ch21.htm

Maximum Security (First Edition) 网络安全 英文版

	System Interface, a standard that has been in the works for many years. This standard
	is an effort on the part of developers to establish a unified UNIX. In other words,
	if a program is fully POSIX compliant, it should run on any fully POSIX-compliant
	platform, be it SunOS, Linux, AIX, HP-UX, or other versions of UNIX. For many years
	(and even now) there have been both sharp and subtle differences between various
	UNIX platforms that prevent easy porting of applications. The POSIX standard will
	likely change that. To learn more about POSIX, visit <TT>http://csrc.ncsl.nist.gov/nistbul/csl91-10.txt</TT>.
	
<HR>


</BLOCKQUOTE>

<P>Garden-variety throwaway programming can also be done in rc, the shell environment
of Plan 9.</P>
<P>The complete distribution of Plan 9 also comes with extensive libraries, including
one for the development of windowed applications intended to run within 8<FONT SIZE="1"><SUP>
1</SUP></FONT>/<FONT SIZE="1">2</FONT> (windows are actually referred to as <I>panels</I>).
Tom Duff has written quite a good paper on the development of panels in Plan 9. He
likens the panel library to the popular development packages Tcl and Tk. Linux users
will be familiar with Tcl and Tk. Both are languages (and development libraries)
for use in generating X Window System applications. One of the most popular features
about Tk is that you can build a windowed application using a language very similar
to a macro language. It is possible to quickly develop applications using these tools
because objects within the window environment are placed by the use of direct statements.
For example, the command within a Tk script to create a button is:</P>
<PRE><FONT COLOR="#0066FF">button .name_of_button &lt;options&gt;
pack .name_of_button &lt;options&gt;
</FONT></PRE>
<P>Similarly, the development syntax for windowed applications intended for use in
Plan 9 is reduced to direct statements (although this is still done using basic C).


<BLOCKQUOTE>
	<P>
<HR>
<FONT COLOR="#000077"><B>Cross Reference:</B></FONT><B> </B>If you are interested
	in developing windowed applications in Plan 9, Tom Duff's paper, &quot;A Quick Introduction
	to the Panel Library,&quot; can be found online at <A HREF="ftp://plan9.bell-labs.com/plan9/doc/panel.html"><TT>ftp://plan9.bell-labs.com/plan9/doc/panel.html</TT></A>.
	
<HR>


</BLOCKQUOTE>

<P>Another interesting aspect of Plan 9 is its inclusion of the Alef programming
language. Alef is a relatively new language. Unfortunately, a discussion about the
Alef language is beyond the scope of this book (that is a delicate way of saying
that I know too little about Alef to provide you with quality information).


<BLOCKQUOTE>
	<P>
<HR>
<FONT COLOR="#000077"><B>Cross Reference:</B></FONT><B> </B>To find more information
	about Alef, check out the language reference manual. It can be found online at <A
	HREF="http://plan9.bell-labs.com/plan9/doc/ref.html"><TT>http://plan9.bell-labs.com/plan9/doc/ref.html</TT></A>.</P>
	<P>Another important resource (probably even more valuable than the language reference
	manual, especially for the newcomer to Alef) is the Alef mailing list. It can be
	viewed online at <A HREF="http://plan9.wtf.nyc.ny.us/1996/0001.html"><TT>http://plan9.wtf.nyc.ny.us/1996/0001.html</TT></A>.
	
<HR>


</BLOCKQUOTE>

<P>In all, Plan 9 is a very rich development environment. One thing that makes it
especially exciting is that the field is wide open. It is a whole new operating system
just waiting for new and useful applications to be written.
<H2><FONT COLOR="#000077"><B>Installing the PC Distribution</B></FONT></H2>
<P>You might want to try out a working demo of Plan 9; Bell Labs has generously provided
such a distribution free of charge on the Internet. However, before you install Plan
9, there are some things you should consider. One is whether you should even begin.
As with any new operating system, you should expect bad things to happen. These may
range from simple installation failures to data or disk corruption.


<BLOCKQUOTE>
	<P>
<HR>
<FONT COLOR="#000077"><B>NOTE:</B></FONT><B> </B>If such events occur, it is most
	likely because you are using unsupported hardware. When the right hardware is used,
	Plan 9 works beautifully. Of course, not everyone has the money to go out and acquire
	the exact hardware used at Bell Labs. If your cash is limited, expect a certain amount
	of trouble along the way. 
<HR>


</BLOCKQUOTE>

<P>Moreover, you'll experience a high level of frustration. If you have ever installed
an operating system that is less than user friendly, you know the terrain. Cryptic
errors may appear, and you will undoubtedly be forced to hack here and there. These
obstacles will be particularly prominent if you are installing the four disk, free
PC distribution on dubious hardware.
<H3><FONT COLOR="#000077"><B>The Machine Targeted for Installation</B></FONT></H3>
<P>The machine that you use should be free and clear. That is, under no circumstances
should you install the Plan 9 distribution on a machine that you rely on to make
a living (even if you are installing Plan 9 on a separate disk). There have been
instances in which Plan 9 installations have permanently disabled the boot capabilities
of other operating systems or partitions. The only reason you should make such an
installation is if your job requires it (or if you are a programmer who loves adversity).
Otherwise, use that old DX66 you have lying around in the closet.</P>
<P>If you only have one machine and still want to experiment, get a rack-mount disk
changer. This device allows you to switch hard disk drives quickly and easily. It
works in exactly the same fashion as a slide-out car stereo. Your hard disk drive
is secured in an enclosure that slides into your PC tower. In this manner, you can
switch from your regular disk drive (containing the operating system you use for
work) to the Plan 9 drive.


<BLOCKQUOTE>
	<P>
<HR>
<FONT COLOR="#000077"><B>NOTE:</B></FONT><B> </B>To my knowledge, there have been
	no known instances of Plan 9 installations damaging hardware, so there is no reason
	why you should fear temporarily switching disks. 
<HR>


</BLOCKQUOTE>

<P>The machine need not be particularly fast, though I would recommend 66mHz or better.
I have installed the distribution on a DX33mHz, a DX266mHz, a DX4120mHz, and a 133
Pentium. To be honest, I did not find an incredible increase in speed between the
120 and the 133, nor did I find the difference between the 66 and the 120 unbearable.
However, the DX33 was admittedly quite slow.</P>
<P>Memory is important. You will need at least 8MB. Some documents on the Internet
suggest that there are individuals running Plan 9 with 4MB of RAM, and I believe
it. However, of the seven times that I installed the PC distribution, I was twice
confronted with an <TT>Out of Physical Memory</TT> message. This was, as it happens,
a fatal error. Immediately following this message, the installation failed. On both
occasions, I was using only 8MB of RAM. On an identical machine, after installing
additional RAM, I managed to complete the installation successfully.
<H3><FONT COLOR="#000077"><B>The Hard Disk Drive</B></FONT></H3>
<P>What hard disk drive you use depends on what you are installing. If you are simply
installing the PC distribution, you can successfully use a 40MB hard disk drive.
However, if you intend to install the entire Plan 9 distribution from CD-ROM, you
need a hard disk drive equal to or greater than 540MB.


<BLOCKQUOTE>
	<P>
<HR>
<FONT COLOR="#000077"><B>TIP:</B></FONT><B> </B>It has been reported in documentation
	that a 500MB disk will suffice. As far as I can tell, this is not entirely accurate.
	If you make a direct installation from the CD-ROM, you will require a 540MB disk
	(or approximately 532MB). The only way to get around this is to first install the
	basic four-disk PC distribution, and then more incisively install the remainder of
	the distribution from CD-ROM. This eliminates many items that are intended for use
	on other platforms. Be advised, however, that this is a more difficult path and may
	result in problems getting your CD-ROM to catch. (Sometimes, the CD-ROM driver does
	not properly initialize the CD-ROM drive.) It is a much better idea to make the full
	install and later delete what you do not need. 
<HR>


</BLOCKQUOTE>

<P>I recommend a 540 or 600MB drive. I should state that my installations were performed
entirely with IDE drives and therefore, I cannot give background on SCSI-based installations.
I obtained suitable results with the following drives:

<UL>
	<LI>MiniScribe 8051A (41MB) (Don't laugh. It worked flawlessly.)<BR>
	<BR>
	
	<LI>Conner CFS540A (EZD03) (540MB)<BR>
	<BR>
	
	<LI>Quantum Maverick ProDrive #MV54AO11 (514MB)<BR>
	<BR>
	
	<LI>Maxtor 7245AT (243MB)
</UL>

<H3><FONT COLOR="#000077"><B>The Installation Process</B></FONT></H3>
<P>I will assume that you are installing the four-disk PC distribution. This set
of four diskette images is located online at <TT>ftp://plan9.bell-labs.com/plan9/pcdist/README.html</TT>.
Download these into a temporary directory on your current hard disk drive.


<BLOCKQUOTE>
	<P>
<HR>
<FONT COLOR="#000077"><B>NOTE:</B></FONT><B> </B>The term <I>diskette images</I>
	refers to four files located at the Plan 9 site. These files are exact copies of
	four diskettes required to make an installation set for Plan 9. These files or images
	must be downloaded to your local machine and written to floppy diskettes. 
<HR>
</P>
	<P>
<HR>
<FONT COLOR="#000077"><B>TIP:</B></FONT><B> </B>It is important that you obtain the
	disks from this site. Earlier versions of these boot disks may be available at other
	locations, but you should not use them. On installation, earlier versions have a
	tendency to damage other partitions on the disk drive. A typical example would be
	where Plan 9 disabled a Linux partition during the installation process. Again, I
	strongly advise against installing Plan 9 on any hard disk drive that contains vital
	or irreplaceable information. 
<HR>


</BLOCKQUOTE>

<P>The diskette images at that location are

<UL>
	<LI><TT>disk1</TT>
	<LI><TT>disk2.vd</TT>
	<LI><TT>disk3.vd</TT>
	<LI><TT>disk4.vd</TT>
</UL>

<P>After you download these diskette images, write them directly to a floppy.


<BLOCKQUOTE>
	<P>
<HR>
<FONT COLOR="#000077"><B>NOTE:</B></FONT><B> </B>Copying the diskette images to a
	floppy involves a process that is different from copying files to a floppy. Copying
	the diskette images directly to floppy will not suffice and will result in an installation
	failure. 
<HR>


</BLOCKQUOTE>

<P>A number of utilities for writing disk images to floppy disks are available. The
most popular is a program called <TT>DD.EXE.</TT> A DOS version (suitable for use
under Windows 95) is available on-line at

<UL>
	<LI><A HREF="http://access1.sun.com/drivers/utilities/dd.exe"><TT>http://access1.sun.com/drivers/utilities/dd.exe</TT></A>
</UL>

<P>Another utility used for this purpose (and one that is more widely available on
the Internet) is <TT>RAWRITE.EXE</TT>. Linux users will be familiar with <TT>RAWRITE.EXE</TT>
because it used to write the boot diskette images for Linux to a floppy. <TT>RAWRITE.EXE</TT>
is available online at

<UL>
	<LI><A HREF="ftp://sunsite.unc.edu/pub/Linux/distributions/slackware/install/RAWRITE.EXE"><TT>ftp://sunsite.unc.edu/pub/Linux/distributions/slackware/install/RAWRITE.EXE</TT></A>
</UL>

<P>After you write these images to a floppy, switch to the target machine (or hard
disk drive). On the hard disk drive of the target disk, you must establish a DOS
partition. The size of this partition is not particularly important (I use 10MB).
It really only needs to be large enough to hold DOS and approximately 1.5MB of information
in a directory called <TT>C:\PLAN9</TT>.
<H3><FONT COLOR="#000077"><B>Partitioning the Disk</B></FONT></H3>