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<HTML><HEAD><TITLE> Linux Gazette Table of Contents LG #94</TITLE></HEAD>
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<H2>September 2003, Issue 94 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
Published by <I>Linux Journal</I></H2>
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<LI> <A HREF="lg_bytes.html">News Bytes</A>, <EM>by Michael Conry</EM>
<LI> <A HREF="ecol.html">Ecol</A>, <EM>by Javier Malonda</EM>
<LI> <A HREF="ramankutty.html">From C To Assembly Language</A>, <EM>by Hiran Ramankutty</EM>
<LI> <A HREF="kolp.html">Play Encoded DVDs in Xine</A>, <EM>by LeaAnne Kolp</EM>
<LI> <A HREF="lalji.html">Under /etc (A Simple Guide)</A>, <EM>by AmirAli Lalji</EM>
<LI> <A HREF="yan-fa.html">Linux based Radio Timeshifting</A>, <EM>by Yan-Fa Li</EM>
<LI> <A HREF="zhuravlev.html">USENET groups, email, and ssh tunnels over dial-up connection</A>, <EM>by Nikolay Zhuravlev</EM>
<LI> <A HREF="hughes.html">Python Weather Station</A>, <EM>by Phil Hughes</EM>
<LI> <A HREF="anonymous.html">SCO Interview</A>, <EM>by Anonymous</EM>
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<H3 ALIGN="center"><EM>Linux Gazette</EM> Staff and The Answer Gang</H3>
<BLOCKQUOTE>
<STRONG>TAG Editor:</STRONG> Heather Stern<BR>
<STRONG>Senior Contributing Editor:</STRONG> Jim Dennis<BR>
<STRONG>Contributing Editors:</STRONG>
Ben Okopnik, Dan Wilder, Don Marti
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<H5>Copyright &copy; 1996-2003 Specialized Systems Consultants, Inc.</H5>
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<BIG><BIG><STRONG><FONT COLOR="maroon">News Bytes</FONT></STRONG></BIG></BIG>
<BR>
<STRONG>By <A HREF="../authors/conry.html">Michael Conry</A></STRONG>
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<table cellpadding="7"><tbody><tr><td>
<img src="../gx/bytes.gif" border="1" alt="News Bytes">
</td><td>
<h3>Contents:</h3>
<ul>
<li><a href="#leg">Legislation and More Legislation</a>
</li><li><a href="#links">Linux Links</a>
</li><li><a href="#conferences">Conferences and Events</a>
</li><li><a href="#general">News in General</a>
</li><li><a href="#distro">Distro News</a>
</li><li><a href="#commercial">Software and Product News</a>
</li></ul>
</td></tr></tbody></table>
<strong>Selected and formatted by <a href="mailto:michael.conry@softhome.net">Michael Conry</a></strong>
</center>
<p> Submitters, send your News Bytes items in
<font size="+2"><strong>PLAIN TEXT</strong></font>
format. Other formats may be rejected without reading. You have been
warned! A one- or two-paragraph summary plus URL gets you a better
announcement than an entire press release. Submit items to
<a href="mailto:bytes@linuxgazette.com">bytes@linuxgazette.com</a>
</p><hr> <p>
<!-- =================================================================== -->
</p><h3><img alt=" " src="../gx/bolt.gif">
<font color="green">
September 2003 <i>Linux Journal</i>
</font>
</h3>
<img alt="[issue 113 cover image]" src="misc/bytes/lj-cover113.png" width="200" height="268" align="left" hspace="20">
The September issue of <a href="http://www.linuxjournal.com/"><i>Linux
Journal</i></a> is on newsstands now.
This issue focuses on Community Networks. Click
<a href="http://www.linuxjournal.com/modules.php?op=modload&amp;name=NS-lj-issues/issue113&amp;file=index">here</a>
to view the table of contents, or
<a href="http://www.linuxjournal.com/subscribe/">here</a>
to subscribe.
<p>
<font color="green">All articles in issues 1-102 are available for
public reading at
<a href="http://www.linuxjournal.com/magazine.php">http://www.linuxjournal.com/magazine.php</a></font>.
Recent articles are available on-line for subscribers only at
<a href="http://interactive.linuxjournal.com/">http://interactive.linuxjournal.com/</a>.
<BR CLEAR="all">
<!-- =================================================================== -->
<a name="leg"></a>
<p><hr><p>
<!-- =================================================================== -->
<center><H3><font color="green">Legislation and More Legislation</font></H3></center>
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">European Software Patents
</FONT>
</H3>
<P>
On the 1st of September 2003, the European Parliament will hold a vote
which may have very far reaching and long lasting effects on the software
industry and community within the European Union. The central issue being
addressed in this vote is the patentability of software. In the past,
there has been some vagueness in the attitude of
<a href="http://www.european-patent-office.org/">the European Patent
Office</a> towards the patenting of software. Although official
regulations appeared to make software, mathematics, algorithms and business
methods
<a href="http://swpat.ffii.org/analysis/epc52/index.en.html">
essentially unpatentable</a>, working practise in the EPO has been to
bypass the legal framework intended to constrain it and to allow such
innovations to be patented. The new directive on
<a href="http://europa.eu.int/comm/internal_market/en/indprop/comp/02-277.htm">
the patentability of computer-implemented inventions</a> is supposed to be
a measure aimed at resolving this confusion by regularising the rules
regarding patentability. However, what the EU blurb glosses over is that
the provisions in the new directive significantly alter the legislation
currently governing software patentability. Rather than vindicating the
existing legal situation, the legislation is being recast in the image of
the current operations of the EPO. This is strikingly borne out by some
research performed by the <a href="http://ffii.org/">FFII</a>. The FFII
intended to
<a href="http://swpat.ffii.org/papers/eubsa-swpat0202/tech/index.en.html">
show that the infamous "one click" Amazon.com patent</a> would be
acceptable under the proposed new regulations. During the course of these
investigations, it emerged that Amazon.com had <em>already</em>
<a href="http://swpat.ffii.org/news/03/amaz0818/index.en.html">
been granted a closely related patent</a> covering computerised methods of
gift delivery.
<P>
Of course, when considering these changes we must ask ourselves whether
perhaps these changes may be desirable. Though there are naturally those
who support the initiative, there is a very broad constituency that
strongly opposes this move towards European software patents. An
unscientific measure of the opposition to the software patent proposals can
be obtained by doing a
<a href="http://news.google.com/news?hl=en&edition=us&q=european+software+patents&btnG=Search+News">
search on Google News</a> for the terms "european software patents". The
vast majority of headlines are hostile or gloomy regarding the proposal.
There is a striking absence of outright support, all the more striking
given that this is a search of news outlets rather than personal or
lobby-group websites. This scepticism is
<a href="http://www.arnnet.com.au/index.php?id=1094595024&fp=16&fpid=0">
shared by many economists</a> who fear that the legal changes will lead to
a reduction in innovation and cutbacks in R&amp;D expenditure. These fears
are felt very acutely among small and medium size software companies who
have perhaps the most to lose. Equally, open source developers may be left
<a href="http://swpat.ffii.org/#crn-gates030725">
in a vulnerable position</a> by these proposed changes. As has been seen
in the operation of software patents in the United States, the patent
system tends to work best for parties with large financial resources, such
as multinational corporations. Such deep pockets allow an organisation to
acquire a stock of patents, and then to defend the patents through the
courts. A well resourced holder of even a very spurious patent can thus
intimidate would-be competitors out of the market simply by virtue of the
differences in scale. The only group which will benefit to a greater
degree than large corporations is the legal fraternity.
<P>
It remains to be seen whether the protests and lobbying organised by
anti-patent groups will prove to be effective. Though actions such as
<a href="http://slashdot.org/articles/03/08/29/0510200.shtml?tid=155&tid=185&tid=99">
closing down websites</a> make an impact online, the real world effect can
be quite small. As was pointed out
<a href="http://www.theregister.co.uk/content/4/31472.html">
by the Register</a>, even though open source produces great code, it does
not necessarily produce great lobbying. The key for open-source groups
elsewhere and in the future is to share information about what works and
does not work in the political sphere, and to apply this information in
future struggles.
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">SCO
</FONT>
</H3>
<P>
Writing an article on the SCO lawsuit(s) is getting steadily more difficult
as the volume of material on the subject mounts up. Much of it is simply
noise and it will not be until the case is dropped or reaches court that we
will have a chance to properly judge the true nature of SCO's plans. This
is especially true given SCO's reluctance to release any of the source code
they claim is infringing their "intellectual" property (the words "SCO" and
"intellectual" seem more mutually exclusive to me each day). Perhaps to
impress investors, SCO did deign to
<a href="http://slashdot.org/article.pl?sid=03/08/19/1523236&mode=nested&tid=106&tid=185">
display a couple of samples</a> at their annual reseller show. This was
very nice of them and illustrates why they should perhaps release more of
the "disputed" code. Analysis done
<a href="http://lwn.net/Articles/45019/">
by Linux Weekly News</a>
and
<a href="http://www.perens.org/SCO/SCOSlideShow.html">
by Bruce Perens</a>
indicated that the origination of the code was entirely legal and did not
infringe on SCO's property.
SCO spokesman Blake Stowell's
<a href="http://www.itworld.com/Man/2685/030819scocode/">
rather pointless response</a>
was to show a typically SCO-like disdain for facts and to assert that "at
this point it's going to be his [Perens'] word against ours".
Unfortunately for Blake, Perens' word is backed up by verifiable
documentation and historical record not to mention the fact that people who
worked on and remember the code are
<a href="http://slashdot.org/article.pl?sid=03/08/23/1731245&mode=nested&tid=123&tid=130&tid=185&tid=190&tid=99">
still alive</a>. Meanwhile, SCO's assertions are, at least
at this stage, no more than random bleatings.
<P>
Reaction to the SCO case has been mostly muted, though it is likely that
some more-cautious corporate types are somewhat reluctant to engage further
with Open Source and Free Software under the shadow of the court case. Few
though are likely to be so nervous as to stump up the licence fees
requested by SCO. The advice
<a href"http://www.idg.com.hk/cw/readstory.asp?aid=20030801018">
of Australian lawyer John Collins</a> sounds about right:
<blockquote>
"If you don't know whether or not you have a valid license because
there is uncertainty as to the providence of the software and who
actually owns the copyright, then to walk up and drop your pants to the
person who is likely to sue you sounds a little counter-intuitive and a
bit uncommercial,"
</blockquote>
<P>
Some have speculated that the true purpose of SCO's actions may be
connected to the (mostly positive) effect on its share price these
developments have had. An example of these arguments can be found in the
<a href="http://www.threenorth.com/sco/">
writings of Tim Rushing</a>, though ultimately everybody is still
speculating. Further analyses can be found
<a href="http://radio.weblogs.com/0120124/">
at GrokLaw</a>
and
<a href="http://sco.iwethey.org/">
at sco.iwethey.org</a>, though keeping up with the twists and turns, not to
mention the irrational behaviour of SCO execs, is rather taxing on the grey
matter.
<a name="links"></a>
<p><hr><p>
<!-- =================================================================== -->
<center><H3><font color="green">Linux Links</font></H3></center>
<P>
<a href="http://www.ActiveState.com">
ActiveState</a>
has
<a href="http://www.activestate.com/Corporate/Communications/Releases/Press1058851602.html">made freely available</a>
the
<a href="http://www.activestate.com/Products/PureMessage/Field_Guide_to_Spam/index.plex ">
ActiveState Field Guide to Spam</a>.
This is a living compilation of advanced
tricks used by spammers to hide their messages from spam filters.
<P>
Some links from
<a href="http://www.newsforge.com/">Newsforge</a>
<ul>
<li>
Thoughts on the legal implications of
<a href="http://newsforge.com/article.pl?sid=03/07/21/2118255">
personal music ownership</a>.
</li>
<li>
<a href="http://www.linuxquestions.org/questions/history/78090">
Interview with Asa Dotzler</a> of Mozilla.
</li>
<li>
VIA, SRI
<a href="http://newsvac.newsforge.com/article.pl?sid=03/07/31/1958230">
put Linux-based robots to the test</a>
at LinuxWorld Expo.
</li>
<li>
<a href="http://newsforge.com/article.pl?sid=03/07/29/1727249">
Host-based intrusion detection with samhain</a>.
</li>
<li>
Open Source is
<a href="http://newsforge.com/article.pl?sid=03/08/09/1355255">
good for the Philippine economy</a>.
</li>
<li>
<a href="http://newsvac.newsforge.com/article.pl?sid=03/08/10/0116204">
RubyForge open for business</a>
</li>
<li>
Jordi Carrasco-Munoz has
<a href="http://newsforge.com/article.pl?sid=03/08/14/1223235">
proposed a scheme for the pooling of ideas</a>.
</li>
<li>
TheLinux On Laptops
<a href="http://newsvac.newsforge.com/article.pl?sid=03/08/17/1344249">
Manufacturer Report Card has been updated</a>.
</li>
<li>
<a href="http://newsforge.com/article.pl?sid=03/08/20/1441247">
A new (egovernment) forge in town</a>
<em>Government Forge</em>.
</li>
</ul>
<P>
Some interesting links from the O'Reilly stable of websites:
<ul>
<li>
<a href="http://www.oreillynet.com/pub/a/network/synd/2003/08/05/closed_loop.html">
Introduction to Closed-Loop Control</a>
</li>
<li>
<a href="http://www.onlamp.com/pub/a/python/2003/08/14/gvr_interview.html">
Interview with Guido van Rossum</a>.
</li>
<li>
<a href="http://www.onlamp.com/pub/a/onlamp/2003/08/28/extremeprogramming.html">
Five lessons open source developers should learn from extreme
programming</a>.
</li>
</ul>
<P>
Ernie Ball guitar string company
<a href="http://news.com.com/2008-1082_3-5065859.html?tag=lh">
dumps Microsoft for Linux</a>
after BPA audit.
<P>
<a href="http://www.eweek.com/article2/0,3959,1227128,00.asp">
Linus says SCO is smoking crack</a>.
<P>
<a href="http://www.theregister.co.uk/">
The Register</a> reported on the launch of
Open Groupware.org, an application which claims to
<a href="http://www.theregister.co.uk/content/4/32119.html">
complete the OpenOffice productivity software set</a>.
<P>
Some links of interest from
<a href="http://www.linuxtoday.com/">
Linux Today</a>:
<ul>
<li>
Infoworld
<a href="http://www.infoworld.com/article/03/08/06/HNgplunenforceable_1.html">
report</a>
that the GPL <em>may</em> be unenforceable under German law.
</li>
<li>
A casual
<a href="http://articles.linmagau.org/modules.php?op=modload&name=Sections&file=index&req=viewarticle&artid=238&page=1">
interview with the new Linux 2.6 kernel maintainer, Andrew Morton</a>.
</li>
<li>
V8 Supercar races in Australia feature
<a href="http://news.zdnet.co.uk/software/linuxunix/0,39020390,39115798,00.htm">
onboard Linux-based computers and wireless technology</a> to send
information on crashes to race officials.
</li>
<li>
Could free software development have an influence on society
<a href="http://www.canada.com/technology/story.html?id=5F7655EF-B9CD-4D28-919C-51AF3C9CBDC3">
like that exerted by the King James Bible</a>?
</li>
</ul>
<P>
Bruce Perens
<a href="http://www.perens.com/SCO/SCOSlideShow.html">
analyzes SCO's code samples</a> in detail.
<P>
<a href="http://www.debian.org/News/weekly/2003/31/">
Debian Weekly News highlighted</a>
an article by Ian Murdock arguing that
<a href="http://zdnet.com.com/2100-1107_2-5057755.html">
Linux is a process, not a product</a>.
<a name="conferences"></a>
<p><hr><p>
<!-- =================================================================== -->
<center><H3><font color="green">Upcoming conferences and events</font></H3></center>
<P> Listings courtesy <EM>Linux Journal</EM>. See <EM>LJ</EM>'s
<A HREF="http://www.linuxjournal.com/events.php">Events</A> page for the
latest goings-on.
<!-- *** BEGIN events table [this line needed by Linux Gazette events.py *** -->
<table cellpadding=5 border=0 width=100%>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
<tr><td valign=top>
<b>LinuxWorld UK</b><BR></TD>
<td valign=top>September 3-4, 2003<BR>Birmingham, United Kingdom<BR>
<a href="http://www.linuxworld2003.co.uk" target="_blank">
http://www.linuxworld2003.co.uk</A><BR></TD></TR>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
<tr><td valign=top>
<b>Linux Lunacy</b><BR><i>Brought to you by Linux Journal and
Geek Cruises!</i><br></TD>
<td valign=top>September 13-20, 2003<BR>Alaska's Inside Passage<BR>
<a href="http://www.geekcruises.com/home/ll3_home.html" target="_blank">
http://www.geekcruises.com/home/ll3_home.html</A><BR></TD></TR>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
<tr><td valign=top>
<b>Software Development Conference & Expo</b><BR></TD>
<td valign=top>September 15-18, 2003<BR>Boston, MA<BR>
<a href="http://www.sdexpo.com" target="_blank">
http://www.sdexpo.com</A><BR></TD></TR>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
<tr><td valign=top>
<b>PC Expo</b><BR></TD>
<td valign=top>September 16-18, 2003<BR>New York, NY<BR>
<a href="http://www.techxny.com/pcexpo_techxny.cfm" target="_blank">
http://www.techxny.com/pcexpo_techxny.cfm</A><BR></TD></TR>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
<tr><td valign=top>
<b>COMDEX Canada</b><BR></TD>
<td valign=top>September 16-18, 2003<BR>Toronto, Ontario<BR>
<a href="http://www.comdex.com/canada/" target="_blank">
http://www.comdex.com/canada/</A><BR></TD></TR>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
<tr><td valign=top>
<b>IDUG 2003 - Europe</b><BR></TD>
<td valign=top>October 7-10, 2003<BR>Nice, France<BR>
<a href="http://www.idug.org" target="_blank">
http://www.idug.org</A><BR></TD></TR>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
<tr><td valign=top>
<b>Linux Clusters Institute Workshops</b><BR></TD>
<td valign=top>October 13-18, 2003<BR>Montpellier, France<BR>
<a href="http://www.linuxclustersinstitute.org/"
target="_blank">
http://www.linuxclustersinstitute.org</A><BR></TD></TR>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
<tr><td valign=top>
<b>Coast Open Source Software Technology (COSST) Symposium</b><BR></TD>
<td valign=top>October 18, 2003<BR>Newport Beach, CA<BR>
<a href="http://cosst.ieee-occs.org" target="_blank">
http://cosst.ieee-occs.org</A><BR></TD></TR>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
<tr><td valign=top>
<b>LISA (17th USENIX Systems Administration Conference)</b><BR></TD>
<td valign=top>October 26-30, 2003<BR>San Diego, CA<BR>
<a href="http://www.usenix.org/events/lisa03/" target="_blank">
http://www.usenix.org/events/lisa03/</A><BR></TD></TR>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
<tr><td valign=top>
<b>HiverCon 2003</b><BR></TD>
<td valign=top>November 6-7, 2003<BR>Dublin, Ireland<BR>
<a href="http://www.hivercon.com/" target="_blank">
http://www.hivercon.com/</A><BR></TD></TR>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
<tr><td valign=top>
<b>COMDEX Fall</b><BR></TD>
<td valign=top>November 17-21, 2003<BR>Las Vegas, NV<BR>
<a href="http://www.comdex.com/fall2003/" target="_blank">
http://www.comdex.com/fall2003/</A><BR></TD></TR>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
<tr><td valign=top>
<b>Southern California Linux Expo (SCALE)</b><BR></TD>
<td valign=top>November 22, 2003<BR>Los Angeles, CA<BR>
<a href="http://socallinuxexpo.com/" target="_blank">
http://socallinuxexpo.com/</A><BR></TD></TR>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
<tr><td valign=top>
<b>Linux Clusters Institute Workshops</b><BR></TD>
<td valign=top>December 8-12, 2003<BR>Albuquerque, NM<BR>
<a href="http://www.linuxclustersinstitute.org/"
target="_blank">
http://www.linuxclustersinstitute.org</A><BR></TD></TR>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
<tr><td valign=top>
<b>Storage Expo 2003, co-located with Infosecurity 2003</b><BR></TD>
<td valign=top>December 9-11, 2003<BR>New York, NY<BR>
<a href="http://www.infosecurityevent.com/" target="_blank">
http://www.infosecurityevent.com/</A><BR></TD></TR>
<tr><td colspan=2><HR size=5 width=100% noshade align=center></td></tr>
</table>
<!-- *** END events table [this line needed by Linux Gazette events.py *** -->
<a name="general"></a>
<p><hr><p>
<!-- =================================================================== -->
<center><H3><font color="green">News in General</font></H3></center>
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">GNU Server breach
</FONT>
</H3>
<P>
It emerged over the past month that the main file servers of the
<a href="http://www.fsf.org/">GNU project</a> were compromised by a
malicious cracker in mid-march. Although the breach was only noticed in
July, it appears that no source code was tampered with. Nonetheless, it is
important that individuals and organisation who may have downloaded from
the compromised server verify for themselves that the code they received
was intact and untainted. This incident should also bring home to users
the importance of keeping up to date with patches and software updates, and
also the necessity to have established security procedures and backups in
place.
<P>
Original reporting on this story can be found here:
<ul>
<li>
<a href="http://news.zdnet.co.uk/0,39020330,39115701,00.htm">
ZDNet UK: Free Software servers breached</a>
</li>
<li>
<a href="http://www.searchEnterpriseLinux.com/originalContent/0,289142,sid39_gci920359,00.html">
SearchEnterpriseLinux.com: GNU dodges bullet after security breach</a>
</li>
<li>
<a href="http://www.theregister.co.uk/content/55/32355.html">
The Register: GNU servers 'owned' by crackers for months</a>
</li>
</ul>
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">Alan Cox Sabbatical
</FONT>
</H3>
<P> Kerneltrap reported that
<a href="http://kerneltrap.org/node/view/759">
Alan Cox is to take a one year sabbatical</a>. He plans to spend his year
studying for an MBA and learning Welsh.
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">GNU/Linux Security Certification
</FONT>
</H3>
<P>
Slashdot recently
<a href="http://slashdot.org/article.pl?sid=03/08/05/1217242&mode=nested&tid=106&tid=126&tid=172&tid=185">
highlighted the story</a>
that IBM has
<a href="http://story.news.yahoo.com/news?tmpl=story&cid=569&ncid=738&e=1&u=/nm/20030805/tc_nm/tech_ibm_linux_dc">
succeeded in getting Linux certified</a>
under the Common Criteria
specification. This has implications for government bodies considering Linux
when making purchasing decisions.
The Inquirer reports that this has been a bit of a black-eye for Red Hat,
whose
<a href="http://www.theinquirer.net/?article=11067">
certification effort is stalled, held up indefinitely by the UK-based
testing laboratory Red Hat selected to do the work</a>.
<a name="distro"></a>
<p><hr><p>
<!-- =================================================================== -->
<center><H3><font color="green">Distro News</font></H3></center>
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">Ark
</FONT>
</H3>
<P>
Tux Reports have taken a
<a href="http://www.tuxreports.com/article2251.html">
look at Ark Linux</a>.
This RPM based distribution particularly aims to provide a comprehensive
and useful desktop environment.
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">Debian
</FONT>
</H3>
<P>
<a href="http://www.debian.org/News/weekly/2003/33/">
Debian Weekly News linked</a> to
Jan Ivar Pladsen's document
which describes
<a href="http://www.pvv.org/~pladsen/Indy/HOWTO.html">
how to install Debian GNU/Linux on Indy</a>.
<P>
<hr width="20%" noshade>
<P>
On August 16th, the Debian Project celebrated
<a href="http://www.debian.org/News/2003/20030811">
its 10th birthday</a>.
Linux Planet published a
<a href="http://www.linuxplanet.com/linuxplanet/editorials/4959/1/">
Debian 10-year retrospective</a> to mark the occasion.
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">Knoppix
</FONT>
</H3>
<P>
Klaus Knopper describes the
<a href="http://www.pctechtalk.com/view.php?id=1239">
Philosophy behind Knoppix</a>.
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">Libranet
</FONT>
</H3>
<P>
Linuxiran has
<a href="http://www.linuxiran.org/modules/news/article.php?storyid=232">
reviewed Libranet GNU/Linux 2.8</a>.
Evidently they were impressed: "Only one word can describe Libranet's
installer: 'awesome...'" (Courtesy Linux Today).
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">Mepis
</FONT>
</H3>
<P>
<a href="http://www.debian.org/News/weekly/2003/33/">
As higlighted by DWN</a>,
<a href="http://www.mepis.org/">
Mepis Linux</a>
is a LiveCD derived from Debian GNU/Linux.
LinuxOnline has some articles on this distribution, including
this LiveCD. The first is
<a href="http://www.pclinuxonline.com/modules.php?name=News&file=article&sid=7115">
an overview</a>,
<a href="http://www.pclinuxonline.com/modules.php?name=News&file=article&sid=7143">
a full review</a>
and an
<a href="http://www.pclinuxonline.com/modules.php?name=News&file=article&sid=7171">
interview with Mepis creator Warren Woodford</a>.
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">SuSE
</FONT>
</H3>
<P>
<a href="http://www.sgi.com">
SGI</a>
and
<a href="http://www.suse.de/en">
SuSE Linux</a>
today announced plans to extend the Linux OS to new levels of scalability
and performance by offering a fully supported 64-processor system running a
fully supported, enterprise-grade Linux operating system. Expected to be
available in October, SGI will bundle SuSE Linux Enterprise Server 8 on SGI
Altix 3000 servers and superclusters.
<P>
<hr width="20%" noshade>
<P>
<a href="http://www.siemens.com/sbs">
Siemens Business Servicess</a>
has decided to use SuSE Linux Enterprise Server 8 to underpin its mySAP HR
management system, processing payrolls for more than 170,000 employees
worldwide. The open source operating system and the platform independence
of the SAP R/3 software enable an easy migration to an open, powerful, and
efficient Intel architecture. Linux-based application servers can be
operated independently alongside existing Unix-based servers. Thus, the RM
systems can continue to run until they were amortized and gradually
replaced by Linux servers.
<a name="commercial"></a>
<p><hr><p>
<!-- =================================================================== -->
<center><H3><font color="green">Software and Product News</font></H3></center>
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">Biscom Announces Linux FAXCOM Server
</FONT>
</H3>
<P>
<a href="http://www.biscom.com">
Biscom</a>,
a provider of enterprise fax management solutions, has announced the market
release of its Linux FAXCOM Server. The new product integrates the
reliability and efficiency of the Windows FAXCOM Server with the stability
and security of the Linux operating system. Linux FAXCOM Server has been
thoroughly tested is currently available for market release. Linux FAXCOM
Server features support for multiple diverse document attachments via
on-the-fly document conversion, and up to 96 ports on one fax server.
Expanded fax routing destination options for inbound faxes include: fax
port, dialed digits, sender's Transmitting Station Identifier (TSID) and
Caller ID. Furthermore, if appropriate, the same fax may be routed to
multiple destinations, including one or more printers.
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">GNU Scientific Library 1.4 released
</FONT>
</H3>
<P>
Version 1.4 of the
<a href="http://www.gnu.org/software/gsl/">
GNU Scientific Library</a>
is now available at:
<blockquote>
<a href="ftp://ftp.gnu.org/gnu/gsl/gsl-1.4.tar.gz">
ftp://ftp.gnu.org/gnu/gsl/gsl-1.4.tar.gz</a>
</blockquote>
and from mirrors worldwide (see
<a href="http://www.gnu.org/order/ftp.html">
http://www.gnu.org/order/ftp.html</a>).
<P>
The GNU Scientific Library (GSL) is a collection of routines for
numerical computing in C. This release is backwards compatible with
previous 1.x releases. GSL now includes support for cumulative
distribution functions (CDFs) contributed by Jason H. Stover. The
full NEWS file entry is appended below.
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">Mod_python 3.1.0 Alpha
</FONT>
</H3>
<P>
The Apache Software Foundation and The Apache HTTP Server Project
have announced the 3.1.0 ALPHA release of
<a href="http://www.modpython.org/">
mod_python</a>.
<P> Some feature highlights:
<ul>
<li> Server-side sessions with memory or dbm-based storage and session
locking support.
</li>
<li> PSP - a fast flex-based scanner which allows embedding Python code
within HTML.
</li>
<li> Native cookie support, including support for automatic cryptographic
cookie signing and marshalling.
</li>
<li> Compatibility with Python 2.3, as well as many other enhancements.
</li>
<li> Alpha releases are NOT considered stable and do contain bugs. Some
functionality may change before the first beta release.
</li>
</ul>
<p>
Mod_python 3.1.0a is available for download from:
<a href="http://httpd.apache.org/modules/python-download.cgi">
http://httpd.apache.org/modules/python-download.cgi</a>
<P> <hr> <P>
<!-- =================================================================== -->
<H3><IMG ALT=" " SRC="../gx/bolt.gif">
<FONT COLOR="green">Samba
</FONT>
</H3>
<P>
Linux Today has
<a href="http://linuxtoday.com/infrastructure/2003082901426NWSVSW">
carried the news</a>
that Samba-3.0.0 RC2 is now available for download
<!-- =================================================================== -->
<!-- *** BEGIN bio *** -->
<!-- *** END bio *** -->
<!-- *** BEGIN author bio *** -->
<P>&nbsp;
<P>
<P> Mick is LG's News Bytes Editor.
<!-- *** BEGIN bio *** -->
<P>
<IMG ALIGN="LEFT" VALIGN="top" ALT="[Picture]" SRC="../gx/2002/tagbio/conry.jpg"
WIDTH="128" HEIGHT="158">
<em>Born some time ago in Ireland, Michael is currently working on
a PhD thesis in the Department of Mechanical Engineering, University
College Dublin. The topic of this work is the use of Lamb waves in
nondestructive testing. GNU/Linux has been very useful in this work, and
Michael has a strong interest in applying free software solutions to
other problems in engineering. When his thesis is completed, Michael
plans to take a long walk.
</em>
<br CLEAR="all">
<!-- *** END bio *** -->
<!-- *** END author bio *** -->
<!-- *** BEGIN copyright *** -->
<hr>
<CENTER><SMALL><STRONG>
Copyright &copy; 2003, Michael Conry.
Copying license <A HREF="../copying.html">http://www.linuxgazette.com/copying.html</A><BR>
Published in Issue 94 of <i>Linux Gazette</i>, September 2003
</STRONG></SMALL></CENTER>
<!-- *** END copyright *** -->
<HR>
<TABLE BORDER><TR><TD WIDTH="200">
<A HREF="http://www.linuxgazette.com/">
<IMG ALT="LINUX GAZETTE" SRC="../gx/2002/lglogo_200x41.png"
WIDTH="200" HEIGHT="41" border="0"></A>
<BR CLEAR="all">
<SMALL>...<I>making Linux just a little more fun!</I></SMALL>
</TD><TD WIDTH="380">
<CENTER>
<BIG><BIG><STRONG><FONT COLOR="maroon">Ecol</FONT></STRONG></BIG></BIG>
<BR>
<STRONG>By <A HREF="../authors/malonda.html">Javier Malonda</A></STRONG>
</CENTER>
</TD></TR>
</TABLE>
<P>
<!-- END header -->
The Ecol comic strip is written for <A
HREF="http://escomposlinux.org">escomposlinux.org</A> (ECOL), the web site tha
t supports, es.comp.os.linux, the Spanish USENET newsgroup for Linux. The
strips are drawn in Spanish and then translated to English by the author.
<P>
<EM>These images are scaled down to minimize horizontal scrolling.
To see a panel in all its clarity, click on it.</EM>
<P>
<A HREF="misc/ecol/ecol-122-e-as.png">
<IMG ALT="[cartoon]" SRC="misc/ecol/ecol-122-e-as.png"
WIDTH="640" HEIGHT="240"></A>
<BR CLEAR="all">
<A HREF="misc/ecol/ecol-123-e-as.png">
<IMG ALT="[cartoon]" SRC="misc/ecol/ecol-123-e-as.png"
WIDTH="640" HEIGHT="240"></A>
<BR CLEAR="all">
<A HREF="misc/ecol/ecol-124-e-as.png">
<IMG ALT="[cartoon]" SRC="misc/ecol/ecol-124-e-as.png"
WIDTH="640" HEIGHT="240"></A>
<BR CLEAR="all">
<P>
All Ecol cartoons are at
<A HREF="http://tira.escomposlinux.org/">tira.escomposlinux.org</A> (Spanish),
<A HREF="http://comic.escomposlinux.org/">comic.escomposlinux.org</A> (English)
and
<A HREF="http://tira.puntbarra.com/">http://tira.puntbarra.com/</A> (Catalan).
The Catalan version is translated by the people who run the site; only a few
episodes are currently available.
<P> <SMALL>These cartoons are copyright Javier Malonda. They may be copied,
linked or distributed by any means. However, you may not distribute
modifications. If you link to a cartoon, please <A
HREF="mailto:jmr@escomposlinux.org">notify</A> Javier, who would appreciate
hearing from you.
</SMALL>
<!-- *** BEGIN author bio *** -->
<P>&nbsp;
<P>
<!-- *** BEGIN bio *** -->
<!-- P>
<img ALIGN="LEFT" ALT="[BIO]" SRC="../gx/2002/note.png">
<em>
</em>
<br CLEAR="all" -->
<!-- *** END bio *** -->
<!-- *** END author bio *** -->
<!-- *** BEGIN copyright *** -->
<hr>
<CENTER><SMALL><STRONG>
Copyright &copy; 2003, Javier Malonda.
Copying license <A HREF="../copying.html">http://www.linuxgazette.com/copying.html</A><BR>
Published in Issue 94 of <i>Linux Gazette</i>, September 2003
</STRONG></SMALL></CENTER>
<!-- *** END copyright *** -->
<HR>
<TABLE BORDER><TR><TD WIDTH="200">
<A HREF="http://www.linuxgazette.com/">
<IMG ALT="LINUX GAZETTE" SRC="../gx/2002/lglogo_200x41.png"
WIDTH="200" HEIGHT="41" border="0"></A>
<BR CLEAR="all">
<SMALL>...<I>making Linux just a little more fun!</I></SMALL>
</TD><TD WIDTH="380">
<CENTER>
<BIG><BIG><STRONG><FONT COLOR="maroon">From C To Assembly Language</FONT></STRONG></BIG></BIG>
<BR>
<STRONG>By <A HREF="../authors/ramankutty.html">Hiran Ramankutty</A></STRONG>
</CENTER>
</TD></TR>
</TABLE>
<P>
<!-- END header -->
<html>
<body>
<h2><b>1. Overview</b></h2>
<p>
What is a microcomputer system made up of? A microcomputer system is
made up of a <i>microprocessor unit</i> (MPU), a bus system, a memory
subsystem, an I/O subsystem and an interface among all components. A
typical answer one can expect.
</p>
<p>
This is only the hardware side. Every microcomputer system requires a
software so as to direct each of the hardware components while they
are performing their respective tasks. Computer software can be
thought about at system side (system software) and user side (user
software).
</p>
<p>
The user software may include some in-built libraries and user created
libraries in the form of subroutines which may be needed in preparing
programs for execution.
</p>
<p>
The system software may encompass a variety of high-level language
translators, an assembler, a text editor, and several other programs
for aiding in the preparation of other programs. We already know that
there are three levels of programming and they are Machine language,
Assembly language and High-level language.
</p>
<p>
Machine language programs are programs that the computer can
understand and execute directly (think of programming in any
microprocessor kit). Assembler language instructions match machine
language instructions on a more or less one-for-one basis, but are
written using character strings so that they are more easily
understood, and high-level language instructions are much closer to
the English language and are structured so that they naturally
correspond to the way programmers think. Ultimately, an assembler
language or high-level language program must be converted into machine
language by programs called translators. They are referred to as
<i>assembler</i> and <i>compiler</i> or <i>interpreter</i> respectively.
</p>
<p>
Compilers for high-level languages like C/C++ have the ability to
translate high-level language into assembly code. The GNU C and C++
Compiler option of -S will generate an assembly code equivalent to
that of the corresponding source program. Knowing how the most
rudimentary constructs like loops, function calls and variable
declaration are mapped into assembly language is one way to achieve
the goal of mastering C internals. Before proceeding further, you must
make it a point that you are familiar with Computer Architecture and
Intel x86 assembly language to help you follow the material presented
here.
</p>
<h2><b>2. Getting Started</b></h2>
<p>
To begin with, write a small program in C to print <i>hello world</i>
and compile it with -S options. The output is an assembler code for
the input file specified. By default, GCC makes the assembler file
name by replacing the suffix `.c', with `.s'. Try to interpret the few
lines at the end of the assembler file.
</p>
<p>
The 80386 and above family of processors have myriads of registers,
instructions and addressing modes. A basic knowledge about only a few
simple instructions is sufficient to understand the code generated by
the GNU compiler.
</p>
<p>
Generally, any assembly language instruction includes a <i>label</i>, a
<i>mnemonic</i>, and <i>operands</i>. An operand's notation is
sufficient to decipher the operand's addressing mode. The
<i>mnemonics</i> operate on the information contained in the operands.
In fact, assembly language instructions operate on registers and
memory locations. The 80386 family has general purpose registers (32
bit) called <i>eax</i>, <i>ebx</i>, <i>ecx</i> etc. Two registers,
<i>ebp</i> and <i>esp</i> are used for manipulating the stack. A
typical instruction, written in GNU Assembler (GAS) syntax, would look
like this:
</p>
<p></p>
<pre>
movl $10, %eax
</pre>
<p>
This instruction stores the value 10 in the <i>eax</i> register. The
prefix `%' to the register name and `$' to the immediate value are
essential assembler syntax. It is to be noted that not all assemblers
follow the same syntax.
</p>
<p>
Our first assembly language program, stored in a file named
<i>first.s</i> is shown in <b>Listing 1</b>.
</p>
<p></p>
<pre>
<i>#Listing 1</i>
.globl main
main:
movl $20, %eax
ret
</pre>
<p>
This file can be assembled and linked to generate an <i>a.out</i> by
giving the command <i>cc first.s</i>. The extensions `.s' are
identified by the GNU compiler front end <i>cc</i> as assembly
language files and invokes the assembler and linker, skipping the
compilation phase.
</p>
<p>
The first line of the program is a comment. The <i>.globl</i>
assembler directive serves to make the symbol <i>main</i> visible to
the linker. This is vital as your program will be linked with the C
startup library which will contain a call to <i>main</i>. The linker
will complain about 'undefined reference to symbol main' if that line
is omitted (try it). The program simply stores the value 20 in register
<i>eax</i> and returns to the caller.
</p>
<h2><b>3. Arithmetic, Comparison, Looping</b></h2>
<p>
Our next program is <b>Listing 2</b> which computes the factorial of a
number stored in <i>eax</i>. The factorial is stored in <i>ebx</i>.
</p>
<p></p>
<pre>
<i>#Listing 2</i>
.globl main
main:
movl $5, %eax
movl $1, %ebx
L1: cmpl $0, %eax //compare 0 with value in <i>eax</i>
je L2 //jump to L2 if 0==eax (je - jump if equal)
imull %eax, %ebx // ebx = ebx*eax
decl %eax //decrement eax
jmp L1 // unconditional jump to L1
L2: ret
</pre>
<p>
<i>L1</i> and <i>L2</i> are labels. When control flow reaches
<i>L2</i>, <i>ebx</i> would contain the factorial of the number stored
in <i>eax</i>.
</p>
<h2><b>4. Subroutines</b></h2>
<p>
When implementing complicated programs, we split the tasks to be
solved in systematic order. We write subroutines and functions for
each of the tasks which are called when ever required. <b>Listing 3</b>
illustrates subroutine call and return in assembly language programs.
</p>
<p></p>
<pre>
<i>#Listing 3</i>
.globl main
main:
movl $10, %eax
call foo
ret
foo:
addl $5, %eax
ret
</pre>
<p>
The instruction <i>call</i> transfers control to subroutine <i>foo</i>.
The <i>ret</i> instruction in <i>foo</i> transfers control back to the
instruction after the call in <i>main</i>.
</p>
<p>
Generally, each function defines the scope of variables it uses in
each call of the routine. To maintain the scopes of variables you need
space. The stack can be used to maintain values of the variables in
each call of the routine. It is important to know the basics of how
the activation records can be maintained for repeated, recursive calls
or any other possible calls in the execution of the program. Knowing
how to manipulate registers like <i>esp</i> and <i>ebp</i> and making
use of instructions like <i>push</i> and <i>pop</i> which operate on
the stack are central to understanding the subroutine call and return
mechanism.
</p>
<h2><b>5. Using The Stack</b></h2>
<p>
A section of your program's memory is reserved for use as a stack. The
Intel 80386 and above microprocessors contain a register called stack
pointer, <i>esp</i>, which stores the address of the top of stack.
<b>Figure 1</b> below shows three integer values, 49,30 and 72, stored
on the stack (each integer occupying four bytes) with <i>esp</i>
register holding the address of the top of stack.
</p>
<a href="misc/ramankutty/stack1.bmp">Figure 1</a>
<p>
Unlike the stack analogous to a pile of bricks growing up wards, on
Intel machines stack grows down wards. <b>Figure 2</b> shows the stack
layout after the execution of the instruction <i>pushl $15</i>.
</p>
<a href="misc/ramankutty/stack2.bmp">Figure 2</a>
<p>
The stack pointer register is decremented by four and the number 15 is
stored as four bytes at locations 1988, 1989, 1990 and 1991.
</p>
<p>
The instruction <i>popl %eax</i> copies the value at top of stack (four
bytes) to the <i>eax</i> register and increments <i>esp</i> by four.
What if you do not want to copy the value at top of stack to any
register? You just execute the instruction <i>addl $4, %esp</i> which
simply increments the stack pointer.
</p>
<p>
In <b>Listing 3</b>, the instruction <i>call foo</i> pushes the
address of the instruction after the call in the calling program on to
the stack and branches to <i>foo</i>. The subroutine ends with
<i>ret</i> which transfers control to the instruction whose address is
taken from the top of stack. Obviously, the top of stack must contain
a valid return address.
</p>
<h2><b>6. Allocating Space for Local Variables</b></h2>
<p>
It is possible to have a C program manipulating hundreds and thousands
of variables. The assembly code for the corresponding C program will
give you an idea of how the variables are accommodated and how the
registers are used for manipulating the variables without causing any
conflicts in the final result that is to be obtained.
</p>
<p>
The registers are few in number and cannot be used for holding all the
variables in a program. Local variables are allotted space within the
stack. <b>Listing 4</b> shows how it is done.
</p>
<p></p>
<pre>
<i>#Listing 4</i>
.globl main
main:
call foo
ret
foo:
pushl %ebp
movl %esp, %ebp
subl $4, %esp
movl $10, -4(%ebp)
movl %ebp, %esp
popl %ebp
ret
</pre>
<p>
First, the value of the stack pointer is copied to <i>ebp</i>, the base
pointer register. The base pointer is used as a fixed reference to
access other locations on the stack. In the program, <i>ebp</i> may be
used by the caller of <i>foo</i> also, and hence its value is copied
to the stack before it is overwritten with the value of <i>esp</i>.
The instruction <i>subl $4, %esp</i> creates enough space (four bytes)
to hold an integer by decrementing the stack pointer. In the next line,
the value 10 is copied to the four bytes whose address is obtained by
subtracting four from the contents of <i>ebp</i>. The instruction
<i>movl %ebp, %esp</i> restores the stack pointer to the value it had
after executing the first line of <i>foo</i> and <i>popl %ebp</i>
restores the base pointer register. The stack pointer now has the same
value which it had before executing the first line of <i>foo</i>. The
table below displays the contents of registers <i>ebp</i>, <i>esp</i>
and stack locations from 3988 to 3999 at the point of entry into
<i>main</i> and after the execution of every instruction in
<b>Listing 4</b> (except the return from main). We assume that
<i>ebp</i> and <i>esp</i> have values 7000 and 4000 stored in them and
stack locations 3988 to 3999 contain some arbitrary values 219986,
1265789 and 86 before the first instruction in <i>main</i> is executed.
It is also assumed that the address of the instruction after
<i>call foo</i> in <i>main</i> is 30000.
</p>
<p></p>
<a href="misc/ramankutty/table.bmp">Table 1</a>
<h2><b>6. Parameter Passing and Value Return</b></h2>
<p>
The stack can be used for passing parameters to functions. We will
follow a convention (which is used by our C compiler) that the value
stored by a function in the <i>eax</i> register is taken to be the
return value of the function. The calling program passes a parameter to
the callee by pushing its value on the stack. <b>Listing 5</b>
demonstrates this with a simple function called <i>sqr</i>.
</p>
<p></p>
<pre>
<i>#Listing 5</i>
.globl main
main:
movl $12, %ebx
pushl %ebx
call sqr
addl $4, %esp //adjust esp to its value before the push
ret
sqr:
movl 4(%esp), %eax
imull %eax, %eax //compute eax * eax, store result in eax
ret
</pre>
<p>
Read the first line of <i>sqr</i> carefully. The calling function
pushes the content of <i>ebx</i> on the stack and then executes a
<i>call </i> instruction. The call will push the return address on the
stack. So inside <i>sqr</i>, the parameter is accessible at an offset
of four bytes from the top of stack.
</p>
<h2><b>8. Mixing C and Assembler</b></h2>
<p>
<b>Listing 6</b> shows a C program and an assembly language function.
The C function is defined in a file called <i>main.c</i> and the
assembly language function in <i>sqr.s</i>. You compile and link the
files together by typing <i>cc main.c sqr.s</i>.
</p>
<p>
The reverse is also pretty simple. <b>Listing 7</b> demonstrates a C
function print and its assembly language caller.
</p>
<p></p>
<pre>
<i>#Listing 6</i>
//main.c
main()
{
int i = sqr(11);
printf("%d\n",i);
}
//sqr.s
.globl sqr
sqr:
movl 4(%esp), %eax
imull %eax, %eax
ret
</pre>
<p></p>
<pre>
<i>#Listing 7</i>
//print.c
print(int i)
{
printf("%d\n",i);
}
//main.s
.globl main
main:
movl $123, %eax
pushl %eax
call print
addl $4, %esp
ret
</pre>
<h2><b>9. Assembler Output Generated by GNU C</b></h2>
<p>
I guess this much reading is sufficient for understanding the
assembler output produced by <i>gcc</i>. <b>Listing 8</b> shows the
file <i>add.s</i> generated by <i>gcc -S add.c</i>. Note that
<i>add.s</i> has been edited to remove many assembler directives
(mostly for alignments and other things of that sort).
</p>
<p></p>
<pre>
<i>#Listing 8</i>
//add.c
int add(int i,int j)
{
int p = i + j;
return p;
}
//add.s
.globl add
add:
pushl %ebp
movl %esp, %ebp
subl $4, %esp //create space for integer p
movl 8(%ebp),%edx //8(%ebp) refers to i
addl 12(%ebp), %edx //12(%ebp) refers to j
movl %edx, -4(%ebp) //-4(%ebp) refers to p
movl -4(%ebp), %eax //store return value in eax
leave //i.e. to movl %ebp, %esp; popl %ebp ret
</pre>
<p>
The program will make sense upon realizing the C statement
<b>add(10,20)</b> which gets translated into the following assembler
code:
</p>
<p></p>
<pre>
pushl $20
pushl $10
call add
</pre>
<p>
Note that the second parameter is passed first.
</p>
<h2><b>10. Global Variables</b></h2>
<p>
Space is created for local variables on the stack by decrementing the
stack pointer and the allotted space is reclaimed by simply
incrementing the stack pointer. So what is the equivalent GNU C
generated code for global variables? <b>Listing 9</b> provides the
answer.
</p>
<p></p>
<pre>
<i>#Listing 9</i>
//glob.c
int foo = 10;
main()
{
int p foo;
}
//glob.s
.globl foo
foo:
.long 10
.globl main
main:
pushl %ebp
movl %esp,%ebp
subl $4,%esp
movl foo,%eax
movl %eax,-4(%ebp)
leave
ret
</pre>
<p>
The statement <i>foo: .long 10</i> defines a block of 4 bytes named
foo and initializes the block with zero. The <i>.globl foo</i>
directive makes foo accessible from other files. Now try this out.
Change the statement <b>int foo</b> to <b>static int foo</b>. See how
it is represented in the assembly code. You will notice that the
assembler directive <i>.globl</i> is missing. Try this out for
different storage classes (double, long, short, const etc.).
<h2><b>11. System Calls</b></h2>
<p>
Unless a program is just implementing some math algorithms in
assembly, it will deal with such things as getting input, producing
output, and exiting. For this it will need to call on OS services. In
fact, programming in assembly language is quite the same in different
OSes, unless OS services are touched.
</p>
<p>
There are two common ways of performing a system call in Linux:
through the C library (libc) wrapper, or directly.
</p>
<p>
Libc wrappers are made to protect programs from possible system call
convention changes, and to provide POSIX compatible interface if the
kernel lacks it for some call. However, the UNIX kernel is usually
more-or-less POSIX compliant: this means that the syntax of most libc
"system calls" exactly matches the syntax of real kernel system calls
(and vice versa). But the main drawback of throwing libc away is that
one loses several functions that are not just syscall wrappers, like
printf(), malloc() and similar.
</p>
<p>
System calls in Linux are done through int 0x80. Linux differs from
the usual Unix calling convention, and features a "fastcall"
convention for system calls. The system function number is passed in
eax, and arguments are passed through registers, not the stack. There
can be up to six arguments in ebx, ecx, edx, esi, edi, ebp
consequently. If there are more arguments, they are simply passed
though the structure as first argument. The result is returned in eax,
and the stack is not touched at all.
</p>
<p>Consider Listing 10 given below.</p>
<p></p>
<pre>
<i>#Listing 10
#fork.c</i>
#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;sys/types.h&gt;
#include &lt;unistd.h&gt;
int main()
{
fork();
printf("Hello\n");
return 0;
}
</pre>
<p>
Compile this program with the command <i>cc -g fork.c -static</i>. Use
the <i>gdb</i> tool and type the command <i>disassemble fork</i>.
You can see the assembly code used for fork in the program. The
<i>-static</i> is the static linker option of GCC (see man page). You
can test this for other system calls and see how the actual functions
work.
</p>
<p>
There have been several attempts to write an up-to-date documentation
of the Linux system calls and I am not making this another of them.
</p>
<h2><b>11. Inline Assembly Programming</b></h2>
<p>
The GNU C supports the x86 architecture quite well, and includes the
ability to insert assembly code within C programs, such that register
allocation can be either specified or left to GCC. Of course, the
assembly instruction are architecture dependent.
</p>
<p>
The <i>asm</i> instruction allows you to insert assembly instructions
into your C or C++ programs. For example the instruction:
</p>
<p></p>
<pre>
asm ("fsin" : "=t" (answer) : "0" (angle));
</pre>
<p>
is an x86-specific way of coding this C statement:
</p>
<p></p>
<pre>
answer = sin(angle);
</pre>
<p>
You can notice that unlike ordinary assembly code instructions
<i>asm</i> statements permit you to specify input and output operands
using C syntax. <i>Asm</i> statements should not be used
indiscriminately. So, when should we use them?
</p>
<p></p>
<ul>
<li> <i>Asm</i> statements allow your programs to access the computer
hardware directly. This can produce programs that execute quickly. You
can use them when writing operating system code that directly needs to
interact with the hardware. For example, <i>/usr/include/asm/io.h</i>
contains assembly instructions to access input/output ports directly.
<li> Inline assembly instructions also speed up the innermost loops
of the programs. For instance, <i>sine</i> and <i>cosine</i> of the
same angles can be found by <i>fsincos</i> x86 instruction. Probably,
the two listings given below will help you understand this factor
better.
</ul>
<pre>
<i>#Listing 11
#Name : bit-pos-loop.c
#Description : Find bit position using a loop</i>
#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
int main (int argc, char *argv[])
{
long max = atoi (argv[1]);
long number;
long i;
unsigned position;
volatile unsigned result;
for (number = 1; number &lt;= max; ; ++number) {
for (i=(number&gt;&gt;1), position=0; i!=0; ++position)
i &gt;&gt;= 1;
result = position;
}
return 0;
}
</pre>
<p></p>
<pre>
<i>#Listing 12
#Name : bit-pos-asm.c
#Description : Find bit position using bsrl</i>
#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
int main(int argc, char *argv[])
{
long max = atoi(argv[1]);
long number;
unsigned position;
volatile unsigned result;
for (number = 1; number &lt;= max; ; ++number) {
asm("bsrl %1, %0" : "=r" (position) : "r" (number));
result = position;
}
return 0;
}
</pre>
<p>
Compile the two versions with full optimizations as given below:
</p>
<p></p>
<pre>
$ cc -O2 -o bit-pos-loop bit-pos-loop.c
$ cc -O2 -o bit-pos-asm bit-pos-asm.c
</pre>
<p>
Measure the running time for each version by using the time command
and specifying a large value as the command-line argument to make sure
that each version takes at least few seconds to run.
</p>
<p></p>
<pre>
$ time ./bit-pos-loop 250000000
</pre>
<p>and</p>
<p></p>
<pre>
$ time ./bit-pos-asm 250000000
</pre>
<p>
The results will be varying in different machines. However, you will
notice that the version that uses the inline assembly executes a great
deal faster.
</p>
<p>
GCC's optimizer attempts to rearrange and rewrite program' code to
minimize execution time even in the presence of <i>asm</i> expressions.
If the optimizer determines that an <i>asm's</i> output values are
not used, the instruction will be omitted unless the keyword
<i>volatile</i> occurs between <i>asm</i> and its arguments. (As a
special case, GCC will not move an <i>asm</i> without any output
operands outside a loop.) Any <i>asm</i> can be moved in ways that are
difficult to predict, even across jumps. The only way to guarantee a
particular assembly instruction ordering is to include all the
instructions in the same <i>asm</i>.
</p>
<p>
Using <i>asm's</i> can restrict the optimizer's effectiveness because
the compiler does not know the <i>asms'</i> semantics. GCC is forced
to make conservative guesses that may prevent some optimizations.
</p>
<h2><b>12. Exercises</b></h2>
<ol>
<li>Interpret the assembly code for C program in Listing 6. Modify it
for eliminating errors that are obtained when generating assembly code
with -Wall option. Compare the two assembly codes. What changes do you
observe?
<li>Compile several small C programs with and without optimization
options (like -O2). Read the resulting assembly codes and find out
some common optimization tricks used by the compiler.
<li>Interpret assembly code for switch statement.
<li>Compile several small C programs with inline asm statements. What
differences do you observe in assembly codes for such programs.
<li>A nested function is defined inside another function (the
"enclosing function"), such that:
<ul>
<li> the nested function has access to the enclosing function's
variables; and
<li> the nested function is local to the enclosing function, that is,
it can be called from elsewhere unless the enclosing function gives
you a pointer to the nested function.
</ul>
<p></p>
<p>
Nested functions can be useful because they help control the
visibility of a function.
</p>
<p>
Consider <b>Listing 13</b> given below:
</p>
<p></p>
<pre>
<p>
<i>#Listing 13</i>
/* myprint.c */
#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
int main()
{
int i;
void my_print(int k)
{
printf("%d\n",k);
}
scanf("%d",&amp;i);
my_print(i);
return 0;
}
</p></pre>
<p>
Compile this program with <i>cc -S myprint.c</i> and interpret the
assembly code. Also try compiling the program with the command
<i>cc -pedantic myprint.c</i>. What do you observe?
</p>
</ol>
</body>
</html>
<!-- *** BEGIN author bio *** -->
<P>&nbsp;
<P>
<!-- *** BEGIN bio *** -->
<P>
<img ALIGN="LEFT" ALT="[BIO]" SRC="../gx/2002/note.png">
<em>
I have just given my final year B.Tech examinations in Computer Science and
Engineering and a native of Kerala, India.
</em>
<br CLEAR="all">
<!-- *** END bio *** -->
<!-- *** END author bio *** -->
<!-- *** BEGIN copyright *** -->
<hr>
<CENTER><SMALL><STRONG>
Copyright &copy; 2003, Hiran Ramankutty.
Copying license <A HREF="../copying.html">http://www.linuxgazette.com/copying.html</A><BR>
Published in Issue 94 of <i>Linux Gazette</i>, September 2003
</STRONG></SMALL></CENTER>
<!-- *** END copyright *** -->
<HR>
<TABLE BORDER><TR><TD WIDTH="200">
<A HREF="http://www.linuxgazette.com/">
<IMG ALT="LINUX GAZETTE" SRC="../gx/2002/lglogo_200x41.png"
WIDTH="200" HEIGHT="41" border="0"></A>
<BR CLEAR="all">
<SMALL>...<I>making Linux just a little more fun!</I></SMALL>
</TD><TD WIDTH="380">
<CENTER>
<BIG><BIG><STRONG><FONT COLOR="maroon">Play Encoded DVDs in Xine</FONT></STRONG></BIG></BIG>
<BR>
<STRONG>By <A HREF="../authors/kolp.html">LeaAnne Kolp</A></STRONG>
</CENTER>
</TD></TR>
</TABLE>
<P>
<!-- END header -->
<h2>Play Encoded DVDs in Xine</h2>
<p>First of all, you'll need to download the plugins.</p>
<p>xine_d4d_plugin-0.3.2.tar.gz</p>
<p>xine-d5d-0.2.7.tgz</p>
<p>xine-lib-0.9.12.tar</p>
<p>xine-ui-0.9.12.tar</p>
<p>These plugins will ONLY work with the xine-lib and xine-ui-0.9.12.
If you get 0.9.13 it will NOT work.</p>
<p>After you download those, switch to root</p>
<p><PRE>[tux@linux tux]$ su</PRE></p>
<p><PRE>Password: *****</PRE></p>
<p>Then you'll have to move the files that you just downloaded to your
/root/ directory. Do this by typing in the <br>
following at the command promt.</p>
<p><PRE>mv *.tar.gz /root/</PRE></p>
<p>If that doesn't work, then just type out the following:</p>
<p><PRE>mv xine-lib-0.9.12.tar.gz /root/</PRE></p>
<p>Do this for each of the files. After you get that done, then switch
to your /root/ directory by typing in the following:</p>
<p><PRE>cd /root/ type: ls</PRE></p>
<p>And you'll get a listing of all the files in your /root/ directory.
Now for the good part :)</p>
<p>Now to gunzip and untar it :)</p>
<p>To do this, type in the following:</p>
<p><PRE>gunzip -d xine-lib-0.9.12.tar.gz</PRE></p>
<p>Switch to that directory by typing the following:</p>
<p><PRE>cd xine-lib-0.9.12</PRE></p>
<p>Now type in: <PRE>ls</PRE></p>
<p>Now that you're in the directory, you'll have a README file and
INSTALL file. ALWAYS read the README file. <br>
No matter how many times you've done this before, something might have
changed. If the README doesn't tell <br>
you anything read the INSTALL file.</p>
<p>To do this, type in:</p>
<p><PRE>more README </PRE>(just like it is in the directory, if you don't type it
identical, it won'taccess it)</p>
<p><PRE>more INSTALL</PRE></p>
<p>Normally, a typical installation is done by typing in these
commands:</p>
<p><PRE>./configure
make
make check
make install</PRE></p>
<p>Again, always read the README. Each distribution of Linux is
different and therefore the installation <br>
instructions could be different.</p>
<p>Keep repeating the above steps until all 4 files are installed.</p>
<p>Then type in:</p>
<p><PRE>tar -xvf xine-lib.0.9.12.tar</PRE></p>
<p>Now type in: <PRE>ls</PRE></p>
<p>You'll see a directory (in dark blue) with the name:</p>
<p><PRE>xine-lib-0.9.12</PRE></p>
<p>Then type in the following to update your drive:</p>
<p><PRE>updatedb</PRE></p>
<p>That could take awhile depending on your drive. When that's done,
you'll have to locate xine.</p>
<p>To do so, type in the following:</p>
<p><PRE>locate xine</PRE></p>
<p>It usually puts it in /usr/local/bin/ but to be on the safe side,
locate it. :)</p>
<p>Once you have it located, until you add it to your menus, type in
the directoryof where it was. <br>
So if it was in /usr/local/bin/xine you would type in:
/usr/local/bin/xine</p>
<p>That would start the program running if that's where it was located.</p>
<p>Now here's the tricky part that you'll have to play with and figure
out on your own. When xine comes up, you'll <br>
see the d4d and d5d buttons at the bottom. When you put a dvd into the
dvdrom drive you'll have to click on either the <br>
d4d or d5d button to get it to play the encoded dvd.</p>
<p>Unfortunately, I don't know which one will work with the dvd you put
in.</p>
<p>Some dvds take the d5d, others take the d4d, you'll just have to
play around with it and experiment to find the one that's right. <br>
What I've started doing is when I put a dvd in and find out which
plugin works (i.e. d4d, d5d) I write it down, so I know and <br>
I don't have to play games with it to figure it out! :)</p>
<p>Congratulations! You've just gotten the plugins to work and now you
can sit back and enjoy the movie!</p>
<!-- *** BEGIN author bio *** -->
<P>&nbsp;
<P>
<!-- *** BEGIN bio *** -->
<P>
<img ALIGN="LEFT" ALT="[BIO]" SRC="../gx/2002/note.png">
<em>
Hi, my name is LeaAnne and I've been Windows Free since March
2003.
</em>
<br CLEAR="all">
<!-- *** END bio *** -->
<!-- *** END author bio *** -->
<!-- *** BEGIN copyright *** -->
<hr>
<CENTER><SMALL><STRONG>
Copyright &copy; 2003, LeaAnne Kolp.
Copying license <A HREF="../copying.html">http://www.linuxgazette.com/copying.html</A><BR>
Published in Issue 94 of <i>Linux Gazette</i>, September 2003
</STRONG></SMALL></CENTER>
<!-- *** END copyright *** -->
<HR>
<TABLE BORDER><TR><TD WIDTH="200">
<A HREF="http://www.linuxgazette.com/">
<IMG ALT="LINUX GAZETTE" SRC="../gx/2002/lglogo_200x41.png"
WIDTH="200" HEIGHT="41" border="0"></A>
<BR CLEAR="all">
<SMALL>...<I>making Linux just a little more fun!</I></SMALL>
</TD><TD WIDTH="380">
<CENTER>
<BIG><BIG><STRONG><FONT COLOR="maroon">Under /etc (A Simple Guide)</FONT></STRONG></BIG></BIG>
<BR>
<STRONG>By <A HREF="../authors/lalji.html">AmirAli Lalji</A></STRONG>
</CENTER>
</TD></TR>
</TABLE>
<P>
<!-- END header -->
<H2>Abstract:</H2>
<P>This article is focused towards Linux newbies providing them with a basic
understanding of /etc sub-directory.</P>
<H2>Introduction</H2>
<P>Newcomers to Linux, especially those coming from the Windows background,
often find files in the /etc directory difficult to understand. In this
article I will give a brief explanation of some of these files and their use.
But, before we dive into the /etc directory I would like to point out that
changes to some of these files can render your system unstable or in some
circumstances unbootable. I cannot emphasize this enough that you should make a
backup of the file(s) before making any changes. </P>
<H2>Lets Dive In....</H2>
<b>/etc/exports</b>
<P>This file contains the partition configuration to load NFS (Network File Systems).
It tells how partitions are mounted and shared with other Linux/UNIX systems.</P>
<b>/etc/ftpusers</b>
<P>This file contains login names of users who are not allowed to login via FTP.
It is recommended to add user root in this file for security.</P>
<b>/etc/fstab</b>
<P>This file automatically mounts filesystems which are spread accross multiple
drives or seperate partitions. This file is checked when the system boots and
filesystems mounted.</P>
<b>/etc/hosts.[allow, deny]</b>
<P>You can control access to your network by using these files. You can add hosts
to hosts.allow file to which you want to grant access to your network or add
hosts to hosts.deny to which you dont.</P>
<b>/etc/inetd.conf or /etc/xinetd.conf</b>
<P>The inetd file can be called the father of networking services. This file is
responsible for starting services like FTP, TELNET etc. Some Linux distributions
come with xinetd.conf which stands for Extended Internet Services Daemon, which
provides all the functionnalities and capabilities of inetd but extends them
further.</P>
<P>It is advisable to comment services which you do not use.</P>
<b>/etc/inittab</b>
<P>This file describes what takes place or which processes are started at bootup or
at different runlevels. Runlevel is defined as a state in which the Linux box is
currently in. Linux has 7 runlevels from 0-6.</P>
<b>/etc/motd</b>
<P>This file which stands for "message of the day" is executed and its contents
displayed after a successful login.</P>
<b>/etc/passwd</b>
<P>This file contains user information. Whenever a new user is added, an entry is
added to this file containing the loginname, password etc. This file is readable
by everyone on the system. If the password field contains "x" than encrypted
passwords are stored in /etc/shadow file which is only accessible by user root.</P>
<b>/etc/profile</b>
<P>When a user logs in a number of configuration files are executed, including
/etc/profile. This file contains settings and global startup information for
bash shell.</P>
<b>/etc/services</b>
<P>This file works in conjunction with /etc/inetd.conf or /etc/xinetd.conf files
(see above). This file determines which port a service mentioned in inetd.conf
is to use, for eg. FTP/21, TELNET/23 etc.</P>
<b>/etc/securetty</b>
<P>This file lists ttys from which root is allowed to login. For security reasons
it is recommended to keep just tty1 for root login.</P>
<b>/etc/shells</b>
<P>This file contains names of all shells installed in the system with their full
path names.</P>
<H2>In the end....</H2>
<P>I hope you enjoyed this article and hope it helped in understanding the /etc
directory. You might find other subdirectories beneath the /etc directory which
are application specific for eg. /etc/httpd, /etc/sendmail are
for apache and sendmail respectively.</P>
<P>If you have any comments or suggestions, please feel free to email me at
aalalji@bcs.org.uk</P>
<!-- *** BEGIN author bio *** -->
<P>&nbsp;
<P>
<!-- *** BEGIN bio *** -->
<P>
<img ALIGN="LEFT" ALT="[BIO]" SRC="../gx/2002/note.png">
<em>
AmirAli Lalji is a System Administrator/DBA and lives and works in UK
and Portugal.
</em>
<br CLEAR="all">
<!-- *** END bio *** -->
<!-- *** END author bio *** -->
<!-- *** BEGIN copyright *** -->
<hr>
<CENTER><SMALL><STRONG>
Copyright &copy; 2003, AmirAli Lalji.
Copying license <A HREF="../copying.html">http://www.linuxgazette.com/copying.html</A><BR>
Published in Issue 94 of <i>Linux Gazette</i>, September 2003
</STRONG></SMALL></CENTER>
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<TABLE BORDER><TR><TD WIDTH="200">
<A HREF="http://www.linuxgazette.com/">
<IMG ALT="LINUX GAZETTE" SRC="../gx/2002/lglogo_200x41.png"
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<BR CLEAR="all">
<SMALL>...<I>making Linux just a little more fun!</I></SMALL>
</TD><TD WIDTH="380">
<CENTER>
<BIG><BIG><STRONG><FONT COLOR="maroon">Linux based Radio Timeshifting</FONT></STRONG></BIG></BIG>
<BR>
<STRONG>By <A HREF="../authors/yan-fa.html">Yan-Fa Li</A></STRONG>
</CENTER>
</TD></TR>
</TABLE>
<P>
<!-- END header -->
<h2>1.0 Introduction</h2>
Like a lot of gadget freaks I have a Tivo in the living room. Now while
one could argue that thanks to an infestation of Clear Channel there
really isn't much of interest to listen to anymore, there is still
public radio. I listen to a lot of NPR while driving in the car, and I
often find I miss programs I find interesting, or worse, I arrive at my
destination and have to stop listening. So naturally I'd been thinking
for some months now, why not invest some time and effort and look at
how to build a PRR (Personal Radio Recorder).
<p>
Obviously I'm not the only one. There are now some commercial
offerings like <a href="http://radioyourway.com/">this</a>,
and quite a few people appear to have done <a
href="http://gary.burd.info/content/articles/fmcapture.html">projects</a>
to timeshift radio. There's even a <a
href="http://osl.iu.edu/~tveldhui/radio/">how-to</a>,
and slashdot had a big thread about it <a
href="http://ask.slashdot.org/askslashdot/03/01/10/1053222.shtml?tid=137">recently</a>.
<p>
These notes are all based on using RedHat Linux 7.3, so your mileage may
vary if using something like SuSe or Mandrake. I believe they already
come with Alsa, for example, so you can skip those parts that involve
installing them if your system already comes pre-installed with it.
<p>
<h3>The Basics</h3>
Pretty much all the projects I've seen out there have the same things
in common. They use one of three kinds of setup:
<p>
<ul>
<li>A regular analog radio tuned to a single station connected
to the line-in of your PC. Pros: really cheap and easy.
Cons: single station only.
<li>A programmable tuner card with radio function and built
in audio device. Pros: self contained solution, no sound
card required. Cons: PCs are quite noisy electrically;
perhaps a lack of Linux drivers.
<li>An external programmable Radio and the line-in, like the popular
but discontinued DSB-R100 radio from D-link. Pros: programmable
by the PC; replaceable antenna; outside of the computer. Cons:
possible lack of drivers and potentially more expensive than the
other two options.
</ul>
Naturally I picked the USB radio, since I wanted the flexibility of being
able to replace the radio easily, and knew that drivers already existed
in the Linux kernel for this device under the Video For Linux APIs.
<p>
<h2>3. Architecture</h2>
I had a few requirements:
<ol>
<li> Output straight to mp3, and avoid creating any intermediate
wave files. Two hours of Prairie Home Companion, for example,
would be 1.2GB as 44KHz wave files, so this is definitely
something to be avoided.
<li> Decent ID3 tags so the files had some useful info contained
within them rather than just in the filename.
<li> An automated system of reaping the files at regular intervals
to avoid eating up huge amounts of disk. NPR is highly
topical and current and generally not something I want to
archive long term.
</ol>
<p>
The basic capture system ended up looking like this:
<pre>
Alsa HW Interface -&gt [ ecasound ] -&gt &lt Wav Stream &gt -&gt [ lame encoder ] -&gt &lt mp3 &gt
</pre>
Nice and simple. It just requires a little syntactic sugar to hold
it all together. Since I wanted to encode VBR mp3s on the fly I had a
few worries about CPU usage. I also planned installing it on my main
file server since it's always on and therefore an ideal candidate.
Using an 850MHz celeron, my tests showed the load to be about 40-50%
while capturing and encoding. This still left plenty of CPU for other
tasks like serving files, ssh and http.
<p>
Your mileage will of course vary if you're running X for example, which
notoriously causes skipping with sound cards. However, since my system
is a dedicated file server I've long stopped running a GUI on it. It
never became an issue, but keep it in mind for your target system. <p>
<h3>Encoding FM in real-time as MP3</h3>
A little googling got me a wealth of excellent information about FM
mp3 encoding. Firstly, FM has a hard cut off for all frequencies above
15KHz at the transmitter, so any information above that can be safely
ignored while encoding; secondly, the optimal bitrates for FM appear
to be somewhere between 96 and 112kbits, since it's mostly voice with
only a modicum of music and we're already saving 5KHz in the frequency
range anyway. We therefore have more than enough bits remaining to get
a faithful encoding. Thirdly, since I was planning on using Lame encoder,
joint stereo was a must. Not only is the joint stereo mode of Lame
excellent, but it also leaves more bits for the encoding.
<h3>Hardware Constraints</h3>
At a bare minimum, I wouldn't recommend anything slower than a 450MHz
Pentium III for this task, though if you are willing to switch to Average
Bit Rate and a slightly lower encoding rate from the one I've used, you
could possibly get away with a well tuned 350MHz PII. Having a disk
on the system itself is also optional, as it only needs to keep up with
~112kbps of data plus network overhead, so one could create a completely
diskless system that booted off the network or a flash card which dumped
all its recordings back to the network.
<p>
Check out <a href="http://compgeeks.com">compgeeks</a> or <a
href="http://computersurplusoutlet.com">CSO</a> for low end systems
which would be suitable for this duty.
<p>
<h2>4.0 Recording Audio Under Linux</h2>
This is actually a bigger challenge than it seems. While a large number
of audio cards are supported by Linux for playback, not very many are all
that great for recording. A great source of information can be found
at the Alsa Project <a href="http://www.alsa-project.org/alsa-doc/">web
site</a>. Having already used Alsa on a number of systems and projects
previously, I decided to use it for the PRR project. And don't forget,
it's the future of Linux audio, as it's already in the 2.6 kernels.
<p>
The next problem is figuring out what to use to do
the actual recording. After looking at a variety of
solutions such as sox and alsarecord, I settled on using <a
href="http://www.wakkanet.fi/~kaiv/ecasound/">Ecasound</a>. While it's
probably overkill for this project, some of the features I liked were
the built-in audio conversion routines, the ability to specify realtime
scheduling under Linux if run by root, and support for writing data to
stdout. Audio is really a real-time sort of task with hard requirements
on meeting certain scheduling goals, so being able to specify this was
a big plus for Ecasound. Unix pipes also avoids the creation of large
temporary data files keeping disk requirements down to manageable levels.
<p>
<h3>Preparing to Set Up Alsa Sound System</h3>
First things first, identify what kind of sound card you have and
figure out whether it's supported by Alsa. As I said earlier, not all
audio cards are very good for recording. Interestingly enough, the sound
card I ended up using is one of the most inexpensive available and yet
it works quite well. <p>
I ended up using a <a
href="http://alsa-project.org/alsa-doc/doc-php/template.php3?company=Hercules&card=Game+Fortissimo+II&chip=CS4624&module=cs46xx">
Cirrus Logic 46XX</a> (Hercules Fortissmo) series card. I picked one
these up in the sfbay area for ~35USD at retail. I'm pretty sure they're
not much more than that elsewhere. Alsa has pretty good support for
them and for FM recording they work just fine. I had started out with a
CMI8738, an even cheaper card at around ~20USD, but I could not make it
record audio without a horrible whine and very poor input gain. It was
just fine for playback, but pretty much useless as a recording device.
<p>
Detailed instructions for setting up Alsa are on their website listed
card by card. But here are a few notes before you start. Firstly, Alsa
really needs the kernel source you are compiling against and your running
kernel to be the same. So for example, on a typical RedHat installation,
say 2.4.18-26.7, you would need the same kernel sources installed in
your <code>/usr/src/linux-2.4/</code> directory. By default, this is
not the case, because RedHat specifically renames the kernel sources to
use the extra version string "custom".
<p>
To avoid this problem just re-compile, re-install and boot your new
redhat kernel before attempting to install Alsa. If you don't know how
to do this there are lot of good instructions on the net and I suggest
you look some up before proceeding. If you want the default RedHat
options, simply use something like:
<pre>
cd /usr/src/linux-2.4
make mrproper && \
make oldconfig && \
make dep clean bzImage modules MAKE='make -j2'
</pre>
This will rebuild your kernel sources. You will need to install this
and reboot using it. How you do that depends on whether you're using lilo or
grub, and is beyond the scope of these instructions.
<h3>Additional Build Notes For RedHat Kernel Users</h3>
There's also a problem which seems to happen on RedHat 2.4.20 kernels, which
is quite infruriating. I suspect it's because of all the scheduler
patches they've been packporting from the 2.5 series. Anyway, whenever
you run configure it deletes the file include/linux/workqueue.h from the
working directory. This has the unfortunate side effect of letting the
compile proceed cleanly, but refuse to load because of unknown symbols.
Most annoying. The fix is simple. Run configure, and before running
make once again to compile, un-tar the workqueue.h file from the tarball
again. Something like:
<pre>
tar jxvf alsa-driver-0.9.5.tar.bz2 alsa-driver-0.9.5/include/linux/workqueue.h
</pre>
works for the 0.9.5 release. This will prevent the dreaded complaints about
being unable to install modules due to failed dependencies.
<h3>Building and Installing Alsa</h3>
Assuming you've got your new kernel running, download the Alsa drivers
package, and compile and install it as root. Next, download the Alsa
library package, compile and install this. Finally, at a bare minimum
you'll need the Alsa Utils, otherwise you won't be able to do anything
useful like unmute the audio. Tools and OSS compat are nice to have
but not required at this point.
<p>
As an additional note, by default, recent versions of Alsa install
themselves in the default system paths. Older versions installed
themselves in /usr/local, and on RedHat systems this would cause problems
because the dynamic loader wasn't configured to look there for libraries.
This would cause configure scripts to fail to find libraries and
generally not compile. This is actually pretty easy to fix, just
add the /usr/local/lib path to /etc/ld.so.conf and re-run ldconfig.
This will update your ld cache and also dynamic libs that have been
installed there to run. FYI, this is also one of the main reasons why
a lot of open source packages fail to compile on RedHat systems.
<p>
The new drivers will install in your currently running kernel directory.
You will need to reconfigure your modules.conf to reflect the new sound
card set up. This normally involves removing the entries added by kudzu,
or disabling them using a '#' sign and then adding the new driver
entries. Here's the one from my CS46XX setup:
<pre>
# ALSA portion
alias char-major-116 snd cards_limit=1 device_mode=0660
post-install snd alsactl restore
alias snd-card-0 snd-cs46xx
# module options
# OSS/Free portion
alias char-major-14 soundcore
alias sound-slot-0 snd-card-0
# card #1
alias sound-service-0-0 snd-mixer-oss
alias sound-service-0-1 snd-seq-oss
alias sound-service-0-3 snd-pcm-oss
alias sound-service-0-8 snd-seq-oss
alias sound-service-0-12 snd-pcm-oss
</pre>
Notice the post-install directive. This lets you restore audio settings
on reboots as soon as the driver loads. You can also achieve this by
modifying the <code>/etc/rc.local</code> too, but I like this way better
in case I need to unload the driver. You can also add a pre-remove
directive if you like to save any settings you may have changed before
unloading the sound modules. I prefer to restore to known defaults.
<p>
Next we need to add an entry to the <code>rc.local</code> file. For
whatever reason, the OSS emulation drivers don't load automatically. KDE
complains for example when starting artsd because the sound system hasn't
initialized while it's trying to load. You can force OSS emulation to
pre-load by adding:
<pre>
modprobe snd-pcm-oss
setpci -s 01:09 latency_timer=60
</pre>
to the end of rc.local. The first entry loads the pcm oss driver and
keeps apps which depend on OSS being there to stay none the wiser.
The second entry adjusts the PCI timers for the sound card to give it
a little more time on the bus; that part is optional. I find tweaking
the PCI bus helps avoid pops and clicks in the audio. If you do choose
to tweak your PCI latency this way, remember to use lspci
to find the correct device number for your card. The one listed here
is for my system bus and will likely be different on your system.
<p>
It's probably easiest at this point just to just reboot one more time,
however if you're confident about what you're doing, manually remove
the old OSS audio drivers using <code>rmmod</code> and do a
<pre>modprobe snd-pcm-oss</pre>
Follow up with a <code>lsmod</code> and you should see a lot of bright
and shiny new alsa drivers loaded:
<pre>
Module Size Used by Not tainted
snd-pcm-oss 45668 0
snd-mixer-oss 16536 0 [snd-pcm-oss]
snd-cs46xx 79156 0 (autoclean)
snd-rawmidi 18656 0 (autoclean) [snd-cs46xx]
snd-seq-device 6316 0 (autoclean) [snd-rawmidi]
snd-ac97-codec 44640 0 (autoclean) [snd-cs46xx]
snd-pcm 83264 0 (autoclean) [snd-pcm-oss snd-cs46xx]
snd-timer 19560 0 (autoclean) [snd-pcm]
snd-page-alloc 8520 0 (autoclean) [snd-cs46xx snd-pcm]
gameport 3412 0 (autoclean) [snd-cs46xx]
snd 43140 0 [snd-pcm-oss snd-mixer-oss snd-cs46xx snd-rawmidi snd-seq-device snd-ac97-codec snd-pcm snd-timer]
soundcore 6532 6 [snd]
</pre>
This is an excerpt from a working system. Test it by playing some audio,
anything you have handy will do, like mpg123 for example. Though on a
RedHat system, you'll actually have to download and compile and install
it yourself since they no longer ship mpeg decoders due to patent issues
with Fraunhofer and Philips.
<h2>5.0 Additional Packages to Downloaded</h2>
<h3>Download and Compile ECASOUND</h3>
Since you now have an installed and working alsa sound system, you do have
it working, don't you ? It is now a good time to get ecasound downloaded and
running.
I did my initial implementation using 2.2.1, but I recently upgraded
to 2.2.3 as it seems to have a lot of bugfixes specifically for use with
Alsa. Building it should be fairly straightforward, since it's GNU
autoconf based. Just follow the INSTALL instructions.
<p>
If you want a slightly more optimized build, and you're using a version
of GCC that supports more advanced x86 optimizations, (gcc 3.2 or higher),
I would recommend the following configure line on an PII and above system.
This especially includes the new FPGA2 Celerons.
<pre>
CXXFLAGS='-O2 -march=i686' CFLAGS='-O2 -march=i686' ./configure
</pre>
Or the even more aggressive:
<pre>
CXXFLAGS='-O2 -march=i686 -msse -mmmx' CFLAGS='-O2 -march=i686 -mmmx -msse' ./configure
</pre>
However, be warned this second version may not compile correctly and could
cause more problems than it's worth. On the other hand, it probably
wouldn't hurt to at least give it a try and see if it makes a difference
on your system. In my particular case I see gains in the 2-4% range
with these optimizations.
<h3>Download and Compile Lame</h3>
Now download Lame 3.93.1 and compile that. It's also gnu configure based
so you can use the same flags as we used above. Install it.
I'll also recommend downloading and installing your favorite
mp3 player such as <a href="xmms.org">xmms</a> or <a
href="http://mpg321.sourceforge.net">mpg321</a> as it will be useful
while testing the installation.
<h2>6.0 Configuring The Recording Devices</h2>
This is probably the hardest part of getting this all running. I found
the easiest thing to do was set the volumes before the recording was
going, using the <code>alsamixer</code> tool. It's a curses based
program that lets you adjust sliders for various audio devices and
lets you take a trial and error approach to your particular sound card.
The basic trick is to put the devices you are interested in capturing
from, into capture mode. If anyone has better information on how to
configure this using a command line interface, please drop me a line.
<p>
If you go into the <code>alsamixer</code> interface you'll see a group of
sliders that have values from 0 to 100. Bars which have 6 hyphens above
them are potential capture sources. Because each sound card appears to
have slightly different DACs it's not always clear which ones to activate
to enable recording. <p>
Using a combination of trial and error and <code>ecasound</code>, I was
able to test which devices were capable of recording. Having a pair
of speakers hooked up to the speaker out at this point is very useful,
but headphones would be just as useful at this point too. Typically you
want line-in device. Crank up the volume to around 70%. If you're using
a Video 4 Linux radio you can use the 'radio' util to tune in and turn
on the radio device giving you a source of audio. The Dlink radio is a
line device, meaning it has fixed volume so how loud it sounds will be
directly related to how loud you set the line-in volume.
<P>
If you've hooked it up correctly to the line-in of your sound card
you should now hear some audio. Adjust the volume until it doesn't
sound distorted. Distorted audio will a) sound horrible and b) make
your mp3s sound really crappy. Just play it by ear (sic), and get it to
where it sounds reasonably clear and undistorted. Remember it's FM so
it's already lost about 5KHz of fidelity from being converted, so don't
expect miracles. You may need to look for sources of noise and reposition
your antenna. This will vary from installation to installation.
<h3>Notes on Noise</h3>
Because the source is analog, you really need to pay close attention to
sources of electrical noise, devices such as other computers or monitors
are electrically very noisy. For example, I recently discovered that I
was getting an annoying pulsing static sound from my setup. Turns out
the routing of the audio cable was a little too close to power cords.
A simple re-route solved the problem, but as with a lot of audio you
have to do regular sound checks to make sure you haven't introduced a
new source of interference.
<h2>7.0 Gluing it all together</h2>
So now we have the basic infrastructure going, we need to do some simple
glue scripting to make it all work together. I wrote a couple of
simple scripts to do the functions I needed. The first one is to do
the actual recording. It's started via cron jobs. It simply invokes
all the programs in a big fat pipe with ecasound at the head and lame
at the tail. Works quite well. The name of the file to be created and
any pertinent parameters are passed in via Cron. It's written in bash
and is quite easy to understand.
<h3>Recordshow2: the capture script</h3>
<pre>
#!/bin/bash
echo "Recordshow2 (c)2003 Yan-Fa Li (yanfali@best.com) under GNU LGPL"
# FREQUENCY TIMEINMINS "PROGRAM NAME"
#set -x
tune_channel()
{
echo -n "Tuning to FM Channel $1..."
# Reset and Turn on and Tune Radio
$RADIO -qm 2>/dev/null && sleep 1 && $RADIO -qf $1
}
record_program()
{
echo "Recording $TITLE for $1 Minutes ($TIME seconds) to:"
echo -e "\t$FILENAME"
# Record and Pipe to Lame
TITLE2=${TITLE#*/}
$ARECORD $APARMS | $LAME $LPARMS - "$FILENAME" \
--tt "$TITLE2 on $DATE" \
--ta "KQED/NPR" \
--ty `date +"%Y"` \
--tg 101 \
--tc "$COMMENT"
if [ $? -ne 0 ]
then
echo -n "Error Recording - Check the Soundcard Isn't Recording"
echo " Already"
turn_radio_off
exit 1
fi
}
fix_permissions()
{
# Correct Permissions
if [ -f "$FILENAME" ]
then
chown $OWNER "$FILENAME"
chmod 664 "$FILENAME"
fi
}
turn_radio_off()
{
echo -n "Turning off Radio..."
# Turn off Radio
$RADIO -qm
}
#
# Main Program
#
# Arg Check
if [ $# -ne 3 ]
then
echo "usage: `basename $0` FREQUENCY TIME_IN_MINS \"NAME_OF_PROGRAM\""
exit -1
fi
DEST=/mnt/music/radio
declare -i TIME=$2
TIME=TIME*60
OWNER="yan:music"
RADIO=/usr/bin/radio
ARECORD=/usr/local/bin/ecasound
APARMS="-b 512 -i alsahw,default -o:stdout -t $TIME"
LAME=/usr/local/bin/lame
LPARMS="-r -x -mj -s44.1" # required for ecasound
# -r raw pcm input
# -x swap bytes
# -mj join stereo
# -s incoming sample rate
LPARMS=$LPARMS" -V5 --vbr-new -q0 -b112 --lowpass 15 --cwlimit 10"
# Thanks to: http://www.jthz.com/mp3/ for the settings
# -V5 encoding speed
# --vbr-new
# -q0 highest quality
# -b112 bitrate of 112Kbps
# --lowpass 15 filter all frequencies above 15KHz (FM cutoff)
# --cwlimit 10 acoustic model
DATE=`date +"%a %b %d %Y (%k:%M)"`
SIMPLEDATE=`date +"%Y-%m-%d-%a"`
FILENAME="$DEST/$3-$SIMPLEDATE.mp3"
TITLE="$3"
COMMENT="$1 MHz"
echo "`basename $0`: Recording Started on "$DATE
# Call it twice to avoid radio coming up mute
tune_channel $1
tune_channel $1
record_program $2
fix_permissions
turn_radio_off
echo "`basename $0`: Recording Ended on "`date +"%a %b %e, %Y %k:%M"`
</pre>
<h3>Example Crontab</h3>
<pre>
# usage: recordshow2 FREQUENCY TIME_IN_MINS "NAME_OF_PROGRAM"
# leave a minute at the end otherwise you'll overlap the audio
# device and fail to record
#
# Weekdays
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin:/etc/radio
MAILTO=root
HOME=/
# Daily
0 9 * * Mon-Fri recordshow2 88.5 59 "Forum/Forum H1"
0 10 * * Mon-Fri recordshow2 88.5 59 "Forum/Forum H2"
0 11 * * Mon-Fri recordshow2 88.5 59 "Talk of the Nation/Talk Of The Nation H1"
0 12 * * Mon-Fri recordshow2 88.5 59 "Talk of the Nation/Talk Of The Nation H2"
0 13 * * Mon-Fri recordshow2 88.5 59 "Fresh Air/Fresh Air"
0 16 * * Mon-Fri recordshow2 88.5 29 "Market Place/Marketplace"
30 16 * * Mon-Fri recordshow2 88.5 119 "All Things Considered/All Things Considered"
0 21 * * Mon-Fri recordshow2 88.5 59 "BBC World Service/BBC World Service"
# Weekly Recordings
# Thursday
30 18 * * Thu recordshow2 88.5 29 "Pacific Time/Pacific Time"
# Saturday
0 11 * * Sat recordshow2 88.5 59 "WaitWait/Wait Wait Don't Tell Me"
0 12 * * Sat recordshow2 88.5 59 "This American Life/This American Life"
0 18 * * Sat recordshow2 88.5 119 "Prarie Home Companion/Prarie Home Companion"
# Sunday - in case you messed up saturday
# Sunday
0 11 * * Sun recordshow2 88.5 119 "Prarie Home Companion/Prarie Home Companion"
# Maintenance
0 1 * * Sun weekly_file_cleanup.rb
</pre>
<h3>File Administration</h3>
The second script is more of a util script. Remember my requirement
about automatically removing files after a certain time ? What this script
does is that it scans the date when the file was created and after a
predetermined time, two weeks in my case, it deletes them. I used ruby,
because I was learning it and it actually made writing the program
quite easy. Go figure. Feel free to re-write it in bash, but it really
was much easier to write it in ruby. See for yourself.
<p>
Because there are some recordings I don't ever want to delete, usually
weekly programs, I added the ability to ignore a directory by simply
writing the file .donotreap into the directory. It'll bail on this
directory if it finds it. As a secondary safe guard it will also only
delete mp3 files. Everything else will be ignored. It's not fancy but
it works quite well.
<pre>
#!/usr/bin/ruby -w
=begin
Simple script to clean up the Timeshifted Radio Directories
Looks for files more than two weeks old and removes them
=end
puts "Timeshifted Radio File Cleaner v0.1"
puts "(c) 2003 Yan-Fa Li (yanfali@best.com) under GNU LGPL"
Dir.chdir("/mnt/raid5/music/radio")
TWOWEEKS = 60 * 60 * 24 * 7 * 2
file_list=Dir["**"]
# Find All Directories
dir_list = []
file_list.each { |x| dir_list << x if File.ftype(x) == "directory" }
topdir = Dir.pwd
# Recurse through all directories
dir_list.each do |x|
Dir.chdir(topdir + "/" + x)
# Do Not Reap Flagged Directories
next if File.zero?(".donotreap")
puts "Entering Directory: #{x}"
# Build File List and Filter on name mp3
file_list=Dir["**"]
puts "\tFound #{file_list.length} Files Total"
file_list.each { |y| file_list.delete(y) if not y.include?("mp3") }
puts "\tFound #{file_list.length} MP3 Files"
# Find Files Older than 2 Weeks
del_list = []
file_list.each { |y|
del_list << y if (Time.now - File.stat(y).mtime) > TWOWEEKS }
puts "\t#{del_list.length} Files Scheduled For Deletion"
next if del_list.length == 0
del_list.each { |z| File.delete(z) }
end
</pre>
<h2>8.0 Bugs and Things To Do</h2>
One recurring problem which I have not been able to fix is that
occasionally the recording will be skewed and sound slightly off.
I haven't been able to figure out what's causing it. Most of the
time the recordings are pristine, but every so often one will be off.
You can still listen to it, but it sounds likes it's slightly off
frequency or tinny. Since I'm streaming the audio straight into the
recording software and then compressing, it could be any one of those
elements in the chain; keeping around large wave files is not an option.
Upgrading to the latest greatest versions has not helped. It could also
be the sound card itself. It doesn't bug me enough to want to fix it,
though I do lose some recordings that way. If anyone out there knows
what it might be, I'd appreciate a heads up.
<p>
Since it pretty much all just works, I haven't messed with it much.
I recently used a lot of the recordings on a long road trip: iPods
rule. But I do have a few ideas on things that would be nice to have.
First, it'd be great to scrape NPR program listings and get the
details for each recording, attaching a reference file to each mp3
or changing the id3 comment to match the program listing.
<p>
Second, a dedicated scheduler would also be great. Right now if you
have a clash in using the recording device, due to overruns, the second
recording fails because the audio device is busy. Having a dedicated
scheduler that is recording centric would pretty much fix this problem.
I know Tivo has something similar so it's obviously a known problem
with known solutions. Cron is the wrong solution for this, so the
work around is of course to deliberately stop recording a minute sooner
than necessary. In general this works very well.
<p>
Third, it would be great to have a web based interface for interacting
with the recordings, changing programs to be recorded and listening,
say via shoutcast, to stuff that's already been recorded. I'm far too
lazy to write it myself, so I leave it as a challenge to all you
out there :D
<h2>9.0 Summary</h2>
As you can see, it's a little bit of work to set up Linux to timeshift
radio, but it's really not that difficult. I've been using it now
for about six months and it's a real pleasure not having to miss any
shows that catch my attention while driving. PBS is a great source of
material and I strongly encourage you to support your local station.
When combined with a portable music player like an iPod, long car rides
become much more enjoyable. <p>
The good news about building one is that things will be getting much
easier in the 2.6 timeframe because of the integration of Alsa sound
system into the mainline kernel. While the files it generates by default
are quite large, you can reduce that footprint by choosing a lower
encoding bitrate than my default of 112kbps. As low as 64kbps should
sound fine for just voice, though music will sound pretty horrible at
this bitrate. I haven't experimented with OGG or any other formats
as I don't have portable players that support alternative formats, but
changing it to support them should be a simple matter of modifying the
backend a bit. <p>
Any <a href="mailto:yanfali@best.com">feedback</a> or comments are appreciated,
and if you have a solution to my occasional bad recordings drop me a line.
<!-- *** BEGIN author bio *** -->
<P>&nbsp;
<P>
<!-- *** BEGIN bio *** -->
<P>
<img ALIGN="LEFT" ALT="[BIO]" SRC="../gx/2002/note.png">
<em>
</em>
<br CLEAR="all">
<!-- *** END bio *** -->
<!-- *** END author bio *** -->
<!-- *** BEGIN copyright *** -->
<hr>
<CENTER><SMALL><STRONG>
Copyright &copy; 2003, Yan-Fa Li.
Copying license <A HREF="../copying.html">http://www.linuxgazette.com/copying.html</A><BR>
Published in Issue 94 of <i>Linux Gazette</i>, September 2003
</STRONG></SMALL></CENTER>
<!-- *** END copyright *** -->
<HR>
<TABLE BORDER><TR><TD WIDTH="200">
<A HREF="http://www.linuxgazette.com/">
<IMG ALT="LINUX GAZETTE" SRC="../gx/2002/lglogo_200x41.png"
WIDTH="200" HEIGHT="41" border="0"></A>
<BR CLEAR="all">
<SMALL>...<I>making Linux just a little more fun!</I></SMALL>
</TD><TD WIDTH="380">
<CENTER>
<BIG><BIG><STRONG><FONT COLOR="maroon">USENET groups, email, and ssh tunnels over dial-up connection</FONT></STRONG></BIG></BIG>
<BR>
<STRONG>By <A HREF="../authors/zhuravlev.html">Nikolay Zhuravlev</A></STRONG>
</CENTER>
</TD></TR>
</TABLE>
<P>
<!-- END header -->
<p>
When not at work, I have to use a dial-up modem for all my network needs.
However, I still want to have all the power and flexibility that Linux
provides. More importantly, I want to be able to use the same tools at
home that I am used to at work. Namely, slrn for USENET news and fetchmail
for downloading emails. In this article, I am going to discuss the use of
ssh tunnels and compression for efficient and secure delivery of news
and mail over a dial-up connection.
<p>
As it was <a href="http://www.linuxgazette.com/issue15/slrnpull.html">
previously discussed </a>, a combination of slrnpull and 'slrn --spool'
can be used to fetch USENET news and read them offline.
This is especially useful when there is only one user,
and she is stuck with pay-per-hour dial-up connection.
Let's look more closely into this issue.
<p>
First, one should avoid working under root as much as possible,
and use sudo instead. Use <code>visudo</code> to edit /etc/sudoers and add the following lines
at the bottom:
<pre>
# we want to be specific here
jane localhost=/usr/bin/slrnpull -h news.server.com
</pre>
where jane is the username authorized to run the command
<code>slrnpull -h news.server.com</code> from localhost.
Whenever Jane needs to fetch the news, she runs sudo:
<pre>
jane@localhost ~$ sudo slrnpull -h news.server.com
Password:
jane@localhost ~$ slrn --spool
</pre>
<p>
Fetching a large number of articles from a wide
variety of USENET groups can take quite some time.
Let us consider a scenario where Jane has ssh access
to a machine with fast Internet. This could be a machine at
work, at school, or even abroad. Assuming that the other machine
can access news.server.com, and provided that there are no
other obstacles (for ex. strict firewalling), an ssh tunnel
with compression can be used to significantly speed up the news fetching,
when done over a dial-up connection. A tunnel is established like this:
<pre>
jane@localhost ~$ ssh -C -N -f -L 8081:news.server.com:119 janedoe@work.some.com
jane@localhost ~$
</pre>
Here -C is for compression, -N and -f avoid executing the remote command
and send ssh to background, and -L is for local port forwarding.
Now, the lines in /etc/sudoers need to be adjusted to make use of the
tunnel:
<pre>
# we want to be specific here
#jane localhost=/usr/bin/slrnpull -h news.server.com
# notice the use of backslash
jane localhost=/usr/bin/slrnpull -h localhost\:8081
</pre>
<p>
Jane can now run slrnpull. Instead of trying to connect to
news.server.com directly, slrnpull will connect to local port 8081 and
the traffic will travels through an ssh tunnel between localhost
and work.some.com.
<pre>
jane@localhost ~$ sudo slrnpull -h localhost:8081
Password:
jane@localhost ~$ slrn --spool
</pre>
<p>
The two machines, i.e. the news server news.server.com and the
work.some.com, are on the fast network. The connection between them
is in clear-text and is not compressed. However, the localhost is
connected to work.some.com via dial-up. The traffic between the
later two is encrypted and compressed. The compression is the same
as the one used by gzip. Compression of the ASCII traffic greatly decreases
the download times, which is especially useful if one likes to
subscribe to a lot of USENET groups. The proposed scheme also
provides some privacy for Jane, since the traffic between her machine
and work.some.com is encrypted.
<p>
Finally, to avoid typing long ssh commands to establish a
tunnel, Jane could have something like this in her .ssh/config file:
<pre>
Host work
HostName work.some.com
LocalForward 8081 news.server.com:119
IdentityFile /home/janedoe/.ssh/id_dsa
Protocol 2
User janedoe
CompressionLevel 6
</pre>
Notice that there is only one colon sign in the LocalForward line above.
Now the tunnel can be established with just:
<pre>
jane@localhost ~$ ssh -C -N -f work
</pre>
<p>
Just don't forget to kill the old ssh tunnel before establishing a new one.
If in doubt, use <code>netstat -tupan | grep LIS</code> to see what is
going on. The exact syntax of the commands may depend on the particular
flavor of SSH that you have. The above works for me (RH 9, openssh-3.5p1-1).
Also check out the article on
<a href="http://www.linuxgazette.com/issue67/nazario2.html"> ssh-agent </a>,
which makes dealing with ssh even less painless.
<p>
In a similar fashion, ssh tunnels can be used in combination with
fetchmail to retrieve email from the server. Just add a new LocalForward
entry to the .ssh/config file:
<pre>
Host work
HostName work.some.com
LocalForward 8081 news.server.com:119
LocalForward 8082 pop3.some.com:110
IdentityFile /home/janedoe/.ssh/id_dsa
Protocol 2
User janedoe
CompressionLevel 6
</pre>
and edit .fetchmailrc accordingly:
<pre>
poll localhost with proto POP3 port 8082
user 'Doe0001' there with password "blah" is 'jane' here options fetchall
</pre>
So, now the command <code> ssh -C -N -f work </code> will establish
two tunnels, one for the news and one for the pop3 mail.
Fire the fetchmail to see how it works:
<pre>
fetchmail -e 50 -m "/usr/sbin/sendmail -oem -f %F %T"
</pre>
To learn more about fetchmail and setting up the email system
check the <a href="http://www.linuxgazette.com/issue92/okopnik.html">
recent issue</a> of LG.
My experience was that, on average, mail and news get downloaded
at least twice as fast comparing to the conventional methods.
Over a modem line, that is.
To summarize, the use of ssh tunnels with compression provides
both efficiency and security for your everyday communication.
Use it, love it, and pass the knowledge along ;)
<!-- *** BEGIN author bio *** -->
<P>&nbsp;
<P>
<!-- *** BEGIN bio *** -->
<P>
<img ALIGN="LEFT" ALT="[BIO]" SRC="../gx/2002/note.png">
<em>
Born in Moscow, Russia, in 1976. I have been coding and/or messing
with computers in one way or another since I was 12.
I have entered the realm of *nix in 1995, and I never regretted it.
Currently, I am a Ph.D. student in the Department of Chemistry at
the University of Minnesota, MN.
</em>
<br CLEAR="all">
<!-- *** END bio *** -->
<!-- *** END author bio *** -->
<!-- *** BEGIN copyright *** -->
<hr>
<CENTER><SMALL><STRONG>
Copyright &copy; 2003, Nikolay Zhuravlev.
Copying license <A HREF="../copying.html">http://www.linuxgazette.com/copying.html</A><BR>
Published in Issue 94 of <i>Linux Gazette</i>, September 2003
</STRONG></SMALL></CENTER>
<!-- *** END copyright *** -->
<HR>
<TABLE BORDER><TR><TD WIDTH="200">
<A HREF="http://www.linuxgazette.com/">
<IMG ALT="LINUX GAZETTE" SRC="../gx/2002/lglogo_200x41.png"
WIDTH="200" HEIGHT="41" border="0"></A>
<BR CLEAR="all">
<SMALL>...<I>making Linux just a little more fun!</I></SMALL>
</TD><TD WIDTH="380">
<CENTER>
<BIG><BIG><STRONG><FONT COLOR="maroon">Python Weather Station</FONT></STRONG></BIG></BIG>
<BR>
<STRONG>By <A HREF="../authors/hughes.html">Phil Hughes</A></STRONG>
</CENTER>
</TD></TR>
</TABLE>
<P>
<!-- END header -->
This program is a simple interface that allows you to
build a web page from the Metar data output from
weather stations around the world.
I wouldn't call it exciting but it does work.
<p>
Rather than try to describe what you will see, go <a
href="http://pictures.fylz.com/weather.html">here</a>
and take a look. You should see at least two and
possibly as many as five weather reports from around
Costa Rica.
That is, the program has a list of five weather
stations to check and displays the information from
all that report.
<h2>System Structure</h2>
<p>
The heart of this system is the Pymetar package
available <a href="http://www.schwarzvogel.de/software-pymetar.shtml">
here</a>.
This is a Python program which fetches Metar data
described <a href="http://www.noaa.gov"> here</a>.
Pymetar is a command-line tool but it does all the
dirtywork.
<p>
My goal is to make this information available on a
web page.
I didn't want to turn this into a huge programming
project but I want the implementation to make sense.
The most basic approach would have been to run the
program as a CGI script for each request. However,
this was potentially very inefficient because it
would require the program to grab all the data each
time a CGI request came in.
More important, it would mean the user would have to
wait for all these requests to complete.
<p>
I decided the best compromise was to set up a cron
job to fetch the data and build a weather page.
Then, each page request would just be displaying a
static page.
As the weather data does not change all that often,
this actually offers pretty much current information.
<h2>Implementation</h2>
<p>
First, here is the code:
<pre>
#!/usr/bin/env python
import sys
import time
sys.path.insert(0, "/home/fyl/pymetar-0.5")
import pymetar
def stations(args):
for arg in map(lambda x: x.strip(), args):
try:
weather = pymetar.MetarReport(arg)
except IOError, msg:
# uncomment the following and remove pass line to see the errors
# sys.stderr.write("Problem accessing the weather server: %s\n" % msg)
pass
else:
if weather.valid:
print "&lt;h3>"
print weather.getStationName()
print " ( Lat: %s, Long: %s, Alt: %s m)" % \
weather.getStationPosition()
print "&lt;/h3>"
print "&lt;table border=\"2\">"
print "&lt;tr>&lt;td>Updated&lt;/td>&lt;td> %s&lt;/td>&lt;/tr>" % \
weather.getTime()
if weather.getWindDirection() is not None:
print "&lt;tr>&lt;td>Wind direction&lt;/td>&lt;td> %s<>&lt;/td>&lt;/tr>" % \
weather.getWindDirection()
if weather.getWindSpeed() is not None:
print "&lt;tr>&lt;td>Wind speed&lt;/td>&lt;td> %6.1f m/s&lt;/td>&lt;/tr>" % \
weather.getWindSpeed()
if weather.getTemperatureCelsius() is not None:
print "&lt;tr>&lt;td>Temperature&lt;/td>&lt;td> %.1f<EFBFBD>C (%.1f<EFBFBD>F)&lt;/td>&lt;/tr>" % \
(weather.getTemperatureCelsius(), \
weather.getTemperatureFahrenheit())
if weather.getDewPointCelsius() is not None:
print "&lt;tr>&lt;td>Dew point&lt;/td>&lt;td> %.1f<EFBFBD>C (%.1f<EFBFBD>F)&lt;/td>&lt;/tr>" % \
(weather.getDewPointCelsius(), \
weather.getDewPointFahrenheit())
if weather.getHumidity() is not None:
print "&lt;tr>&lt;td>Humidity&lt;/td>&lt;td> %.0f%%&lt;/td>&lt;/tr>" % \
weather.getHumidity()
if weather.getVisibilityKilometers() is not None:
print "&lt;tr>&lt;td>Visibility&lt;/td>&lt;td> %.1f Km&lt;/td>&lt;/tr>" % \
weather.getVisibilityKilometers()
if weather.getPressure() is not None:
print "&lt;tr>&lt;td>Pressure&lt;/td>&lt;td> %.0f hPa&lt;/td>&lt;/tr>" % \
weather.getPressure()
if weather.getWeather() is not None:
print "&lt;tr>&lt;td>Weather&lt;/td>&lt;td> %s&lt;/td>&lt;/tr>" % \
weather.getWeather()
if weather.getSkyConditions() is not None:
print "&lt;tr>&lt;td>Sky conditions&lt;/td>&lt;td> %s&lt;/td>&lt;/tr>" % \
weather.getSkyConditions()
print "&lt;/table>"
else:
print "Either %s is not a valid station ID, " % arg
print "the NOAA server is down or parsing is severely broken."
print "&lt;html>"
print "&lt;head>"
print "&lt;title>Costa Rica weather from PlazaCR.com&lt;/title>"
print "&lt;/head>"
print "&lt;body>"
print "&lt;h1>Costa Rica weather from PlazaCR.com&lt;/h1>"
print "&lt;p>Latest reports as of %s CST" % time.ctime()
gm = time.gmtime()
print "(%d.%02d.%02d %02d%02d UTC)" % (gm[0], gm[1], gm[2], gm[3], gm[4])
print '&lt;p>&lt;a href="images/costa_rica.gif" target="_blank">Costa Rica map&lt;/a>'
stations(["MROC", "MRLM", "MRCH", "MRLB", "MRPV"])
print "&lt;/body>"
print "&lt;/html>"
</pre>
<p>
I chose to just import the pymetar.py code in the
wrapper than generated the HTML page.
To do this, I added the Pymetar directy to the path
being searched by Python.
<p>
Next I define <b>stations</b>, a function that queries the
weather stations using the Pymetar code and then
formats the output into HTML.
It looks pretty ugly because it is just some long
print statements building HTML strings with some if
statements tossed in to see if we actually got the
data.
The important point is that you pass it a list of the
station names and you get the body of the web page
back.
<p>
Finally, the last maybe 15 lines of code just build
the HTML boilerplace and call stations to produce
the guts.
<h2>Testing and Installation</h2>
<p>
Because of the design, testing is very easy.
There are no web-based dependencies in the design so
you can just run the program from the command line.
<p>
In my case, I called the program wcr, so just typing
./wcr will run the program and display the HTML on
standard output.
If all goes well, run the program again, redirecting
the output to a file. For example,
<pre>
./wcr > /tmp/weather.html
</pre>
<p>
You can now point a web browser at the file and see
if it renders the page the way you want.
If not, now is the time to make changes in wcr and
continue testing.
<p>
Once you are happy with the output, upload the code
to your web server and set up a cron job to run it.
Normally, crontab -e will allow you to edit your
crontab entry.
<p>
I elected to run the program twice an hour, at 5 and
35 minutes past.
The crontab entry must execute the program and write
the output file to a location the web server can get
to. I used:
<pre>
5,35 * * * * /home/fyl/pymetar-0.5/bin/wcr > /var/www/htdocs/weather.html
</pre>
<p>
The four asterisks tell cron that the 5 and 35 minute
times apply to every hour of every day.
The next field is the name of the program to run.
Finally the redirect operator (>) is followed by
location where the HTML file is to be stored.
<p>
Assuming you set all the permissions right--that is,
the program can write to the file and the web server
can read the file, you are all done.
Just point to this file and you have a weather page.
<h2>Conclusion</h2>
<p>
For the perfectionist, you probably need a fancier
soluution.
Why?
Well, there will be a point in time when the contents
of the HTML file will not be valid.
When cron fires of the job the contents of the output
file are truncated.
Then the program runs and builds a new file.
<p>
Because of the way the program works this time is
not just a short execution time of some Python code
as the program queries the various weather stations
and has to wait for a response.
With the five stations I poll, I see elapsed times
between one and ten seconds.
If having bad data on the site for a maximum of 10
seconds every 30 minutes is acceptable to you, all is
well.
If not, write the output to a temporary file and then
move it to the real file when all is done.
Still not perfect but really close.
<p>
Now, for us mortals, we have a quick and dirty
weather page. Have fun.
<!-- *** BEGIN author bio *** -->
<P>&nbsp;
<P>
Phil Hughes is the publisher of <I>Linux Journal</I>, and thereby <I>Linux
Gazette</I>. He dreams of permanently tele-commuting from his home on the
Pacific coast of the Olympic Peninsula.
As an employer, he is &quot;Vicious, Evil,
Mean, & Nasty, but kind of mellow&quot; as a boss should be.
<!-- *** END author bio *** -->
<!-- *** BEGIN copyright *** -->
<hr>
<CENTER><SMALL><STRONG>
Copyright &copy; 2003, Phil Hughes.
Copying license <A HREF="../copying.html">http://www.linuxgazette.com/copying.html</A><BR>
Published in Issue 94 of <i>Linux Gazette</i>, September 2003
</STRONG></SMALL></CENTER>
<!-- *** END copyright *** -->
<HR>
<TABLE BORDER><TR><TD WIDTH="200">
<A HREF="http://www.linuxgazette.com/">
<IMG ALT="LINUX GAZETTE" SRC="../gx/2002/lglogo_200x41.png"
WIDTH="200" HEIGHT="41" border="0"></A>
<BR CLEAR="all">
<SMALL>...<I>making Linux just a little more fun!</I></SMALL>
</TD><TD WIDTH="380">
<CENTER>
<BIG><BIG><STRONG><FONT COLOR="maroon">SCO Interview</FONT></STRONG></BIG></BIG>
<BR>
<STRONG>By <A HREF="../authors/anonymous.html">Anonymous</A></STRONG>
</CENTER>
</TD></TR>
</TABLE>
<P>
<!-- END header -->
This is Bob Chumps, President of Chumps News Network. We're here today
for our Washington Insider Interview Luncheon with Baryl O'Hubris,
President of the Sexy Condom Operation Corp.
<p>
CNN: Baryl, you're controversial suit has been in the news a lot lately.
Can you give us a little background? Where did you first get the idea
for all this?
<p>
Baryl: Well, we'd been talking one day in the board room about how we
didn't have a lawyer's chance in hell in making any money over the next
five years. All these new glow-in-the dark and French tickler designs
have really screwed up our market, so to speak; we just don't have the
R&D funding to get any of this done by our group, and we couldn't
compete if we had to license them from anyone else. It looked bleak. I was
so bummed, I went home and tried to take my mind off the whole situation.
I had just picked up a copy of that new Open Source biography, "Pulling
the Wool: Adventures With Our Own Bush". Well, I couldn't relax and
concentrate, so I took a viagra, two peyote buttons, and did a couple of
lines. I felt better immediately and went back to reading. After the
chapter on doing up the election, a small idea was forming. When I got to
the part about 9/11, I could really feel it taking hold. By the time I got
to the chapter called "Bombing the Browns & Marketing the Oil War", I
couldn't contain it any longer. I could see it all, people in the US have
been prepared for this type of thing for years. We could do it!
<p>
CNN: What happened then?
<p>
Baryl: I immediately called Pukinda Djellow, our Chairman of the Board.
"Puke," I said. "Get the lawyers in here tomorrow. I've got an idea."
Puke listened, told me it was brilliant, that I'm a genius, emphasized
just how amazing I am; he's great, a real team player. We met the next
day and formed our basic plan.
<p>
We had the lawyers take apart the licensing agreement on our condom
packs. It couldn't be clearer, Bob. The way it's written, if you've used
one of our prophylactics, you've implicitly agreed that we have a
license on your having sex for the rest of your life. We had been
sitting on a gold mine without even knowing it!
<p>
Basically, the way the lawyers have it, anytime you slide an SCO scumbag
on your schlong, you owe us more money. So the lawyers worked
feverishly, came up with the idea for a *big* suit. Now, we knew we
couldn't identify individual purchasers of our condoms, the Total
Information Awareness thing isn't quite up yet. So, we just sued
everybody. It's the Kill 'em All, Let Moroni Sort 'em Out approach.
Eventually everyone's going to either pay up or pack their peter away
for good.
<p>
CNN: Didn't anyone object?
<p>
Baryl: Sure, one guy, Uphinder Bowwow didn't like it and quit. We don't
need him, it's no big deal.
<p>
CNN: Yes, but how are you really going to make money? Eventually people
are going to figure this out!
<p>
Baryl: That's the brilliant part. We knew it would take years for the
whole thing to get to court. In the meantime, we could be reduced to
drinking T-Bird. We had to find a way to cash in faster. Well, I
remembered we'd hired this guy named Veg Roughage, VP of Worldwide
Intercourse, which of course left him with not a whole lot to do. We
brought him into the meeting. Turns out he's had some past experience in
this stuff, knows how to do the stock and option thing. He said it was
really simple, came up with this plan how we could issue options to all
of us who were "in the know". Got him off his duff and on to something
he knows about. Ya know, it worked; as soon as we made the announcement,
our stock took off. We're all rolling in dough now, no thoughts of
having to drink the cheap stuff anymore!
<p>
CNN: All of this seems a little far-fetched.
<p>
Baryl: After I came down the first time, I thought so too, Bob. I was
frankly worried. But, I just did the same mix again: viagra, peyote, and
toot, and soon relized everything was Ok. And it's working! The main
thing is keeping up the hype, keeping the general public and the
employees confused but motivated.
<p>
CNN: How did you do that?
<p>
Baryl: Well, it turns out to be pretty simple. First of all, we hired
professional script writers so we all know what to say all the time;
sort of synchronizes our processes so to speak. Then, we call regular
press and phone conferences. Krisp Blaughjob, Senior VP, has been a
leader in this area, bought himself a couple of nice Armanis and some
new ties. When he wears that outfit, everyone believes anything he says,
I'm sure you've seen him on TV. Of course, the other employees were
still a problem, but I figured that one out myself. Since everyone eats
at the SCO cafeteria, we just put up some cool subliminal motivational
posters and spiked the food with my mix. Of course, we couldn't afford
coke for everyone, so we knocked it out of my original recipe and
substituted 2,000 milligrams of caffeine. Does a pretty good job, costs
about 98% less.
<p>
CNN: I guess you can't argue with success. What do you think you're
biggest problem is going to be in all this?
<p>
Baryl: So far, it's been clear sailing inside the US, so we're
concentrating on that market. We're realistic, we know we can't control
the world yet, they just haven't been properly prepared. Domestically
the media has really made our job easy.
<p>
Our biggest concern is that most people will just switch to
masturbation. Right now, we don't know how to handle that one for sure.
But we've got the script writers doing research. Turns out with the
right ads, we can probably convince most people that it really does grow
hair on your palms and eventually cause blindness.
<p>
CNN: Wow, the whole thing is amazing. Any last comments?
<p>
Baryl: Well, I'd just like to thank God people are stupid. Oh yeah, the
lawyers think it's really funny: all those people who bought our stock
(symbol SCOC) are going to be known as SCOC suckers.
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Anonymous,...
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Copyright &copy; 2003, Anonymous.
Copying license <A HREF="../copying.html">http://www.linuxgazette.com/copying.html</A><BR>
Published in Issue 94 of <i>Linux Gazette</i>, September 2003
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