Is it possible to hibernate a Linux machine? What is the difference between sleep, suspend, stand-by and hibernation? Why isn’t my machine waking up after pressing keys on my keyboard?
I can finally answer these questions after a long time wondering why something does not work. Let me explain some of the concepts first.
These concepts are general but what I’m describing here might be specific for Ubuntu based Linux systems.
These terms are used interchangeably. The state of your machine is saved to RAM and the computer puts as much as it can to some low power consumption mode. Energy is still consumed and there is a risk of losing unsaved work in case energy is no longer available (e.g. empty battery). The advantage is, that suspending and waking up is fast (couple of seconds in my experience).
When a computer hibernates it saves its state to hard drive and then shuts down. Someone might call it suspend to disk. When it wakes up it restores its state from hard drive into memory. You need space on your hard drive in other to save the state.
Hibernation has most issues, probably because it is dependant on the combination of hardware and operating system. You might not need hibernation—sleep might save enough energy and power off might be fast enough.
Update: Hibernation might be useful. A hibernated system does not consume power and hibernation protects from some class of possible attacks when the drive is encrypted as mentioned in this article from System76.
Is a normal process of properly shutting down a computer. Halting a computer might be slightly different. As I understand it powering off is a more complete process.
When you manually lock your computer or when you are away for some time it provides you with a prompt for password—your computer is locked. The same happens when the computer is waking up.
Shuts down your running applications (it might not stop all of the background processes) and effectively locks the screen.
Is a time when the computer evaluates that it is doing nothing. From the practical point of view the computer can be configured to do something useful after some specific time of beiing idle and it might lock the screen or suspend itself.
I believe you can’t directly force your computer to go into those states, those are probably internal. In awake state all components are running, while in standby state harddisks and other peripherials might be turned off.
Or rather sleeping down because at least for me, suspending is way more convenient (read: faster) way of ending my work. I usually hit a dedicated key on my keyboard (a cheep Cherry keyboard). Another way is to let your machine sleep after a specific time. In Gnome settings there is an item called Automatic suspend (Settings ➙ Power), where you can set it up. Wierdly enough you need Gnome Tweaks to set the suspend action after closing a lid of your notebook (it is in General section there).
A reasonable way to wake up your computer is to hit some key on a keyboard. It might sound simple, but there are issues with external keyboards for notebooks or wireless keyboards. In my case I have checked askUbuntu and my BIOS settings and found a disabled option. Now I can wake up my notebook (from sleep) using keyboard (not mouse—but I like it) which is connected via USB dongle.