First of all, it is worth mentioning that Linux is not the only option available; other freely available operating systems include the BSDs (FreeBSD, NetBSD, OpenBSD), Solaris Express,Nexenta, and others. However, there are many GNU/Linux distributions available, and thesegenerally have support for the widest range of hardware and software. Most of these distributionscan be downloaded and used totally legally, even for production use. Of the Linuxdistributions mentioned here, RedHat Enterprise Linux (RHEL) and SuSE Linux EnterpriseServer (SLES) have restricted availability and access to updates; Oracle Solaris is restricted to a90-day trial period for production use.
gnu/linux
RHEL is the commercial distribution based on Fedora. It is particularly popular in North America and much of Europe. Because the RHEL media includes RedHat trademarks andsome non-Free Software (such as the RedHat Cluster), distribution of the media is restrictedto licensed customers. However, the CentOS project rebuilds RHEL from source, removing
RedHat trademarks, providing a Linux distribution that is totally binary and source code–compatible with RHEL. This can be very useful as a lot of commercial software for Linux is tested andsupported only on RHEL, but those vendors will often also support the application running onCentOS, even if they do not support the OS itself.RHEL itself is available by paid subscription only. However, CentOS and Oracle Enterprise Linux aretwo clones built by stripping the RedHat trademarks from the source code and rebuilding in exactlythe same way as the RedHat binaries are built. CentOS is available from , andOracle Enterprise Linux is available from Fedora is the community-maintained distribution that feeds into RHEL. It has a highly active,generally very technical user base, and a lot of developments tested in Fedora first are then pushedupstream (to the relevant project, be it GNOME, KDE, the Linux kernel, and so on). Like Ubuntu,it has six-month releases, but a much shorter one-year support cycle. The technologies that havebeen proven in Fedora make their way into RedHat Enterprise Linux. As with Ubuntu, KDE,XFCE, and LXDE respins are available as well as the main GNOME-based desktop. DVD imagescan be obtained from SLES is Novell’s enterprise Linux. It is based on OpenSUSE, which is the community edition. SLESand OpenSUSE are particularly popular in Europe, partly due to SuSE’s roots as a German companybefore Novell purchased it in 2004. SuSE’s biggest differentiator from other Linux distributions isits YaST2 configuration tool. SLES has a fairly stable release cycle; with a new major release every2–3 years, it is updated more frequently than RHEL but less frequently than most other Linuxdistributions.SLES is available for evaluation purposes from LikeRedHat Enterprise Linux, a support contract is required to use the full version.OpenSUSE is to SLES as Fedora is to RHEL — a possibly less stable but more community-focused,cutting-edge version of its Enterprise relative. Test versions are available before the official release.OpenSUSE is available from The main OpenSUSE website isUbuntu is based on the Debian “testing” branch, with additional features and customizations. It isvery easy to install and configure, has lots of Internet forums providing support, and is a polishedGNU/Linux distribution. Ubuntu offers a Long-Term Support (LTS) release once every 2 years,which is supported for 2 years on the desktop and 5 years for servers. There are also regular releasesevery 6 months, which are numbered as YY-MM, so the 10-10 release (Lucid Lynx) was released inOctober 2010. Although widely known for its desktop OS, the server version, without the graphicalfeatures, is growing in popularity.Ubuntu can be installed in many ways — from a CD/DVD, a USB stick, or even from within anexisting Windows installation. Instructions and freely downloadable media and torrents are availablefrom Many rebuilds of Ubuntu are also available: Kubuntu with KDEinstead of GNOME and Xubuntu with the XFCE window manager, as well Edubuntu, whichincludes educational software, and the Netbook Edition tailored for netbook computers.Debian is one of the older GNU/Linux distributions in mainstream use. It has a team of over 1,000Debian developers, providing over 30,000 packages. The stable branch is generally released every5 years or so, so the current stable release can be rather old, although plans are to increase thefrequency of stable releases. The testing branch is popular with many users, providing the latest
packages but without the unpredictability of the unstable branch. Debian CD/DVD images are available for direct download, or via BitTorrent, from Many hundreds of GNU/Linux distributions are available. The website is an excellent resource with information on just about every distribution that exists, as well as otherUnix and Unix-like software. Some other popular distributions worth highlighting include Gentoo,Damn Small Linux, Knoppix, Slackware, and Mandriva.
The BSDs再发展下来才有了：大霞美的花卉基地和清源山的花博园。
