M2 MacBook Pro - Failed Update from Tahoe v26.01 to v26.1: The Mac "Мас" could not be updated. An unknown error occurred (21).

While attempting to update my M2 MacBook Pro from macOS Tahoe v26.0.1 to v26.1, the update failed and triggered a continuous boot loop. The Mac would power on, show the Apple logo without a progress bar, turn off, turn on again, and repeat this cycle until eventually displaying an exclamation mark inside a circle. 

 

 

According to Apple’s support page, this error requires placing the affected Mac into DFU mode and attempting a revive using another Mac.

Although I followed the key-combination instructions from Apple’s documentation, I noticed something was wrong. Even while holding the required keys, the Mac continued its boot loop and returned to the same error screen.

 After connecting my Mac to another Mac and following several boot loops, when my Mac reached the above screen, it appeared on the other Mac, as seen in Apple's documentation here and I was presented with the "Revive" and "Restore" options. I tried both, unsuccessfully, each time leading to the error "The Mac "Мас" could not be updated. An unknown error occurred (21)."

 Searching online it might be that error 21 is a generic error that can be displayed for various faults.

 SOLUTION 

In my case, the issue was that, even though the Mac appeared to connect to the other Mac, it was not actually entering DFU mode. I confirmed this using Apple's own Apple Configurator app (search in the App Store). If the connected Mac appears with a normal device icon, it is not in DFU mode. What you want to see is the DFU icon:

To reliably enter DFU mode, without finger gymnastics and counting seconds, use the macvdmtool by following the instructions. Once the Mac enters DFU mode successfully, you should be seeing a blank screen on the target Mac and the DFU icon in the other Mac within Apple Configurator. Right click the DFU icon and initiate a "Revive" or "Restore" as appropriate.

HDMI Audio issues (Pin 19 fix)

Found at: https://forum.kodi.tv/showthread.php?tid=224196

Pasting here for safekeeping:

2015-04-12, 17:08 RavynDarkcraft

Hello Community,

So, a while back I ran into some infuriatingly annoying issues related to HDMI audio from my HTPC to my Onkyo Receiver, and in some ways every device connected. The primary purpose of this thread is to spread some advice I received after tinkering with different solutions for about a month.This surprisingly works, but is apparently not common knowledge. I've seen threads about Kodi/XBMC switching audio devices from WASAPI to DirectSound, and the recommendations have been to buy HDMI splitters or some other device to 'fool' the HDMI handshake. Sure, that solution does work, and may even be a good route to go for some situations, but for I have an easier/cheaper option.

So, the underlying cause of all of these HDMI issues is the Handshake between the receiver and the HTPC. Now, I have an evga Nvidia GTX 970, so I'm certainly not using old hardware. That being said, even top end video cards these days are pitiful when it comes to HDMI audio. So, if you want to know who to blame for these frustrations, there you go. I'm sure M$ is somewhat to blame here as well, but I'm not sure. For example, the $35 Raspberry pi supports a feature called HDMI-CEC, yet these $500 video cards dont. It's ridiculous.

So, when you turn your TV off, Windows goes a bit wonky, and assumes that your audio device has been fully disconnected, not just turned off. This is why things get strange when turning your TV/receiver back on in terms of your audio. So the goal of this fix is to forcibly fool the system into thinking it's still connected.

This is the "Pin 19 fix", and it is called that because what you will need to do is cover up pin 19 on your HDMI cable. I can not see why it would matter which end of the cable (where it plugs into the receiver, or where it plugs into the HTPC) is covered, but I personally cover pin 19 on the end that plugs into my HTPC. A tiny sliver of electrical tape, like the image (from a Microsoft blog) shown below, should suffice.

Once you cover up pin 19 you'll want to go ahead and restart your computer. After that, you'll be good to go!

All this does is block the Hot Plug detection, as seem in the image below.

Well, I hope that this information proves to be helpful to others out there who have run into these annoyances.

Remove Google FRP (Factory reset protection) - Tested on OnePlus 3 running Android O

I bought a used OnePlus 3 for a friend and the previous owner had not logged out before wiping the phone so I was faced with the "This device was reset. To continue, sign in with a Google Account that was previously synced on this device" message.

The solution was to boot the phone, tap the Emergency call button and enter/dial *#812# as illustrated in the following video:

While searching for a solution I also found the following video with a more "complicated" solution that might be of use if the above does not work:

Launch VM machine on startup Windows Server

I wanted to launch a VM on startup. The way that VMware suggests you do this is by creating a shared VM which was not an option for me as those have some limitations. I tried running VMware Workstation as a service but that didn't quite work either as it would run the VM but when I logged on as the Administrator in Windows Server and try to logon to the VM it would be locked with a message popping up asking if I want to take over.

The solution to this problem was found on a StackExchange Server Fault thread. I am pasting the solution posted by the user Marcus here:

Figured out how to do it myself. It's somewhat of a workaround but that's what I expected to get.

• Alright, first step is to grab a program called AutoLogon.exe from Microsoft:
  http://technet.microsoft.com/sv-se/sysinternals/bb963905.aspx

Stop! Don't cringe just yet. Read on...

• Run it, set it so that Administrator should log on automatically.
• Create a task in Task Scheduler. Set it to run only when user (Administrator) is logged on. Trigger is "at log on" and specify that it's only when Administrator logs on.
• Create a second task. Run only when user is logged on, trigger at admin log on. Action should be "start a program" and program is "C:\Windows\System32\rundll32.exe" with the argument field set to "user32.dll, LockWorkStation".

What happens now if you restart the computer is that Administrator automatically logs on, the program you want to start is started and the work station becomes locked. If I log in via Remote Desktop Connection I can see the program window and use the GUI. I can lock/unlock the computer with no problem and disconnect/reconnect as I please. There's no issue if I go to the server and log in at the actual workstation either. Since Administrator is already signed in the task will not run again (it doesn't create some infinite log-in-lock-loop that you can't break out of).

Simple as that. Granted there is a one second time period before the computer becomes locked after the auto login and I guess a pro hacker with physical access to the computer could do something sneaky during this time window but in my case I can overlook that security risk. As long as I don't let any pro hackers into my home and show them the computer the system should be relatively safe. Above all there isn't that much of value on the computer that needs super-vault protection so I'm quite happy with this solution.

This virtual machine appears to be in use. - Take Ownership fix

If after a power failure, or reboot of you machine, you encounter the "This virtual machine appears to be in use." message when attempting to connect to your VM's, follow the steps below to remove the message:

1. Shutdown VMware.
2. Locate the folder where your VM is stored.
3. Locate one or more .lck or .lock files and delete them. If you are uncomfortable deleting these files, back them up in a separate folder.
4. Restart VMware and run your VM.

The message should not appear.

Delete all files of a specific extension from the directory that is executed, and all it's subfolders - Ubuntu - OSX

The following commands will affect all files of the specified extension from the directory that is executed, and all it's subfolders. It should work on all UNIX based operating systems:

Execute this command first in order to display all the files that are to be deleted (replace EXT with the desired extension):

find . -name "*.EXT" -type f

Executing this command will delete the list of files that the previous command returned (replace EXT with the desired extension):

find . -name "*.EXT" -type f -delete

What is /Users/Shared/adi in MacOS

I noticed there was an exclusion in my Time Machine for the folder /Users/Shared/adi that I had not placed there. According to galvanist.com "It is used by the Mac App Store and the new iBooks app."

Pasting here from the source to preserve it. Visit galvanist.com for potential updates:

If you’re running Mac OS X ~v10.8 (or later), you’ve probably got a folder at the path /Users/Shared/adi. Like me, you might be wondering what it is. I did some googling and got nothing. I dug a little further and found (part of) the answer: It is used by the Mac App Store and the new iBooks app.

In case you’re interested, here are the steps I took to arrive at this answer:

• Googled it. Didn’t get any signal.
• I made a shell loop that checks system packages:

  $ (IFS=$'\n'
  > for pkg in `pkgutil --packages`; do
  >   pkgutil --files "$pkg" | grep --label "$pkg" -H "Users/Shared"
  > done)
  com.apple.pkg.Essentials:Users/Shared
  com.apple.pkg.Essentials:Users/Shared/.localized
  

  No luck there…
• I looked in /Applications (sudo was already authenticated):

  $ sudo grep -r 'Shared/adi' /Applications 2>/dev/null
  # ...20 minutes later...
  $
  

  Rats.
• Finally, I looked for sandbox entries:

  $ grep -rl 'Users/Shared/adi' /System/Library/Sandbox
  /System/Library/Sandbox/Profiles/com.apple.bookstoreagent.sb
  /System/Library/Sandbox/Profiles/com.apple.storeagent.sb
  

  Bingo! com.apple.bookstoreagent is obviously used by iBooks.app. But just to be extra sure:

  $ grep iBooks /System/Library/Sandbox/Profiles/com.apple.bookstoreagent.sb
     (regex #"/Library/Preferences/com\.apple\.iBooksX\.secure\.plist$")
     (regex #"^/private/var/folders/[^/]+/[^/]+/[A-Z]/com\.apple\.iBooksX"))
  

  And com.apple.storeagent is used by the Mac App Store:

  $ egrep -i 'app.?store' /System/Library/Sandbox/Profiles/com.apple.storeagent.sb
         (regex #"/Library/Preferences/com\.apple\.appstore\.plist$")
         (regex #"/Library/Caches/com\.apple\.storeagent/updates-com\.apple\.appstore\.updateQueue\.plist$"))
         (regex #"/Library/Application Support/App Store(/|$)")
         (regex #"/Library/Logs/appstore\.log$")
         (regex #"/Library/Preferences/com\.apple\.appstore\.plist$")
         (regex #"^/private/var/folders/[^/]+/[^/]+/[A-Z]/com\.apple\.appstore")
         (global-name "com.apple.appstore.CKSignInPrompt.hostclient")
         (global-name "com.apple.dock.appstore")
         (right-name "system.install.app-store-software")
         (right-name "system.install.app-store-software.standard-user")
  

Update

Thanks to a helpful anonymous commenter for pointing out that it wasn’t just 10.9 and iBooks.

I’ve been wondering about the name adi, and the possibility that it could be “Apple Distribution International”, the apple business unit responsible for electronic download sales. I’ve got no idea. That’s just wild guess that I don’t have much faith in myself.

CommerceKit

We already have a link between ADI and the Mac App Store & iBooks Store.

1. “/Users/Shared/adi” appears under /System/Library/Sandbox/Profiles in com.apple.storeagent.sb and com.apple.bookstoreagent.sb.
2. storeagent and bookstoreagent appear in the apple private CommerceKit.framework

   % locate storeagent
   [...]
   /System/Library/PrivateFrameworks/CommerceKit.framework/Versions/A/Resources/bookstoreagent
   /System/Library/PrivateFrameworks/CommerceKit.framework/Versions/A/Resources/storeagent
   [...]
   

3. CommerceKit is used by the App Store, Apple Configurator, and iBooks apps:

   % for app in /Applications{,/Utilities}/*.app/Contents/MacOS/*; do
   (otool -L "$app" | grep -i -H --label "$(basename $app)" 'CommerceKit') 2>/dev/null
   done
   
   App Store:  /System/Library/PrivateFrameworks/CommerceKit.framework/Versions/A/CommerceKit (compatibility version 1.0.0, current version 232.0.0)
   Apple Configurator: /System/Library/PrivateFrameworks/CommerceKit.framework/Versions/A/CommerceKit (compatibility version 1.0.0, current version 135.6.0)
   iBooks: /System/Library/PrivateFrameworks/CommerceKit.framework/Versions/A/CommerceKit (compatibility version 1.0.0, current version 232.0.0)
   

4. CommerceKit’s code contains these method references to adi

   % strings /System/Library/PrivateFrameworks/CommerceKit.framework/Versions/A/CommerceKit | grep adi
   [some items omitted for bloggish reasons]
   _adiActionInResponse
   _adiSilentActionRetryCount
   %@: Saw ADI action in response to %@, set _adiActionInResponse=YES
   

CoreADI

You might also note that there’s a CoreADI framework:

/System/Library/PrivateFrameworks/CoreADI.framework
/System/Library/PrivateFrameworks/CoreADI.framework/CoreADI
/System/Library/PrivateFrameworks/CoreADI.framework/Resources
/System/Library/PrivateFrameworks/CoreADI.framework/Versions
/System/Library/PrivateFrameworks/CoreADI.framework/Versions/A
/System/Library/PrivateFrameworks/CoreADI.framework/Versions/A/CoreADI
/System/Library/PrivateFrameworks/CoreADI.framework/Versions/A/Resources
/System/Library/PrivateFrameworks/CoreADI.framework/Versions/A/Resources/Info.plist
/System/Library/PrivateFrameworks/CoreADI.framework/Versions/A/Resources/version.plist
/System/Library/PrivateFrameworks/CoreADI.framework/Versions/A/_CodeSignature
/System/Library/PrivateFrameworks/CoreADI.framework/Versions/A/_CodeSignature/CodeResources
/System/Library/PrivateFrameworks/CoreADI.framework/Versions/Current

And a receipt:

/private/var/db/receipts/com.apple.pkg.CoreADI.bom
/private/var/db/receipts/com.apple.pkg.CoreADI.plist

There is very little information in those files… even extracting text strings from the binary gives very little info. There are some references to encryption.

Its dependencies:

% otool -L /System/Library/PrivateFrameworks/CoreADI.framework/CoreADI
/System/Library/PrivateFrameworks/CoreADI.framework/CoreADI:
    /System/Library/PrivateFrameworks/CoreADI.framework/CoreADI (compatibility version 1.1.0, current version 1.34.0)
    /usr/lib/libcrypto.0.9.8.dylib (compatibility version 0.9.8, current version 44.0.0)
    /System/Library/Frameworks/Foundation.framework/Versions/C/Foundation (compatibility version 300.0.0, current version 833.25.0)
    /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 635.21.0)
    /System/Library/Frameworks/IOKit.framework/Versions/A/IOKit (compatibility version 1.0.0, current version 275.0.0)
    /System/Library/Frameworks/CoreServices.framework/Versions/A/CoreServices (compatibility version 1.0.0, current version 53.0.0)
    /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 159.1.0)