Chapter  26

Remote Access and Sharing

Chances are you connect to remote servers and networks every day without really thinking about it. When you open your favorite web browser to read the news, check the weather, or catch up on Facebook, you're sending out packets of information requesting data. Those packets adhere to a particular protocol, in this case the Hypertext Transfer Protocol, and they traverse networks around the globe seeking the particular port at the particular address of the particular server that has your requested content.

The server will consider your request and, if all goes well, package the information you've requested and send it flying through the vast network of networks until it ends up back at your machine. Most people probably never realize how much work they're doing just by slacking off on the Web!

In this chapter we are going to look more closely at not only how you can access remote services and files but also how you can share files and services right from your Mac. While we probably won't talk too much about the Web (we'll cover that in the next chapter), we will cover the following:

• Connecting to file servers over a network (and the Internet)
• Creating small private networks
• Sharing files through AirDrop
• Activating and configuring formal sharing services on your Mac

Making the Remote Connection

The Web is just one part of the Internet, which is in turn just one type of network. There are as many ways to connect to another machine as there are reasons to do so, which has resulted in an alphabet soup of capabilities, methods, and protocols. Fortunately, Mac OS X has integrated, easy-to-use networking built right in. In fact, it's quite possible that, as with surfing the Web, you won't even have to think about the fact you're accessing a remote machine.

Accessing Remote Systems from the Finder

The easiest way to browse your local network is in the Finder. Machines that have enabled an appropriate type of sharing, such as file sharing, will be listed in the Finder window under the Shared category, as if they were part of the system.

If the selected resource has guest (or public) sharing available, those folders or resources will be presented in the Finders view window (Figure 26–1). If guest sharing is not available or you want to access other resources not available to guests, click the Connect As… button to open a dialog allowing you to sign in as a registered user (Figure 26–2).

Figure 26–1. If guest sharing is enabled on the remote system, you will be able to view publicly shared items as a guest user.

Figure 26–2. If you want to connect as a registered user on a remote system, click Connect As… and enter your user info in the dialog.

If the machine has screen sharing enabled, the Share Screen… button will appear to the left of the Connect As… button (unless you are in column view, in which case it will be below the Connect As… button). Clicking the Share Screen… button lets you activate screen sharing (Figure 26–3) once you enter your user information in the resulting dialog. The Screen Sharing application descends from the Apple Remote Desktop application, which has roots going all the way back to Mac OS 8. The upshot is Lion's screen-sharing feature can connect to machines running previous versions of Mac OS X. Even Tiger (10.4) and Panther (10.3) come with the necessary client software already installed.

Figure 26–3. Screen Sharing allows you to remotely access another Mac as if it were right in front of you. Screen Sharing even allows you to access systems running previous version of Mac OS X.

The Screen Sharing application has a few preferences worth checking out. By default, the remote screen is scaled to fit your screen, data is minimally encrypted to improve network performance, and drawing quality is adjusted on the fly depending on the quality of your connection. You can instead elect to view the screen at full size, to encrypt all data, or to draw the screen at full quality regardless of performance.

Connecting to Other Remote Servers

The Finder's network browsing is limited to machines on your local network, but the Finder can connect to any machine, local or remote. As long as you know the IP address or a domain name to the resource, you can connect to it directly using the Finder's Connect to Server window, as shown in Figure 26–4.

Figure 26–4. Connecting to a server by name in the Finder

Launch the Connect to Server window from the Finder's menu bar by selecting Go > Connect to Server (Command-K). To connect to a machine, type its address in URL form into the Server Address text field. If you intend to connect to the machine on a regular basis, click the + button to add it to the Favorite Servers list.

Earlier, we connected to a machine using the Connect As… button in the Finder. We could have also established that connection directly by typing the machine's URL, like so:

Connecting to a machine in the Finder will use the default protocol. Connecting directly allows you to explicitly specify the protocol. Valid protocol declarations include the following:

• afp: The Apple Filing Protocol is the standard protocol used for addressing remote volumes in the Finder. Although it is Apple's standard, AFP support is available for many operating systems, including Windows, NetWare, and several flavors of Unix and Linux. If you do not specify a protocol, afp is assumed.
• at: AppleTalk is an obsolete networking protocol that is included for backward compatibility. Previous versions of AFP used AppleTalk behind the scenes, but modern AFP uses the Virtual Network Computing (VNC) standard on top of standard TCP/IP.
• nfs: The Network File System protocol is a remote file access protocol developed by Sun Microsystems. It is similar to AFP and is available for several flavors of Unix, as well as for operating systems such as NetWare, Windows, and, of course, Mac OS X.
• smb: The Server Message Block protocol is the Windows equivalent to AFP. From within Windows, it's referred to simply as Microsoft Windows Network. The SMB protocol is sometimes called Samba, though technically Samba is a free reimplementation of SMB and not simply another name for the same thing.
• cifs: The Common Internet File System, despite its name, is actually just a rebranding of SMB to reflect changes Microsoft made to the protocol since its invention at IBM. It was submitted, but not accepted, as an Internet standard. It can be considered to be the same as SMB.
• http: The Hypertext Transfer Protocol is the standard protocol of the World Wide Web. Taking advantage of the ubiquity of the Web, HTTP is used for transporting more than web pages. For example, the WebDAV standard is used to mount remote file systems over HTTP.
• https: The secure version of HTTP is not a true protocol. Instead, it simply refers to the use of standard HTTP over a connection that has been encrypted by either the Secure Sockets Layer (SSL) protocol or the Transport Layer Security (TLS) protocol.
• ftp: The File Transfer Protocol is a very old standard for moving files from one computer to another. Because of its age and that it's compatible with every known operating system, it's in widespread use all over the Internet.
• ftps: Analogous to HTTPS, FTPS refers to the use of regular FTP over an SSL or TLS connection.

The list of protocols supported by the Finder's Connect to Server window is impressive but not all-encompassing. Absent are sftp, the Secure Shell File Transfer Protocol; svn, the Subversion file transfer protocol (although Subversion can be transacted over other protocols, such as HTTP); and file, as used in standard file URLs. The absence of file URLs is notable not because they have much meaning in a dialog intended for connecting to servers but because they are used extensively throughout the system. Using them in the Connect to Server window simply returns an error.

Connecting Remotely from the Command Line

Although using a computer's graphical interface via screen sharing is relatively new, the concept of using one computer to log in to and control another computer remotely is anything but. Unix is, by its very nature, a remotely controllable operating system, and old-fashioned shell-to-shell networking is very much alive in Terminal.

To connect remotely to another machine, open Terminal, and from the command line, invoke ssh with the username and address of the machine you want to connect to, separated by the “at” sign. For example, to connect to a machine at the local IP address 10.0.1.5 with the username booksystem, you would type this:

If you are connecting to a machine for the first time, you will be asked whether it is safe to proceed. Confirm this by typing yes. Unlike most Unix programs, you have to type the entire word. You will then be prompted for a password, and then, assuming you can authenticate properly, you'll be presented with a welcome message and the command prompt.

From this prompt you can create, delete, and alter files and folders, as well as list, run, and kill processes. You can even launch new shells and Secure Shell sessions in other servers. It's the same as if you were sitting at the remote machine typing into a Terminal window.

This can have unexpected consequences. For example, any DNS resolution will be in terms of the remote machine. If you have domains listed as default, a custom hosts file, or discrepancies in the closest name server's routing table, the remote machine might behave differently than would your local host.

To log out of the remote server, type exit. This is the same as exiting any shell, so bear in mind that if you've launched a new shell from within Secure Shell, typing exit will not log you out. Fortunately, when you log out of a Secure Shell session, Secure Shell will let you know the connection is closed. If you don't get that confirmation, assume you are still logged in.

Remote login via Secure Shell can be enabled from System Preferences, as discussed in the “Sharing” section later in this chapter.

The command line also includes an FTP program for using the File Transfer Protocol to move files between machines. As opposed to shell access, which allows for all manner of shenanigans, FTP access is much more limited, restricting user privileges to basic file operations.

To use FTP from the command line, simply type ftp. Unlike Secure Shell, FTP can be invoked without actually opening a connection. To connect to a remote machine, type open, and then, when prompted, enter the address of the machine, your username, and your password.

Unlike the Finder's Connect to Server menu, by default there is no ftps command available from the command line, but there is an sftp command, which works just like the regular ftp command. However, although opening a connection and supplying your username at invocation time are optional in ftp, they are required in sftp.

Enter your password when prompted and then proceed as normal.

Whatever the advantage to using sftp, moving files back and forth in the terminal is almost too complicated to make it worthwhile, but if you really want to know, type man ftp or man sftp in the terminal to read all about it. A much better idea would be to use a dedicated FTP client.

Third-Party Graphical Clients

As mentioned earlier, FTP and SFTP from the command line are not particularly intuitive or user friendly, so when you hit the limitation of what the Finder can do, it's time to go shopping for third-party solutions.

While there are quite a few clients to choose from, three of them get my recommendation: Fetch, Transmit, and Cyberduck.

• Fetch ($28.99 from the App Store) has a long history as the FTP client of choice for Mac users. Originally developed at Dartmouth College in the pre–Mac OS X, since then it has spawned its own company, Fetch Softworks (http://fetchsoftworks.com), and has been constantly maintained and updated to provide all the features one could expect from a file transfer client. Fetch supports FTP, SFTP, and FTPS.
• Transmit ($33.99 from the App Store) is a beautiful, feature-rich file transfer client from Panic Software (http://panic.com). Although it's the most expensive client here, for many people it's worth it. In addition to supporting FTP and SFTP, Transmit also supports transferring to and from WebDAV and Amazon's S3 cloud.
• Last but not least is Cyberduck ($23.99 from the App Store). Cyberduck is an open source file transfer client that supports connecting to the widest range of services including FTP, SFTP, FTPS, WebDAV, Amazon S3, Google Storage, Google Docs, Windows Azure, and Rackspace Cloud files. While it lacks some of the graphical flair and Finder integration that Transmit has, it is certainly capable.

Besides these excellent dedicated clients, many pieces of software include built-in file transfer capability. Applications such as BBEdit, Coda, and Espresso have built-in FTP and SFTP capabilities. Jumping back to Apple software, Xcode has built-in support for remote SVN (Subversion) and Git repositories (which we will talk about in Chapter 32).

Creating Local, Private Networks

It wasn't that long ago when there was no Internet to which regular people could connect. Back then, setting up a local area network in your house was far too expensive to be feasible, and wireless networking wasn't even something most people could fathom. Yet, whenever two people had a file they wanted to exchange that wouldn't fit on a 1.44 MB floppy disk or they wanted to play some head-to-head Doom, they were always faced with the same problem—how the heck do we connect these two computers?

Even when the Internet was well established and routers were cheap, creating a small, informal network between two or three computers was always a big challenge. Fortunately, the modern Macintosh makes these arrangements, known as ad hoc networks, extremely easy to set up and use.

Target Disk Mode

The first question you have to ask yourself is, why would I want to connect two computers? A lot of times it's to exchange files. Whether it's to copy some work from a laptop to a desktop or to move some videos from a desktop to a TV server, people are forever connecting two machines just to facilitate getting files from computer A to computer B.

In this case, a network is not actually necessary. Any two Macs with FireWire or Thunderbolt ports can take advantage of a special trick called Target Disk mode. To put a computer into Target Disk mode, hold the T key while booting, or select Target Disk Mode… from the Startup Disk pane of System Preferences. The machine will start, but instead of a login screen, the computer's monitor will display the FireWire (or Thunderbolt) symbol.

When it's in Target Disk mode, a computer is treated as just another FireWire or Thunderbolt peripheral. That means if you plug it into another computer, that machine will mount the targeted machine's drives as if they were regular external drives. This includes the hard drive, as well as connected drives such as the DVD drive.

To copy, move, or delete files, just do so in the Finder as you would with an external drive. You can also read or eject removable media in the usual way. A direct connection with a FireWire 800 cable is much easier and just as fast as a Gigabit Ethernet connection, which is theoretically faster,  and it's hard to beat the performance of two Macs connected via Thunderbolt.

Target Disk mode can do some pretty interesting things. For example, you can boot your computer as a different machine by putting that machine in Target Disk mode. That means you could put your laptop into Target Disk mode and boot your Mac Pro from its drive so you'd be using your laptop, except it would be your Mac Pro. Then you put the Mac Pro into Target Disk mode and use it from your laptop.

Why would you ever do that? Well, maybe your laptop got run over by a car and the screen is busted but the mechanics are still good. That sounds far-fetched, but it's actually a documented occurrence. Or maybe your friend brings over a Mac mini and you want to boot it up but you don't have a monitor. As long as you have your laptop, Target Disk mode is all you need.

AirPort

If you want to connect machines that all have AirPort cards, it's easy to connect them. One machine can create a computer-to-computer (or ad hoc) AirPort network if you simply select the Create Network… option from the AirPort menu bar item and fill in the information in the resulting dialog (Figure 26–5). After you give it a name and an optional password, other people can join the network from the AirPort menu bar item as well.

Figure 26–5. Creating a computer-to-computer network with AirPort

If you don't use the AirPort menu bar item, you can accomplish the same thing through the Network pane of System Preferences. Simply select the AirPort icon on the sidebar, and then, from the Network Name drop-down menu, select Create New Network. Other AirPort users can connect the same way.

I've never had a lot of luck setting up Wi-Fi on non-Macintosh computers, but since AirPort is just Apple's brand of Wi-Fi, it's at least theoretically possible to connect to Windows machines the same way.

FireWire and Ethernet

If you don't have AirPort or want a faster way to connect, you can always plug the two machines together with FireWire. Aside from Target Disk mode, FireWire is actually a full network interface. After connecting the two machines, open the Networking pane of System Preferences.

You will have a self-assigned IP address. It doesn't really matter what it is, as long as the other person's self-assigned address is not the same. If it is the same, one of you should edit the last number so it's different.

Ethernet works the same way. Connect two machines, check the IP addresses, and change one if necessary. With Ethernet there is a trick, however. Some types of Ethernet cables are specially designed for connecting two machines directly. These so-called crossover cables are typically green in color.

If you're both using Macs, it doesn't matter whether you're using a crossover cable. If you connect two Macs with a standard cable, they will automatically cross over their Ethernet connections, so it makes no difference at all. If you're trying to connect to a machine that isn't a Mac or the machine is a Mac that's too old to run Mac OS X, be aware that you might need the special cable.

Assuming you have the latest versions of each and the proper cables, there's no particular advantage between FireWire and Ethernet as network adapters. There is, however, an advantage to having two network adapters.

You can connect your computer to another computer using one and then connect your computer to a different computer using the other. By switching off between the two, you can chain together any number of computers into an arbitrarily long daisy chain.

AirDrop

Lion introduces a new way of sharing files wirelessly with a feature called AirDrop. AirDrop is a feature that is built into the Finder and allows you to identify other AirDrop-capable Macs and transfer files to them by dragging and dropping files on their systems through the AirDrop view in the Finder (Figure 26–6).

Figure 26–6. AirDrop makes sharing files with nearby Macs very easy, even if no network is available.

As mentioned earlier, to share a file over AirDrop, simply select the desired destination system from the AirDrop view in Finder and drag the file or files you want to share to the appropriate icon of the system you want to share the files with. Once you have dragged your files to the icon, a dialog will pop up asking to confirm that you want to share the selected files.

If you are on the receiving end of an AirDrop share, a dialog will pop up letting you know that someone is trying to share a file with you and asking you what you would like to do with it. Your options are to save and open, decline, or save(Figure 26–7).

Figure 26–7. When someone is attempting to share a file with you over AirDrop, you will be asked what you want to do with the files.

Sharing Services in Mac OS X

If this chapter has taught you anything, it should be that there are a lot of different ways to connect to another computer. Even though the standard version of Mac OS X is different from the Server version, in Unix the line between client and server is tenuous at best. With Mac OS X, if you can be a client, you can probably be a server. To see this for yourself, open the Sharing pane in System Preferences, and read the long list of services you can offer, as shown in Figure 26–8.

Selecting a service from the list on the left will open status and preference information on the right. To activate or deactivate a service, toggle the check box next to its name. System changes, such as opening the relevant port and making necessary adjustments to the firewall, are done for you.

Figure 26–8. Many ways to share your Mac in System Preferences

Although each type of sharing has a description, it's not necessarily obvious exactly to which protocols or services they relate. Make sure you have the right service before you check the box and run out the door, or you might be in for an unpleasant surprise.

DVD or CD Sharing

Optical drives are such anachronisms, or so the MacBook Air would have you believe. However, if you have an optical drive and want to share the contents of a disk in it, Mac OS X provides DVD or CD sharing. You wouldn't want to use this to watch a movie, but for installing software once in a while, it gets the job done.

Screen Sharing

This allows people to connect to your machine using Mac OS X's built-in screen sharing but not Apple Remote Desktop. It bears noting that screen sharing is more than just being able to see your machine. People who share your screen can actually use your computer as if they were sitting at it, as shown in Figure 26–3. It's the graphical equivalent of logging in with ssh.

Options include explicitly naming which users can connect using this protocol, whether people can request to control the screen, and whether to protect screen control with a password. Note that turning on screen sharing will cause your computer to become browseable from your local network, so don't turn it on unless you need it.

When might you use screen sharing? Traditionally, its primary purpose is administrative. Apple Remote Desktop is, above all, a tool to help system administrators manage a network of machines. By bundling screen sharing with Mac OS X, Apple is expanding it to more informal uses. For example, if your mom calls you for tech support, you can just show her how to create a new album in iPhoto instead of trying to describe it over the phone.

File Sharing

When you connect to another machine in the Finder, you are using file sharing. In some previous versions of Mac OS X, different protocols were listed separately. In Snow Leopard, AFP, FTP, and SMB are all covered by the same service. You can decide which protocols are allowed by clicking the Options button.

In addition to the protocol list, you can decide which folders you'd like to share and explicitly list which users should be allowed to connect to your machine. As with screen sharing, enabling file sharing will make your machine visible on the local network, so make sure you need it before activating it. Also, SMB requires storing passwords in a less-secure way than Mac OS X prefers, so make double sure you need to let people connect to you with SMB before activating it.

Access to folders and files on your machine is determined by the permissions and access lists you've already set up. If you'd like to exchange files with other people on the network without having to worry about all that stuff, you can use the default Public folder, which is set up automatically on each new account.

By default, people who connect to your machine can read files from the Public folder, but they cannot edit or delete them, and they cannot put files in the Public folder itself. Within the Public folder, there's a folder called Drop Box, which works in the opposite way. People can put files in the Drop Box folder, but they cannot open the Drop Box folder to access the files it contains.

If you have a file you want people to access, simply put it in the Public folder. If someone else needs to give you a file, they can simply drop it in the Drop Box folder. It doesn't get much easier than that!

Printer Sharing

When printer sharing is enabled, printers connected to your machine are also connected to the network. Other machines on the network can see the printer in the printing system and negotiate the protocol on their own, typically via Bonjour. If you have a desktop machine hooked up to the printer, this a great way to print from your laptop.

Scanner Sharing

Many, if not most, of the printers sold these days are multifunction machines that also serve as scanners. Scanner sharing is a case in point. It's just like printer sharing but for scanners.

Web Sharing

This simple, ambiguous name covers a lot of ground—so much ground, in fact, the entire next chapter is devoted to it. In a nutshell, though, web sharing means you will host web sites from your machine.

Remote Login

Unlike file sharing, which covers all manner of file transfer protocols, remote login specifically enables SSH connections to your system. Although Remote Login is conceptually similar to screen sharing (and sounds similar to Remote Desktop), as far as the Sharing pane is concerned, they are completely unrelated. The only option is an access control list.

Remote Management

Not to be mistaken for Remote Login or screen sharing, Remote Management controls whether people can connect to your machine using Apple Remote Desktop. The options are almost identical to screen sharing.

Traditionally, a given protocol used a given port, so enabling access to a particular service was an all-or-nothing affair. As discussed in the previous chapter, Mac OS X's firewall is able to route or block requests at the application level. As such, even though Apple Remote Desktop and screen sharing use the same protocols, they can be enabled, disabled, and configured separately.

Remote Apple Events

The Apple Events system underlies interapplication communication, as used by AppleScript. To control a remote machine with AppleScript, therefore, a machine would have to respond to remote Apple Events. This would be useful if you were trying to use AppleScript to automate some administrative task over a network.

For example, if your remote machine were at IP address 10.0.1.5, you could make it sleep with the following bit of AppleScript:

You can scale this technique to do amazing things with scriptable applications such as iTunes. For an example, check out the remote access section of Doug's AppleScripts for iTunes (http://dougscripts.com/itunes/itinfo/remcontrol.php). We talk more about Doug, and AppleScript, in Chapter 31.

Xgrid Sharing

If you have a bunch of Macs and a copy of Mac OS X Server, you have a supercomputer. Mac OS X includes Xgrid, the same cluster computing software used in university supercomputers. The Xgrid Admin application bundled with Mac OS X Server makes it easy to set up computing clusters using Bonjour.

Internet Sharing

Contrary to what you might be led to believe by its ambiguous name, enabling Internet sharing does not allow you to connect to your computer from other computers on the Internet. Rather, it allows you to share the Internet from your computer with other computers.

The typical Mac has at least three network interfaces: Ethernet, FireWire, and AirPort. At any moment, only one of those interfaces is usually connected to the Internet, while other interfaces could be connected to another computer or even an entirely different network. By enabling Internet sharing, you're able to let the computers on one network interface connect to the Internet on another.

For example, a typical setup might have the Internet coming into your home via a cable or DSL modem, which, in turn, is connected to an AirPort base station. All the computers in your home would then be connected to the AirPort base station, sharing its Internet connection.

With Internet sharing, you could instead plug one computer directly into the modem via Ethernet and then use that machine's AirPort card to create an ad hoc network that other computers could use to share the Internet connection, eliminating the need for the AirPort base station altogether.

This kind of setup is particularly convenient when you are away from home. If your hotel room has an Internet connection via Ethernet, several people can share that connection without having to pack an AirPort base station or other network hardware.

Bluetooth Sharing

Although it's usually associated with headsets and other simple gadgets, Bluetooth is a general short-range wireless standard that can connect two machines with file systems, such as two computers, or a computer and a phone. To move files around over a Bluetooth connection, you'll need to enable Bluetooth sharing, though connecting a Bluetooth device will usually activate Bluetooth sharing foryou.

Summary

When it comes to connecting to remote machines, you have a lot of options. Networking is built into the Finder, integrating the entire web publishing experience into the Mac's legendary interface. Third-party applications expand this integration by offering direct connections to the Internet, through technologies such as FTP and Secure Shell.

In the next chapter, we will focus on one specific form of sharing, web sharing.