I am trying to write a script that will shut down the computer if a few requirements are filled with the command
os.system("shutdown now -h")
Many of the linux distributions out there require super user privileges to execute
halt, but then, how come that if you're sitting on your computer you can power it off without being root? Well... the idea behind this is that if you have physical access to the computer, you could pretty much pull the power cord and power it off anyways, so nowadays, many distributions allow power-off though access to the local System Bus accessible through
dbus. Problem with
dbus (or the services exposed through it, rather)? It's constantly changing. I'd recommend installing a dbus viewer tool such as D-feet (be advised: it's still pretty hard to visualize, but it may help)
Take a look to these Dbus shutdown scripts.
If you still have HAL in your distrubution (is on the way to being deprecated) try this:
import dbus sys_bus = dbus.SystemBus() hal_srvc = sys_bus.get_object('org.freedesktop.Hal', '/org/freedesktop/Hal/devices/computer') pwr_mgmt = dbus.Interface(hal_srvc, 'org.freedesktop.Hal.Device.SystemPowerManagement') shutdown_method = pwr_mgmt.get_dbus_method("Shutdown") shutdown_method()
This works on a Ubuntu 12.04 (I just powered off my computer to make sure it worked). If you have something newer... well, it may not work. It's the downside of this method: it is very distribution specific.
You might have to install the
dbus-python package for this to work (http://dbus.freedesktop.org/doc/dbus-python/doc/tutorial.html)
I've been doing a little bit of research and it looks like this is done in newer Ubuntu versions through ConsoleKit. I've tested the code below in my Ubuntu 12.04 (which has the deprecated HAL and the newer ConsoleKit) and it did shut my computer off:
>>> import dbus >>> sys_bus = dbus.SystemBus() >>> ck_srv = sys_bus.get_object('org.freedesktop.ConsoleKit', '/org/freedesktop/ConsoleKit/Manager') >>> ck_iface = dbus.Interface(ck_srv, 'org.freedesktop.ConsoleKit.Manager') >>> stop_method = ck_iface.get_dbus_method("Stop") >>> stop_method()
Probably why can you do this without being
root deserves a bit of a wider explanation. Let's focus on the newer
HAL is way more complicated and messy, IMHO).
ConsoleKit is a service running as
root in your system:
borrajax@borrajax:/tmp$ ps aux|grep console-kit root 1590 0.0 0.0 1043056 3876 ? Sl Dec05 0:00 /usr/sbin/console-kit-daemon --no-daemon
d-bus is just a message passing system. You have a service, such as ConsoleKit that exposes an interface to
d-bus. One of the methods exposed is the
Stop (shown above). ConsoleKit's permissions are controlled with PolKit, which (despite on being based on regular Linux permissions) offers a bit of a finer grain of control for "who can do what". For instance, PolKit can say things like "If the user is logged into the computer, then allow him to do something. If it's remotely connected, then don't.". If PolKit determines that your user is allowed to call ConsoleKit's
Stop method, that request will be passed by (or through)
d-bus to ConsoleKit (which will subsequently shutdown your computer because it can... because it worth's it... because it's
To summarize: You can't switch a computer off without being
root. But you can tell a service that is running as
root to shutdown the system for you.
I read in one of your comments that you wanna switch the computer off after a time consuming task to prevent it from overheating... Did you know that you can probably power it on at a given time using RTC? (See this and this) Pretty cool, uh? (I got so excited when I found out I could do this... ) :-D