Q: Why is my imac shutting down by itself?

the link to download it no longer exists

Are you referring to the link to iStat Pro?  It's been discontinued, however, CNET has it here,

I had a client with an iMac that randomly shut down several times a day. After trying many things, the solution I found was this:

1. Go to Library/Preferences/SystemConfiguration/

2. Delete the file com.apple.PowerManagement.plist

3. You will have to authenticate with an administrator password to trash the file

4. Reboot the computer

That's it! No more shutdowns after using this procedure.

Hopefully this will help someone who's having this issue.

That method seems to be working, thanks :)

My five month old iMac started shutting itself down a month ago.  It was not possible to restart until I'd unplug it and plug it into a different outlet (I was desperate).  This kept happening so I took it to the Apple Store and they were unable to replicate the problem.  So back home I went and soon my computer was having the same problem.  So I asked for a replacement iMac and Apple provided it.  No sooner was I home with everything transferred to the new iMac than the problem resurfaced.  I even plugged it into different circuits in my house and suffered the same problem.  It just might be a design fault.  A friend told me it sounded like the automatic shutdown in the Energy Saver setting wascausing the problem so he said move it to Never, which I did.  No problem since, but this isn't a good fix for those who like to have their computer turned on for long periods.  Good luck fellow sufferers!  Nothing else I tried helped, but this did.

Same happening here. I am thinking that maybe Lightroom have something to do with it. It looks like Lightroom makes the temperature rise a lot.

I live in The Netherlands and bought a new iMac earlier this year. After three months it started shutting itself down for no reason and the only way I could get it back was to pull out the power cord, plug it back in and press the on/off button at the back. After a few days of interuptions, I called Apple Support and we did some various checks. Sometime later, it switched itself off again - it didn't matter whether it was idle or I was writing an email or whatever - infuriating, especially as emails were not saved. Apple Support then had me erase all the data and reload the Mavericks. That didn't make any difference. So I took it to the shop and they sent it off to Apple who returned it a few days later saying they had checked all the hardware and reloaded the software and it was all fixed. However, I was expecting a system similar to when I first bought it - pretty much ready to go. But they had loaded up some Dutch version and I had to go on top the internet and download and install Mavericks again and then restore my data and files. The computer worked fine for two weeks and then it started switching off again last week. I tried deleting the file powermanagement.plist as suggested above - but the next day it shut off again several times in succession. I am hoping they will give me a new machine as this one clearly has a major problem - maybe to do with temperature (though I am not sure what Lightroom is) or power or something in the system software. It is VERY irritating because I simply cannot trust the machine.

If you iMac is still doing this. Go back to Apple and ask for a new Mac. Its clearly faulty!

My iMac has been doing this for three years. Apple doesn't seem to want to acknowledge or address this problem. It's impossible to use the system for work, because I can't afford to have it shut down in the middle of a project. Nothing seems to make any difference. I've tried all the posted fixes. They don't work. It has nothing to do with software or timing or anything I can discern, except maybe my moods!! I'm beginning to think the thing shuts down in response to some fluctuation in my own bio-electrical vibrations.

This worked for me!!!!! I thought I was going to have to reimage my system. Such an easy fix. I recall changing the setting a few months ago and suddenly the problems started happening, but would only happen when I walked away from my Mac. It became frustrating when I would stream over AirPlay and I'd have to wake up my Mac all over again. So glad its working now.

Much appreciated!

It worked for five days - and now it starts again. Apple Support want me to do a clean install and see how that goes. I will have to put back my docs though - but won't do any of the config files. We'll see!

Any news, people...? I'm desperate. I simply can't work.

I think this is important, people:

"I suggest launching the Console application that can be found in the Applications/Utilities folder. Once it launches, type 'shut' into the upper right corner 'String Matching' field and then press return. You should see log entries for each system shutdown event whether intentional or unintentional. You will see an entry reporting the shutdown event, then a 'Previous Shutdown Cause' entry with a reason code that is logged at the next power ON. I suggest capturing this information and pasting it here for others to review. If there are no entries during the times that you experienced the shutdown event then that would indicate that the system was still alive during this period even though the display may have been black. A Previous Shutdown Cause of 5 indicates a normal shutdown, while a 0 indicates the power cord was removed or the power supply output failed. There are other possible codes, but I don't know what they mean. Hopefully others can chime in if you post the results. Be sure to remove any identifying information from the logs (if there is any) before posting. If you search just on 'shut' s I described above there shouldn't be any personal info in those entries."

I have a macbook, which works fine and gives me a shutdown cause 5. The iMac that shut itself down gives me a shutdown cause 0. Isn't it proof that this is a power supply issue?

Hi, I've just started getting this issue this morning and I don't know how to find this  .....Library/Preferences/SystemConfiguration/

I don't know where library is haha.

there is a feature on Mac that you can set when you Mac starts and shuts down. So for example, every morning 8 o'clock it will turn on, and it shuts at 4 pm. Make sure you have that feature off.