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+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook V4.1//EN">
+<book>
+  <title>Nagios Plug-in Developer Guidelines</title>
+
+  <bookinfo>
+    <authorgroup>
+      <author>
+	<firstname>Karl</firstname>
+	<surname>DeBisschop</surname>
+	<affiliation>
+	  <address><email>karl@debisschop.net</email></address>
+	</affiliation>
+      </author>
+
+      <author>
+	<firstname>Ethan</firstname>
+	<surname>Galstad</surname>
+	<authorblurb>
+	  <para>Author of Nagios</para>
+	  <para><ulink url="http://www.nagios.org"></ulink></para>
+	</authorblurb>
+	<affiliation>
+	  <address><email>netsaint@linuxbox.com</email></address>
+	</affiliation>
+      </author>
+
+      <author>
+	<firstname>Hugo</firstname>
+	<surname>Gayosso</surname>
+	<affiliation>
+	  <address><email>hgayosso@gnu.org</email></address>
+	</affiliation>
+      </author>
+
+	  
+	<author>
+	<firstname>Subhendu</firstname>
+	<surname>Ghosh</surname>
+	<affiliation>
+		<address><email>sghosh@sourceforge.net</email></address>
+	</affiliation>
+	</author>
+	
+	<author>
+	<firstname>Stanley</firstname>
+	<surname>Hopcroft</surname>
+	<affiliation>
+		<address><email>stanleyhopcroft@sourceforge.net</email></address>
+	</affiliation>
+	</author>	
+
+    </authorgroup>
+
+    <pubdate>2002</pubdate>
+    <title>Nagios plug-in development guidelines</title>
+	
+    <revhistory>
+       <revision>
+          <revnumber>0.4</revnumber>
+          <date>2 May 2002</date>
+       </revision>
+    </revhistory>
+
+	<copyright>
+		<year>2000 2001 2002</year> 
+		<holder>Karl DeBisschop, Ethan Galstad, 
+		Hugo Gayosso, Stanley Hopcroft, Subhendu Ghosh</holder>
+	</copyright>
+
+</bookinfo>
+
+
+  <preface id=preface>
+    <title>About the guidelines</title>
+
+    <para>The purpose of this guidelines is to provide a reference for
+    the plug-in developers and encourage the standarization of the
+    different kind of plug-ins: C, shell, perl, python, etc.</para>
+
+
+    <section> <title>Copyright</title>
+
+        <para>Nagios Plug-in Development Guidelines Copyright (C) 2000 2001
+		2002
+        Karl DeBisschop, Ethan Galstad, Hugo Gayosso, Stanley Hopcroft, 
+		Subhendu Ghosh</para>
+
+        <para>Permission is granted to make and distribute verbatim
+        copies of this manual provided the copyright notice and this
+        permission notice are preserved on all copies.</para>
+
+		<para>The plugins themselves are copyrighted by their respective
+		authors.</para>
+
+    </section>
+</preface>
+
+<article>
+<section id="PlugOutput"><title>Plugin Output for Nagios</title>
+	
+		<para>You should always print something to STDOUT that tells if the 
+		service is working or why its failing. Try to keep the output short - 
+		probably less that 80 characters. Remember that you ideally would like 
+		the entire output to appear in a pager message, which will get chopped
+		off after a certain length.</para>
+
+		<section><title>Print only one line of text</title>
+		<para>Nagios will only grab the first line of text from STDOUT
+		when it notifies contacts about potential problems. If you print
+		multiple lines, you're out of luck. Remember, keep it short and
+		to the point.</para>
+	    </section>
+
+		<section><title>Screen Output</title>
+		<para>The plug-in should print the diagnostic and just the
+		synopsis part of the help message.  A well written plugin would
+		then have --help as a way to get the verbose help.</para>
+		<para>Code and output should try to respect the 80x25 size of a
+		crt (remember when fixing stuff in the server room!)</para>
+		</section>
+		
+	    <section><title>Return the proper status code</title>
+		<para>See <xref linkend="ReturnCodes"> below
+		for the numeric values of status codes and their
+		description. Remember to return an UNKNOWN state if bogus or
+		invalid command line arguments are supplied or it you are unable
+		to check the service.</para>
+		</section>
+		
+		<section><title>Plugin Return Codes</title>
+		<para>The return codes below are based on the POSIX spec of returning
+		a positive value.  Netsaint prior to v0.0.7 supported non-POSIX
+		compliant return code of "-1" for unknown.  Nagios supports POSIX return
+		codes by default.</para>
+
+		<para>Note: Some plugins will on occasion print on STDOUT that an error
+		occurred and error code is 138 or 255 or some such number.  These
+		are usually caused by plugins using system commands and having not 
+		enough checks to catch unexpected output.  Developers should include a
+		default catch-all for system command output that returns an UNKOWN
+		return code.</para>
+		
+		<table id="ReturnCodes"><title>Plugin Return Codes</title>
+			<tgroup cols="3">
+				<thead>
+					<row>
+						<entry><para>Numeric Value</para></entry>
+						<entry><para>Service Status</para></entry>
+						<entry><para>Status Description</para></entry>
+					</row>
+				</thead>
+				<tbody>
+					<row>
+						<entry align=center><para>0</para></entry>
+						<entry valign=middle><para>OK</para></entry>
+						<entry><para>The plugin was able to check the service and it 
+						appeared to be functioning properly</para></entry>
+					</row>
+					<row>
+						<entry align=center><para>1</para></entry>
+						<entry valign=middle><para>Warning</para></entry>
+						<entry><para>The plugin was able to check the service, but it 
+						appeared to be above some "warning" threshold or did not appear 
+						to be working properly</para></entry>
+					</row>
+					<row>
+						<entry align=center><para>2</para></entry>
+						<entry valign=middle><para>Critical</para></entry>
+						<entry><para>The plugin detected that either the service was not 
+						running or it was above some "critical" threshold</para></entry>
+					</row>
+					<row>
+						<entry align=center><para>3</para></entry>
+						<entry valign=middle><para>Unknown</para></entry>
+						<entry><para>Invalid command line arguments were supplied to the 
+						plugin or the plugin was unable to check the status of the given 
+						hosts/service</para></entry>
+					</row>
+				</tbody>
+			</tgroup>
+		</table>
+
+      
+		</section>
+
+
+</section>
+
+<section id="SysCmdAuxFiles"><title>System Commands and Auxiliary Files</title>
+
+		<section><title>Don't execute system commands without specifying their
+		full path</title>
+		<para>Don't use exec(), popen(), etc. to execute external
+		commands without explicity using the full path of the external
+		program.</para>
+
+		<para>Doing otherwise makes the plugin vulnerable to hijacking
+		by a trojan horse earlier in the search path. See the main
+		plugin distribution for examples on how this is done.</para>
+		</section>
+
+		<section><title>Use spopen() if external commands must be executed</title>
+
+	    <para>If you have to execute external commands from within your
+    	plugin and you're writing it in C, use the spopen() function
+		that Karl DeBisschop has written.</para>
+
+		<para>The code for spopen() and spclose() is included with the
+		core plugin distribution.</para>
+		</section>
+
+		<section><title>Don't make temp files unless absolutely required</title>
+
+		<para>If temp files are needed, make sure that the plugin will
+		fail cleanly if the file can't be written (e.g., too few file
+		handles, out of disk space, incorrect permissions, etc.) and
+		delete the temp file when processing is complete.</para>
+		</section>
+
+    	<section><title>Don't be tricked into following symlinks</title>
+
+		<para>If your plugin opens any files, take steps to ensure that
+		you are not following a symlink to another location on the
+		system.</para>
+		</section>
+
+		<section><title>Validate all input</title>
+
+		<para>use routines in utils.c or utils.pm and write more as needed</para>
+		</section>
+
+</section>
+	
+
+
+
+<section id="PerlPlugin"><title>Perl Plugins</title>
+
+		<para>Perl plugins are coded a little more defensively than other
+		plugins because of embedded Perl.  When configured as such, embedded
+		Perl Nagios (ePN) requires stricter use of the some of Perl's features.
+		This section outlines some of the steps needed to use ePN
+		effectively.</para>
+	  
+		<orderedlist>
+			
+			<listitem><para> Do not use BEGIN and END blocks since they will be called 
+			the first time and when Nagios shuts down with Embedded Perl (ePN).  In 
+			particular, do not use BEGIN blocks to initialize variables.</para>
+			</listitem>
+	  
+			<listitem><para>To use utils.pm, you need to provide a full path to the
+			module in order for it to work with ePN.</para>
+			
+	  <literallayout>
+	  e.g.
+		use lib "/usr/local/nagios/libexec";
+		use utils qw(...);
+	  </literallayout>
+	  		</listitem>
+
+			<listitem><para>Perl scripts should be called with "-w"</para>
+	  		</listitem>
+			
+			<listitem><para>All Perl plugins must compile cleanly under "use strict" - i.e. at
+			least explicitly package names as in "$main::x" or predeclare every
+			variable. </para>
+			
+
+			<para>Explicitly initialize each varialable in use.  Otherwise with
+			caching enabled, the plugin will not be recompilied each time, and
+			therefore Perl will not reinitialize all the variables.  All old
+			variable values will still be in effect.</para>
+	  		</listitem>
+			
+			<listitem><para>Do not use < DATA > (these simply do not compile under ePN).</para>
+	   		</listitem>
+
+			<listitem><para>Do not use named subroutines</para> 
+			</listitem>
+
+			<listitem><para>If writing to a file (perhaps recording
+			performance data) explicitly close close it.  The plugin never
+			calls <emphasis role=strong>exit</emphasis>; that is caught by
+			p1.pl, so output streams are never closed.</para>
+			</listitem>
+		
+			<listitem><para>As in <xref linkend="runtime"> all plugins need 
+			to monitor their runtime, specially if they are using network
+			resources.  Use of the <emphasis>alarm</emphasis> is recommended.
+			Plugins may import a default time out ($TIMEOUT) from utils.pm.
+			</para>
+			</listitem>
+
+			<listitem><para>Perl plugins should import %ERRORS from utils.pm
+			and then "exit $ERRORS{'OK'}" rather than "exit 0"
+			</para>
+			</listitem>
+			
+		</orderedlist>
+	  
+</section>
+
+<section id="runtime"><title>Runtime Timeouts</title>
+
+		<para>Plugins have a very limited runtime - typically 10 sec.
+		As a result, it is very important for plugins to maintain internal
+		code to exit if runtime exceeds a threshold. </para>
+
+		<para>All plugins should timeout gracefully, not just networking
+		plugins. For instance, df may lock if you have automounted
+		drives and your network fails - but on first glance, who'd think
+		df could lock up like that.  Plus, it should just be more error
+		resistant to be able to time out rather than consume
+		resources.</para>
+		
+		<section><title>Use DEFAULT_SOCKET_TIMEOUT</title>
+
+		<para>All network plugins should use DEFAULT_SOCKET_TIMEOUT to timeout</para>
+
+		</section>
+
+		
+		<section><title>Add alarms to network plugins</title>
+
+		<para>If you write a plugin which communicates with another
+		networked host, you should make sure to set an alarm() in your
+		code that prevents the plugin from hanging due to abnormal
+		socket closures, etc. Nagios takes steps to protect itself
+		against unruly plugins that timeout, but any plugins you create
+		should be well behaved on their own.</para>
+
+		</section>
+
+		
+
+</section>
+
+<section id="PlugOptions"><title>Plugin Options</title>
+	
+		<para>A well written plugin should have --help as a way to get 
+		verbose help. Code and output should try to respect the 80x25 size of a
+		crt (remember when fixing stuff in the server room!)</para>
+		
+		<section><title>Option Processing</title>
+
+		<para>For plugins written in C, we recommend the C standard
+		getopt library for short options. If using getopt_long, check to
+		be sure that HAVE_GETOPT_H is defined (configure checks this and
+		sets the #define in common/config.h).</para>
+
+		<para>For plugins written in Perl, we recommend Getopt::Long module.</para>
+
+		<para>Positional arguments are strongly discouraged.</para>
+
+		<para>There are a few reserved options that should not be used
+		for other purposes:</para>
+
+		<literallayout>
+          -V version (--version)
+          -h help (--help)
+          -t timeout (--timeout)
+          -w warning threshold (--warning)
+          -c critical threshold (--critical)
+          -H hostname (--hostname)
+		</literallayout>
+
+		<para>In addition to the reserved options above, some other standard options are:</para>
+
+		<literallayout>
+          -C SNMP community (--community)
+          -a authentication password (--authentication)
+          -l login name (--logname)
+          -p port or password (--port or --passwd/--password)monitors operational
+          -u url or username (--url or --username)
+		</literallayout>
+	  
+		<para>Look at check_pgsql and check_procs to see how I currently
+		think this can work.  Standard options are:</para>
+
+	  
+		<para>The option -V or --version should be present in all
+		plugins. For C plugins it should result in a call to print_revision, a
+		function in utils.c which takes two character arguments, the
+		command name and the plugin revision.</para>
+
+		<para>The -? option, or any other unparsable set of options,
+		should print out a short usage statement. Character width should
+		be 80 and less and no more that 23 lines should be printed (it
+		should display cleanly on a dumb terminal in a server
+		room).</para>
+
+		<para>The option -h or --help should be present in all plugins.
+		In C plugins, it should result in a call to print_help (or
+		equivalent).  The function print_help should call print_revision, 
+		then print_usage, then should provide detailed
+		help. Help text should fit on an 80-character width display, but
+		may run as many lines as needed.</para>
+
+    </section>
+
+    <section>
+      <title>Plugins with more than one type of threshold, or with
+      threshold ranges</title>
+
+      <para>Old style was to do things like -ct for critical time and
+      -cv for critical value. That goes out the window with POSIX
+      getopt. The allowable alternatves are:</para>
+
+      <orderedlist>
+	<listitem>
+	  <para>long options like -critical-time (or -ct and -cv, I
+	  suppose).</para>
+	</listitem>
+
+	<listitem>
+	  <para>repeated options like `check_load -w 10 -w 6 -w 4 -c
+	  16 -c 10 -c 10`</para>
+	</listitem>
+
+	<listitem>
+	  <para>for brevity, the above can be expressed as `check_load
+	  -w 10,6,4 -c 16,10,10`</para>
+	</listitem>
+
+	<listitem>
+	  <para>ranges are expressed with colons as in `check_procs -C
+	  httpd -w 1:20 -c 1:30` which will warn above 20 instances,
+	  and critical at 0 and above 30</para>
+	</listitem>
+
+	<listitem>
+	  <para>lists are expressed with commas, so Jacob's check_nmap
+	  uses constructs like '-p 1000,1010,1050:1060,2000'</para>
+	</listitem>
+
+	<listitem>
+	  <para>If possible when writing lists, use tokens to make the
+	  list easy to remember and non-order dependent - so
+	  check_disk uses '-c 10000,10%' so that it is clear which is
+	  the precentage and which is the KB values (note that due to
+	  my own lack of foresight, that used to be '-c 10000:10%' but
+	  such constructs should all be changed for consistency,
+	  though providing reverse compatibility is fairly
+	  easy).</para>
+	</listitem>
+
+      </orderedlist>
+
+      <para>As always, comments are welcome - making this consistent
+      without a host of long options was quite a hassle, and I would
+      suspect that there are flaws in this strategy. Perhaps clear
+      long-options is the most important of the above choices, but not
+      all POSIX systems have C libraries for long options, so the
+      short forms must exist as well.</para>
+    </section>
+</section>
+
+<section id="SubmittingChanges"><title>New submissions and patches</title>
+
+	<para>If you would like other to use your plugins and have it included in
+	the standard distribution, please include patches for the relavant
+	configuration files, in particular "configure.in" Otherwise submitted 
+	plugins will be included in the contrib directory.</para>
+	
+	<para>Plugins in the contrib directory are going to be migrated to the
+	standard plugins/plugin-scripts directory as time permits and per user
+	requests</para>
+
+	<para>Patches should be submitted via the SourceForge and be announced to
+	the mailing list.</para>
+	
+	<para>For new plugins, provide a diff to add to the EXTRAS list (configure.in) 
+	unless you are fairly sure that the plugin will work for all platforms with 
+	no non-standard	software added.</para>
+
+	<para>If possible please submit a test harness. Documentation on sample
+	tests coming soon.</para>
+
+</section>
+</article>
+  
+</book>