collectd - exec plugin: Unable to parse command - metrics

Question

I'm trying to return a value from a simple script. However, I'm getting the following error.
Feb 26 09:26:37 localhost systemd[1]: Starting Collectd statistics daemon...
Feb 26 09:26:37 localhost collectd[834]: plugin_load: plugin "exec" successfully loaded.
Feb 26 09:26:37 localhost collectd[834]: Systemd detected, trying to signal readyness.
Feb 26 09:26:37 localhost systemd[1]: Started Collectd statistics daemon.
Feb 26 09:26:37 localhost collectd[834]: Initialization complete, entering read-loop.
Feb 26 09:26:37 localhost collectd[834]: exec plugin: Unable to parse command, ignoring line: "73"
Feb 26 09:26:47 localhost collectd[834]: exec plugin: Unable to parse command, ignoring line: "74"
Feb 26 09:26:57 localhost collectd[834]: exec plugin: Unable to parse command, ignoring line: "73"
Feb 26 09:27:07 localhost collectd[834]: exec plugin: Unable to parse command, ignoring line: "73"
My config is
LoadPlugin exec
<Plugin exec>
Exec "cwagent" "/opt/aws/amazon-cloudwatch-agent/bin/supervisor.sh"
</Plugin>
and my script is
#!/bin/bash
VALUE=$(/bin/systemctl status | wc -l)
echo "$VALUE"
I realise that this is probably a silly mistake I'm making. I have spent a bit of time playing around and googling to try to understand the problem. But I'm afraid I've made little progress. Grateful for any advice :¬)

Answer 1

Number of things, your plugin is forked off by collectd with the expectation that it keeps running and producing consumable output, so you need to use a while loop like it lays out here: https://collectd.org/wiki/index.php/Plugin:Exec
Second, your output format is wrong. I found this bit of the documentation badly written because it isn't completely clear how the gauge name and metric name are constituted out of the string. Taking the example in the page above:
echo "PUTVAL \"$HOSTNAME/exec-magic/gauge-magic_level\" interval=$INTERVAL N:$VALUE"
Then:
exec-magic is the plugin name
magic_level is the metric name
gauge is the data source type from collectd types
N: is the abbreviation for "now" as defined in the exec plugin
So putting this together you'd something similar to:
#!/bin/bash
HOSTNAME="${COLLECTD_HOSTNAME:-localhost}"
INTERVAL="${COLLECTD_INTERVAL:-60}"
while sleep "$INTERVAL"; do
VALUE=$(/bin/systemctl status | wc -l)
echo "PUTVAL ${HOSTNAME}/cwagent/counter-line_count\" N:$VALUE"
done
In this case you are using the simple counter type and returning a single value equivalent to the number of lines you counted in your command.