[systemd-devel] Needs help for on charging activation

WaLyong Cho walyong.cho at samsung.com
Mon Mar 9 07:21:42 PDT 2015


I want to find best solution on our case. Our product is mobile device.
But I don't think that is only problem of mobile device. That also can
be problem of laptop. So, please comment to me.

We have some of services are always running after system is started up
as default. They don't need to be running always. They are just needed
only charger is plugged in.
So I thought lets only active them when only charger is plugged in.

I thought two methods.

method 1:
Charger also can be detected by udev. So udev hardware activation can be
I wrote below udev rules.

TAG+="systemd", ENV{SYSTEMD_WANTS}+="foo.service"

It looked working well. foo.service is only activated when charger was
plugged in.
But I have some of problems with hardware activation.
I want to be stopped foo.service when the charger is plugged out. As I
know, this is impossible with udev hardware activation.
To do this, foo.service have to determine the charger state itself and
if the charger is plugged out, it have to stop itself.
And it is working only at the first time.
After foo.service was activated, I stopped foo.service by "systemctl
stop foo.service". And plug out and plug in the charger again. Then
foo.service was not activated. (Is it normal? I did not try to find the
reason. If you say it's a problem, then I will try to find.)

method 2:
We have another device daemon. Let's call that as deviced and its
service name is deviced.service. deviced know about plug in/out of the
So, I made a new charging.target. foo.service have Wants= dependency for
charging.target. (Installed on charging.target.wants.) And I added
"BindsTo=charging.target" to foo.service.
Then foo.service is activated well when the charging.target is entered
to active state. And also deactivated when charging.target was deactivated.

In this method, there are limitations what some of other daemon is
needed and new charging.target is needed.

Is there any more good way for this?
I want to find best appropriate way.

Thank you in advance for comment.


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