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Modern Operating Systems by Herbert Bos and Andrew...
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Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 753
CHAP. 10
One unusual feature of Linux is its business model: it is free software. It can
be downloaded from various sites on the Internet, for example:
Linux comes with a license devised by Richard Stallman, founder of the Free Soft-
ware Foundation. Despite the fact that Linux is free, this license, the
Public License
), is longer than Microsoft’s Windows license and specifies what
you can and cannot do with the code. Users may use, copy, modify, and redis-
tribute the source and binary code freely.
The main restriction is that all works
derived from the Linux kernel may not be sold or redistributed in binary form only;
the source code must either be shipped with the product or be made available on
Although Torvalds still rides herd on the kernel fairly closely, a large amount
of user-level software has been written by numerous other programmers, many of
them having migrated over from the MINIX, BSD, and GNU online communities.
However, as Linux evolves, an increasingly smaller fraction of the Linux commun-
ity wants to hack source code (witness the hundreds of books telling how to install
and use Linux and only a handful discussing the code or how it works). Also,
many Linux users now forgo the free distribution on the Internet to buy one of the
many CD-ROM distributions available from numerous competing commercial
companies. A popular Website listing the current top-100 Linux distributions is at
As more and more software companies start selling their
own versions of Linux and more and more hardware companies offer to preinstall
it on the computers they ship, the line between commercial software and free soft-
ware is beginning to blur substantially.
As a footnote to the Linux story, it is interesting to note that just as the Linux
bandwagon was gaining steam, it got a big boost from a very unexpected source—
In 1992, Berkeley, by now running out of funding, decided to terminate
BSD development with one final release, 4.4BSD (which later formed the basis of
FreeBSD). Since this version contained essentially no AT&T code, Berkeley
issued the software under an open source license (not GPL) that let everybody do
whatever they wanted with it except one thing—sue the University of California.
The AT&T subsidiary controlling UNIX promptly reacted by—you guessed it—
suing the University of California.
It also sued a company, BSDI, set up by the
BSD developers to package the system and sell support, much as Red Hat and
other companies now do for Linux. Since virtually no AT&T code was involved,
the lawsuit was based on copyright and trademark infringement, including items
such as BSDI’s 1-800-ITS-UNIX telephone number. Although the case was even-
tually settled out of court, it kept FreeBSD off the market long enough for Linux to
get well established. Had the lawsuit not happened, starting around 1993 there
would have been serious competition between two free, open source UNIX sys-
tems: the reigning champion, BSD, a mature and stable system with a large aca-
demic following dating back to 1977, versus the vigorous young challenger, Linux,
just two years old but with a growing following among individual users. Who
knows how this battle of the free
would have turned out?

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