power management in hal

Richard Hughes hughsient at gmail.com
Thu Aug 31 14:18:04 PDT 2006


On Thu, 2006-08-31 at 13:43 -0700, Arvind Ayyangar wrote:
> hi ppl,
>   my system runs 3 acpi related  threads for power management viz
> [kacpid],/usr/sbin/acpid -c /etc/acpi/events -s /var/run/acpid.socket
> and an addon thread created by hal.. How do these differ in their
> functionalities, all are reading the events from the same events file
> (/proc/acpi/*/events) 

I think kacpid is a kernel thing, i.e. it has to stay.

acpid is a system service, that takes the acpi events from the kernel
and copies then to a special file that is easier to read. You can also
write shell scripts for acpi events that do clever things.

The hal addon can use either the kernel event source or the information
supplied by acpid. Personally I've uninstalled acpid as nothing I use
requires the acpid functionality.

> 
> Also, could someone plz tell me how the actions are taken when a power
> evnt become critical i.i. battery has no charge etc. Hal just stores
> this data in the device object created, no actions are taken in such
> conditions... Is g-p-m responsible for that? 

As the author of g-p-m, I would say yes, although there are other system
daemons available such as powersaved.

When g-p-m calculates that the battery is critically low (which isn't as
simple as you might think) it then asks HAL to perform the actions.

I hope this is clearer.

Richard.

> "Success is not measured by what a man accomplishes, but by the
> opposition he has encountered, and the courage with which he
> maintained the struggle against overwhelming odds." 
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