My iMac retina 4k, 21.5inch, late 2015, refuses to install Big Sur. No problem downloading, but the installation process fails after about 40 seconds, reboots, fails, reboots....... I gave up after 10 reboots, but found it looping again today having failed to auto update overnight. I have tried starting from Recovery, reinstalled Catalina, run Diagnostics with no error (ADP000), reset NVRAM, all to no avail. Anybody got any clues about this?
iMac 21.5″, macOS 10.15
Looks like you've identified the problem. There's another community thread about it here;
https://discussions.apple.com/thread/252034376?answerId=253913988022&page=1
Apparently Big Sur tries to install exclusively on the SSD part of the Fusion Drive, but during the installation demands > 40GB storage , which is then much reduced afterwards. My Fusion Drive SSD (disk0) only has 24GB:-
diskutil list
/dev/disk0 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *24.0 GB disk0
1: EFI EFI 314.6 MB disk0s1
2: Apple_APFS Container disk2 23.7 GB disk0s2
/dev/disk1 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *1.0 TB disk1
1: EFI EFI 209.7 MB disk1s1
2: Apple_APFS Container disk2 1000.0 GB disk1s2
/dev/disk2 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +1.0 TB disk2
Physical Stores disk0s2, disk1s2
1: APFS Volume Macintosh HD - Data 290.7 GB disk2s1
2: APFS Volume Preboot 86.8 MB disk2s2
3: APFS Volume Recovery 528.9 MB disk2s3
4: APFS Volume VM 3.2 GB disk2s4
5: APFS Volume Mac Built In 11.2 GB disk2s5
I don't hold out much hope of Apple fixing this for Fusion Drive 2015 iMacs because they're next in line for obsolescence :( I'm staying with Catalina!
You would have thought Apple engineers might have put a simple size check on the disks before the download even started, let alone letting the install itself fall into an infinite loop. This is basic stuff. I'm amazed that Apple a) haven't put this simple fix in already to warn about the size needed, and b) haven't done something about the bigger issue of needing > 24GB of size to install an OS. That's a lot of memory! However I'm guessing Apple have no interest in fixing this issue otherwise they already would have (it's been months already), as it probably forces people to buy new hardware. A shame.
Thanks for the suggestion - I have no "maintenance" apps or third party anti-virus installed.
Thanks - here's the most recent Etrecheck report
I’ve exactly the same issue. Have you found a solution yet?
Same problem with Big Sur install crash in an infinite loop reboot on iMac 21,5 Fusion Drive late 2015......
We are expecting Apple to solve thin annoying issue that a lot of users seems to have
I’m having the exact same problem with the same model iMac. Infinite reboot loop. Please do something about this Apple.
Same problem, stuck in a install loop. Get to about 10% and then reboots..again and again and again........ running Catalina on Imac Retina 5k, 27inch, Late 2015
This needs to be fixed.
Hi,
Same Issue with an iMac 2017 21" infinity Loop. Please Help
Installer Big Sur 11.1
Just tried with big sur 11.2.
Same issue! Does anyone from Apple monitor these forums? If so appreciate if you can at recognise there is an issue for folks!
I've also tried with 11.2 and again failed exactly like it did with 11.1. And yep I agree with Jock_King. Someone from Apple needs to look into this.
Thanks for that suggestion. My Mac has over 700GB of available storage, so whatever my problem is, it's not lack of storage :(
Seems like this is impacting lots of people - surely Apple must be able to put a fix in to address the issue! (well you would think!)
You can save you and us a lot of time and effort if you do the following:
Please navigate to the Mac App Store or navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.
When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again.
For instructions on how to download your EtreCheck report and attach it to your reply to this message please click https://discussions.apple.com/docs/DOC-250000211
The best antivirus, cleaning app, and overall maintenance app for Mac OS is Mac OS itself. All you need to do with Mac OS to keep it secure and running well is to keep it up-to-date and do periodic (about 1x per week) restarts. Other than that, leave it alone. Adding third party antivirus, cleaning, security and other types of maintenance apps to Mac OS adds no additional level of security. The only thing these apps do is have the opposite affect users want. They make Mac OS slow, unstable, generate odd behavior (much like you are experiencing) and make Mac OS appear buggy.
Please locate the developers uninstall instructions for Trusteer and follow to the letter. Then restart in Safe Mode per the directions in Use safe mode to isolate issues with your Mac and then restart normally.
No, and the problem persists with the latest version of Big Sur. I've also tried reinstalling Catalina, but I can't get rid of the Big Sur installer volume, so I have to use the Startup Manager to boot into Catalina. Big Sur persists in trying to install itself overnight unless I disconnect power altogether.
Big Sur Install Loop
