12.8. Fast User Switching
The account system described so far in this chapter has its charms. It keeps everyone's
stuff separate, it keeps your files safe, and it lets you have the desktop picture of your
Unfortunately, it can go from handy to hassle in one split second. That's when you're
logged in, and somebody else wants to duck in just for a second—to check email or a
calendar, for example. What are you supposed to do—log out completely, closing all
your documents and quitting all your programs, just so the interloper can look something
up? Then afterward, you'd have to log back in and fire up all your stuff again, praying
that your inspirational muse hasn't fled in the meantime.
Fortunately, that's all over now. Fast User Switching—a feature modeled on a similar
Windows feature, which itself was modeled on a Unix feature—lets Person B log in and
use the Mac for a little while. All of your stuff, Person A, simply slides into the
background, still open the way you had it; see Figure 12-14.
When Person B is finished working, you can bring your whole work environment back to
the screen without having to reopen anything. All your windows and programs are still
open, just as you left them.
To turn on this feature, open the Accounts panel of System Preferences (and click the
, if necessary, to unlock the panel). Click Login Options, and turn on "Enable fast
user switching." (You can see this dialog box in Figure 12-12.)
The only change you notice immediately is the appearance of your own account name in
the upper-right corner of the screen (Figure 12-14, top). You can change what this menu
looks like by using the "View as" pop-up menu, also shown in Figure 12-12.
That's all there is to it. Next time you need a fellow account holder to relinquish control
so that you can duck in to do a little work, just choose your name from the Accounts
menu. Type your password, if one is required, and feel guiltless about the interruption.
And now, the finer points of Fast User Switching:
• Depending on how many programs are open and how much memory the Mac has,
switching accounts may entail a delay and a good deal of hard drive activity.
That's Mac OS X's virtual memory scheme "setting down" what was in memory in
your account to make room for the incoming account's stuff.
• To exit an open account, choose Log Out as usual. Or just choose Login
Window from the Accounts menu. It ensures that you can get to your own account
no matter whose is running at the moment.
• Weirdly enough, a bunch of account holders can be using the same program
simultaneously in their own parallel universes. Even if Microsoft Word was open
in your account, Chris, Casey, and Robin can each open the same copy of the same
program simultaneously when they fast-switch into their own accounts. (Word, in
that case, uses up four times as much memory, of course.)
Figure 12-14. Top: The appearance of the Accounts menu lets you know that
Fast User Switching is turned on. The circled checkmark indicates people
who are already logged in, including those who have been "fast user
switched" into the background. The dimmed name shows who's logged in
Bottom: When the screen changes from your account to somebody else's,
your entire world slides visibly offscreen as though it's mounted on the side of
a rotating cube—a spectacular animation made possible by Mac OS X's
Quartz Extreme graphics software.
• You can't make changes to accounts (in System Preferences) that are still logged
in. Nor, as you'd expect, can you turn off Fast User Switching while other people
are logged in. Can't turn on FileVault, either.
• If you try to shut the Mac down or rest art it while other people are logged in, a
dialog box tells you, "There are currently logged in users who may lose unsaved
changes if you shut down this computer." And you're asked to type in an
administrator's name and password to establish that you know what the heck
Here's a moral dilemma for the modern age. If you proceed by typing the
password and clicking Shut Down, you shut down all accounts that were open in
the background and any open documents—and if those documents hadn't been
saved, any changes are gone forever. If you click Cancel, you can't shut down the
Mac until you hunt down the account holders whose stuff is still open in the
background so they can log out.
Tip: You can avoid this awkward situation in either of two ways: (1) Trust each
other completely, or (2) save all your documents before you let anyone else cut in
and send your account to the background.
• Remember the Shared folder (in the Users folder on the hard drive)? It's still the
wormhole connecting all accounts. If you want to share a file with another account
holder, put it there.
• Your account isn't anesthetized completely when it's switched into the
background. In fact, it keeps on doing whatever you set it to doing. If you were
downloading some big file, for example, it keeps right on downloading when the
next guy logs in.