Linux servers for Windows folk: go on, give it a bash
A piece of cake – even for non open-saucy types
Similar to the core
All three offer the same core functionality. The stuff most organisations need are there – they'll all work as a file server, print server, email server including an LDAP directory and webmail, and as a web server if you feel the need to host your own site. They'll do spam-filtering, attachment-blocking, virus-scanning and so on, and all can act as a Web proxy, doing the same for direct downloads as well as emails. Also, though a bit less relevant in these days of inexpensive hardware routers, they can act as a network gateway, providing a VPN endpoint and so on.
This could be quite handy – Linux makes an excellent firewall and offers the flexibility of some seriously expensive enterprise-class devices, but costs nothing – but there is a snag: if you've already got a router, you'll either have to reconfigure or replace it. If you want public Internet server functionality, such as hosting Web sites, then you need a direct connection between your server and the Internet. You don't want a firewall in the way, as this will complicate matters; instead, the external IP address of the server should be visible from the outside world. At the very least, if all you want is Web serving and webmail, you'd need to reconfigure your router/firewall to pass through HTTP and HTTPS traffic to the server. If you want VPN clients to connect to it as well, rather more is involved. It's not trivial, and it might prove much quicker to buy a suitable router – which may mean negotiating with your ISP.
All the distros can also act as Windows domain controllers, meaning that Windows PCs on the LAN will delegate authentication duties to the server. This has two advantages: firstly, anyone can use their login name and password on any machine on the LAN, with no need for the admin to manually keep all the accounts in sync. Secondly, users get roaming profiles, so that their personalised desktop, Start menu and so on follow them around the network onto whichever machine they happen to use.
In terms of tick-boxes in a features table, all three of these systems are closely comparable. They can be installed and used for free, perform the same core roles, are administered remotely using a browser, and can be configured using just forms in the web browser – no command line required at any time.
If the Ubuntu project were to take Zentyal under its wing and make it the official Ubuntu Server, bestowing the same degree of polish on it that Ubuntu's desktop OS has, it could trump both the others. In just two years, it's come very close to rivalling its 10-year-old CentOS competitors. It's not quite there just yet, though, unless you particularly want something Ubuntu-based.
The most powerful and flexible of the trio is definitely ClearOS, which until recently, as ClarkConnect, was an expensive piece of professional software with only a limited freebie version. To get the whole thing for nothing is a bargain. However, it is also the most complex, with a lot of options to fill in or tick to configure it just the way you want it. If you want modularity and control, especially if you have some server-admin experience, it's the one to go for.
SME Server is the simplest of them all. It's not remotely modular, does not offer extensive high-end firewall facilities, has the dullest possible interface on the server itself – and its web GUI is a little plain-looking too. However, it is the easiest to get working, does everything a small office would need and works with Windows and Macs and Linux without any issues. If you just want something easy to install and run, the oldest is still the best.
For now, at least. SME Server 8 will be only a modest, incremental upgrade, whereas in 2011, ClearOS 6 should integrate Zarafa, which might swing the balance strongly in its direction. Zentyal 3, in 2012, will be interesting, too.
If your needs are more modest and you just need some more storage space to hang off your network, there are also a growing number of NAS-specific distros. Several are as yet immature or unfinished, but two are quite well-established: FreeNAS and Openfiler. Both will turn a very modestly-specced generic x86 PC into a network-attached storage device far more cheaply than a dedicated box – and be faster and far more expandable.
There are also some other dedicated-server distros out there aimed at slightly different functions, such as EnGarde Linux, a free distro aimed at Internet-facing servers – essentially, a ready-to-go LAMP and email server. There are also a few servers aimed more at the home user who wants to experiment than at business use, such as Devil Linux and the modestly-named Superb Mini Server. Straddling the line between server and desktop is SLAMPP, a live CD with a graphical desktop as well as server functionality, designed to boot a PC from CD and instantly make it a file and Internet server.
It's a bit surprising that there aren't more commercial alternatives. Xandros, quondam doyen of corporate Linux, used to be a contender, but it is losing relevance today. Xandros' website does still offer its GUI-based server product, Xandros Server 2, to complement its Windows-like desktop offering, as seen on the original Asus Eee PC – but as with Xandros Desktop, it's not been updated in several years. From Russia comes ALT Linux Server. ALT is only marketed in Russia, Brazil and Israel, but it's cheap and it might be worth a look for Russophones. For NAS users, there is the inexpensive NASLite, but most businesses would probably prefer a purpose-built device. These are generally much cheaper to run over time, in any case.
How we tested
We tried each distro on two servers: a shiny new Gateway GT350 F1 with a quad-core 2.16GHz Xeon, 6GB of RAM and a 150GB hard disk, and on an elderly dual Pentium II machine with 400MHz processors, 256MB of RAM and a pair of 40GB EIDE drives. Client workstations were attached via a Netgear GS110TP Gigabit Ethernet hub. Clients were running a mixture of Windows, Mac OS X and Linux.