How do I prevent my iMac from going to sleep?

[DaniGirl]

I'm doing an initial backup through Backblaze, but it won't run while my iMac is asleep and I can't figure out how to prevent it from going to sleep. I found this post in their help section, but I don't have the top slider in my System Preferences, only the one about display sleep. I searched system preferences on sleep but nothing seemed to come up. I slid the display sleep slider to "never" thinking that would keep it awake, but it did not.

Ideas?

[Brian]

Head to your System Preferences. Click on Energy Saver and uncheck the box "Prevent Computer from Sleeping Automatically when the display is off." at the top. Also make sure "Wake for network access" is checked as well. If you have a laptop, this option may not be available. Here is a screen shot from my iMac:

 

[DaniGirl]

Thanks! But I can't get that top box to untick. Do I have to do something to unlock it?

[DaniGirl]

Okay, so I think I figured it out. If I slide "turn display off after" all the way to "never" I can't untick the box. But if I pull it back to three hours, I can untick it. So as long as the box is unticked, the computer won't go to sleep even if the monitor is off?

Edited January 20, 2019 by DaniGirl
clarity

[Brian]

Yes. Though I would set your slider to 15 min or turn on a screen saver. (Just like my screen shot above.) You don't want your display idling. While LED based displays aren't as prone to burn-in as older plasma-based displays, it is still good practice to either let them go dark or at the very least display a screen saver for long periods of inactivity.

Head to your System Preferences and click on Desktop & Screen Saver. Click the Screen Saver Tab at the top. I usually choose "Flurry" in the left column for my Screen Saver. Then set the time to "Start after 10 Minutes or even 20 Minutes" if you prefer.