DESCRIPTION

The "exec plugin" forks of 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).

EXECUTABLETYPES

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 I
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.

EXECDATAFORMAT

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.
PUTVALIdentifier [OptionList] Valuelist
Submits one or more values (identified by Identifier, see below) to
the daemon which will dispatch it to all it's 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 U to a counter the behavior
is undefined. The time is given as epoch (i. e. standard UNIX
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 unixsockplugin, 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:
leeloo/cpu-0/cpu-idle N:2299366
alice/interface/if_octets-eth0 interval=10 1180647081:421465:479194
Since this action was the only one supported with older versions of
the "exec plugin" all lines were treated as if they were prefixed
with PUTVAL. This is still the case to maintain backwards
compatibility but deprecated.
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=Hostnameplugin=Pluginplugin_instance=Plugin-Instancetype=Typetype_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.
Please note that this is the same format as used in the unixsockplugin, see collectd-unixsock(5).
When collectd exits it sends a SIGTERM to all still running child-
processes upon which they have to quit.

NOTIFICATIONDATAFORMAT

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
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.
HostPluginPluginInstanceTypeTypeInstance
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.

USINGNAGIOSPLUGINS

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

o 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.