which ran a complete open source software stack. </p>
<p> The success of Linux, or <em>GNU/Linux</em> as some prefer to
-call it for reasons that should now be clear, has only increased
-over time, to the point where commercial Unix systems are mostly
-irrelevant. Today Linux runs on a wide variety of machines ranging
-from supercomputers to workstations, smart phones and IOT (internet
-of things) devices with very limited resources.
-
-<p> The same companies which almost killed Unix by commercializing it
-in order to maximize their profit make money with Linux today. However,
-they had to adjust their business model in order to comply with the
-GPL. Rather than selling proprietary software, they bundle open source
-software and sell support to paying customers. Some companies also
-sell hardware with Linux pre-installed. </p>
+call it for reasons that should now be clear, steadily increased over
+time. In 2003 the SCO group, a company which sold a proprietary Unix
+system, was unhappy about this progress and sued IBM, which offered
+various Linux products. SCO claimed to be the owner of Unix, and that
+Linux contained "millions of lines" of code copied from Unix. SCO's
+lawyers argued that the success of Linux originated from this theft
+of intellectual property and asked for $5 billion as compensation
+for the resulting losses. The company also tried to collect taxes
+from other Linux users. Microsoft funded SCO in these efforts. </p>
+
+<p> In the end SCO lost the lawsuit since it was evident that all that
+copied code never existed. In fact, the court ruled that SCO did not
+even own the Unix copyrights to begin with. Another fun fact is that
+the large number of bugs in the early Linux code actually helped to
+prove that Linux was original work. The long term effects of this
+lawsuit, an improved position of Linux and its ecosystem, last until
+the presence. Commercial Unix systems have become irrelevant as Linux
+runs on a wide variety of machines ranging from supercomputers to
+workstations, smart phones and IOT (internet of things) devices with
+very limited resources. </p>
+
+<p> While SCO went bankrupt eventually, some of the companies which
+almost killed Unix by maximizing their own profit still exist, and
+make money with Linux today. However, they had to adjust their
+business model in order to comply with the GPL. Rather than selling
+proprietary software, they bundle open source software and sell
+support to paying customers. Some companies also sell hardware with
+Linux pre-installed. </p>
SUBSECTION(«Linux Distributions»)
<li> Run <code>uname -a</code> on various Unix machines to see the
OS type and the kernel version. </li>
- <li> Nice read on the
- <a href="http://www.catb.org/~esr/writings/taoup/html/ch02s01.html">Origins and
- History of Unix</a>, 1969-1995. </li>
-
<li> Explore the <a
href="https://upload.wikimedia.org/wikipedia/commons/7/77/Unix_history-simple.svg">Unix
time line</a>. </li>
href="http://www.gnu.org/cgi-bin/license-quiz.cgi">Free Software
licensing quiz</a>. </li>
- <li> Read the <a
- href="https://www.newyorker.com/business/currency/the-gnu-manifesto-turns-thirty">
- notes on the 30th anniversary</a> of the GNU Manifesto. </li>
-
- <li> Read the <a
- href="http://www.catb.org/~esr/writings/unix-koans/end-user.html">
- Koan of Master Foo and the End User</a>. </li>
-
<li> On a Debian or Ubuntu system, run <code>aptitude search
python</code> to list all python-related Ubuntu packages. Run
<code>aptitude show python-biopython</code> to see the description
<table>
<tr>
- <td> </td>
- <td> <em>Directories</em> </td>
- <td> <em>Non-directories</em> </td>
+ <th> </th>
+ <th> Directories </th>
+ <th> Non-directories </th>
</tr> <tr>
- <td> <code> r </code> </td>
+ <th> <code>r</code> </th>
<td> The permission to list the directory contents. More precisely,
this bit grants the permission to call <code>opendir(3)</code>
fail for other reasons, though.
</tr> <tr>
- <td> <code> w </code> </td>
+ <th> <code>w</code> </th>
<td> The permission to add or remove directory entries. That is,
to create new files or to remove existing files. Note that write
permissions. </td>
</tr> <tr>
- <td> <code> x </code> </td>
+ <th> <code>x</code> </th>
<td> The permission to <em>search</em> the directory. Searching
a directory means to access its entries, either by retrieving
<table>
<tr>
- <td> octal value </td>
- <td> symbolic representation </td>
- <td> meaning </td>
+ <th> Octal Value </th>
+ <th> Symbolic Representation </th>
+ <th> Meaning </th>
</tr> <tr>
<td> 0 </td>
<td> <code>---</code> </td>
particular, there is no such thing like "the list of paths which have
changed since yesterday".
-The concept of hard- and soft links complicates
-the situation further. This topic is discussed in a <a
-href="#soft_and_hard_links">subsequent section</a>. See the exercises
-therein for more information.
-
+The concept of hard- and soft links complicates the situation further.
»)
HOMEWORK(«
<p> The <code>pipe(2)</code> system call takes no arguments and
creates two file descriptors for the calling process which are tied
-together as a unidirectional first in, first out data channel that
-works just like a fifo, but without any files being involved. One
+together as a unidirectional first in, first out data channel. One
file descriptor is the <em>read end</em> of the pipe, the other is
the <em>write end</em>. Data written to the write end is buffered by
the kernel and can be obtained by reading from the read end. </p>
communicate with the child by writing a message to the write end of
the pipe for the child to read. </p>
+<p> This approach depends on file descriptor inheritance across
+<code>fork(2)</code>, so it does not work in the situation
+where neither process is an ancestor of the other. Files of
+type <em>fifo</em> (named pipes) overcome this restriction. To
+establish a connection between two <em>unrelated</em> processes,
+both processes call <code>open(2)</code> to obtain a file
+descriptor which is associated with the fifo. One process passes
+the <code>O_WRONLY</code> flag to open the file for writing while
+the other passes <code>O_RDONLY</code> to open it for reading. The
+two processes may then communicate in the same way as with the
+<code>pipe(2)/fork(2)</code> approach. </p>
+
<p> The POSIX <code>dup(2)</code> and <code>dup2(2)</code> system
calls allow a process to manipulate the entries of its file descriptor
array. In particular the standard file descriptors 0, 1, and 2 can be
and <code>wc(1)</code> reads from stdin, <code>wc(1)</code> processes
the output of <code>ls(1)</code>. </p>
-<p> Note that this trick does not work to establish a connection
-between two <em>existing</em> processes because it depends on file
-descriptor inheritance across <code>fork(2)</code>. In the general
-case one has to fall back to sockets or fifos to create the data
-channel. </p>
-
SUBSECTION(«Stdio»)
<p> The POSIX standard requires a compliant Unix system to provide
SECTION(«Further Reading»)
<ul>
+ <li> <a
+ href="http://www.catb.org/~esr/writings/taoup/html/ch02s01.html">Origins
+ and History of Unix, 1969-1995</a> by Eric Steven Raymond. </li>
+
+ <li> <a
+ href="https://www.newyorker.com/business/currency/the-gnu-manifesto-turns-thirty">
+ The GNU Manifesto Turns Thirty</a>, by Maria Bustillos. </li>
+
+ <li> <a href="https://lwn.net/Articles/924577/">The SCO lawsuit,
+ 20 years later</a> </li>
+
+ <li> <a
+ href="http://www.catb.org/~esr/writings/unix-koans/end-user.html">
+ The Koan of Master Foo and the End User</a>. </li>
+
<li> <a href="https://lwn.net/Articles/411845/">Ghosts of Unix Past:
a historical search for design patterns</a>, by Neil Brown. </li>
projects / aple.git / blobdiff