[nagiosplug.git] / doc / developer-guidelines.sgml

<!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>Preface</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>

        <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>
</preface>

<article>
<section id="DevRequirements"><title>Development platform requirements</title>
        <para>
        Nagios plugins are developed to the GNU standard, so any OS which is supported by GNU
        should run the plugins. While the requirements for compiling the Nagios plugins release 
        is very small, to develop from CVS needs additional software to be installed. These are the 
        minimum levels of software required:

        <literallayout>
        gnu make 3.79
        automake 1.6
        autoconf 2.54
        gettext 0.11.5
        </literallayout>

        To compile from CVS, after you have checked out the code, run:
        <literallayout>
        tools/setup
        ./configure
        make
        make install
        </literallayout>
        </para>
</section>

<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>Verbose output</title>
                <para>Use the -v flag for verbose output. You should allow multiple
                -v options for additional verbosity, up to a maximum of 3. The standard
                type of output should be:</para>

                <table id="verbose_levels"><title>Verbose output levels</title>
                        <tgroup cols="2">
                                <thead>
                                        <row>
                                                <entry><para>Verbosity level</para></entry>
                                                <entry><para>Type of output</para></entry>
                                        </row>
                                </thead>
                                <tbody>
                                        <row>
                                                <entry align=center><para>0</para></entry>
                                                <entry><para>Single line, minimal output. Summary</para></entry>
                                        </row>
                                        <row>
                                                <entry align=center><para>1</para></entry>
                                                <entry><para>Single line, additional information (eg list processes that fail)</para></entry>
                                        </row>
                                        <row>
                                                <entry align=center><para>2</para></entry>
                                                <entry><para>Multi line, configuration debug output (eg ps command used)</para></entry>
                                        </row>
                                        <row>
                                                <entry align=center><para>3</para></entry>
                                                <entry><para>Lots of detail for plugin problem diagnosis</para></entry>
                                        </row>
                                </tbody>
                        </tgroup>
                </table>
                </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 UNKNOWN
                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 id="thresholdformat"><title>Threshold range format</title>
                <para>Thresholds ranges define the warning and critical levels for plugins to 
                alert on. The theory is that the plugin will do some sort of check which returns
                back a numerical value, or metric, which is then compared to the warning and 
                critical thresholds.
                This is the generalised format for threshold ranges:</para>

                <literallayout>
                [@]start:end
                </literallayout>
        
                <para>Notes:</para>
                <orderedlist>
                <listitem><para>start < end</para>
                        </listitem>
                <listitem><para>start and ":" is not required if start=0</para>
                        </listitem>
                <listitem><para>if range is of format "start:" and end is not specified, 
                        assume end is infinity</para>
                        </listitem>
                <listitem><para>to specify negative infinity, use "~"</para>
                        </listitem>
                <listitem><para>alert is raised if metric is outside start and end range
                        (inclusive of endpoints)</para>
                        </listitem>
                <listitem><para>if range starts with "@", then alert if inside this range
                        (inclusive of endpoints)</para>
                        </listitem>
                </orderedlist>
                
                <para>Note: Not all plugins are coded to expect ranges in this format. It is
                planned for a future release to
                provide standard libraries to parse and compare metrics against ranges. There
                will also be some work in providing multiple metrics.</para>
                </section>

                <section><title>Performance data</title>
                <para>Performance data is defined by Nagios as "everything after the | of the plugin output" -
                please refer to Nagios documentation for information on capturing this data to logfiles.
                However, it is the responsibility of the plugin writer to ensure the 
                performance data is in a "Nagios plugins" format.
                This is the expected format:</para>

                <literallayout>
                'label'=value[UOM];[warn];[crit];[min];[max]
                </literallayout>

                <para>Notes:</para>
                <orderedlist>
                <listitem><para>space separated list of label/value pairs</para>
                        </listitem>
                <listitem><para>label can contain any characters</para>
                        </listitem>
                <listitem><para>the single quotes for the label are optional. Required if 
                        spaces, = or ' are in the label</para>
                        </listitem>
                <listitem><para>label length is arbitrary, but ideally the first 19 characters
                        are unique (due to a limitation in RRD). Be aware of a limitation in the
                        amount of data that NRPE returns to Nagios</para>
                        </listitem>
                <listitem><para>to specify a quote character, use two single quotes</para>
                        </listitem>
                <listitem><para>warn, crit, min or max may be null (for example, if the threshold is 
                        not defined or min and max do not apply). Trailing unfilled semicolons can be
                        dropped</para>
                        </listitem>
                <listitem><para>min and max are not required if UOM=%</para>
                        </listitem>
                <listitem><para>value, min and max in class [-0-9.]. Must all be the
                        same UOM</para>
                        </listitem>
                <listitem><para>warn and crit are in the range format (see 
                        <xref linkend="thresholdformat">)</para>
                        </listitem>
                <listitem><para>UOM (unit of measurement) is one of:</para>
                        <orderedlist>
                        <listitem><para>no unit specified - assume a number (int or float) 
                                of things (eg, users, processes, load averages)</para>
                                </listitem>
                        <listitem><para>s - seconds (also us, ms)</para></listitem>
                        <listitem><para>% - percentage</para></listitem>
                        <listitem><para>B - bytes (also KB, MB, TB)</para></listitem>
                        <listitem><para>c - a continous counter (such as bytes
                                transmitted on an interface)</para></listitem>
                        </orderedlist>
                        </listitem>
                </orderedlist>

                <para>It is up to third party programs to convert the Nagios plugins 
                performance data into graphs.</para>
                </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. Getopt_long is always available.
                </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)
          -v verbose (--verbose)
                </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>

                <para>The option -v or --verbose should be present in all plugins.
                The user should be allowed to specify -v multiple times to increase
                the verbosity level, as described in <xref linkend="verbose_levels">.</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 alternatives 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. 
      </para>
    </section>
</section>

<section id="CodingGuidelines"><title>Coding guidelines</title>
        <para>See <ulink url="http://www.gnu.org/prep/standards_toc.html">GNU
        Coding standards</ulink> for general guidelines.</para>
        <section><title>Comments</title>
        <para>You should use /* */ for comments and not // as some compilers
        do not handle the latter form.</para>
        <para>There should not be any named credits in the source code - contributors
        should be added 
        into the AUTHORS file instead. The only exception to this is if a routine
        has been copied from another source.</para>
        </section>

        <section><title>CVS comments</title>
        <para>When adding CVS comments at commit time, you can use the following prefixes:
        <variablelist>
          <varlistentry><term>- comment</term>
          <listitem>
            <para>for a comment that can be removed from the Changelog</para>
          </listitem>
          </varlistentry>
          <varlistentry><term>* comment</term>
          <listitem>
            <para>for an important amendment to be included into a features list</para>
          </listitem>
          </varlistentry>
        </variablelist>
        </para>
        <para>If the change is due to a contribution, please quote the contributor's name 
        and, if applicable, add the SourceForge Tracker number. Don't forget to 
update the AUTHORS file.</para>
        </section>
</section>

<section id="SubmittingChanges"><title>Submission of new plugins and patches</title>

        <section id="Patches"><title>Patches</title>
        <para>If you have a bug patch, please supply a unified or context diff against the
        version you are using. For new features, please supply a diff against
        the CVS HEAD version.</para>

        <para>Patches should be submitted via 
        <ulink url="http://sourceforge.net/tracker/?group_id=29880&amp;atid=397599">SourceForge's
        tracker system for Nagiosplug patches</ulink> 
        and be announced to the nagiosplug-devel mailing list.</para>
        </section>

        <section id="New_plugins"><title>New plugins</title>
        <para>If you would like others to use your plugins and have it included in
        the standard distribution, please include patches for the relevant
        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. The minimum requirements are:</para>

      <orderedlist>
        <listitem>
          <para>The standard command options are supported (--help, --version,
          --timeout, --warning, --critical)</para>
        </listitem>
        <listitem>
          <para>It is determined to be not redundant (for instance, we would not 
                add a new version of check_disk just because someone had provide 
                a plugin that had perf checking - we would incorporate the features 
                into an exisiting plugin)</para>
        </listitem>
        <listitem>
          <para>One of the developers has had the time to audit the code and declare
                it ready for core</para>
        </listitem>
        <listitem>
          <para>It should also follow code format guidelines, and use functions from
utils (perl or c or sh) rather than cooking it's own</para>
        </listitem>
      </orderedlist>

        <para>New plugins should be submitted via 
        <ulink url="http://sourceforge.net/tracker/?group_id=29880&amp;atid=541465">SourceForge's
        tracker system for Nagiosplug new plugins</ulink> 
        and be announced to the nagiosplug-devel 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>

</section>

</article>
  
</book>