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I saw the option Suspend in Ubuntu. What does it do?

I tried this option, but my PC goes to low power mode and then, I can't bring it to a normal condition. So I had to power off my PC.

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You've really got two questions in this one - it would be a lot more beneficial if you split up the "What is suspend" and "Why doesn't my laptop wake up from suspension" so each can be objectively answered. –  Marco Ceppi Mar 3 '11 at 18:36
    
I have the same problem with Ubuntu on my new laptop. Using Suspend I can't bring it back to a normal condition. So I had to power off my PC. After I power off, then on, it comes back. It then runs well. I don't know if it's the laptop, or Ubuntu that is at fault. But I know I don't like it. –  user163947 Jun 2 '13 at 22:10

2 Answers 2

up vote 15 down vote accepted

Suspend mode is a special low-power mode, often used on laptops, that preserves the contents of RAM while conserving power.

There are two main forms of suspend - suspend-to-RAM and suspend-to-disk (also known as "software suspend" or "hibernation"). Suspend-to-RAM uses more power, but is almost instant. Suspend-to-disk, on the other hand, uses no power (the system actually powers off), but takes longer to suspend/resume.

You can find more info in this wiki page.

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In fact, the power usage to support RAM contents alive is extremely low. My laptop managed to survive at least 24 hours of suspend-to-RAM mode, and I was still able to bring it into normal mode; and that happened instantly. I didn't have to wait while the whole 2 billion of bytes were read off the hard drive into RAM. I get my laptop ready to work right the second I hit the spacebar to wake it up. Contrary to this, suspend-to-disk a.k.a. hibernate is SLOW and actually sucks IMO. –  ulidtko Mar 3 '11 at 19:50

When you click on suspend, everything on your system goes into a low-power mode, except for memory which is placed in such a state that it will retain its contents. The peripheral bus lose power and devices attached to your client are also suspended. Typically, it should take around 1-3 seconds to enter suspend (or suspend-to-RAM) state.

On mobile clients, like laptops, you can enter a suspend state (or sleep) by simply closing the lid, or choosing suspend from the power menu options. To wake up the system from suspend, you simply have to open the lid.

On some models of laptops the lid switch does not enable a wake. In that case, you could hit any key or the power button to wake the system from suspend. On desktops you could hit the dedicated sleep key (if there is one) on the keyboard, or simply push the power button to wake up the system from the suspend state.

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