.

CAUTION

When you start up in single-user mode, you will be using the root account. Under this account, you can do anything to the files on your Mac, so be careful that you don't do something you didn't mean to do. Some actions you perform under the root account can't be undone.

To start up in single-user 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 will see the localhost Unix prompt. This means you can start entering Unix commands.

NOTE

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 might also 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

 /sbin/fsck --y 

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).

NOTE

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, p. 299.

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.

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If you want to eject a disc when you restart your Mac, hold down the mouse button while you restart.

Starting Up in Verbose Mode

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.

Starting Up in Safe Mode

If you are having trouble starting up your Mac, try starting in Safe mode. When you do this, you'll start up in a basic system where many features are disabled. However, this can be useful when you are troubleshooting problems. To start up in Safe mode, start or restart your Mac. When the startup sound plays, hold down the Shift key. When you see the spinning progress indicator underneath the Apple logo, release the Shift key. You will then start up in Safe mode.

Starting Up in Target Disk Mode

If you'd like to connect two computers together so you can easily move files between them, you can use FireWire to have one computer act like a mounted volume on another. The computer you want to use as a disk must be started up in Target Disk mode.

NOTE

Target Disk Mode is different than networking computers because the computer that is operating in Target Disk mode works like a hard drive instead of like a computer. You can't use it to do anything beyond what an external drive can do.

First, configure the Mac you want to use as a disk to start in Target Disk mode. Open the Startup Disk pane of the System Preferences application, and click the Target Disk Mode button located at the bottom of the pane. Click Restart at the prompt. When the Mac restarts, you'll see a FireWire symbol in its screen. This indicates that it is in Target Disk mode.

Connect the Mac to another one using a FireWire cable. The Target Disk Mac will appear as a mounted disk on the second Mac. You can then use its hard drive just like one installed on the second machine. For example, you can move files to it, install software on it, and so on.

To return the Mac to normal condition, press the Power button. The Mac will shut down. Disconnect the FireWire cable and then press the Power button again to restart it normally.

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Using Target Disk mode can be an easy way to back up all the files on a mobile Mac. Restart the mobile Mac in Target Disk mode and connect it to a desktop machine with some free hard drive space. Drag all the files from the mobile Mac onto the disk on which you want to store the backed-up files.

Using Other Startup Options

Table 8.2 lists various startup options and their keyboard shortcuts.

Table 8.2. Mac OS X Startup Options

Startup Option	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.
Start up from a computer connected via FireWire in Target Disk Mode	Press T during startup.
Eject a CD during the startup process	Hold down the mouse button.