Several people have commented that they can stop their laptop from suspending when closed, but the screen stays on. Maybe this is due to differences in firmware? There is an alternative feature that might work.
At one point, the Linux kernel text console had a default setting that blanked itself after a period of inactivity. An equivalent to the screensaver in your favourite graphical environment :).
Some people like to set the blank time using the kernel boot option
consoleblank=, which takes a value in seconds. However, the documentation I find does not say this is sufficient to achieve full power saving, or any real level of power saving. Maybe it does what they want it to on their system! Or maybe it doesn't. The documentation is unhelpful on this point.
Remember the original function of a screensaver, was to avoid burning-in a permanent ghost image on your CRT display. It does not necessarily save power. When full power saving was introduced, it was used after a longer delay. Bringing the display back up and running could take a few seconds, which would be much more annoying to the user.
Apparently it is possible to enable console blanking at runtime, using
setterm --consoleblank [1-60]. And then
setterm has another option
--powerdown [1-60], to eventually enable "powerdown mode" after a timeout.
If I'm reading it correctly, there's a sequence. First the console blank timeout applies. Then after one powerdown timeout, it applies "vsync suspend mode". Finally after a second powerdown timeout, it applies "powerdown mode". These timeouts are all specified in minutes, not seconds.
So I think you can use a command like this:
/bin/setterm -term linux -blank 10 -powerdown 5 </dev/tty1 >/dev/tty1
I'm not sure whether CoreOS lets you add arbitrary commands to the boot process (as in
rc.local on other distributions, for example). I imagine you can always use a privileged container :).
setterm --blank says that blanking uses APM if available. Narrator voice: APM is not available on modern hardware. I don't know if blanking will use any modern power saving scheme.
"powerdown" mentions "VESA" display power saving. "VESA" power saving is still a thing. I don't know if "powerdown" is necessary or even sufficient to work for modern stuff.
setterm does not say what the default "powerdown" settings are. If I had to guess, I would say it is not enabled by default.