Monit shows zero percent CPU usage for a few seconds after Monit (or a process) starts/stops

[Former user]

Is this normal?

Monit shows most process at 0% CPU for a few moments after startup or a program is started/stopped. This causes incorrect flags in the monitoring such as "if CPU <" or "if CPU = 0" etc.

This is also reflected in the web page Monit Service Manager, which is much slower to update with correct values.

[BST May 11 08:40:49] info     : Starting Monit HTTP server at [*]:22812
[BST May 11 08:40:49] info     : Monit HTTP server started
[BST May 11 08:40:49] info     : 'encoder-1A' Monit reloaded
[BST May 11 08:40:49] error    : 'itv2' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:40:49] error    : 'bbconehd' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:40:49] error    : 'bbcfourhd' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:40:49] error    : 'itvhd' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:40:49] error    : 'pbsamerica' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:40:49] error    : 'sonycrime2' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:40:49] error    : 'freesports' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:40:49] error    : 'bbctwohd' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:40:49] error    : 'channel4hd' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:40:49] error    : 'channel5hd' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:40:49] error    : 'film4plus1' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]

an example of similar when a process is started/stopped etc:

[BST May 11 08:27:46] error    : 'bbcfourhd' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:27:46] info     : 'bbcfourhd' exec: /home/user/monit-restart-service.sh
[BST May 11 08:27:46] info     : 'bbcfourhd' stop on user request
[BST May 11 08:27:46] info     : Monit daemon with PID 4110 awakened
[BST May 11 08:27:46] info     : Awakened by User defined signal 1
[BST May 11 08:27:46] info     : 'bbcfourhd' stop: /etc/init.d/bbcfourhd
[BST May 11 08:27:46] info     : 'bbcfourhd' stop action done
[BST May 11 08:27:46] error    : 'mutp110' cpu usage of 15.9% matches resource limit [cpu usage>8.0%]
[BST May 11 08:27:46] error    : 'itv2' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:27:46] error    : 'itvhd' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:27:46] error    : 'sonycrime2' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:27:46] error    : 'freesports' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:27:46] error    : 'bbctwohd' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:27:46] error    : 'channel4hd' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:27:46] error    : 'channel5hd' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]
[BST May 11 08:27:46] error    : 'film4plus1' cpu usage of 0.0% matches resource limit [cpu usage=0.0%]

Thank you.

[Tildeslash]

Please can you verify the monit version?:

monit -V

The problem should be fixed in monit 5.25.0 and later, changelog snip:

Fixed: Issue #676: Process CPU usage is reported always as 0.0% in the first cycle after process start

[welshdemon]

It's definitely version 5.25.1

Thank you.

[Tildeslash]

I'm unable to reproduce the issue. I used the following configuration:

set daemon 5

set httpd port 2812 allow localhost

check process test matching test
    if cpu usage > 10% then alert

and the following cpu-hog script executed with "bash test.sh":

while true; do echo hello; done

When i reloaded monit, it reported the CPU usage correctly.

Please can you provide some test case with monit configuration example that will allow to reproduce the issue? (some cpu-hog shell script).

Note that monit reflects the number of threads and CPU cores when calculating the CPU usage, the formula is described in the manual: https://mmonit.com/monit/documentation/monit.html#Process-resource-tests If your processes have lots of idle threads and the machine has enough CPU cores, the average CPU usage of your process can be close to 0%. You can check the number of threads for example this way:

ps -eo pid,nlwp,args

[Massimo Sala]

@welshdemon

did you watch the processes with top or htop, at the same moment ? what does it report ?