Update: We've covered the new features in updates 2.1 and 2.2 here.

Even long-time Mac users could be forgiven for not knowing anything about OS X Server, the business-oriented version of the operating system that has been developed alongside the better-known consumer version for as long as OS X has existed. For a long while, the software shipped only with the Xserve, Apple's enterprise-class server hardware. Standalone licenses for the unlimited client version of the software cost $1,000 all the way up until Snow Leopard, when the price dropped to a still-imposing $500.

All this changed in early 2011 when Apple discontinued the Xserve and replaced it with repurposed configurations of the Mac Mini and Mac Pro. The former sold (and continues to sell) at the $1,000 price so appealing to power users and small businesses, though the Mini lacks the Xserve's hardware monitoring features or expandability.

With Lion Server and now Mountain Lion Server, the software has followed the hardware in becoming cheaper and simpler, and in shifting its focus from large businesses to small ones. At $50, Lion Server cost only five percent of what Leopard Server did; at $20, Mountain Lion Server costs less than half of that. As the product has gotten cheaper and within reach of regular people, the tools used to administer it have become correspondingly less complex, both in terms of how difficult they are to use and in how powerful they are.

Because of OS X Server's newly lowered price, because so much has changed since Snow Leopard, and because Ars Technica's lengthy OS X reviews have never touched on Server before (with the exception of a piece we ran in January about using Lion Server in the home), we've got a lot of ground to cover. This article should serve as an introduction to the software's capabilities, an evaluation of how those services work compared to the competition, and a basic how-to guide for getting everything up and running. By the time you're done reading, you should have a decent working knowledge of what this software can do, how to configure it, and whether it's right for you.

Introduction and installation

Unlike Windows Server, which contains a huge number of under-the-hood changes that make it substantially different from the client versions of Windows, Mac OS X Server is and always has been more or less indistinguishable in operation from Mac OS X. The server OS is really just the client OS with the server bits tacked on, and all of the observations made in John Siracusa's characteristically thorough review of Mountain Lion also apply to the server product.

Installing Mountain Lion Server is done through the Mac App Store, just as Lion Server was. Downloading the OS X Server app (hereafter "Server.app") will turn any Mac running Mountain Lion into a server. Snow Leopard Server and previous versions of the software required you to run the software on some sort of desktop, like an iMac or a Mac Mini or an XServe, but Lion Server dropped that stipulation and Mac laptops can now be used as servers, too. Once you've purchased Server.app, you can make as many Macs into OS X Servers as you want. You can also use Server.app to remotely manage your OS X Server from an OS X client.

When you first run Server.app, its wizard will get your server up and running in a few uncomplicated steps. It first walks you through configuring your server for use on a local network or with a domain name you've registered, setting up the server's host name and IP address, and enabling Push Notifications. We'll talk more about how Push Notifications in OS X Server work a little later, but all you need to set them up is an Apple ID (Apple recommends you use a separate Apple ID for your organization, not a personal Apple ID used to purchase apps), which will get you a Push Notifications certificate that needs to be renewed yearly. Once those steps are complete, you're ready to configure your server.

Downloading and running Server.app prompts a few changes to the operating system itself: the Screen Sharing and Remote Login features are both enabled automatically to make remote administration easier, for example. A Lion server would also set itself never to go to sleep while plugged in, and it would also change the About This Mac dialog to tell you that you were in fact running OS X Server—but these changes aren't made in Mountain Lion.

The first issue is easy enough to correct if you need an always-on server. The second was only ever a superficial change, but it makes a point: "OS X Server" no longer exists as a separate product. There's only OS X, which runs something called Server.app. OS X Server lives on in Apple's branding, but such a distinction is no longer made in the operating system itself. Depending on how Apple chooses to proceed, this could be the beginning of an effort to separate Server from the normal OS X development cycle, making it a version-agnostic app instead, but that's something we probably won't know for sure until we start hearing about OS X 10.9.

Goodbye Server Admin Tools, hello again Server.app

The primary tools used to administer past OS X Server versions were called the Server Admin Tools. These tools—which included Server Admin, Workgroup Manager, and System Image Utility—were each separate applications that gave users fairly comprehensive control over their server's settings. Server Admin, in particular, was the bread-and-butter administration tool that exposed the settings for most of OS X Server's features. (For you Windows Server admins out there, Server Admin in OS X is roughly analogous to Server Manager in Windows.)

Lion changed that with something called Server.app, which took some of OS X Server's services and greatly simplified their administration, to mixed effect. Server.app's role was to make the product more appealing to users and to novice server administrators, and it's no mistake that the services managed by Server.app in Lion were the ones of most use to home users and small offices: file-sharing, mail, calendar, chat, Time Machine, VPN, podcast, the Web and Wiki servers, and basic user, group, and device management. And talk about simplicity—many of these services were reduced to big On/Off switches and a couple of checkboxes. If you wanted to do anything more complicated, the GUI wasn't going to help you much.

To unlock all of Lion Server's features, however, you still needed the Server Admin Tools, which were and still are available as a separate download. Installing and running Server Admin granted access to some of the more advanced services (DHCP, DNS, NAT, the NetBoot service, the Software Update server, Open Directory, the firewall, and a few others) while exposing more advanced settings for the Mail service, while things like Workgroup Manager enabled more advanced user and computer management. Other services that had been present in Snow Leopard Server and older versions (Print, QuickTime Server, and others, most of which could safely be considered vestigial) didn't make the jump, and aren't present in either Server.app or Server Admin.

In Mountain Lion, though, the Server Admin Tools are dead with only a couple of exceptions. Server.app picks up most of the slack, adding DNS, FTP, NetBoot, Open Directory, Software Update, and Xsan to the list of things it could already do, but basic networking functions like DHCP and NAT are gone from the GUI, and are now handled through the command line and by Internet Sharing in the System Preferences, as is the server's software firewall. The Podcast service is gone entirely.

The move to bury things like DHCP makes sense: most home users and small offices are going to have a router that already takes care of DHCP and NAT for them, while medium-to-large businesses will likely have Windows or Linux-based implementations already in place. Mountain Lion's subtractions should be harmless for many users, but if you relied on OS X Server for any of this before, you'll either have to re-learn the GUI or look elsewhere to provide these services now.

Notes for upgraders

When upgrading a computer running Snow Leopard Server to Lion from the App Store, the installer was intelligent enough to download and install Server.app along with it, transferring settings from Server Admin to Server.app. The Server Admin Tools were still a separate download, but settings for services managed by Server Admin were still there.

The upgrade path from Lion Server to Mountain Lion Server is slightly less automated: Mountain Lion will keep Lion's version of Server.app (which won't run in Mountain Lion), and you'll need to download the current version from the App Store separately. Happily, most of your Lion Server's settings remain intact (with the notable exception of File Sharing share points), and the settings from the last of the old Server Admin services seem to come over into Server.app without any issues, but it's odd that upgrading requires a manual download of Server.app when Apple is clearly able to provide it automatically. Once you've installed the Mountain Lion version of Server.app, the Lion version can be trashed; if the Server Admin Tools were present on your Lion computer, they are uninstalled automatically during the upgrade.

One final recommendation for upgraders: I recommend patience even when upgrading OS X clients since the updates that fix the most severe bugs usually come out quickly, and this recommendation is doubly prudent for OS X Server. Check out the release notes from the server version of 10.7.4 and compare them to the client version—OS X Server's updates contain major and far-reaching fixes for services, and the unreliability and inconsistency that new OS X versions often exhibit at first is much, much harder to tolerate in a server room than on your desktop. If you're the type to install new OS X versions on your Macs as soon as they're out, you should wait until at least 10.8.2 before you even think about upgrading a server. The fact that Mountain Lion Server doesn't drastically change or upgrade many of Lion Server's services should make this wait easier.