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Power Management and Encryption



Daniel Feenberg wrote:
> Further search on google suggests the only way to accomplish this is to 
> write a cron job that periodically consults the "w" command for idle 
> times.

While that may be the most general solution, if you're talking about
specifically a system running GNOME (or possibly other freedesktop.org
compliant desktops), then a cleaner solution is polling the previously
mentioned API, or better yet, I believe you can create a DBUS client
that will receive notification of screensaver events.

Take a look at:
http://www.newegg.com/Product/Product.aspx?Item=N82E16880121002

A 2006-era message describing the GNOME Power Manager DBUS API and GNOME
Screensaver DBUS API, which includes methods to query the current state,
and issue a shutdown.

(Google also references:
http://live.gnome.org/GnomePowerManager/DbusInterface
but the links there don't seem to lead to the API documentation.)

Both APIs are described as being unstable:
http://live.gnome.org/GnomeScreensaver/FrequentlyAskedQuestions#I.27m_developing_an_application_that_has_a_fullscreen_mode.__Is_there_a_way_that_I_can_disable_the_screensaver.3F
"Please be warned that the gnome-screensaver DBus API is currently
unstable and may change in the future."

That links to the screensaver DBUS API documentation:
http://people.gnome.org/~mccann/gnome-screensaver/docs/gnome-screensaver.html

which describes, for example, the SessionIdleChanged signal.

Using the GNOME Power Manager DBUS API might cover more situations than
using the screensaver API. For example, if you assume your user isn't
necessarily knowledgeable or cooperative with your security policies,
and you want to prevent them from being able to manually suspend or
hibernate the machine.

What I'm not seeing in the GNOME Power Manager DBUS API is a mechanism
by which a program can register to receive notification of events like
suspend and hibernate, and then reply to that signal in a way that halts
the operation. There is an inhibit() method to prevent
suspend/hibernate, but then it isn't clear that the DpmsModeChanged
signal would ever fire on idle or the user's attempt to
suspend/hibernate. And if you don't inhibit(), it's hard to say whether
your code would receive the DpmsModeChanged signal and have time to act
on it before the suspend/hibernate commenced. (It also seems that
DpmsModeChanged documents a suspend state, but not a hibernate state.
Could be a documentation oversight, or a reflection that DPMS is
intended for monitors, where the distinction is irrelevant.)

 -Tom

-- 
Tom Metro
Venture Logic, Newton, MA, USA
"Enterprise solutions through open source."
Professional Profile: http://tmetro.venturelogic.com/






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