I use Fluxbox window manager on Ubuntu Linux where I don’t have all the bells and whistles of GNOME or KDE.
so I thought I’d make myself a daemon program that will automatically put my computer to hibernate when my laptop battery is almost empty
usually I take care that my battery doesn’t get to the red zone but this is for those few cases I forget
I wrote this small programm in C++
why c++
well because I don’t programm in c++ and I found it interesting to do so 
main.cpp looks like this
so, you see the locations of the info and state file for the laptop battery, the percent at which we go to hibernation (I’ve set it to 12%), and the sleep interval before checking the battery state again (10 seconds)
I use my own hibernate script but you could use something like /usr/sbin/hibernate
you can change all of these
in the main function you can se that:
- we work only as a root user
- we daemonize (detach from the terminal and run in background)
- instantiate a worker class object
- and do our work
and what is our work? check out this picture
well we get the battery total capacity and current capacity and then we calculate the percent
if the percent is less that what I want (12%) then I want my laptop to go to hibernaton
but I also made a security check (that you can remove if you like)
that makes sure my laptop doesn’t go twice into hibernation in succession
why did I do that?
well because I parse data from some files I have no influence over
and those files can change their format anytime
so this is just a precaution
I have a simple makefile that compiles this code, copies it to /usr/local/bin/medved (medved in my language means a bear and bears hibernate 
) and adds an entry to /etc/rc.local so that it starts next time you reboot your box automatically
you can also start it by hand and see how it works before the reboot
and that’s it, now I have a daemon that puts my laptop to hibernation before my battery runs dry
I’ve published the source code under GPL licence version 3
you can get source code here
