了解NetBSD

NetBSD runs on more hardware platforms than any other UNIX® derivative due to smart design decisions and a commitment to portable code. Whether you're porting an operating system to a proprietary embedded system or looking for stability and compatibility across hardware platforms in the lab, NetBSD and its open license is a compelling alternative to Linux® and the GNU Public License (GPL).

NetBSD比任何一种Unix变种的操作系统所能允许运行的平台都要多。这主要是由它灵活的设计决策和对可移植代码的不懈追求所决定的。无论你是将它移植到专有嵌入式设备中，或者是将它安装在对稳定性和兼容性都要求非常高的实验室机器上，NetBSD都会满足你的要求。NetBSD及其开源授权协议，比起Linux®和GNU协议一点都不差。

One feature listed on the NetBSD Web site is that the operating system is hype free. I can do without hype, but generating some buzz for this operating system that is often overlooked certainly wouldn't hurt.

NetBSD has an interesting architecture, which is often taken for granted and rarely commented on outside Berkeley Software Distribution (BSD) circles. The system's well thought-out design allows for wide hardware support, a small footprint, stability, and security. NetBSD's unique features include a new paradigm for handling device drivers and other interesting innovations.

These design decisions and commitment to source code, which not only works but works right, have helped NetBSD lay claim to being the most portable UNIX® derivative in existence. It particularly excels in embedded systems, but you should also consider it as a compelling alternative to more mainstream servers, desktops, and laptop operating systems.

An introduction to BSD

Three major BSD-derived operating systems are freely available: NetBSD, FreeBSD, and OpenBSD. All three systems are related to the original BSD distribution of UNIX, which dates back to the 1970s. In the early 1990s, at about the same time Linux® was coming together as a legitimate competitor to UNIX, a separate track was being forged to create a free UNIX-like operating system based on BSD. All three BSD versions have strong points, with FreeBSD leading the way in user base, OpenBSD leading in security, and NetBSD leading in portability.

Of course it runs on NetBSD

You can port NetBSD to run on just about anything with a processor -- hence the motto, "Of course it runs on NetBSD." NetBSD supports more than 50 platforms, ranging from old 68K and million instructions per second (MIPS) systems to the newest x86_64 processors from Advanced Micro Devices, Inc. (AMD) and Intel®. Furthermore -- and possibly more importantly -- NetBSD has been ported for use on a massive number of embedded systems.

Embedded systems

Embedded systems are huge part of everyday life in the 21st century, far outselling traditional computing devices such as desktops, laptops, and servers. From mobile phones to automobiles to cable boxes, you're more than likely using a computer in some aspect of your life. The operating system and software that sit inside these devices is often as important as the traditional engineering decisions that go into their design.

Examples of NetBSD embedded systems range from the useful (routers and switches) to the bizarre (a NetBSD toaster). The variety of architectures commonly used in embedded systems far exceeds common choices for traditional computers, so portability is vital.

NetBSD's small footprint, ease of portability, and BSD license make it a perfect choice for embedded systems. The small footprint is extremely important, as most embedded systems have a small amount of memory. Therefore, the operating system must be as thin as possible. Ease of portability significantly cuts development time to bring new products to market, which is key to staying ahead of competitors. The BSD license allows companies to build commercial products based on NetBSD and sell them for a profit while keeping the source code proprietary.

The BSD license

The BSD license is a big factor in corporate decision making when an organization is choosing NetBSD (or other BSD variants) over Linux for commercial products. The Linux kernel and most Linux software is released under the General Public License (GPL), which requires the release of the source for all modified codes. In contrast, the BSD license allows companies to modify and sell NetBSD code without releasing the modified source, thereby allowing companies to keep intellectual property close to the vest while leveraging open source software for the base of their product.

In recent years, numerous companies have been sued over the improper use of GPL software. Choosing software released under the BSD license gives wider operating room for commercial products, which is another reason NetBSD is so well suited for embedded systems. For instance, if Company A were to use NetBSD in a new smart phone running on Intel XScale® technology, the company might add kernel support for Evolution-Data Optimized (EV-DO) devices. Under the BSD license, the company can keep this code proprietary so that Company B can't use the same code for their new phone. Had Company A decided to use a Linux kernel, their source for any modifications to the kernel would have to be released back to the community under a GPL license.

Note: Find information in the BSD newsletter in the Resources section on building a small NetBSD kernel as a starting point for an embedded system.

NetBSD: Not just for embedded systems

Any system administrator who has been in the business for a while understands the inevitability of hardware changes. You see it everyday when looking through an information technology (IT) room filled with architectures that were hot one day but failed to stand the test of time -- be it for technical or commercial reasons. Unfortunately, when many of these systems pass, their operating systems pass along with them. A big advantage of running a highly portable operating system, such as NetBSD, is consistency across platforms. If a system administrator can be confident that an operating system runs on the oldest workstation in the lab and the newest server comes off the assembly line, that administrator's job becomes substantially simpler. This simplification can be referred to as hardware compatibility through software homogeneity. A similar example is sharing productivity documents across computers running Microsoft® Windows® and Mac OS X by using Microsoft Office programs on both platforms. Sharing at the operating system level is an advanced extension of the same concept, suitable for developers rather than everyday users.

Some system administrators might argue that they have always, and will always, run on an x86 platform. So why should they be interested in an operating system that prides itself on portability? There are two answers (and one of them includes a question):

• A large component of the portability of NetBSD can be credited to an intelligently designed system and well-defined implementation standards. Portability and good design often go hand in hand, making the benefits of these decisions evident throughout the operating system.
• Can you define always? While many companies and labs have been using x86 architectures for quite some time and don't anticipate variations, disruptive changes in technology are always difficult to predict. Knowing that your operating system won't restrict purchasing decisions opens up a cornucopia of choices that otherwise could not have been considered.

Saving money and gaining peace of mind by knowing that they won't need to port software and control systems to a new operating system are real and tangible benefits. Through these benefits, system administrators and programmers can focus on moving forward rather than simply keeping pace.

The NetBSD kernel

Every part of the NetBSD kernel is carefully thought out, with clean design and portability in mind. Here's a brief look at some design components of the NetBSD kernel.

NetBSD device drivers

NetBSD's machine-independent driver framework is a unique method of handling device drivers, and it's crucial for simple and quick ports. In most operating systems, a device driver is specific to a piece of hardware (video card, network interface card (NIC), and so on), bus (such as Peripheral Component Interconnect (PCI), Industry Standard Architecture (ISA), Universal Serial Bus (USB)), and platform (i386, 68k, PowerPC®, and so on). In NetBSD, device drivers are written to extend across multiple buses and multiple platforms, enabling developers to include addenda to the device driver's code to add compatibility to a new setup rather than writing a whole new driver. This is a huge shift from the typical operating system device driver paradigm that helps in overcoming one of the biggest stumbling blocks for operating system developers, system administrators, and component manufactures.

File system support

NetBSD, again encouraging portability and interoperability, includes support for many different file systems. Berkeley Fast File System (FFS) is the default choice, with support in 32-bit and 64-bit configurations. Other major file systems that NetBSD supports include the Linux ext2 and the Windows NTFS and FAT32 file systems. The standard CD file system, International Standards Organization (ISO) 9660, is also supported, with both Rockridge and Joliet extensions.

Cryptographic device driver

The combined effect of today's wide-spread use of laptop computers and the increased amount of sensitive company and personal information stored digitally is a recipe for disaster. Every few months, you read a story in the headlines about a lost computer, or hard disk, containing sensitive data -- be it a government lab, a credit card company, or an individual who had all his or her banking information, including their Social Security number, on a personal computer. The fact is aclearcase/" target="_blank" >ccounts, passwords, and permissions can only protect your data in the context of an operating system that obeys stated rules. Bits are bits, and any hard disk pulled out of one computer and put into another can easily be read -- unless that data is encrypted. File encryption can be accomplished in a variety of ways, but it's rarely used because of the burden on system administrators or users. Most data encryption methods require explicit decisions of where and when to encrypt data, manual mounting and unmounting of encrypted images, and entering passwords.

NetBSD uses the cryptographic device driver (CGD) to implement an encrypted file system with a virtual device. By sitting between the rest of the operating system and the actual disk, CGD looks and acts like any other disk drive attached to the system, allowing for transparent access to secure storage.

Note: See the NetBSD Guide in the Resources section for information on how to enable CGD.

General security

NetBSD takes security very seriously; the inclusion of the CGD is only one of many examples. If portability is rule number one for the NetBSD community, security doesn't sit far behind. An absolute dedication to well-written code is paramount, including procedures for code auditing and continued checks. Second, like OpenBSD, the default installation includes a bare minimum of packages installed, or configured. The first thing a system administrator is likely to do after a NetBSD installation on a server is to configure the network and enable Secure Shell (SSH), which gives you an indication of how little the default configuration enables. While some new users might argue that this approach makes things more difficult on them, learning to control and configure services is an important part of any UNIX-like operating system, and learning to do so doesn't take long. A quick read through the official NetBSD Guide helps get new users off the ground.

Note: See the Resources section for an additional link from gna.org to a great document for new NetBSD users.

Application support: Package source and binary emulation

Application support in NetBSD is both wide and varied. Most standard software familiar to administrators of UNIX-like operating systems is natively available to NetBSD and easily installed through the NetBSD Packages Collection (pkgsrc), which includes more than 5000 packages. If you can't find what you are looking for through pkgsrc, you can always run through a series of binary emulators built into NetBSD, the most prominent of which is the Linux emulator running on i386.

The default installation of NetBSD, however, is quite thin. Not only is it configured with most services turned off, it has few packages installed, period. The kernel, compilers, network services, XFree, and standard UNIX utilities are all that's included in the base distribution. To install packages you're used to finding in a UNIX-like operating system (such as MySQL or PostgreSQL), use the pkg_add command to extract and install software (from local disk, CD/DVD, or over the network). If you're installing an x86 system, you can use /cdrom/packages/i386/All/ on the i386pkg-3.0.iso CD. Packages installed through the pkg_add command are installed in /usr/pkg/ and do not interfere with the core components of NetBSD.

For non-native applications, NetBSD can transparently run binaries from a variety of UNIX-like operating systems with a negligible impact on performance. While most of the popular open source applications have been ported to run natively on NetBSD, some commercial applications, such as Matlab and Mathematica, cannot be ported by the user community because the code is proprietary. This is where binary emulation becomes important for NetBSD users. The emulation process is streamlined because the binaries are native to the underlying architecture of the system. Don't confuse binary emulation with the CPU-hungry process of hardware emulation, which is not at play here. Binary emulation is often suitable for running processor-intensive applications in a production environment.

Decisions, decisions

NetBSD's attention to detail, well-written code, and vast portability make it a solid choice for a number of deployment scenarios. Unfortunately, BSD derivatives are flying just low enough to stay under the radar and many developers and system administrators are missing important opportunities. The most important part of making a good decision is to be well informed. BSD might or might not be the right choice for you, but don't make the mistake of overlooking it just because you're familiar with something else. Use this article as a starting point to familiarize yourself with NetBSD, then give the distribution a shot -- the least you can do is learn.

Resources