SYNOPSIS
# See collectd.conf(5)
LoadPlugin exec
# ...
<Plugin exec>
Exec "myuser:mygroup" "myprog"
Exec "otheruser" "/path/to/another/binary" "arg0" "arg1"
NotificationExec "user" "/usr/lib/collectd/exec/handle_notification"
</Plugin>
DESCRIPTION
The exec plugin forks off an executable either to receive values or to dispatch notifications to the outside world. The syntax of the configuration is explained in collectd.conf(5) but summarized in the above synopsis.
If you want/need better performance or more functionality you should take a long look at the perl plugin, collectd-perl(5).
EXECUTABLE TYPES
There are currently two types of executables that can be executed by the exec plugin:
Exec
These programs are forked and values that it writes to STDOUT are read back. The executable is forked in a fashion similar to init: It is forked once and not again until it exits. If it exited, it will be forked again after at most Interval seconds. It is perfectly legal for the executable to run for a long time and continuously write values to STDOUT.
See "EXEC DATA FORMAT" below for a description of the output format expected from these programs.
Warning: If the executable only writes one value and then exits it will be executed every Interval seconds. If Interval is short (the default is 10 seconds) this may result in serious system load.
NotificationExec
The program is forked once for each notification that is handled by the daemon. The notification is passed to the program on STDIN in a fashion similar to HTTP-headers. In contrast to programs specified with Exec the execution of this program is not serialized, so that several instances of this program may run at once if multiple notifications are received.
See "NOTIFICATION DATA FORMAT" below for a description of the data passed to these programs.
EXEC DATA FORMAT
The forked executable is expected to print values to STDOUT. The expected format is as follows:
Comments
Each line beginning with a # (hash mark) is ignored.
PUTVAL Identifier [OptionList] Valuelist
Submits one or more values (identified by Identifier, see below) to the daemon which will dispatch it to all its write-plugins.
An Identifier is of the form host/plugin-instance/type-instance with both instance-parts being optional. If they're omitted the hyphen must be omitted, too. plugin and each instance-part may be chosen freely as long as the tuple (plugin, plugin instance, type instance) uniquely identifies the plugin within collectd. type identifies the type and number of values (i. e. data-set) passed to collectd. A large list of predefined data-sets is available in the types.db file. See types.db(5) for a description of the format of this file.
The OptionList is an optional list of Options, where each option is a key-value-pair. A list of currently understood options can be found below, all other options will be ignored. Values that contain spaces must be quoted with double quotes.
Valuelist is a colon-separated list of the time and the values, each either an integer if the data-source is a counter, or a double if the data-source is of type "gauge". You can submit an undefined gauge-value by using U. When submitting Uto a counter the behavior is undefined. The time is given as epoch (i. e. standard UNIX time) or N to use the current time.
You can mix options and values, but the order is important: Options only effect following values, so specifying an option as last field is allowed, but useless. Also, an option applies to all following values, so you don't need to re-set an option over and over again.
The currently defined Options are:
interval=seconds
Gives the interval in which the data identified by Identifier is being collected.
Please note that this is the same format as used in the unixsock plugin, see collectd-unixsock(5). There's also a bit more information on identifiers in case you're confused.
Since examples usually let one understand a lot better, here are some:
PUTVAL leeloo/cpu-0/cpu-idle N:2299366
PUTVAL alice/interface/if_octets-eth0 interval=10 1180647081:421465:479194
PUTNOTIF [OptionList] message=Message
Submits a notification to the daemon which will then dispatch it to all plugins which have registered for receiving notifications.
The PUTNOTIF if followed by a list of options which further describe the notification. The message option is special in that it will consume the rest of the line as its value. The message, severity, and time options are mandatory.
Valid options are:
message=Message (REQUIRED)
Sets the message of the notification. This is the message that will be made accessible to the user, so it should contain some useful information. As with all options: If the message includes spaces, it must be quoted with double quotes. This option is mandatory.
severity=failure|warning|okay (REQUIRED)
Sets the severity of the notification. This option is mandatory.
time=Time (REQUIRED)
Sets the time of the notification. The time is given as "epoch", i. e. as seconds since January 1st, 1970, 00:00:00. This option is mandatory.
host=Hostname
plugin=Plugin
plugin_instance=Plugin-Instance
type=Type
type_instance=Type-Instance
These "associative" options establish a relation between this notification and collected performance data. This connection is purely informal, i. e. the daemon itself doesn't do anything with this information. However, websites or GUIs may use this information to place notifications near the affected graph or table. All the options are optional, but plugin_instance without plugin or type_instance without type doesn't make much sense and should be avoided.
type:key=value
Sets user defined meta information. The type key is a single character defining the type of the meta information.
The current supported types are:
s A string passed as-is.
Please note that this is the same format as used in the unixsock plugin, see collectd-unixsock(5).
When collectd exits it sends a SIGTERM to all still running child-processes upon which they have to quit.
NOTIFICATION DATA FORMAT
The notification executables receive values rather than providing them. In fact, after the program is started STDOUT is connected to /dev/null.
The data is passed to the executables over STDIN in a format very similar to HTTP: At first there is a "header" with one line per field. Every line consists of a field name, ended by a colon, and the associated value until end-of-line. The "header" is ended by two newlines immediately following another, i.e. an empty line. The rest, basically the "body", is the message of the notification.
The following is an example notification passed to a program:
Severity: FAILURE
Time: 1200928930.515
Host: myhost.mydomain.org
\n
This is a test notification to demonstrate the format
The following header files are currently used. Please note, however, that you should ignore unknown header files to be as forward-compatible as possible.
Severity
Severity of the notification. May either be FAILURE, WARNING, or OKAY.
Time
The time in epoch, i.e. as seconds since 1970-01-01 00:00:00 UTC. The value currently has millisecond precision (i.e. three decimal places), but scripts should accept arbitrary numbers of decimal places, including no decimal places.
Host
Plugin
PluginInstance
Type
TypeInstance
Identification of the performance data this notification is associated with. All of these fields are optional because notifications do not need to be associated with a certain value.
ENVIRONMENT
The following environment variables are set by the plugin before calling exec:
COLLECTD_INTERVAL
Value of the global interval setting.
COLLECTD_HOSTNAME
Hostname used by collectd to dispatch local values.
USING NAGIOS PLUGINS
Though the interface is far from perfect, there are tons of plugins for Nagios. You can use these plugins with collectd by using a simple transition layer, exec-nagios.px, which is shipped with the collectd distribution in the contrib/ directory. It is a simple Perl script that comes with embedded documentation. To see it, run the following command:
perldoc exec-nagios.px
This script expects a configuration file, exec-nagios.conf. You can find an example in the contrib/ directory, too.
Even a simple mechanism to submit "performance data" to collectd is implemented. If you need a more sophisticated setup, please rewrite the plugin to make use of collectd's more powerful interface.
CAVEATS
The user, the binary is executed as, may not have root privileges, i. e. must have an UID that is non-zero. This is for your own good.
Early versions of the plugin did not use a command but treated all lines as if they were arguments to the PUTVALcommand. When the PUTNOTIF command was implemented, this behavior was kept for lines which start with an unknown command for backwards compatibility. This compatibility code has been removed in collectd 5.
