The Cathedral and the BazaarEricStevenRaymond
Thyrsus Enterprisesesr@thyrsus.com$Date: 2000/08/24 22:37:44 $This is version 3.02000Eric S. RaymondCopyrightPermission is granted to copy, distribute and/or modify
this document under the terms of the Open Publication License,
version 2.0.1.5124 August 2000esr
First DocBook version. Minor updates to Fall 2000 on the
time-sensitive material.
1.495 May 2000esr
Added the HBS note on deadlines and scheduling.
1.5131 August 1999esr
This the version that O'Reilly printed in the first edition
of the book.
1.458 August 1999esr
Added the endnotes on the Snafu Principle, (pre)historical examples
of bazaar development, and originality in the bazaar.
1.4429 July 1999esr
Added the ``On Management and the Maginot Line'' section, some
insights about the usefulness of bazaars for exploring design space,
and substantially improved the Epilog.
1.4020 Nov 1998esr
Added a correction of Brooks based on the Halloween Documents.
1.3928 July 1998esr
I removed Paul Eggert's 'graph on GPL vs. bazaar in response
to cogent aguments from RMS on
1.31February 10 1998 esr
Added ``Epilog: Netscape Embraces the Bazaar!''
1.29February 9 1998esr
Changed ``free software'' to ``open source''.
1.2718 November 1997esr
Added the Perl Conference anecdote.
1.207 July 1997esr
Added the bibliography.
1.1621 May 1997esr
First official presentation at the Linux Kongress.
I anatomize a successful open-source project, fetchmail, that was
run as a deliberate test of some surprising theories about software
engineering suggested by the history of Linux. I discuss these
theories in terms of two fundamentally different development styles,
the ``cathedral'' model of most of the commercial world versus the ``bazaar''
model of the Linux world. I show that these models derive from
opposing assumptions about the nature of the software-debugging task.
I then make a sustained argument from the Linux experience for the
proposition that ``Given enough eyeballs, all bugs are shallow'',
suggest productive analogies with other self-correcting systems of
selfish agents, and conclude with some exploration of the implications
of this insight for the future of software.The Cathedral and the BazaarLinux is subversive. Who would have thought even five years ago
(1991) that a world-class operating system could coalesce as if by
magic out of part-time hacking by several thousand developers
scattered all over the planet, connected only by the tenuous strands
of the Internet?Certainly not I. By the time Linux swam onto my radar screen in early
1993, I had already been involved in Unix and open-source development
for ten years. I was one of the first GNU contributors in the
mid-1980s. I had released a good deal of open-source software onto
the net, developing or co-developing several programs (nethack, Emacs's
VC and GUD modes, xlife, and others) that are still in wide use today.
I thought I knew how it was done.Linux overturned much of what I thought I knew. I had been preaching
the Unix gospel of small tools, rapid prototyping and evolutionary
programming for years. But I also believed there was a certain
critical complexity above which a more centralized, a priori approach
was required. I believed that the most important software (operating
systems and really large tools like the Emacs programming editor)
needed to be built like cathedrals, carefully crafted by individual
wizards or small bands of mages working in splendid isolation, with no
beta to be released before its time.Linus Torvalds's style of development - release early and often,
delegate everything you can, be open to the point of promiscuity -
came as a surprise. No quiet, reverent cathedral-building here --
rather, the Linux community seemed to resemble a great babbling bazaar
of differing agendas and approaches (aptly symbolized by the Linux
archive sites, who'd take submissions from
anyone) out of which a coherent and stable system
could seemingly emerge only by a succession of miracles.The fact that this bazaar style seemed to work, and work well,
came as a distinct shock. As I learned my way around, I worked hard
not just at individual projects, but also at trying to understand why
the Linux world not only didn't fly apart in confusion but seemed to
go from strength to strength at a speed barely imaginable to
cathedral-builders.By mid-1996 I thought I was beginning to understand. Chance
handed me a perfect way to test my theory, in the form of an
open-source project that I could consciously try to run in the bazaar
style. So I did -- and it was a significant success.This is the story of that project. I'll use it to propose some
aphorisms about effective open-source development. Not all of these
are things I first learned in the Linux world, but we'll see how the
Linux world gives them particular point. If I'm correct, they'll help
you understand exactly what it is that makes the Linux community such
a fountain of good software -- and, perhaps, they will help you become
more productive yourself.The Mail Must Get ThroughSince 1993 I'd been running the technical side of a small
free-access Internet service provider called Chester County InterLink
(CCIL) in West Chester, Pennsylvania. I co-founded CCIL and wrote our
unique multiuser bulletin-board software -- you can check it out by
telnetting to locke.ccil.org. Today it
supports almost three thousand users on thirty lines. The job allowed
me 24-hour-a-day access to the net through CCIL's 56K line -- in fact,
the job practically demanded it!I had gotten quite used to instant Internet email. I found having to
periodically telnet over to locke to check my mail annoying. What I
wanted was for my mail to be delivered on snark (my home system) so
that I would be notified when it arrived and could handle it using all
my local tools.The Internet's native mail forwarding protocol, SMTP (Simple Mail
Transfer Protocol), wouldn't suit, because it works best when machines
are connected full-time, while my personal machine isn't always on the
net, and doesn't have a static IP address. What I needed was a program
that would reach out over my intermittent dialup connection and pull
across my mail to be delivered locally. I knew such things existed, and
that most of them used a simple application protocol called POP (Post
Office Protocol). POP is now widely supported by most common mail
clients, but at the time, it wasn't built-in to the mail reader I was
using.I needed a POP3 client. So I went out on the net and found one.
Actually, I found three or four. I used one of them for a while, but it
was missing what seemed an obvious feature, the ability to hack the
addresses on fetched mail so replies would work properly.The problem was this: suppose someone named `joe' on locke sent me
mail. If I fetched the mail to snark and then tried to reply to it,
my mailer would cheerfully try to ship it to a nonexistent `joe' on
snark. Hand-editing reply addresses to tack on `@ccil.org' quickly
got to be a serious pain.This was clearly something the computer ought to be doing for me. But
none of the existing POP clients knew how! And this brings us to the
first lesson:
1. Every good work of software starts by scratching
a developer's personal itch.
Perhaps this should have been obvious (it's long been proverbial that
``Necessity is the mother of invention'') but too often software
developers spend their days grinding away for pay at programs they
neither need nor love. But not in the Linux world -- which may
explain why the average quality of software originated in the Linux
community is so high.So, did I immediately launch into a furious whirl of coding up a
brand-new POP3 client to compete with the existing ones? Not on your
life! I looked carefully at the POP utilities I had in hand, asking
myself ``which one is closest to what I want?'' Because
2. Good programmers know what to write. Great ones
know what to rewrite (and reuse).
While I don't claim to be a great programmer, I try to imitate one.
An important trait of the great ones is constructive laziness. They
know that you get an A not for effort but for results, and that it's
almost always easier to start from a good partial solution than from
nothing at all.Linus
Torvalds, for example, didn't actually try to write Linux from
scratch. Instead, he started by reusing code and ideas from Minix, a
tiny Unix-like operating system for PC clones. Eventually all the
Minix code went away or was completely rewritten -- but while it was
there, it provided scaffolding for the infant that would eventually
become Linux.In the same spirit, I went looking for an existing POP utility that
was reasonably well coded, to use as a development base.The source-sharing tradition of the Unix world has always been
friendly to code reuse (this is why the GNU project chose Unix as a
base OS, in spite of serious reservations about the OS itself). The
Linux world has taken this tradition nearly to its technological
limit; it has terabytes of open sources generally available. So
spending time looking for some else's almost-good-enough is more
likely to give you good results in the Linux world than anywhere
else.And it did for me. With those I'd found earlier, my second
search made up a total of nine candidates -- fetchpop, PopTart,
get-mail, gwpop, pimp, pop-perl, popc, popmail and upop. The one I
first settled on was `fetchpop' by Seung-Hong Oh. I put my
header-rewrite feature in it, and made various other improvements
which the author accepted into his 1.9 release.A few weeks later, though, I stumbled across the code for `popclient'
by Carl Harris, and found I had a problem. Though fetchpop had some
good original ideas in it (such as its background-daemon mode), it
could only handle POP3 and was rather amateurishly coded (Seung-Hong
was at that time a bright but inexperienced programmer, and both
traits showed). Carl's code was better, quite professional and solid,
but his program lacked several important and rather
tricky-to-implement fetchpop features (including those I'd coded
myself).Stay or switch? If I switched, I'd be throwing away the coding I'd
already done in exchange for a better development base.A practical motive to switch was the presence of multiple-protocol
support. POP3 is the most commonly used of the post-office server
protocols, but not the only one. Fetchpop and the other competition
didn't do POP2, RPOP, or APOP, and I was already having vague thoughts
of perhaps adding IMAP
(Internet Message Access Protocol, the most recently designed and most
powerful post-office protocol) just for fun.But I had a more theoretical reason to think switching might be as
good an idea as well, something I learned long before Linux.
3. ``Plan to throw one away; you will, anyhow.''
(Fred Brooks, ``The Mythical Man-Month'', Chapter
11)
Or, to put it another way, you often don't really understand the
problem until after the first time you implement a solution. The
second time, maybe you know enough to do it right. So if you want to
get it right, be ready to start over at least
once [JB].Well (I told myself) the changes to fetchpop had been my first try.
So I switched.After I sent my first set of popclient patches to Carl Harris on 25
June 1996, I found out that he had basically lost interest in
popclient some time before. The code was a bit dusty, with minor bugs
hanging out. I had many changes to make, and we quickly agreed that
the logical thing for me to do was take over the program.Without my actually noticing, the project had escalated. No longer
was I just contemplating minor patches to an existing POP client.
I took on maintaining an entire one, and there were ideas bubbling in
my head that I knew would probably lead to major changes.In a software culture that encourages code-sharing, this is a natural
way for a project to evolve. I was acting out this principle:
4. If you have the right attitude, interesting
problems will find you.
But Carl Harris's attitude was even more important. He
understood that
5. When you lose interest in a program, your last
duty to it is to hand it off to a competent
successor.
Without ever having to discuss it, Carl and I knew we had a common
goal of having the best solution out there. The only question for
either of us was whether I could establish that I was a safe pair of
hands. Once I did that, he acted with grace and dispatch. I hope I
will do as well when it comes my turn.The Importance of Having UsersAnd so I inherited popclient. Just as importantly, I inherited
popclient's user base. Users are wonderful things to have, and
not just because they demonstrate that you're serving a need, that
you've done something right. Properly cultivated, they can
become co-developers.Another strength of the Unix tradition, one that Linux pushes to
a happy extreme, is that a lot of users are hackers too. Because
source code is available, they can be effective
hackers. This can be tremendously useful for shortening debugging
time. Given a bit of encouragement, your users will diagnose
problems, suggest fixes, and help improve the code far more quickly
than you could unaided.
6. Treating your users as co-developers is your
least-hassle route to rapid code improvement and effective
debugging.
The power of this effect is easy to underestimate. In fact, pretty
well all of us in the open-source world drastically underestimated
how well it would scale up with number of users and against system
complexity, until Linus Torvalds showed us differently.In fact, I think Linus's cleverest and most consequential hack
was not the construction of the Linux kernel itself, but rather his
invention of the Linux development model. When I expressed this
opinion in his presence once, he smiled and quietly repeated something
he has often said: ``I'm basically a very lazy person who likes to get
credit for things other people actually do.'' Lazy like a fox. Or,
as Robert Heinlein famously wrote of one of his characters, too lazy
to fail.In retrospect, one precedent for the methods and success of
Linux can be seen in the development of the GNU Emacs Lisp library and
Lisp code archives. In contrast to the cathedral-building style of
the Emacs C core and most other GNU tools, the evolution of the Lisp
code pool was fluid and very user-driven. Ideas and prototype modes
were often rewritten three or four times before reaching a stable
final form. And loosely-coupled collaborations enabled by the
Internet, a la Linux, were frequent.Indeed, my own most successful single hack previous to fetchmail
was probably Emacs VC (version control) mode, a Linux-like
collaboration by email with three other people, only one of whom
(Richard Stallman, the author of Emacs and founder of the Free Software Foundation) I have met
to this day. It was a front-end for SCCS, RCS and later CVS from
within Emacs that offered ``one-touch'' version control operations.
It evolved from a tiny, crude sccs.el mode somebody else had written.
And the development of VC succeeded because, unlike Emacs itself,
Emacs Lisp code could go through release/test/improve generations very
quickly. Release Early, Release OftenEarly and frequent releases are a critical part of the Linux
development model. Most developers (including me) used to believe
this was bad policy for larger than trivial projects, because early
versions are almost by definition buggy versions and you don't want to
wear out the patience of your users.This belief reinforced the general commitment to a
cathedral-building style of development. If the overriding objective
was for users to see as few bugs as possible, why then you'd only
release a version every six months (or less often), and work like a
dog on debugging between releases. The Emacs C core was developed
this way. The Lisp library, in effect, was not -- because there were
active Lisp archives outside the FSF's control, where you could go to
find new and development code versions independently of Emacs's
release cycle [QR].The most important of these, the Ohio State elisp archive, anticipated
the spirit and many of the features of today's big Linux archives.
But few of us really thought very hard about what we were doing, or
about what the very existence of that archive suggested about problems
in the FSF's cathedral-building development model. I made one serious
attempt around 1992 to get a lot of the Ohio code formally merged
into the official Emacs Lisp library. I ran into political trouble
and was largely unsuccessful.But by a year later, as Linux became widely visible, it was clear that
something different and much healthier was going on there. Linus's
open development policy was the very opposite of cathedral-building.
Linux's Internet archives were burgeoning, multiple distributions were
being floated. And all of this was driven by an unheard-of frequency
of core system releases.Linus was treating his users as co-developers in the most effective
possible way:
7. Release early. Release often. And listen to
your customers.
Linus's innovation wasn't so much in doing quick-turnaround releases
incorporating lots of user feedback (something like this had been
Unix-world tradition for a long time), but in scaling it up to a level
of intensity that matched the complexity of what he was developing.
In those early times (around 1991) it wasn't unknown for him to
release a new kernel more than once a day! Because he
cultivated his base of co-developers and leveraged the Internet for
collaboration harder than anyone else, this worked.But how did it work? And was it something
I could duplicate, or did it rely on some unique genius of Linus
Torvalds?I didn't think so. Granted, Linus is a damn fine hacker. How
many of us could engineer an entire production-quality operating
system kernel from scratch?. But Linux didn't represent any awesome
conceptual leap forward. Linus is not (or at least, not yet) an
innovative genius of design in the way that, say, Richard Stallman or
James Gosling (of NeWS and Java) are. Rather, Linus seems to me to be
a genius of engineering and implementation, with a sixth sense for
avoiding bugs and development dead-ends and a true knack for finding
the minimum-effort path from point A to point B. Indeed, the whole
design of Linux breathes this quality and mirrors Linus's essentially
conservative and simplifying design approach.So, if rapid releases and leveraging the Internet medium to the hilt
were not accidents but integral parts of Linus's engineering-genius
insight into the minimum-effort path, what was he maximizing? What
was he cranking out of the machinery?Put that way, the question answers itself. Linus was keeping
his hacker/users constantly stimulated and rewarded -- stimulated by
the prospect of having an ego-satisfying piece of the action, rewarded
by the sight of constant (even daily) improvement
in their work.Linus was directly aiming to maximize the number of person-hours
thrown at debugging and development, even at the possible cost of
instability in the code and user-base burnout if any serious bug
proved intractable. Linus was behaving as though he believed
something like this:
8. Given a large enough beta-tester and co-developer
base, almost every problem will be characterized quickly and
the fix obvious to someone.
Or, less formally, ``Given enough eyeballs, all bugs are
shallow.'' I dub this: ``Linus's Law''.My original formulation was that every problem ``will be
transparent to somebody''. Linus demurred that the person who
understands and fixes the problem is not necessarily or even usually
the person who first characterizes it. ``Somebody finds the
problem,'' he says, ``and somebody else
understands it. And I'll go on record as saying that finding it is the
bigger challenge.'' But the point is that both things tend to happen
rapidly.Here, I think, is the core difference underlying the cathedral-builder
and bazaar styles. In the cathedral-builder view of programming, bugs
and development problems are tricky, insidious, deep phenomena.
It takes months of scrutiny by a dedicated few to develop confidence
that you've winkled them all out. Thus the long release intervals,
and the inevitable disappointment when long-awaited releases are not
perfect.In the bazaar view, on the other hand, you assume that bugs are
generally shallow phenomena -- or, at least, that they turn shallow
pretty quickly when exposed to a thousand eager co-developers pounding on
every single new release. Accordingly you release often in order to
get more corrections, and as a beneficial side effect you have less to
lose if an occasional botch gets out the door.And that's it. That's enough. If ``Linus's Law'' is false, then any
system as complex as the Linux kernel, being hacked over by as many
hands as the Linux kernel, should at some point have collapsed under
the weight of unforseen bad interactions and undiscovered ``deep'' bugs.
If it's true, on the other hand, it is sufficient to explain Linux's
relative lack of bugginess and its continuous uptimes spanning months
or even years.Maybe it shouldn't have been such a surprise, at that. Sociologists
years ago discovered that the averaged opinion of a mass of equally
expert (or equally ignorant) observers is quite a bit more reliable a
predictor than that of a single randomly-chosen one of the observers.
They called this the ``Delphi effect''. It appears that what Linus
has shown is that this applies even to debugging an operating system
-- that the Delphi effect can tame development complexity even at the
complexity level of an OS kernel.One special feature of the Linux situation that clearly helps
along the Delphi effect is the fact that the contributors for any
given project are self-selected. An early respondent pointed out that
contributions are received not from a random sample, but from people
who are interested enough to use the software, learn about how it
works, attempt to find solutions to problems they encounter, and
actually produce an apparently reasonable fix. Anyone who passes all
these filters is highly likely to have something useful to
contribute.I am indebted to my friend Jeff Dutky <dutky@wam.umd.edu> for
pointing out that Linus's Law can be rephrased as ``Debugging is
parallelizable''. Jeff observes that although debugging requires
debuggers to communicate with some coordinating developer, it doesn't
require significant coordination between debuggers. Thus it doesn't
fall prey to the same quadratic complexity and management costs that
make adding developers problematic.In practice, the theoretical loss of efficiency due to duplication of
work by debuggers almost never seems to be an issue in the Linux
world. One effect of a ``release early and often policy'' is to
minimize such duplication by propagating fed-back fixes quickly
[JH].Brooks (the author of ``The Mythical Man-Month'') even made an
off-hand observation related to Jeff's: ``The total cost of
maintaining a widely used program is typically 40 percent or more of
the cost of developing it. Surprisingly this cost is strongly affected
by the number of users. More users find more bugs.'' (my
emphasis).More users find more bugs because adding more users adds more
different ways of stressing the program. This effect is amplified
when the users are co-developers. Each one approaches the task
of bug characterization with a slightly different perceptual set
and analytical toolkit, a different angle on the problem. The
``Delphi effect'' seems to work precisely because of this variation.
In the specific context of debugging, the variation also tends to
reduce duplication of effort.So adding more beta-testers may not reduce the complexity of the
current ``deepest'' bug from the developer's
point of view, but it increases the probability that someone's toolkit
will be matched to the problem in such a way that the bug is shallow
to that person.Linus coppers his bets, too. In case there
are serious bugs, Linux kernel version are
numbered in such a way that potential users can make a choice either
to run the last version designated ``stable'' or to ride the cutting
edge and risk bugs in order to get new features. This tactic is not
yet formally imitated by most Linux hackers, but perhaps it should be;
the fact that either choice is available makes both more
attractive. [HBS] When Is A Rose Not A Rose?Having studied Linus's behavior and formed a theory about why it
was successful, I made a conscious decision to test this theory on my
new (admittedly much less complex and ambitious) project.But the first thing I did was reorganize and simplify popclient
a lot. Carl Harris's implementation was very sound, but exhibited a
kind of unnecessary complexity common to many C programmers. He
treated the code as central and the data structures as support for the
code. As a result, the code was beautiful but the data structure
design ad-hoc and rather ugly (at least by the high standards of this
old LISP hacker).I had another purpose for rewriting besides improving the code and the
data structure design, however. That was to evolve it into something
I understood completely. It's no fun to be responsible for fixing
bugs in a program you don't understand.For the first month or so, then, I was simply following out the
implications of Carl's basic design. The first serious change I made
was to add IMAP support. I did this by reorganizing the protocol
machines into a generic driver and three method tables (for POP2,
POP3, and IMAP). This and the previous changes illustrate a general
principle that's good for programmers to keep in mind, especially
in languages like C that don't naturally do dynamic typing:
9. Smart data structures and dumb code works a lot
better than the other way around.
Brooks, Chapter 9: ``Show me your [code] and conceal your [data
structures], and I shall continue to be mystified. Show me your [data
structures], and I won't usually need your [code]; it'll be
obvious.''Actually, he said ``flowcharts'' and ``tables''. But allowing
for thirty years of terminological/cultural shift, it's almost the
same point.At this point (early September 1996, about six weeks from zero)
I started thinking that a name change might be in order -- after all,
it wasn't just a POP client any more. But I hesitated, because there
was as yet nothing genuinely new in the design. My version of
popclient had yet to develop an identity of its own.That changed, radically, when fetchmail learned how to forward fetched
mail to the SMTP port. I'll get to that in a moment. But first: I
said above that I'd decided to use this project to test my theory
about what Linus Torvalds had done right. How (you may well ask) did
I do that? In these ways:I released early and often (almost never less often
than every ten days; during periods of intense development, once
a day).I grew my beta list by adding to it everyone who contacted me
about fetchmail.I sent chatty announcements to the beta list whenever I
released, encouraging people to participate.And I listened to my beta testers, polling them about design
decisions and stroking them whenever they sent in patches
and feedback.The payoff from these simple measures was immediate. From the
beginning of the project, I got bug reports of a quality most
developers would kill for, often with good fixes attached. I
got thoughtful criticism, I got fan mail, I got intelligent
feature suggestions. Which leads to:
10. If you treat your beta-testers as if they're
your most valuable resource, they will respond by becoming
your most valuable resource.
One interesting measure of fetchmail's success is the sheer size
of the project beta list, fetchmail-friends. At the time of last
revision (August 2000) it has 249 members and is adding two or three a
week.Actually, as I revise in late May 1997 the list is beginning to
lose members from its high of close to 300 for an interesting reason.
Several people have asked me to unsubscribe them because fetchmail is
working so well for them that they no longer need to see the list
traffic! Perhaps this is part of the normal life-cycle of a mature
bazaar-style project.Popclient becomes FetchmailThe real turning point in the project was when Harry Hochheiser
sent me his scratch code for forwarding mail to the client machine's
SMTP port. I realized almost immediately that a reliable
implementation of this feature would make all the other mail delivery
modes next to obsolete.For many weeks I had been tweaking fetchmail rather
incrementally while feeling like the interface design was serviceable
but grubby -- inelegant and with too many exiguous options hanging out
all over. The options to dump fetched mail to a mailbox file or
standard output particularly bothered me, but I couldn't figure out
why.(If you don't care about the technicalia of Internet mail, the
next two paragraphs can be safely skipped.)What I saw when I thought about SMTP forwarding was that popclient had
been trying to do too many things. It had been designed to be both a
mail transport agent (MTA) and a local delivery agent (MDA). With
SMTP forwarding, it could get out of the MDA business and be a pure
MTA, handing off mail to other programs for local delivery just as
sendmail does.Why mess with all the complexity of configuring a mail delivery agent
or setting up lock-and-append on a mailbox when port 25 is almost
guaranteed to be there on any platform with TCP/IP support in the
first place? Especially when this means retrieved mail is guaranteed
to look like normal sender-initiated SMTP mail, which is really what
we want anyway.(Back to a higher level...)Even if you didn't follow the preceding technical jargon, there are
several important lessons here. First, this SMTP-forwarding concept
was the biggest single payoff I got from consciously trying to emulate
Linus's methods. A user gave me this terrific idea -- all I had to do
was understand the implications.
11. The next best thing to having good ideas is
recognizing good ideas from your users. Sometimes the latter
is better.
Interestingly enough, you will quickly find that if you are completely
and self-deprecatingly truthful about how much you owe other people,
the world at large will treat you like you did every bit of the
invention yourself and are just being becomingly modest about your
innate genius. We can all see how well this worked for Linus! (When I gave my talk at the Perl conference in August 1997, hacker
extraordinaire Larry Wall was in the front row. As I got to the last
line above he called out, religious-revival style, ``Tell it, tell it,
brother!''. The whole audience laughed, because they knew this had
worked for the inventor of Perl, too.)After a very few weeks of running the project in the same spirit,
I began to get similar praise not just from my users but from other
people to whom the word leaked out. I stashed away some of that
email; I'll look at it again sometime if I ever start wondering
whether my life has been worthwhile :-).But there are two more fundamental, non-political lessons here that
are general to all kinds of design.
12. Often, the most striking and innovative
solutions come from realizing that your concept of the problem
was wrong.
I had been trying to solve the wrong problem by continuing to
develop popclient as a combined MTA/MDA with all kinds of funky local
delivery modes. Fetchmail's design needed to be rethought from the
ground up as a pure MTA, a part of the normal SMTP-speaking Internet
mail path.When you hit a wall in development -- when you find yourself hard put
to think past the next patch -- it's often time to ask not whether
you've got the right answer, but whether you're asking the right
question. Perhaps the problem needs to be reframed.Well, I had reframed my problem. Clearly, the right thing to do was
(1) hack SMTP forwarding support into the generic driver, (2) make it
the default mode, and (3) eventually throw out all the other delivery
modes, especially the deliver-to-file and deliver-to-standard-output
options.I hesitated over step 3 for some time, fearing to upset long-time
popclient users dependent on the alternate delivery mechanisms. In
theory, they could immediately switch to .forward files or their
non-sendmail equivalents to get the same effects. In practice the
transition might have been messy.But when I did it, the benefits proved huge. The cruftiest parts of
the driver code vanished. Configuration got radically simpler -- no
more grovelling around for the system MDA and user's mailbox, no more
worries about whether the underlying OS supports file locking.Also, the only way to lose mail vanished. If you specified delivery
to a file and the disk got full, your mail got lost. This can't
happen with SMTP forwarding because your SMTP listener won't return OK
unless the message can be delivered or at least spooled for later
delivery.Also, performance improved (though not so you'd notice it in a single
run). Another not insignificant benefit of this change was that the
manual page got a lot simpler.Later, I had to bring delivery via a user-specified local MDA
back in order to allow handling of some obscure situations involving
dynamic SLIP. But I found a much simpler way to do it.The moral? Don't hesitate to throw away superannuated features
when you can do it without loss of effectiveness. Antoine de
Saint-Exupéry (who was an aviator and aircraft designer when he
wasn't being the author of classic children's books) said:
13. ``Perfection (in design) is achieved not when
there is nothing more to add, but rather when there is nothing
more to take away.''
When your code is getting both better and simpler, that is when you
know it's right. And in the process, the fetchmail
design acquired an identity of its own, different from the ancestral
popclient.It was time for the name change. The new design looked much more like
a dual of sendmail than the old popclient had; both are MTAs, but
where sendmail pushes then delivers, the new popclient pulls then
delivers. So, two months off the blocks, I renamed it fetchmail.There is a more general lesson in this story about how SMTP delivery
came to fetchmail. It is not only debugging that is parallelizable;
development and (to a perhaps surprising extent) exploration of design
space is, too. When your development mode is rapidly iterative,
development and enhancement may become special cases of debugging --
fixing `bugs of omission' in the original capabilities or concept of
the software.Even at a higher level of design, it can be very valuable to have the
thinking of lots of co-developers random-walking through the design
space near your product. Consider the way a puddle of water finds a
drain, or better yet how ants find food: exploration essentially by
diffusion, followed by exploitation mediated by a scalable
communication mechanism. This works very well; as with Harry
Hochheiser and me, one of your outriders may well find a huge win nearby
that you were just a little too close-focused to see.Fetchmail Grows UpThere I was with a neat and innovative design, code that I knew worked
well because I used it every day, and a burgeoning beta list. It
gradually dawned on me that I was no longer engaged in a trivial
personal hack that might happen to be useful to few other people. I
had my hands on a program every hacker with a Unix box and a SLIP/PPP
mail connection really needs.With the SMTP forwarding feature, it pulled far enough in front of the
competition to potentially become a ``category killer'', one of those
classic programs that fills its niche so competently that the
alternatives are not just discarded but almost forgotten.I think you can't really aim or plan for a result like this. You have
to get pulled into it by design ideas so powerful that afterward the
results just seem inevitable, natural, even foreordained. The only
way to try for ideas like that is by having lots of ideas -- or by
having the engineering judgment to take other peoples' good ideas
beyond where the originators thought they could go.Andy Tanenbaum had the original idea to build a simple native Unix for
IBM PCs, for use as a teaching tool (he called it Minix). Linus
Torvalds pushed the Minix concept further than Andrew probably thought
it could go -- and it grew into something wonderful. In the same way
(though on a smaller scale), I took some ideas by Carl Harris and
Harry Hochheiser and pushed them hard. Neither of us was `original'
in the romantic way people think is genius. But then, most science
and engineering and software development isn't done by original
genius, hacker mythology to the contrary.The results were pretty heady stuff all the same -- in fact, just the
kind of success every hacker lives for! And they meant I would have
to set my standards even higher. To make fetchmail as good as I now
saw it could be, I'd have to write not just for my own needs, but also
include and support features necessary to others but outside my orbit.
And do that while keeping the program simple and robust.The first and overwhelmingly most important feature I wrote after
realizing this was multidrop support -- the ability to fetch mail from
mailboxes that had accumulated all mail for a group of users, and then
route each piece of mail to its individual recipients.I decided to add the multidrop support partly because some users
were clamoring for it, but mostly because I thought it would shake
bugs out of the single-drop code by forcing me to deal with addressing
in full generality. And so it proved. Getting RFC
822 address parsing right took me a remarkably long time, not
because any individual piece of it is hard but because it involved a
pile of interdependent and fussy details.But multidrop addressing turned out to be an excellent design decision
as well. Here's how I knew:
14. Any tool should be useful in the expected way,
but a truly great tool lends itself to uses you never
expected.
The unexpected use for multi-drop fetchmail is to run mailing
lists with the list kept, and alias expansion done, on the
client side of the Internet connection. This
means someone running a personal machine through an ISP account can
manage a mailing list without continuing access to the ISP's alias
files.Another important change demanded by my beta testers was support for
8-bit MIME (Multipurpose Internet Mail Extensions) operation. This
was pretty easy to do, because I had been careful to keep the code
8-bit clean. Not because I anticipated the demand for this feature,
but rather in obedience to another rule:
15. When writing gateway software of any kind, take
pains to disturb the data stream as little as possible -- and
*never* throw away information unless the recipient forces you
to!
Had I not obeyed this rule, 8-bit MIME support would have been
difficult and buggy. As it was, all I had to do is read the MIME
standard (RFC
1652) and add a trivial bit of header-generation logic.Some European users bugged me into adding an option to limit the
number of messages retrieved per session (so they can control costs
from their expensive phone networks). I resisted this for a long
time, and I'm still not entirely happy about it. But if you're
writing for the world, you have to listen to your customers --
this doesn't change just because they're not paying you in money.A Few More Lessons From FetchmailBefore we go back to general software-engineering issues, there are
a couple more specific lessons from the fetchmail experience to
ponder. Nontechnical readers can safely skip this section.The rc (control) file syntax includes optional `noise' keywords that are
entirely ignored by the parser. The English-like syntax they allow is
considerably more readable than the traditional terse keyword-value
pairs you get when you strip them all out.These started out as a late-night experiment when I noticed how
much the rc file declarations were beginning to resemble an imperative
minilanguage. (This is also why I changed the original popclient
`server' keyword to `poll').It seemed to me that trying to make that imperative minilanguage more
like English might make it easier to use. Now, although I'm a
convinced partisan of the ``make it a language'' school of design as
exemplified by Emacs and HTML and many database engines, I am
not normally a big fan of ``English-like'' syntaxes.Traditionally programmers have tended to favor control syntaxes
that are very precise and compact and have no redundancy at all. This
is a cultural legacy from when computing resources were expensive, so
parsing stages had to be as cheap and simple as possible. English,
with about 50% redundancy, looked like a very inappropriate model
then.This is not my reason for normally avoiding English-like syntaxes; I
mention it here only to demolish it. With cheap cycles and core,
terseness should not be an end in itself. Nowadays it's more
important for a language to be convenient for humans than to be cheap
for the computer.There remain, however, good reasons to be wary. One is the complexity
cost of the parsing stage -- you don't want to raise that to the point
where it's a significant source of bugs and user confusion in itself.
Another is that trying to make a language syntax English-like often
demands that the ``English'' it speaks be bent seriously out of shape,
so much so that the superficial resemblance to natural language is as
confusing as a traditional syntax would have been. (You see this bad
effect in a lot of so-called ``fourth generation'' and commercial
database-query languages.)The fetchmail control syntax seems to avoid these problems
because the language domain is extremely restricted. It's nowhere
near a general-purpose language; the things it says simply are not
very complicated, so there's little potential for confusion in moving
mentally between a tiny subset of English and the actual control
language. I think there may be a wider lesson here:
16. When your language is nowhere near
Turing-complete, syntactic sugar can be your
friend.
Another lesson is about security by obscurity. Some fetchmail users
asked me to change the software to store passwords encrypted in the rc
file, so snoopers wouldn't be able to casually see them.I didn't do it, because this doesn't actually add protection.
Anyone who's acquired permissions to read your rc file will
be able to run fetchmail as you anyway -- and if it's your password
they're after, they'd be able to rip the necessary decoder out of
the fetchmail code itself to get it.All .fetchmailrc password encryption would have done is give a false
sense of security to people who don't think very hard. The general
rule here is:
17. A security system is only as secure as its
secret. Beware of pseudo-secrets.
Necessary Preconditions for the Bazaar StyleEarly reviewers and test audiences for this paper consistently raised
questions about the preconditions for successful bazaar-style
development, including both the qualifications of the project leader
and the state of code at the time one goes public and starts to try to
build a co-developer community.It's fairly clear that one cannot code from the ground up in
bazaar style [IN]. One can test, debug
and improve in bazaar style, but it would be very hard to
originate a project in bazaar mode. Linus didn't
try it. I didn't either. Your nascent developer community needs to
have something runnable and testable to play with.When you start community-building, what you need to be able to
present is a plausible promise. Your program
doesn't have to work particularly well. It can be crude, buggy,
incomplete, and poorly documented. What it must not fail to do is (a)
run, and (b) convince potential co-developers that it can be evolved
into something really neat in the foreseeable future.Linux and fetchmail both went public with strong, attractive basic
designs. Many people thinking about the bazaar model as I have
presented it have correctly considered this critical, then jumped from
it to the conclusion that a high degree of design intuition and
cleverness in the project leader is indispensable.But Linus got his design from Unix. I got mine initially from the
ancestral popclient (though it would later change a great deal, much
more proportionately speaking than has Linux). So does the
leader/coordinator for a bazaar-style effort really have to have
exceptional design talent, or can he get by on leveraging the design
talent of others?I think it is not critical that the coordinator be able to
originate designs of exceptional brilliance, but it is absolutely
critical that the coordinator be able to recognize good
design ideas from others.Both the Linux and fetchmail projects show evidence of this. Linus,
while not (as previously discussed) a spectacularly original designer,
has displayed a powerful knack for recognizing good design and
integrating it into the Linux kernel. And I have already described
how the single most powerful design idea in fetchmail (SMTP
forwarding) came from somebody else.Early audiences of this paper complimented me by suggesting that I am
prone to undervalue design originality in bazaar projects because I
have a lot of it myself, and therefore take it for granted. There may
be some truth to this; design (as opposed to coding or debugging) is
certainly my strongest skill.But the problem with being clever and original in software design is
that it gets to be a habit -- you start reflexively making things cute
and complicated when you should be keeping them robust and simple. I
have had projects crash on me because I made this mistake, but I
managed not to with fetchmail.So I believe the fetchmail project succeeded partly because I
restrained my tendency to be clever; this argues (at least) against
design originality being essential for successful bazaar projects.
And consider Linux. Suppose Linus Torvalds had been trying to pull
off fundamental innovations in operating system design during the
development; does it seem at all likely that the resulting kernel
would be as stable and successful as what we have?A certain base level of design and coding skill is required, of
course, but I expect almost anybody seriously thinking of launching a
bazaar effort will already be above that minimum. The open-source
community's internal market in reputation exerts subtle pressure on
people not to launch development efforts they're not competent to
follow through on. So far this seems to have worked pretty
well.There is another kind of skill not normally associated with
software development which I think is as important as design
cleverness to bazaar projects -- and it may be more important. A
bazaar project coordinator or leader must have good people and
communications skills.This should be obvious. In order to build a development
community, you need to attract people, interest them in what you're
doing, and keep them happy about the amount of work they're doing.
Technical sizzle will go a long way towards accomplishing this, but
it's far from the whole story. The personality you project matters,
too.It is not a coincidence that Linus is a nice guy who makes
people like him and want to help him. It's not a coincidence that I'm
an energetic extrovert who enjoys working a crowd and has some of the
delivery and instincts of a stand-up comic. To make the bazaar model
work, it helps enormously if you have at least a little skill at
charming people. The Social Context of Open-Source SoftwareIt is truly written: the best hacks start out as personal solutions to
the author's everyday problems, and spread because the problem turns
out to be typical for a large class of users. This takes us back to
the matter of rule 1, restated in a perhaps more useful way:
18. To solve an interesting problem, start by
finding a problem that is interesting to you.
So it was with Carl Harris and the ancestral popclient, and so with me
and fetchmail. But this has been understood for a long time. The
interesting point, the point that the histories of Linux and fetchmail
seem to demand we focus on, is the next stage -- the evolution of
software in the presence of a large and active community of users and
co-developers.In ``The Mythical Man-Month'', Fred Brooks observed that
programmer time is not fungible; adding developers to a late software
project makes it later. He argued that the complexity and
communication costs of a project rise with the square of the number of
developers, while work done only rises linearly. This claim has since
become known as ``Brooks's Law'' and is widely regarded as a truism.
But if Brooks's Law were the whole picture, Linux would be
impossible.Gerald Weinberg's classic ``The Psychology Of Computer Programming''
supplied what, in hindsight, we can see as a vital correction to
Brooks. In his discussion of ``egoless programming'', Weinberg
observed that in shops where developers are not territorial about
their code, and encourage other people to look for bugs and potential
improvements in it, improvement happens dramatically faster than
elsewhere.Weinberg's choice of terminology has perhaps prevented his
analysis from gaining the acceptance it deserved -- one has to smile
at the thought of describing Internet hackers as ``egoless''. But I
think his argument looks more compelling today than ever.The history of Unix should have prepared us for what we're
learning from Linux (and what I've verified experimentally on a
smaller scale by deliberately copying Linus's methods [EGCS]). That is, that while coding remains
an essentially solitary activity, the really great hacks come from
harnessing the attention and brainpower of entire communities. The
developer who uses only his or her own brain in a closed project is
going to fall behind the developer who knows how to create an open,
evolutionary context in which feedback exploring the design space,
code contributions, bug-spotting, and other improvements come back
from hundreds (perhaps thousands) of people.But the traditional Unix world was prevented from pushing this
approach to the ultimate by several factors. One was the legal
contraints of various licenses, trade secrets, and commercial
interests. Another (in hindsight) was that the Internet wasn't
yet good enough.Before cheap Internet, there were some geographically compact
communities where the culture encouraged Weinberg's ``egoless''
programming, and a developer could easily attract a lot of skilled
kibitzers and co-developers. Bell Labs, the MIT AI Lab, UC Berkeley
-- these became the home of innovations that are legendary and still
potent.Linux was the first project to make a conscious and successful
effort to use the entire world as its talent
pool. I don't think it's a coincidence that the gestation period of
Linux coincided with the birth of the World Wide Web, and that Linux
left its infancy during the same period in 1993-1994 that saw the
takeoff of the ISP industry and the explosion of mainstream interest
in the Internet. Linus was the first person who learned how to play
by the new rules that pervasive Internet access made possible.While cheap Internet was a necessary condition for the Linux model to
evolve, I think it was not by itself a sufficient condition. Another
vital factor was the development of a leadership style and set of
cooperative customs that could allow developers to attract
co-developers and get maximum leverage out of the medium.But what is this leadership style and what are these customs?
They cannot be based on power relationships -- and even if they could
be, leadership by coercion would not produce the results we see.
Weinberg quotes the autobiography of the 19th-century Russian
anarchist Pyotr Alexeyvich Kropotkin's Memoirs of a
Revolutionist to good effect on this subject:
Having been brought up in a serf-owner's family, I entered active
life, like all young men of my time, with a great deal of confidence
in the necessity of commanding, ordering, scolding, punishing and the
like. But when, at an early stage, I had to manage serious enterprises
and to deal with [free] men, and when each mistake would lead at once to
heavy consequences, I began to appreciate the difference between
acting on the principle of command and discipline and acting on the
principle of common understanding. The former works admirably in a
military parade, but it is worth nothing where real life is concerned,
and the aim can be achieved only through the severe effort of many
converging wills.
The ``severe effort of many converging wills'' is precisely what a
project like Linux requires -- and the ``principle of command'' is
effectively impossible to apply among volunteers in the anarchist's
paradise we call the Internet. To operate and compete effectively,
hackers who want to lead collaborative projects have to learn how to
recruit and energize effective communities of interest in the mode
vaguely suggested by Kropotkin's ``principle of understanding''. They
must learn to use Linus's Law.[SP]Earlier I referred to the ``Delphi effect'' as a possible explanation
for Linus's Law. But more powerful analogies to adaptive systems in
biology and economics also irresistably suggest themselves. The Linux
world behaves in many respects like a free market or an ecology, a
collection of selfish agents attempting to maximize utility which in
the process produces a self-correcting spontaneous order more
elaborate and efficient than any amount of central planning could have
achieved. Here, then, is the place to seek the ``principle of
understanding''.The ``utility function'' Linux hackers are maximizing is not
classically economic, but is the intangible of their own ego
satisfaction and reputation among other hackers. (One may call their
motivation ``altruistic'', but this ignores the fact that altruism is
itself a form of ego satisfaction for the altruist). Voluntary
cultures that work this way are not actually uncommon; one other in
which I have long participated is science fiction fandom, which unlike
hackerdom has long explicitly recognized ``egoboo'' (ego-boosting, or
the enhancement of one's reputation among other fans) as the basic
drive behind volunteer activity.Linus, by successfully positioning himself as the gatekeeper of a
project in which the development is mostly done by others, and
nurturing interest in the project until it became self-sustaining, has
shown an acute grasp of Kropotkin's ``principle of shared
understanding''. This quasi-economic view of the Linux world enables
us to see how that understanding is applied.We may view Linus's method as a way to create an efficient market in
``egoboo'' -- to connect the selfishness of individual hackers as firmly
as possible to difficult ends that can only be achieved by sustained
cooperation. With the fetchmail project I have shown (albeit on a
smaller scale) that his methods can be duplicated with good results.
Perhaps I have even done it a bit more consciously and systematically
than he.Many people (especially those who politically distrust free markets)
would expect a culture of self-directed egoists to be fragmented,
territorial, wasteful, secretive, and hostile. But this expectation
is clearly falsified by (to give just one example) the stunning
variety, quality and depth of Linux documentation. It is a hallowed
given that programmers hate documenting; how is it, then,
that Linux hackers generate so much of it? Evidently Linux's free
market in egoboo works better to produce virtuous, other-directed
behavior than the massively-funded documentation shops of commercial
software producers.Both the fetchmail and Linux kernel projects show that by properly
rewarding the egos of many other hackers, a strong
developer/coordinator can use the Internet to capture the benefits of
having lots of co-developers without having a project collapse into a
chaotic mess. So to Brooks's Law I counter-propose the
following:
19: Provided the development coordinator has a
medium at least as good as the Internet, and knows how to lead
without coercion, many heads are inevitably better than
one.
I think the future of open-source software will increasingly
belong to people who know how to play Linus's game, people who leave
behind the cathedral and embrace the bazaar. This is not to say that
individual vision and brilliance will no longer matter; rather, I
think that the cutting edge of open-source software will belong to
people who start from individual vision and brilliance, then amplify
it through the effective construction of voluntary communities of
interest.Perhaps this is not only the future of
open-source software. No closed-source developer
can match the pool of talent the Linux community can bring to bear on
a problem. Very few could afford even to hire the more than two
hundred (1999: six hundred, 2000: eight hundred) people who have
contributed to fetchmail!Perhaps in the end the open-source culture will triumph not because
cooperation is morally right or software ``hoarding'' is morally wrong
(assuming you believe the latter, which neither Linus nor I do), but
simply because the closed-source world cannot win an evolutionary arms
race with open-source communities that can put orders of magnitude
more skilled time into a problem.On Management and the Maginot LineThe original ``Cathedral and Bazaar'' paper of 1997 ended with
the vision above -- that of happy networked hordes of
programmer/anarchists outcompeting and overwhelming the hierarchical
world of conventional closed software.A good many skeptics weren't convinced, however; and the questions
they raise deserve a fair engagement. Most of the objections to the
bazaar argument come down to the claim that its proponents have
underestimated the productivity-multiplying effect of conventional
management.Traditionally-minded software-development managers often object that
the casualness with which project groups form and change and dissolve
in the open-source world negates a significant part of the apparent
advantage of numbers that the open-source community has over any
single closed-source developer. They would observe that in software
development it is really sustained effort over time and the degree to
which customers can expect continuing investment in the product that
matters, not just how many people have thrown a bone in the pot and
left it to simmer.There is something to this argument, to be sure; in fact, I have
developed the idea that expected future service value is the key to
the economics of software production in The Magic
Cauldron.But this argument also has a major hidden problem; its implicit
assumption that open-source development cannot deliver such sustained
effort. In fact, there have been open-source projects that maintained a
coherent direction and an effective maintainer community over quite
long periods of time without the kinds of incentive structures or
institutional controls that conventional management finds essential.
The development of the GNU Emacs editor is an extreme and instructive
example; it has absorbed the efforts of hundreds of contributors over
fifteen years into a unified architectural vision, despite high
turnover and the fact that only one person (its author) has been
continuously active during all that time. No closed-source editor has
ever matched this longevity record.This suggests a reason for questioning the advantages of
conventionally-managed software development that is independent of the
rest of the arguments over cathedral vs. bazaar mode. If it's
possible for GNU Emacs to express a consistent architectural vision
over fifteen years, or for an operating system like Linux to do the
same over eight years of rapidly changing hardware and platform
technology; and if (as is indeed the case) there have been many
well-architected open-source projects of more than five years duration
-- then we are entitled to wonder what, if anything, the tremendous
overhead of conventionally-managed development is actually buying
us.Whatever it is certainly doesn't include reliable execution by
deadline, or on budget, or to all features of the specification; it's
a rare `managed' project that meets even one of these goals, let alone
all three. It also does not appear to be ability to adapt to changes
in technology and economic context during the project lifetime,
either; the open-source community has proven far
more effective on that score (as one can readily verify, for example,
by comparing the thirty-year history of the Internet with the short
half-lives of proprietary networking technologies -- or the cost of
the 16-bit to 32-bit transition in Microsoft Windows with the nearly
effortless up-migration of Linux during the same period, not only
along the Intel line of development but to more than a dozen other
hardware platforms including the 64-bit Alpha as well).One thing many people think the traditional mode buys you is somebody
to hold legally liable and potentially recover compensation from if
the project goes wrong. But this is an illusion; most software
licenses are written to disclaim even warranty of merchantability, let
alone performance -- and cases of successful recovery for software
nonperformance are vanishingly rare. Even if they were common,
feeling comforted by having somebody to sue would be missing the
point. You didn't want to be in a lawsuit; you wanted working
software.So what is all that management overhead buying?In order to understand that, we need to understand what software
development managers believe they do. A woman I know who seems to
be very good at this job says software project management has five
functions: To define goals and keep
everybody pointed in the same direction. To monitor and make sure crucial
details don't get skipped.To motivate people to do boring but necessary drudgework.To organize the deployment of
people for best productivity.To marshal resources needed to
sustain the project.Apparently worthy goals, all of these; but under the open-source
model, and in its surrounding social context, they can begin to seem
strangely irrelevant. We'll take them in reverse order.My friend reports that a lot of resource
marshalling is basically defensive; once you have your
people and machines and office space, you have to defend them from
peer managers competing for the same resources, and higher-ups trying
to allocate the most efficient use of a limited pool.But open-source developers are volunteers, self-selected for both
interest and ability to contribute to the projects they work on (and
this remains generally true even when they are being paid a salary to
hack open source.) The volunteer ethos tends to take care of the
`attack' side of resource-marshalling automatically; people bring
their own resources to the table. And there is little or no need for
a manager to `play defense' in the conventional sense.Anyway, in a world of cheap PCs and fast Internet links, we find
pretty consistently that the only really limiting resource is skilled
attention. Open-source projects, when they founder, essentially
never do so for want of machines or links or office space; they
die only when the developers themselves lose interest.That being the case, it's doubly important that open-source
hackers organize themselves for maximum
productivity by self-selection -- and the social milieu selects
ruthlessly for competence. My friend, familiar with both the
open-source world and large closed projects, believes that open source
has been successful partly because its culture only accepts the most
talented 5% or so of the programming population. She spends most of
her time organizing the deployment of the other 95%, and has thus
observed first-hand the well-known variance of a factor of one hundred
in productivity between the most able programmers and the merely
competent.The size of that variance has always raised an awkward question: would
individual projects, and the field as a whole, be better off without
more than 50% of the least able in it? Thoughtful managers have
understood for a long time that if conventional software management's
only function were to convert the least able from a net loss to a
marginal win, the game might not be worth the candle.The success of the open-source community sharpens this question
considerably, by providing hard evidence that it is often cheaper and
more effective to recruit self-selected volunteers from the Internet
than it is to manage buildings full of people who would rather be
doing something else.Which brings us neatly to the question of
motivation. An equivalent and often-heard way to
state my friend's point is that traditional development management is
a necessary compensation for poorly motivated programmers who would
not otherwise turn out good work.This answer usually travels with a claim that the open-source
community can only be relied on to do work that is `sexy' or
technically sweet; anything else will be left undone (or done only
poorly) unless it's churned out by money-motivated cubicle peons with
managers cracking whips over them. I address the psychological and
social reasons for being skeptical of this claim in ``Homesteading the
Noosphere''. For present purposes, however, I think it's more
interesting to point out the implications of accepting it as true.If the conventional, closed-source, heavily-managed style of
software development is really defended only by a sort of Maginot line
of problems conducive to boredom, then it's going to remain viable in
each individual application area for only so long as nobody finds
those problems really interesting and nobody else finds any way to
route around them. Because the moment there is open-source competition
for a `boring' piece of software, customers are going to know that it
was finally tackled by someone who chose that problem to solve because
of a fascination with the problem itself -- which, in software as in
other kinds of creative work, is a far more effective motivator than
money alone.Having a conventional management structure solely in order to
motivate, then, is probably good tactics but bad strategy; a
short-term win, but in the longer term a surer loss.So far, conventional development management looks like a bad bet
now against open source on two points (resource marshalling,
organization), and like it's living on borrowed time with respect to a
third (motivation). And the poor beleaguered conventional manager is
not going to get any succour from the monitoring
issue; the strongest argument the open-source community has is that
decentralized peer review trumps all the conventional methods for
trying to ensure that details don't get slipped.Can we save defining goals as a
justification for the overhead of conventional software project
management? Perhaps; but to do so, we'll need good reason to believe
that management committees and corporate roadmaps are more successful
at defining worthy and widely-shared goals than the project leaders
and tribal elders who fill the analogous role in the open-source
world.That is on the face of it a pretty hard case to make. And it's not so
much the open-source side of the balance (the longevity of Emacs, or
Linus Torvalds's ability to mobilize hordes of developers with talk of
``world domination'') that makes it tough. Rather, it's the
demonstrated awfulness of conventional mechanisms for defining the
goals of software projects.One of the best-known folk theorems of software engineering is that
60% to 75% of conventional software projects either are never
completed or are rejected by their intended users. If that range is
anywhere near true (and I've never met a manager of any experience who
disputes it) then more projects than not are being aimed at goals
that are either (a) not realistically attainable, or (b) just plain
wrong.This, more than any other problem, is the reason that in today's
software engineering world the very phrase ``management committee'' is
likely to send chills down the hearer's spine -- even (or perhaps
especially) if the hearer is a manager. The days when only programmers
griped about this pattern are long past; `Dilbert' cartoons hang over
executives' desks now.Our reply, then, to the traditional software development manager, is
simple -- if the open-source community has really underestimated the
value of conventional management, why do so many of you display
contempt for your own process?Once again the existence of the open-source community sharpens
this question considerably -- because we have fun
doing what we do. Our creative play has been racking up technical,
market-share, and mind-share successes at an astounding rate. We're
proving not only that we can do better software, but that
joy is an asset.Two and a half years after the first version of this essay, the most
radical thought I can offer to close with is no longer a vision of an
open-source-dominated software world; that, after all, looks plausible
to a lot of sober people in suits these days.Rather, I want to suggest what may be a wider lesson about
software, (and probably about every kind of creative or professional
work). Human beings generally take pleasure in a task when it falls
in a sort of optimal-challenge zone; not so easy as to be boring, not
too hard to achieve. A happy programmer is one who is neither
underutilized nor weighed down with ill-formulated goals and stressful
process friction. Enjoyment predicts
efficiency..Relating to your own work process with fear and loathing (even in the
displaced, ironic way suggested by hanging up Dilbert cartoons) should
therefore be regarded in itself as a sign that the process has failed.
Joy, humor, and playfulness are indeed assets; it was not mainly for
the alliteration that I wrote of "happy hordes" above, and it is no
mere joke that the Linux mascot is a cuddly, neotenous penguin.It may well turn out that one of the most important effects of
open source's success will be to teach us that play is the
most economically efficient mode of creative work.AcknowledgementsThis paper was improved by conversations with a large number of people
who helped debug it. Particular thanks to Jeff Dutky
<dutky@wam.umd.edu>, who suggested the ``debugging is
parallelizable'' formulation, and helped develop the analysis that
proceeds from it. Also to Nancy Lebovitz
<nancyl@universe.digex.net> for her suggestion that I emulate
Weinberg by quoting Kropotkin. Perceptive criticisms also came from
Joan Eslinger <wombat@kilimanjaro.engr.sgi.com> and Marty Franz
<marty@net-link.net> of the General Technics list. Glen
Vandenburg <glv@vanderburg.org> pointeed out the importance of
self-selection in contributor populations and suggested the fruitful
idea that much development rectifies `bugs of omission'; Daniel Upper
<upper@peak.org> suggested the natural analogies for this. I'm
grateful to the members of PLUG, the Philadelphia Linux User's group,
for providing the first test audience for the first public version of
this paper. Paula Matuszek <matusp00@mh.us.sbphrd.com>
enlightened me about the practice of software management. Phil Hudson
<phil.hudson@iname.com> reminded me that the social organization
of the hacker culture mirrors the organization of its software, and
vice-versa. Finally, Linus Torvalds's comments were helpful and his
early endorsement very encouraging. For Further ReadingI quoted several bits from Frederick P. Brooks's classic
The Mythical Man-Month because, in many respects,
his insights have yet to be improved upon. I heartily recommend the
25th Anniversary edition from Addison-Wesley (ISBN 0-201-83595-9),
which adds his 1986 ``No Silver Bullet''
paper.The new edition is wrapped up by an invaluable 20-years-later
retrospective in which Brooks forthrightly admits to the few
judgements in the original text which have not stood the test of time.
I first read the retrospective after the first public version of this
paper was substantially complete, and was surprised to discover that
Brooks attributes bazaar-like practices to Microsoft! (In fact,
however, this attribution turned out to be mistaken. In 1998 we
learned from the Halloween Documents
that Microsoft's internal developer community is heavily balkanized,
with the kind of general source access needed to support a bazaar not
even truly possible.)Gerald M. Weinberg's The Psychology Of Computer
Programming (New York, Van Nostrand Reinhold 1971)
introduced the rather unfortunately-labeled concept of ``egoless
programming''. While he was nowhere near the first person to realize
the futility of the ``principle of command'', he was probably the
first to recognize and argue the point in particular connection with
software development.Richard P. Gabriel, contemplating the Unix culture of the
pre-Linux era, reluctantly argued for the superiority of a primitive
bazaar-like model in his 1989 paper Lisp: Good News, Bad
News, and How To Win Big. Though dated in some respects,
this essay is still rightly celebrated among Lisp fans (including me).
A correspondent reminded me that the section titled ``Worse Is
Better'' reads almost as an anticipation of Linux. The paper is
accessible on the World Wide Web at http://www.naggum.no/worse-is-better.html.De Marco and Lister's Peopleware: Productive Projects
and Teams (New York; Dorset House, 1987; ISBN
0-932633-05-6) is an underappreciated gem which I was delighted to see
Fred Brooks cite in his retrospective. While little of what the
authors have to say is directly applicable to the Linux or open-source
communities, the authors' insight into the conditions necessary for
creative work is acute and worthwhile for anyone attempting to import
some of the bazaar model's virtues into a commercial context.Finally, I must admit that I very nearly called this paper ``The
Cathedral and the Agora'', the latter term being the Greek for an open
market or public meeting place. The seminal ``agoric systems'' papers
by Mark Miller and Eric Drexler, by describing the emergent properties
of market-like computational ecologies, helped prepare me to think
clearly about analogous phenomena in the open-source culture when
Linux rubbed my nose in them five years later. These papers are
available on the Web at http://www.agorics.com/agorpapers.html.Epilog: Netscape Embraces the BazaarIt's a strange feeling to realize you're helping make history....On January 22 1998, approximately seven months after I first
published ``The Cathedral and the Bazaar'', Netscape Communications,
Inc. announced plans to give
away the source for Netscape Communicator. I had had no clue
this was going to happen before the day of the announcement.Eric Hahn, Executive Vice President and Chief Technology Officer at
Netscape, emailed me shortly afterwards as follows: ``On behalf of
everyone at Netscape, I want to thank you for helping us get to this
point in the first place. Your thinking and writings were fundamental
inspirations to our decision.''The following week I flew out to Silicon Valley at Netscape's
invitation for a day-long strategy conference (on Feb 4 1998) with
some of their top executives and technical people. We designed
Netscape's source-release strategy and license together.A few days later I wrote the following:
Netscape is about to provide us with a large-scale, real-world test of
the bazaar model in the commercial world. The open-source culture
now faces a danger; if Netscape's execution doesn't work, the
open-source concept may be so discredited that the commercial world
won't touch it again for another decade.On the other hand, this is also a spectacular opportunity. Initial
reaction to the move on Wall Street and elsewhere has been cautiously
positive. We're being given a chance to prove ourselves, too. If
Netscape regains substantial market share through this move, it just
may set off a long-overdue revolution in the software industry.The next year should be a very instructive and interesting
time.
And indeed it was. As I write in mid-1999, the development of what
was later named `Mozilla' has been only a qualified success. It
achieved Netscape's original goal, which was to deny Microsoft a
monopoly lock on the browser market. It has also achieved some
dramatic successes (notably the release of the next-generation Gecko
rendering engine).However, it has not yet garnered the massive development effort from
outside Netscape that the Mozilla founders had originally hoped for.
The problem here seems to be that for a long time the Mozilla
distribution actually broke one of the basic rules of the bazaar
model; they didn't ship something potential contributors could easily
run and see working. (Until more than a year after release, building
Mozilla from source required a license for the proprietary Motif
library.)Most negatively (from the point of view of the outside world) the
Mozilla group has yet to ship a production-quality browser -- and one
of the project's principals caused a bit of a sensation by resigning,
complaining of poor management and missed opportunities. ``Open
source,'' he correctly observed, ``is not magic pixie dust.''And indeed it is not. The long-term prognosis for Mozilla looks
dramatically better now (in August 2000) than it did at the time of Jamie
Zawinski's resignation letter -- but he was right to point out that
going open will not necessarily save an existing project that suffers
from ill-defined goals or spaghetti code or any of the software
engineering's other chronic ills. Mozilla has managed to provide an
example simultaneously of how open source can succeed and how it
could fail.In the mean time, however, the open-source idea has scored successes
and found backers elsewhere. 1998 and late 1999 saw a tremendous
explosion of interest in the open-source development model, a trend
both driven by and driving the continuing success of the Linux
operating system. The trend Mozilla touched off is continuing at
an accelerating rate.Endnotes[JB] In
Programing Pearls, the noted computer-science
aphorist Jon Bentley comments on Brooks's observation with ``If you
plan to throw one away, you will throw away two.''. He is almost
certainly right. The point of Brooks's observation, and Bentley's,
isn't merely that you should expect first attempt to be wrong, it's
that starting over with the right idea is usually more effective than
trying to salvage a mess.[QR] Examples of successful
open-source, bazaar development predating the Internet explosion and
unrelated to the Unix and Internet traditions have existed. The
development of the
info-Zip
compression utility during 1990-1992, primarily for DOS machines, was
one such. Another was the RBBS bulletin board system (again for DOS),
which began in 1983 and developed a sufficiently strong community that
there have been fairly regular releases up to the present (mid-1999)
despite the huge technical advantages of Internet mail and
file-sharing over local BBSs. While the info-Zip community relied to
some extent on Internet mail, the RBBS developer culture was actually
able to base a substantial on-line community on RBBS that was
completely independent of the TCP/IP infrastructure.[JH] John Hasler has suggested
an interesting explanation for the fact that duplication of effort
doesn't seem to be a net drag on open-source development. He proposes
what I'll dub ``Hasler's Law'': the costs of duplicated work tend to
scale sub-qadratically with team size -- that is, more slowly than the
planning and management overhead that would be needed to eliminate
them.This claim actually does not contradict Brooks's Law. It may be
the case that total complexity overhead and vulnerability to bugs
scales with the square of team size, but that the costs from
duplicated work are nevertheless a special case
that scales more slowly. It's not hard to develop plausible reasons
for this, starting with the undoubted fact that it is much easier to
agree on functional boundaries between different developers' code that
will prevent duplication of effort than it is to prevent the kinds of
unplanned bad interactions across the whole system that underly most
bugs.The combination of Linus's Law and Hasler's Law suggests that there
are actually three critical size regimes in software projects. On
small projects (I would say one to at most three developers) no
management structure more elaborate than picking a lead programmer is
needed. And there is some intermediate range above that in which the
cost of traditional management is relatively low, so its benefits from
avoiding duplication of effort, bug-tracking, and pushing to see that
details are not overlooked actually net out positive.Above that, however, the combination of Linus's Law and Hasler's Law
suggests there is a large-project range in which the costs and
problems of traditional management rise much faster than the expected
cost from duplication of effort. Not the least of these costs is a
structural inability to harness the many-eyeballs effect, which (as
we've seen) seems to do a much better job than traditional management
at making sure bugs and details are not overlooked. Thus, in the
large-project case, the combination of these laws effectively drives
the net payoff of traditional management to zero.[HBS] The split between Linux's
experimental and stable versions has another function related to, but
distinct from, hedging risk. The split attacks another problem: the
deadliness of deadlines. When programmers are held both to an
immutable feature list and a fixed drop-dead date, quality goes out
the window and there is likely a colossal mess in the making. I am
indebted to Marco Iansiti and Alan MacCormack of the Harvard Business
School for pointing me at evidence that relaxing either one of these
constraints can make scheduling workable.One way to do this is to fix the deadline but leave the feature list
flexible, allowing features to drop off if not completed by deadline.
This is essentially the strategy of the "stable" kernel branch; Alan
Cox (the stable-kernel maintainer) puts out releases at fairly regular
intervals, but makes no guarantees about when particular bugs will
be fixed or features back-ported from the experimental branch.The other way to do this is to set a desired feature list and deliver
only when it is done. This is essentially the strategy of the
"experimental" kernel branch. De Marco and Lister cited research
showing that this scheduling policy ("wake me up when it's done")
produces not only the highest quality but, on average, shorter
delivery times than either "realistic" or "aggressive" scheduling.I have come to suspect (as of early 2000) that in earlier versions of
this paper I severely underestimated the importance of the "wake me up when
it's done" anti-dealine policy to the open-source community's productivity and
quality. General experience with the rushed GNOME 1.0 in 1999 suggests that
pressure for a premature release can neutralize many of the quality
benefits open source normally confers.It may well turn out to be that the process transparency of open
source is one of three coequal drivers of its quality, along with
"wake me up when it's done" scheduling and developer self-selection.[IN] An issue related to
whether one can start projects from zero in the bazaar style is
whether the bazaar style is capable of supporting truly innovative
work. Some claim that, lacking strong leadership, the bazaar can only
handle the cloning and improvement of ideas already present at the
engineering state of the art, but is unable to push the state of the
art. This argument was perhaps most infamously made by the Halloween
Documents, two embarrassing internal Microsoft memoranda
written about the open-source phenomenon. The authors compared
Linux's development of a Unix-like operating system to ``chasing
taillights'', and opined ``(once a project has achieved "parity" with
the state-of-the-art), the level of management necessary to push
towards new frontiers becomes massive.''There are serious errors of fact implied in this argument. One is
exposed when the Halloween authors themseselves later observe that
``often [...] new research ideas are first implemented and available
on Linux before they are available / incorporated into other
platforms.''If we read ``open source'' for ``Linux'', we see that this is far from
a new phenomenon. Historically, the open-source community did not
invent Emacs or the World Wide Web or the Internet itself by chasing
taillights or being massively managed -- and in the present, there
is so much innovative work going on in open source that one is spoiled
for choice. The GNOME project (to pick one of many) is pushing the
state of the art in GUIs and object technology hard enough to have
attracted considerable notice in the computer trade press well outside
the Linux community. Other examples are legion, as a visit to Freshmeat on any given day will
quickly prove.But there is a more fundamental error in the implicit assumption
that the cathedral model (or the bazaar model, or
any other kind of management structure) can somehow make innovation
happen reliably. This is nonsense. Gangs don't have breakthrough
insights -- even volunteer groups of bazaar anarchists are usually
incapable of genuine originality, let alone corporate committees of
people with a survival stake in some status quo ante.
Insight comes from individuals. The most their
surrounding social machinery can ever hope to do is to be
responsive to breakthrough insights -- to nourish
and reward and rigorously test them instead of squashing them.Some will characterize this as a romantic view, a reversion to
outmoded lone-inventor stereotypes. Not so; I am not asserting that
groups are incapable of developing breakthrough
insights once they have been hatched; indeed, we learn from the
peer-review process that such development groups are essential to
producing a high-quality result. Rather I am pointing out that every
such group development starts from -- is necessarily sparked by -- one
good idea in one person's head. Cathedrals and bazaars and other
social structures can catch that lightning and refine it, but they
cannot make it on demand.Therefore the root problem of innovation (in software, or anywhere
else) is indeed how not to squash it -- but, even more fundamentally,
it is how to grow lots of people who can have insights in the
first place.To suppose that cathedral-style development could manage this
trick but the low entry barriers and process fluidity of the bazaar
cannot would be absurd. If what it takes is one person with one good
idea, then a social milieu in which one person can rapidly attract the
cooperation of hundreds or thousands of others with that good idea is
going inevitably to out-innovate any in which the person has to do a
political sales job to a hierarchy before he can work on his idea
without risk of getting fired.And, indeed, if we look at the history of software innovation by
organizations using the cathedral model, we quickly find it is rather
rare. Large corporations rely on university research for new ideas
(thus the Halloween Documents authors' unease about Linux's facility
at coopting that research more rapidly). Or they buy out small
companies built around some innovator's brain. In neither case is the
innovation native to the cathedral culture; indeed, many innovations
so imported end up being quietly suffocated under the "massive level of
management" the Halloween Documents' authors so extol.That, however, is a negative point. The reader would be better served
by a positive one. I suggest, as an experiment, the following; Pick a criterion for originality that you believe you
can apply consistently. If your definition is ``I know it when
I see it'', that's not a problem for purposes of this
test.Pick any closed-source operating system competing with Linux,
and a best source for accounts of current development work on
it.Watch that source and Freshmeat for one month. Every
day, count the number of release announcements on Freshmeat
that you consider `original' work. Apply the same definition
of `original' to announcements for that other OS and count
them.Thirty days later, total up both figures.The day I wrote this, Freshmeat carried twenty-two release
announcements, of which three appear they might push state of the art
in some respect, This was a slow day for Freshmeat, but I will be
astonished if any reader reports as many as three likely innovations
a month in any closed-source channel.[EGCS] We how have
history on a project that, in several ways, may provide a more
indicative test of the bazaar premise than fetchmail; EGCS, the Experimental GNU
Compiler System.This project was announced in mid-August of 1997 as a conscious
attempt to apply the ideas in the early public versions of ``The
Cathedral and the Bazaar''. The project founders felt that the
development of GCC, the Gnu C Compiler, had been stagnating.
For about twenty months afterwards, GCC and EGCS continued as
parallel products -- both drawing from the same Internet developer
population, both starting from the same GCC source base, both using
pretty much the same Unix toolsets and development environment. The
projects differed only in that EGCS consciously tried to apply the
bazaar tactics I have previously described, while GCC retained a
more cathedral-like organization with a closed developer group and
infrequent releases.This was about as close to a controlled experiment as one could ask
for, and the results were dramatic. Within months, the EGCS versions
had pulled substantially ahead in features; better optimization,
better support for FORTRAN and C++. Many people found the EGCS
development snapshots to be more reliable than the most recent
stable version of GCC, and major Linux distributions began to
switch to EGCS.In April of 1999, the Free Software Foundation (the official
sponsors of GCC) dissolved the original GCC development group and
officially handed control of the project to the the EGCS steering
team.[SP] Of course,
Kropotkin's critique and Linus's Law raise some wider issues about the
cybernetics of social organizations. Another folk theorem of software
engineering suggests one of them; Conway's Law -- commonly stated as
``If you have four groups working on a compiler, you'll get a 4-pass
compiler''. The original statement was more general: ``Organizations
which design systems are constrained to produce designs which are
copies of the communication structures of these organizations.'' We
might put it more succinctly as ``The means determine the ends'', or
even ``Process becomes product''.It is accordingly worth noting that in the open-source community
organizational form and function match on many levels. The network is
everything and everywhere: not just the Internet, but the people doing
the work form a distributed, loosely coupled, peer-to-peer network
which provides multiple redundancy and degrades very gracefully.
In both networks, each node is important only to the extent that other
nodes want to cooperate with it.The peer-to-peer part is essential to the community's astonishing
productivity. The point Kropotkin was trying to make about power
relationships is developed further by the `SNAFU Principle': ``True
communication is possible only between equals, because inferiors are
more consistently rewarded for telling their superiors pleasant lies
than for telling the truth.'' Creative teamwork utterly depends on
true communication and is thus very seriously hindered by the presence
of power relationships. The open-source community, effectively free
of such power relationships, is teaching us by contrast how dreadfully
much they cost in bugs, in lowered productivity, and in lost
opportunities.Further, the SNAFU principle predicts in authoritarian organizations
a progressive disconnect between decision-makers and reality, as more
and more of the input to those who decide tends to become pleasant
lies. The way this plays out in conventional software development
is easy to see; there are strong incentives for the inferiors to
hide, ignore, and minimize problems. When this process becomes
product, software is a disaster.