- 13.5. Screen Sharing
The prayers of baffled beginners and exasperated experts everywhere have now been
answered. Now, when the novice needs help from the guru, the guru doesn't have to run
all the way downstairs or down the hall to assist. Thanks to the new screen-sharing
feature of Leopard, you can see exactly what's on the screen of another Mac, from across
the network —and even seize control of the other Mac's mouse and keyboard (with the
newbie's permission, of course).
(Anyone who's ever tried to help someone troubleshoot over the phone knows exactly
what this means. If you haven't, this small example may suffice: "OK, open the Apple
menu and choose 'About This Mac.'" Pause. "What's the Apple menu?")
Nor is playing Bail-Out-the-Newbie the only situation when screen sharing is useful. It's
also great for collaborating on a document, showing something to someone for approval,
or just freaking each other out. It can also be handy when you are the owner of both Macs
(a laptop and a desktop, for example), and you want to run a program that you don't have
on the Mac that's in front of you. (You might want to adjust the playlist selection on the
upstairs Mac that's connected to your sound system, for example.)
Or maybe you just want to keep an eye on what your kids are doing on the Macs upstairs
in their rooms.
The controlling person can do everything on the controlled Mac, including running
programs, messing around the folders and files, and even shutting down the controlled
Note: Leopard is crawling with different ways to use screen sharing. You can do it over a
network, over the Internet, and even during an iChat chat.That method, described in
Section 18.104.22.168, is much simpler and better than the small-network method described
here. It doesn't require names or passwords, it's easy to flip back between seeing the other
guy's screen and your own, and you can transfer files by dragging them from your screen
to the other guy's (or vice versa).Then again, the small-network method described here is
built right into the Finder, doesn't require logging into iChat, and doesn't require Leopard
running on both computers.
As always, trying to understand meta concepts like seeing one Mac's screen on the
monitor of another can get confusing fast. So in this example, suppose that you want to
take control of Mac #1 while seated at Mac #2.
- 13.5.1. Mac #1: Give Permission in Advance
It would be a chaotic world (although greatly entertaining) if any Mac could randomly
take control of any other Mac. Fortunately, though, nobody can share your screen or take
control of your Mac without your explicit permission.
To give such permission, choose System Preferences Sharing, and then turn
on Screen Sharing.
Note: If a message appears to the effect that "Screen Sharing is currently being controlled
by the Remote Management service," turn off the Remote Management checkbox and
then try again.
At this point, there are three levels of security to protect your Mac against unauthorized
• Secure. If you stop here, anyone with an account on your Mac will be able to tap
in and take control any time they like, even when you're not around. They'll just
have to enter the same name and password that they'd use if they were sitting in
front of your machine.
If "anyone" means "you and your spouse" or "you and the other two fourth-grade
teachers," then that's probably perfectly fine.
• Securer. For greater security, though, you can limit who's allowed to stop in. Click
"Only these users" and then click the + sign. A small panel appears, listing
everyone with an account on your Mac. Choose the ones you trust not to mess
things up while you're away from your Mac (Figure 13-17).
Figure 13-17. Your Mac is now ready to be observed and even controlled by
other machines across the network. The people listed here are allowed to tap
in anytime they like, even when you're not at your machine.
• Securest. If you click "Only these users" and then don't add anyone to the list, then
nobody can tap into your screen.
- Alternatively, if you're only a little bit of a Scrooge, you can set things up so that
they can request permission to share your screen —as long as you're sitting in
front of your Mac at the time and feeling generous.
To set this up, click Computer Settings and turn on "Anyone may request
permission to share screen." Now your fans will have to request permission to
enter, and you'll have to grant it (by clicking OK on the screen), in real time, while
you're there to watch what they're doing.
13.5.2. Mac #2: Take Control
All right, Mac #1 has been prepared for invasion. Now suppose you're the person on the
other end. You're the guru, or the parent, or whoever wants to take control.
Sit at Mac #2 elsewhere on your home or office network. Open a Finder window. Expand
the Sharing list in the Sidebar, if necessary, so that you see the icon of Mac #1.
When you click that Mac's icon, the dark strip at the top of the main window displays a
button that wasn't there before: Share Screen. Proceed as shown in Figure 13-18.
Tip: In theory, you can also connect from across the Internet, assuming you left your Mac
at home turned on and connected to a broadband modem, and assuming that you've
worked through the port-forwarding issue described on Section 22.1.In this case, though,
you'd begin by choosing Go Connect to Server in the Finder; in the Connect to Server
box, you'd type in vnc://123.456.78.90 (or whatever your home Mac's public IP address
is). The rest of the steps are the same.
Figure 13-18. Top: Start by clicking Share Screen in the strip at the top of the other
Middle: If you've been pre-added to the V.I.P. list of authorized screen sharers, as
described above, you can sign in with your name and password. If not, you can
request permission to share Mac #1's screen. You'll be granted permission only if
Mac #1's owner happens to be sitting in front of it at the moment, and has opted to
accept such requests.
Bottom: If you request permission, the other person (sitting at Mac #1) sees your
request in this form.
- If you signed in successfully, or if permission is granted, then a weird and wonderful
sight appears. As shown in Figure 13-19, your screen now fills with a second screen—
from the other Mac. You have full keyboard and mouse control to work with that other
machine exactly as though you're sitting in front of it.
Figure 13-19. Don't be alarmed. You're looking at the other Mac's desktop in a
window on your Mac desktop. You have keyboard and mouse control, and so does
the other guy (if he's there); when you're really bored, you can play King of the
Cursor. (Note the Screen Sharing toolbar, which has been made visible by choosing
View Show Toolbar.)
Well, maybe not exactly. There are a few caveats.
• Mismatched screen sizes. If the other screen is smaller than yours, no big deal. It
floats at actual size on your monitor, with room to spare.
But if it's the same size as yours or larger, then the other Mac's screen gets
shrunken down to fit in a window.
If you'd prefer to see it at actual size, choose View Turn Scaling Off. Of
course, now you have to scroll in the Screen Sharing window to see the whole
Tip: Another way to turn scaling on and off is to click the first button on the
Screen Sharing toolbar (Figure 13-19).
• The speed-vs.-blurriness issue. Remember, you're asking the other Mac to pump
its video display across the network —and that takes time. Entire milliseconds at a
time, in fact.
So ordinarily, the Mac uses something called adaptive quality, which just means
that the screen gets blurry when you scroll, quit a program, or do anything else
that creates a sudden change in the picture. You can turn off this feature by
- choosing View Full Quality. Now you get full sharpness all the time —but
things take longer to scroll, appear, and disappear.
• Manage the Clipboard. Believe it or not, you can actually copy and paste material
from the remote-controlled Mac to your own —or the other way —thanks to a
freaky little wormhole in the time-space continuum.
Just make the toolbar visible (you can see it in Figure 13-19). Click the second
button on it to copy the faraway Mac's clipboard contents onto your Clipboard. Or
click the third button to put what's on your Clipboard onto the other Mac's
Clipboard. Breathe slowly and drink plenty of fluids, and your brain won't
Note: Unfortunately, there's no way to transfer files while screen sharing —only
material you've copied out of documents.
• Quitting. When you hit the -Q keystroke, you don't quit Screen Sharing; you
quit what ever program is running on the other Mac! So when you're finished
having your way with the other computer, choose Screen Sharing Quit Screen
Sharing to return to your own desktop (and your own sanity).
13.5.3. Variations on Screen Sharing
The steps above guide you through screen sharing between two Leopard Macs. But
Leopard's screen-sharing technology is based on a standard technology called VNC, and
Mac OS X is bristling with different permutations.
22.214.171.124. Screen Sharing through iChat
Two people who both have Mac OS X 10.5 or later can perform exactly the same screen-
sharing stunt Over the Internet. No accounts, passwords, or setup are required — only the
granting of permission by the other guy. Just initiate an iChat chat, and then proceed as
described on Section 13.5.3. It's really awesome.
GEM IN THE ROUGH
Screen Sharing with Windows and Other Oddball Machines
- The beauty of Leopard's screen-sharing technology is that it isn't Leopard's
screen-sharing technology. It's a popular, open standard called VNC (Virtual
Once you've turned on Screen Sharing on your Leopard Mac, any computer on
earth with a free VNC client program —sort of a viewer program —can pop
onto your machine for a screen share. VNC clients are available for Windows,
Linux, pre-Leopard Macs, and even some cellphones.
To prepare your Leopard Mac for invasion, open the Sharing pane of System
Preferences. Click Screen Sharing, and click Computer Settings. Turn on "VNC
viewers may control screen with password," and make up a password. (VNC
doesn't know anything about Mac OS X account passwords, so you're making
up one password for sharing your whole Mac.)
Give that password to the lucky few who have your trust. Let them plug your
Mac's public IP address (Section 22.1) into their VNC clients —or let them
connect over your office network, using the address displayed on the Screen
Sharing pane ("vnc://Black-MacBook," for example) —and let the sharing
126.96.36.199. Screen Sharing with a pre-Leopard Mac
Both Macs don't have to be running Mac OS X 10.5 to use screen sharing. As it turns out,
Mac OS X 10.3 and 10.4 are capable of sharing their screens, too —it's just that the
on/off switch has a different name. Figure 13-20 has details.
Once you've turned on Apple Remote Desktop on the older Mac, as shown in Figure 13-
20, you can sit at your Leopard Mac and take control by clicking Share Screen in the
Sidebar, exactly as described above.
Note: At this point, the screen sharing is one-way: The Leopard Mac can see the older
Mac's screen. If you want the older Mac to access the Leopard Mac's screen, return to the
box shown in Figure 13-20. Turn on "VNC viewers may control screen with password,"
and make up a password. Now download the free Chicken of the VNC software; it's
available from this book's "Missing CD" page at www.missingmanuals.com. Use it to
access the Leopard Mac; the box on Section 13.5.3 has more details on this concept.
- Figure 13-20. On pre-10.5 Macs, there's no option for Screen Sharing in the Sharing
pane of System Preferences. There is one, however, called Apple Remote Desktop —
and that's the one that permits screen sharing with 10.5 machines. When you click
it, you're offered many of the same options that Leopard offers. More, in fact.
188.8.131.52. Screen Sharing the manual way
Screen Sharing is an actual, double-clickable program, with its own icon on your Mac.
(It's in the System Library CoreServices folder.) When you double-click it, you
can type in the public IP address (Section 22.1) or domain name of the computer you
want to connect to, and presto: You're connected!
184.108.40.206. Screen Sharing with Back to My Mac
"Back to My Mac" is a new Leopard feature that's intended to simplify the nightmare of
remote networking. It works only if:
• You're a .Mac member.
• You have at least two Macs, both running Leopard. On each one, you've entered
your .Mac information into the .Mac pane of System Preferences, and logged in.
Once that's all in place, your Macs behave exactly as though they're on the same home
network, even though they're thousands of miles apart across the network.
To set it up, proceed as shown in Figure 13-21.
Figure 13-21. On the first Mac, open System Preferences. Click .Mac, and then click
Back to My Mac. Click Start. Close System Preferences. Repeat on each Mac,
making sure that they all have the same .Mac account information.
- Now, on each Mac you'll want to "visit" from afar, open the System Preferences
Sharing pane and turn on File Sharing and/or Screen Sharing.
Then, on your laptop in New Zealand, you'll see an entry for Back to My Mac in the
Sharing section of your Sidebar. Click to see the icon of your Mac back at home. At this
point, you can connect to it for file sharing by clicking Connect As (Section 13.3.2), or
take control of it by clicking Share Screen (Section 13.5.2).
In theory, Back to My Mac spares you an awful long visit to networking hell (including
the port-forwarding headache described on Section 22.1), because Apple has done all the
configuration work for you.
Note: Lots of people can't get Back to My Mac to work. Apple says that the problems are
related to (a) this being a new service with some kinks to be worked out, (b) firewall
problems, and (c) router incompatibilities. Apple also says that you'll have the best luck
on networks that involve only an AirPort base station —and not a hardware router.All the
technical details are available online. Go to http://search.info.apple.com and do a search
for 306672. (That's the article number that explains the Back to My Mac issues.)