On other operating systems, there are ways to see what process or event woke them from suspend. I leave my laptop often for multiple days in suspend, sometimes to find that it has woken itself up and is heating whatever surface it is resting on :)
Is there a way to find out what woke it up so that I can prevent that thing from happening again? On Ubuntu 12.04 (elementary Luna).
The only thing I'm aware of that's commonly used to force a wake (besides, I guess, the hardware interrupts) is the rtcwake command. The source for that uses ioctl() calls on the real time clock device (by default, /dev/rtc0) meaning it must have privileges (so it cannot be anything you start on your desktop as a normal user).
I would be very surprised to learn that there is a privileged service on Ubuntu set up to do anything like that (why?). However, I do notice that occasionally a sleeping system has woken up for no apparent reason while left alone. I do not have a cat, so I assume this is something having vibrated the mouse, or maybe some weird voltage fluctuation, or some other random cause.
If this happens regularly, it may indicate a bug in the ACPI driver.
