My iMac starts up super slow and is generally unresponsive. What's up?

July 25, 2017 2:37 AM

I've got a retina iMac, the original one, circa 2014. Until recently, it's been amazing, problem free. But yesterday i booted it up and it gave me a black screen, with a movable mouse. Several tries later, it booted regularly, but extremely slowly, like it took 20 minutes until I could load even a single app/program. Even now that it's up to speed, everything is opening slowly, and the slowdown involves all my favorite programs. Chrome is slow, finder is slow, it's all slow. What's happening?

Is there an easy fix? Or do I need to bring this machine to an Apple store?

posted by flod to Computers & Internet (10 answers total)

How much RAM does it report having? Some of its memory may have died (or gotten loose somehow).
posted by Too-Ticky at 2:57 AM on July 25, 2017 [1 favorite]

Do you have the Fusion drive or just a straight-up SSD? It sounds like the HDD half of the Fusion drive may be failing. Try opening Disk Utility and running First Aid on the drive.
posted by Venadium at 5:03 AM on July 25, 2017 [1 favorite]

Also, download and give EtreCheck a try if First Aid doesn't mention anything.
posted by deezil at 5:17 AM on July 25, 2017 [3 favorites]

You should launch Console.app and see if there's any obvious repeating error messages. My guess is the same as Venadium's, a failing spinning hard drive. I think suddenly-dead-RAM is unlikely. But if your machine was bought with only 4 gigabytes there's a tiny chance that some recent software patch recently pushed you over the limit and your machine is now thrashing for want of RAM.
posted by Nelson at 7:38 AM on July 25, 2017

I came here to second the recommendation for EtreCheck. My 2017 iMac, which is only a few months old, began to show similar symptons (mysterious reboots, irritating pop-up windows in Safari and Chrome, occasional slowness).

I am a diligent Apple owner (I've held four Apple certifications) and still some cretins managed to load adware on my system. Sometimes you just need to get under the hood and clear out some junk. EtreCheck did it for me in a few clicks.
posted by the matching mole at 8:00 AM on July 25, 2017

Best answer: It may be an issue with your user account getting corrupt or just having a lot of cruft. Try creating another administrator account on your Mac and see if that improves your bootup time. If so, it's pretty straightforward to switch over from there.
posted by homesickness at 11:00 AM on July 25, 2017

Sudden extreme sloth is a pretty reliable sign of a hard disk drive that's going bad. A newly bad block in a critical directory can cause the HDD to need to seek and seek and retry and seek and seek every time it tries to open a file linked from that directory.

If you brought that machine to me to diagnose, I'd be using a utility that interrogates the disk drive's SMART log and tells me the values for the reallocated sectors count, the current pending sectors count and the offline uncorrectable count.

If the current pending sectors count is nonzero, that can slow a drive anywhere from imperceptibly to massively depending on exactly which sector(s) are slow to read. Pending sectors get fixed by rewriting them, which either overwrites failed magnetic traces with fresh ones that work properly, or rewrites new data to an entirely different spot on the disk surface which from then on will get transparently substituted for the failed spot; the reallocated sectors count shows the number of times the second thing has happened.

Pending sectors that don't actually get rewritten typically stay pending forever; the Web is full of claims that they get automatically reallocated as soon as they become slow to read, but I've never once encountered a drive where this appears to have happened.

If the offline uncorrectable and/or reallocated sectors counts are more than about 10 each, the drive is on the way out and needs to be imaged and replaced, or (preferably) replaced and restored from backups.
posted by flabdablet at 11:27 AM on July 25, 2017 [1 favorite]

I realize this runs against the proud MeFi tradition of fixing it ourselves, but I would be taking your machine to a local Genius Bar. I look back to the time I spent endless time on my own beloved MacBook Pro (circa 2013) because I could not get a decent wifi connection at work. I finally carted it to a local Apple store and they had it humming in 15 minutes. It's still going strong.
posted by bearwife at 12:43 PM on July 25, 2017

Response by poster: homesickness for the win! Disk Utility First Aid didn't identify any problems with the hard drive, but setting up a new admin account seems to have made all the slowdown magically disappear. Whew! Of course, now I've got to transfer all my settings and files over, but that's a small price to pay for such an easy fix.

Thanks, all, for your help!
posted by flod at 11:05 PM on July 25, 2017

If the problem is the disk dying and something in your old profile got corrupted, you've just bought yourself some time not actually solved the problem. Make sure your backups are all up to date and be prepared to go through this again.
posted by russm at 12:05 AM on July 26, 2017 [2 favorites]