Update to 11.6 Big Sur fails

First thing to check is Empty Disk Space. The lack of empty Space will be a factor and if leas than 15% of the total disk capacity - there will probably be issue now or later.

If this update is for Big Sur 11.6 the error message can be misleading. There are factors like poor Wifi connection, slow wifi connection.

Too many other people downloading at the same time and Apple Severs are overloaded.

Software on the computer interfering with the download process, running behind a VPN.

If via wifi too many Other devices using the wifi at the same time reducing the Bandwidth to your computer.

Best Results are via Ethernet Cable to Router

There are several ways to download the Big Sur 11.6 update. 

1 - Connect to Router via Ethernet connection and restart the computer in Safe Mode and then open the Apple Apps Store and get the Full Installer of Big Sur. It will be the 11.6 version and once downloaded run the installer from the Applications folder.

2 - Restart the computer in Recovery Mode ( INTEL Command + r ) and choose Reinstall macOS. It too will download the full Installer and commence the installation. For M1 CPU the Recovery Mode is Here

3 - This method may seem unnecessary but sometimes the Router Restart clears Network issues from ISP to Apple Servers

Shutdown Router. Shutdown computer and disconnect all External Drives. Restart Router. Connect to Router via Ethernet Cable. If via Wifi - Disconnect all other Devices using the Wifi - want the Maximum Bandwidth only for this computer. Restart computer in  Safe Mode. It does a Repair Disk, Clear System Cache files and only load Apple Software, extensions and Fonts. Will load slowly - Normal. Once Logged in - open Apple Apps Store and  Get the Full Version of Big Sur. It will take some time and several pauses will occur - normal. Countdown clock may say 15 minutes but in Real time may be 30 minutes. Same goes for clock at 10 minutes could be 20 minutes in Real time. Eventually , Full Installer will download and a New Application in Applications Folder will present called Install Big Sur. Stop there and perform a Time Machine Backup. If desired - have an External Drive - Copy & Paste the Install Big Sur Application to external drive for future usage - making a Bootable Installer. Now run the Installer.

Have found this method more reliable than the Software Update which is very iffy at best

Are there any AntiVirus, Disk Cleaner, Optimizers, Defrag, VPNs etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation.

The below suggestion is predicated on the following have been completely addressed >> > Are there any AntiVirus, Disk Cleaner, Optimizers, Un-installers, etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation. The Built-in Security of Big Sur is all that is required.

Before doing anything - stop and do the Time Machine Backup and if possible use a good Cloning Software to make a Bootable Clone of the computer as it is now. Each of the two previous suggestions should be done to separate external Drives.

Open Terminal and copy and paste this command, without quotation marks, " softwareupdate -l " This will run and search for available updates to Big Sur. What is the output of this command ??

Should the output read Big Sur 11.6 - good. So the system actually sees the update. If it does not - there are other issues to explore.

Still in Terminal, again run this command without quotation marks " softwareupdate --fetch-full-installer --full-installer-version 11.6 " It is going to pull the Full Installer of Big Sur 11.6 with a running countdown % clock as it advances.

It should install a new application in the Applications folder called Install Big Sur - it will not auto launch.

Stop there if successful and make yet another TM Backup

Restart in Safe Mode - hold Shift - immediately at restart and keep holding until the Apple Logo is presented - then, release. Going to load slowly - normal. Now, run the Install Big Sur.

Have seen this same issue elsewhere https://discussions.apple.com/thread/253143319 and that person has not come back to advise if it was resolved or Not.

If you follow that discussion - personally ran the two command on MBA M1 running Big Sur 11.5.2 yesterday - an presto - downloaded the Full Installer of Big Sur 11.6 without issue

The same questions were put forth regarding AntiVirus, Cleaners, Optimizers, UnInstaller, VPNs etc were asked there and here too.

Without more reliable information -this is a bit difficult to proceed

You can get the full installer here:

https://support.apple.com/en-us/HT211683

You HAVE to download this using Safari, it does not seem to work with other browsers.

I suppose this is what you are trying, right?

What exactly happens when you try to install?

You may want to run Etrecheck and post its report here. As it is often the case, we may be able to spot something in the report that can help.

1. I have approximately 1.8Tb of available disk space (this MacBook is quite new)
2. The download completes.
3. Updates apply for some time.
4. I then get the failure message about the boot sector.
5. Then the system rolls back.

Based on all the "I have the same problem" votes, this seems to be a common problem.

woodchal wrote:

More than 1 Gb of disk space available

Connected to router by Ethernet - no problems

I have tried in safe mode, but not recovery mode

Will try restarting router, when other users go to bed!

No security software installed

1Gb?????

You need to have at least some 40GB+ free disk space, preferably more.

Phillips than you so much for keeping everybody alive! Could it be possible that issues are coming up when one upgrades from versions of Big Sur prior to 11.5.2 ? I have had the same issues as all others and have abandoned the update until there is clarity. I have over 2TB of hard drive space, a FIOS internet connection and an iMAC 27 inch late 2014 model running BigSur 11.4. After repeated attempts last night, upon complete of download I still see the same error message( "error occurred while downloading selected updates... pls check internet connection") at 15 minutes remaining. Clearly this update has been written in a hurry.

Meanwhile I have downloaded the BigSur 11.2 but am yet to install it. I am thinking of first updating to 11.2 and then trying 11.6 but am somewhat nervous about this whole thing. So waiting until we have more light on the issue. And needless to add I did have an MalwareByte installed by one of Apple support way back in 2014 which I have now deleted completely from the Trash bin.

cheers,

raj

Phillips I tried the steps and get this message:

rajats-iMac:~ rajatbhu$ softwareupdate -l

Software Update Tool

Finding available software

Software Update found the following new or updated software:

* Label: macOS Big Sur 11.6-20G165

Title: macOS Big Sur 11.6, Version: 11.6, Size: 2865587K, Recommended: YES, Action: restart, 

rajats-iMac:~ rajat$ softwareupdate --fetch-full-installer --full-installer-version 11.6

Scanning for 11.6 installer

Install failed with error: Update not found 

So it finds the update and then gives this message

Big Sur 11.4 still - that goes back to May 25, 2021. That is four version out of date. Have never every allowed any of my computer lag that far behind.

To Really get a good look at both the Hardware and Software involved in this situation >>>

Etrecheck

Suggest downloading the Application Etrecheck  directly from a Well Respected ASC Contributor. The application is free or paid from added features. Run the application with Full Disc Access ( Security & Privacy - Full Disc Access ). It will take a Snap Shot -  both the hardware and software. The Report will Not Reveal Any Personal Information. Post back the Full Report - copy and paste - using the Additional Text Icon ( 3rd Icon to last )

We can have a look at the report for possible issues and may have possible suggestions to resolve the issues.

Any Third Party Applications that will interfere with the normal operation of the OS, alter, modify, remove or delete or attempt to do so is an invitation for disaster and may require a Reinstallation of the OS.

As you said, maybe the problem comes from user that try to update to 11.6. from version prior to 11.5.2

I'm trying to update from 11.1 its been a week of downloading and fail it took me 14 hour just to get 6gb file update and its crazy considering i can download 11gb games file in 1 hour on my PC.

Last night I successfully upgraded from 11.2 to 11.5.2 using the current BigSur edition on Apple website. I am now waiting to backup upon which I will try the normal download of 11.6 which was failing earlier. Everything running perfectly at the moment...iMac 27 late 2014 3TB. Will keep you posted.

I have yet to try Etrecheck since it is not on the Apple store and I was not entirely comfortable downloading something that is very difficult to remove completely.

Thanks to everybody for their useful inputs.

Cheers.

It is entirely possible., because the version of Big Sur was so out dated 11.4 , the 11.5.2 was a prerequisite before allowing the 11.6 could be downloaded. You may have Hit on Something - Good Work : -)).

I may have also learned something new in this quirky Big Sur OS.

Thanks for your thoughtful posts. Yes indeed I am guilty :( of lagging behind rather too long in upgrades. That is somewhat driven by the idea of letting the bugs to play out and the update stabilize before I jump in. The same applies to the iPhone updates.

However, there is delicate balance when you are missing critical security updates such as in this case!

Will keep you posted.