karl@debisschop.net
netsaint@linuxbox.com
hgayosso@gnu.org
sghosh@sourceforge.net
stanleyhopcroft@sourceforge.net
Copyright © 2000 2001 2002 by Karl DeBisschop, Ethan Galstad, - Hugo Gayosso, Stanley Hopcroft, Subhendu Ghosh
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.
Nagios Plug-in Development Guidelines Copyright (C) 2000 2001 - 2002 - Karl DeBisschop, Ethan Galstad, Hugo Gayosso, Stanley Hopcroft, - Subhendu Ghosh
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.
The plugins themselves are copyrighted by their respective - authors.
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.
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.
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.
Code and output should try to respect the 80x25 size of a - crt (remember when fixing stuff in the server room!)
See Table 1 in the section called Plugin Return Codes 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.
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.
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.
Table 1. Plugin Return Codes
Numeric Value | Service Status | Status Description |
|---|---|---|
0 | OK | The plugin was able to check the service and it - appeared to be functioning properly |
1 | Warning | 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 |
2 | Critical | The plugin detected that either the service was not - running or it was above some "critical" threshold |
3 | Unknown | Invalid command line arguments were supplied to the - plugin or the plugin was unable to check the status of the given - hosts/service |
Don't use exec(), popen(), etc. to execute external - commands without explicity using the full path of the external - program.
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.
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.
The code for spopen() and spclose() is included with the - core plugin distribution.
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.
If your plugin opens any files, take steps to ensure that - you are not following a symlink to another location on the - system.
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.
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.
To use utils.pm, you need to provide a full path to the - module in order for it to work with ePN.
e.g.
- use lib "/usr/local/nagios/libexec";
- use utils qw(...);
-
Perl scripts should be called with "-w"
All Perl plugins must compile cleanly under "use strict" - i.e. at - least explicitly package names as in "$main::x" or predeclare every - variable.
Explicitly initialize each varialable in use. Otherwise with - caching enabled, the plugin will not be recompilied each time, and - therefore Perl will not reinitialize all the variables. All old - variable values will still be in effect.
Do not use < DATA > (these simply do not compile under ePN).
Do not use named subroutines
If writing to a file (perhaps recording - performance data) explicitly close close it. The plugin never - calls exit; that is caught by - p1.pl, so output streams are never closed.
As in the section called Runtime Timeouts all plugins need - to monitor their runtime, specially if they are using network - resources. Use of the alarm is recommended. - Plugins may import a default time out ($TIMEOUT) from utils.pm. -
Perl plugins should import %ERRORS from utils.pm - and then "exit $ERRORS{'OK'}" rather than "exit 0" -
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.
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.
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.
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!)
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).
For plugins written in Perl, we recommend Getopt::Long module.
Positional arguments are strongly discouraged.
There are a few reserved options that should not be used - for other purposes:
-V version (--version)
- -h help (--help)
- -t timeout (--timeout)
- -w warning threshold (--warning)
- -c critical threshold (--critical)
- -H hostname (--hostname)
-
In addition to the reserved options above, some other standard options are:
-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)
-
Look at check_pgsql and check_procs to see how I currently - think this can work. Standard options are:
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.
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).
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.
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:
long options like -critical-time (or -ct and -cv, I - suppose).
repeated options like `check_load -w 10 -w 6 -w 4 -c - 16 -c 10 -c 10`
for brevity, the above can be expressed as `check_load - -w 10,6,4 -c 16,10,10`
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
lists are expressed with commas, so Jacob's check_nmap - uses constructs like '-p 1000,1010,1050:1060,2000'
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).
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.
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.
Plugins in the contrib directory are going to be migrated to the - standard plugins/plugin-scripts directory as time permits and per user - requests
Patches should be submitted via the SourceForge and be announced to - the mailing list.
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.
If possible please submit a test harness. Documentation on sample - tests coming soon.