📄 ch21.htm
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"><HTML><HEAD> <TITLE>Maximum Security -- Ch 21 -- Plan 9 from Bell Labs</TITLE></HEAD><BODY TEXT="#000000" BGCOLOR="#FFFFFF"><CENTER><H1><IMG SRC="../button/samsnet.gif" WIDTH="171" HEIGHT="66" ALIGN="BOTTOM" BORDER="0"><BR><FONT COLOR="#000077">Maximum Security: </FONT></H1></CENTER><CENTER><H2><FONT COLOR="#000077">A Hacker's Guide to Protecting Your Internet Site and Network</FONT></H2></CENTER><CENTER><P><A HREF="../ch20/ch20.htm"><IMG SRC="../button/previous.gif" WIDTH="128" HEIGHT="28"ALIGN="BOTTOM" ALT="Previous chapter" BORDER="0"></A><A HREF="../ch22/ch22.htm"><IMGSRC="../button/next.gif" WIDTH="128" HEIGHT="28" ALIGN="BOTTOM" ALT="Next chapter"BORDER="0"></A><A HREF="../index.htm"><IMG SRC="../button/contents.gif" WIDTH="128"HEIGHT="28" ALIGN="BOTTOM" ALT="Contents" BORDER="0"></A> <HR></CENTER><CENTER><H1><FONT COLOR="#000077">21</FONT></H1></CENTER><CENTER><H1><FONT COLOR="#000077">Plan 9 from Bell Labs</FONT></H1></CENTER><P>Almost thirty years ago, the team at Bell Labs (now Lucent Technologies) changedthe world by developing what would later become the most popular networked operatingsystem in history. From then until now, UNIX has ruled the Internet. Even if thatwere the only contribution ever made by Bell Labs personnel, it would have been sufficient.They would been have been held in high regard as having achieved something trulyuseful and important. As any programmer will tell you, however, the contributionsfrom Bell Labs kept coming.</P><P>In the early 1990s, the folks at Bell Labs were still busy. This time, however,they had more than 25 years of experience under their belts. With that experience,they challenged themselves to create the <I>ultimate</I> networked operating system.Did they succeed? You bet. It is called <I>Plan 9 from Bell Labs</I>.<H2><FONT COLOR="#000077"><B>The Basics</B></FONT></H2><P>The team at Bell Labs (which includes such heavy-duty names as Ken Thompson andDennis Ritchie) were reportedly dissatisfied with the then-current trends in computertechnology. They realized that hardware considerations made networking a difficultproposition, one that didn't always work out in terms of cost effectiveness or performance.Hardware dependencies and proprietary design make networking more of a forced environmentthan a truly fluid, easy one. By <I>forced environment</I>, I mean that dozens ofoften disparate and incompatible protocols, drivers, and software are patched togetherto provide a shaky and sometimes unreliable integration of networks.</P><P>Alas, although the Internet may sometimes be referred to as a miracle of distributedcomputing, it isn't. The current system works only because we have forced the TCP/IPstack upon a handful of architectures (many that were never designed to run theseprotocols). Thus, the Internet has the <I>appearance</I> of being an amalgamated,united network. On closer examination, however, it is clear that the Internet isexploiting only a very meager portion of the networking power at its disposal.</P><P>Consider this: FTP is one of the most commonly used techniques to move informationfrom one place to another. When a user transfers a file via FTP, he is a <I>remote</I>user, accessing some resource on a server in the void. The word <I>remote</I> isthe key feature here. It denotes a condition wherein the user is isolated. To accessthe resources at the other end, the user must perform several actions (these mayinclude initiating the FTP session, unzipping the file, placing it in the properdirectory, and so on). FTP therefore places the user at arm's length. The use ofthe resource does not occur in a fluid environment.</P><P>Similarly, and to an even greater extent, HTTP isolates the user. True, it appearsto the user as though he is working interactively with a Web site, but he isn't.In fact, HTTP may isolate the user more than any other network protocol. For example,you are not logged in as you are with Telnet or FTP. In fact, you are connected onlyfor the brief periods--seconds, actually--necessary for your client to relate whichresources it needs. This is the farthest thing from a traditional shared networkenvironment.</P><P>In contrast, suppose that instead of retrieving a file and placing it in yourphysical location, you simply want to use the file momentarily. This is sometimesachieved through file sharing in proprietary network environments (environments wherea directory or a file can be attached to the local machine). In such cases, the resourceappears and behaves as though it is on the local machine. This technique is moreakin to true, networked computing. It is a one-step process.</P><P>Now imagine an operating system that was designed to interface in this mannerwith many different types of systems and hardware, an operating system that couldprovide this real networking to hundreds (or even thousands) of workstations, irrespectiveof hardware constraints. Imagine an operating system that makes FTP directories ofremote machines appear as local directories (regardless of where the target servermay be located). If you can imagine this, you are well on your way to understandingthe basic characteristics of Plan 9.<H3><FONT COLOR="#000077"><B>What Plan 9 Is Not</B></FONT></H3><P>Plan 9 is not UNIX, or any variant thereof. But if you install the demo distribution,you may initially be confused on this point. At first glance, it looks a lot likeUNIX (particularly when you make a directory listing). Make no mistake, though. Plan9 is an entirely new operating system. As explained in the Plan 9 from AT&T BellLaboratories FAQ:<DL> <DD>Plan 9 is itself an operating system; it doesn't run as an application under another system. It was written from the ground up and doesn't include other people's code. Although the OS's interface to applications is strongly influenced by the approach of UNIX, it's not a replacement for UNIX; it is a new design.</DL><BLOCKQUOTE> <P><HR><FONT COLOR="#000077"><B>NOTE:</B></FONT><B> </B>Visit the Plan 9 FAQ <A HREF="http://www.ecf.toronto.edu/plan9/plan9faq.html"><TT>http://www.ecf.toronto.edu/plan9/plan9faq.html</TT></A>. <HR></BLOCKQUOTE><P>Despite the fact that Plan 9 is an entirely different operating system, it doesretain some of the look and feel of UNIX. There is still a shell (called <TT>rc</TT>)and that shell appears much like the popular shells available in most distributionsof UNIX. Files, for example, can still be displayed in a UNIX-like long format, alongwith their attending permissions. Moreover, one can still differentiate between filesand directories using the standard <TT>-F</TT> switch (in fact, many of the stockUNIX commands are available and most of these behave pretty much as they do on aUNIX box). However, the resemblance to UNIX is largely superficial. The underlyingoperating system works very differently.</P><P>One of the chief differences is the way that Plan 9 treats objects (objects inthis case being directories, files, processes, and so forth). Under Plan 9, all objectsare treated as files. This technique has been implemented in UNIX as well (for example,UNIX treats many devices as files), but not to the extent that it has in Plan 9.<H3><FONT COLOR="#000077"><B>Machines That Run Plan 9</B></FONT></H3><P>The reported architectures include<UL> <LI>MIPS <LI>SPARC <LI>68020 (NeXT) <LI>IBM compatibles</UL><P>It is reported in the Plan 9 from AT&T Bell Laboratories FAQ that variousports are also underway for the following systems:<UL> <LI>SGI Indy <LI>DEC Alpha <LI>PowerPC <LI>DECstation 2100 and 3100</UL><P>My experience with installing the Plan 9 distribution has been on the IBM compatibleplatform. As you will see, I went through several generations of hardware beforelanding on the right combination.<BLOCKQUOTE> <P><HR><FONT COLOR="#000077"><B>Cross Reference:</B></FONT><B> </B>If you intend to install Plan 9 as a hacking project, you would do well to visit <A HREF="http://www.ecf.toronto.edu/plan9/clone.html"><TT>http://www.ecf.toronto.edu/plan9/clone.html</TT></A>. This page describes the hardware that was used at Bell Labs, and will provide you with a nice guideline of hardware that is known to work with Plan 9. <HR></BLOCKQUOTE><H2><FONT COLOR="#000077"><B>Some Concepts</B></FONT></H2><P>Plan 9 was designed from the beginning as a networked operating system. As such,the concepts behind it relate more to networking than to the needs of the individualuser. Its defining characteristics are the ways in which it handles networking. Asnoted in the press release for the product:<DL> <DD>The Plan 9 system is based on the concept of distributed computing in a networked, client-server environment. The set of resources available to applications is transparently made accessible everywhere in the distributed system, so that it is irrelevant where the applications are actually running.</DL><BLOCKQUOTE> <P><HR><FONT COLOR="#000077"><B>Cross Reference:</B></FONT><B> </B>Find the press release from which the preceding paragraph is excerpted at <A HREF="http://www.lucent.com/press/0795/950718.bla.html"><TT>http://www.lucent.com/press/0795/950718.bla.html</TT></A>. <HR></BLOCKQUOTE><P>To understand how the Plan 9 system differs from other networked operating systems,examine Figure 21.1.</P><P><A NAME="01"></A><A HREF="01.htm"><B>FIGURE 21.1.</B></A> <BR><I>The typical network configuration (without Plan 9).</I></P><P>The typical network configuration (the one most often seen in offices) uses afile server and a series of workstations. Each of the workstations is outfitted witha host of hardware and software (hard disk drives, adequate memory, a windowing system,and so forth) that provides it with the necessary power and networking to connect.System administrators and other, administrative personnel will recognize this setupto be an expensive one.</P><P>Because the computer industry has enjoyed tremendous growth (particularly in thelast few years), network designs like the one shown in Figure 21.1 are common. Nodeson such networks are usually Pentiums or PowerPCs. You may own such a network yourself.If you do, consider this: Is it necessary that you have such a powerful machine ateach node? Or, could it be that this type of configuration is a profligate wasteof enormous CPU power? For example, how much CPU power does the accounting departmentactually require? It depends on what operating system you are running. If you arerunning DOS-based applications over NetWare, the accounting department doesn't needmuch power at all. However, if you are running Windows 95, it will need speed andmemory.</P><P>That speed and memory, by the way, is being eaten purely by features that makeyour platform prettier and more user friendly. In practice, the average accountingtask done in a DOS-based application would be barely noticeable to a Pentium processor.Contrast that with accounting done in Microsoft Excel on the Windows 95 platform.In reality, processor-intensive tasks requiring real power might include tasks likecompiling large programs in C++. These tasks, even in a DOS environment, can taxa processor.</P><P>So the first point is this: Modern network design wastes processor power by dispersingit, often where it is not most needed. But there are other key disadvantages to thistypical network implementation. One is that files are strewn throughout the network,many of them deposited on this or that hard disk drive. How many times have you encounteredthe following situation:<DL> <DD><B>1. </B>A machine along the network fails.<BR> <BR> <B>2. </B>The machine that failed has a file vital to office operations.<BR> <BR> <B>3. </B>You recover that file (usually by depositing the hard disk drive from the failed machine into another, operable one, or by performing a restore).</DL><P>If you have never encountered this situation, consider yourself lucky. I haveseen it happen many times. Also, because users often store files locally (on theirown workstation), employees must file share and therefore, their machines must alwaystrust each other.</P><P>Plan 9 takes a totally different approach. In Plan 9, the jobs of processing andfile storage and separated, as are the machines that perform these tasks (see Figure21.2).</P><P><A NAME="02"></A><A HREF="02.htm"><B>FIGURE 21.2.</B></A> <BR><I>The Plan 9 networking concept.</I></P><P>Note the CPU server in Figure 21.2. This would typically be a very powerful machine(probably multiprocessor) that would provide CPU services to remote workstationsor terminals. This is complemented by a file server.</P><P>This system has some important advantages. First, there is centralized controlof files. This has obvious security advantages. Centralized file control also allowseasier management of files. Moreover, it provides an environment in which permissionsmay be easily viewed and alteration of files may be more readily detected.</P><P>Also (though this has little to do with security), as mentioned in the Plan 9documentation, this centralized file management is of benefit to a programming team.Project management is more easily accomplished and the system offers a sense of communityfor the programming team.</P><P>Moreover, the Plan 9 system performs without a root operator. Users must be authenticatedto gain access to privileged files or processes, and this authentication has been⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -