Problem with MacOS update 10.15.7 2020-001

Hello all,

I have an 2003 iMac, with 10.15.7 installed (Catalina) on an external SSD drive. The iMac boots on an external disk. Usually all security updates install correctly on the external SSD disk. For the last one, the installation seems ok, but the iMac reboots always on the internal HD. When I reboot on the external disk, the security updates seems not installed. I redo this operation multiple times, without success: the lastest update is proposed for installation, but when I do it, it does not install on the external disk...


What is happens ?

Thanks in advance


iMac 21.5″, macOS 10.13

Posted on Dec 15, 2020 4:42 AM

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Question marked as Top-ranking reply

Posted on Dec 16, 2020 8:23 AM

Also had issues with this 10.15.7 2020-001 update. Here is what worked running an Imac 2013 from external SSD.


  • When starting the update, still on black screen, it had a brief reboot.
  • After that the Mac failed to load from SSD every time.
  • As my internal drive is a clone the Mac was only starting up with the internal disk, and not recognising the SSD as target disk.
  • Pressing option key wasn't working to select SSD disk.


What worked for me:

  1. I unplugged everything connected to the Mac and plugged my SSD in a different USB (the closest to the edge)
  2. Did a PRAM reset (once)
  3. Switched on, loud startup sound and the Mac loaded my internal drive with the clone, then I shut down after loading
  4. Switched on again and pressed option key (the SSD disk appeared)
  5. After loading the SSD I noticed the update was still pending on Systems Pref
  6. Shut down again
  7. Switched on again to check it would load from SSD, and it did!
  8. Performed the update with no problem after that


Hope this helps..

Similar questions

151 replies

Jan 1, 2021 8:32 AM in response to SkyFires

Apple did make it clear that they won't support models as they go, meaning during updates under Catalina, they just did not say what machines, when.


Conspiracy theories have nothing to do with my comment, Apple wants to provide a high standard, its their market and many who dont adopt to newer devices miss out with out knowing it., I know I did as I had an iPad 2 and finally upgraded to a iPad Pro v2 and love it.

Jan 2, 2021 10:03 AM in response to CapsuleFab

I keep saying the same thing over and over about the EFI issues and Apple, think EFI as a computer for your car and what garage can fix it other then the dealer if you lost your keys or need to re program a part you replaced.


Apple and most tech companies have been turning to this trend to prevent frauds while at the same time your files maybe trapped on a encrypted drive soldered unto a motherboard bricked from a Catalina update and only a Genius Bar can help you with this.....and within time and way they are operating its likely impossible, my solution was to bring the computer to a apple reseller, in a town far away from a Genius Bar...they usually tell you the dirt on Apple but dont get me wrong, ALL tech companies fallow this trend now. you won't be able to even swap parts of your computer with out problems, not even soldering a bigger drive, more ram is possible.

all components register IDs and this Chip2 set is another ball game.


Certain countries prohibit this and Genius bars do return Catalina bricked computers but reports from people show they swore parts are not the same, swapped, re programmed to work with the same motherboard., example one owner posted comments on a reddit thread accusing the Genius Bar of lying about her magsafe power supply claiming it was only supplying 5v when this was debunked online by a number of techs warning people that their machines can get bricked and which countries take action., unfortunately the US won't.

So unless you buy a new machine your at risk if you upgrade to Catalina.

Jan 3, 2021 6:09 AM in response to GavrielTech

Well since my iMac is 2013 vintage I suppose that makes it seven years old. But performance wise I would say it isn’t much slower than a new equivalent. Mine is an i5 at 2.9 ghz compared to i5 at 3.4ghz? I know there improvements in clock cycles and the like... But nothing mind blowing.


Thing is I only really use it for web, e-mail, music and photos rather than 3D or video work.


I will definitely not be trying to put that security update on now I have my iMac back where it was! And I might get a new iMac in the summer especially if they go M1.

Jan 3, 2021 7:18 AM in response to GazzaMataz

It's def slower, I know it by experience, 'cause it was my 2013 iMac too, which suffered, and I can compare it with other iMacs around ;-) But anyway, it's a lovely workhorse, and I still love him, so don't have plans to replace this one before summer neither, same as you.


However, I think it's a good decision not to install this update for now, unless you do have too much spare time these days ;-) Let's wait, when Apple is going to fix it, as there are more and more having the same (or similar) issue.

Jan 4, 2021 2:51 AM in response to ElkyOne

Just did a quick look at the Cinebench scores for the iMac 2.9ghz (late 2013) vs the iMac 3.0ghz (current 6-core) and 2.9ghz scores 1167, 3.0ghx scores 2171 so nearly twice as quick and better GPU plus a few extra ports.


Sorry to sidetrack slightly :-) But going back to the topic in hand I am wondering now if my old SSD has failed, it's less that two years old so if it has I am surprised.

Jan 6, 2021 8:21 PM in response to GazzaMataz

Congress is responsible for allowing this, its a political issue.


In certain countries tech companies are obliged to repair anything they are responsible for damaging (not in the USA) thanks to lobbying.... its why France slapped fines etc,


but sometimes 200 million dollar fines are worth it...Apple makes more then 450 million an hour and 60 billion a year...the feedback link only reaches web masters....are you suggesting some ideas to improve the Apple website? Anything else goes to the trash bin,

Jan 6, 2021 8:54 PM in response to steve626

I thought you guys where complaining about planned or forced obsolescence, this is not legal in certain countries and if any manufacture is responsible for out of warranty damages (example Catalina update) depending on the number of cases or if a deliberate targeting took place the EU identifies it as forced forced obsolescence if refused service even if warranty is up.


but take this into consideration,

Android is the epitome of planned obsolescenceApple's phones receive five to six years of software updates from the date of release. ... This doesn't happen in the world of Android. The average Android receives no operating system upgrades and even premium devices only ever experience one or two upgrades.

Jan 6, 2021 9:28 PM in response to GavrielTech

Well said, but the worshippers of all things Apple fail to recognize that if it walks like a duck, quacks like a duck, it’s a duck. So I received my ifixit kit, replaced the obsolete HDD and installed my SSD. My 14,2 runs like a top now. Folks can say what the want about their new Mac but at least I own mine and can repair, bupgrade as I see fit and it performs perfectly well for the Photoshop and Lightroom tasks I demand of it as a semi pro photographer. But still upset that Apple messed with my T5 external SSD.

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Problem with MacOS update 10.15.7 2020-001

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