Can't boot from SSD following security update

Question

Level 1

8 points

Can't boot from SSD following security update

For some time I have been booting my late 13 iMac from an external SSD. I found that the SSD gave hugely improved speed and performance. I run Catalina on the SSD but have kept High Sierra on the Hard Disk for occasional use with older applications.

After installing an Apple update this week – I think it was a security update my Mac will no longer boot from the SSD and reverts to booting from the Hard Disk. In the startup preferences the SSD is shown as the boot disk but the machine will only boot from the Hard Disk.

I have tried restoring both the Hard Disk and the SSD from Time Machine backups. I have also reset the PRAM and SMS but to no avail.

If I hold down the ALT key on startup the usual menu of startup disk options doesn't appear and the machine continues to boot into High Sierra on the Hard Disk.

If I disconnect the SSD and restart holding down the ALT key the menu of startup options DOES appear. If I then plug in the SSD it appears as a startup option and if I select it the Mac finally boots up from the SSD. Everything then works fine but if I shut down or restart I go back to square one and the machine boots from the Hard Disk once more.

Now despairing! Any suggestions much appreciated!

iMac 21.5″, macOS 10.15

Posted on Dec 18, 2020 9:15 AM

Reply

Answer 1

Best reply

HWTech

Level 9

56,372 points

Dec 19, 2020 5:09 PM in response to maythyme

Run Disk Utility First Aid on your external SSD. Within Disk Utility click on "View" and select "Show All Devices" so that the physical drives appear on the left pane of Disk Utility. Then select the external physical drive and run First Aid. Then select the "Container" of the external SSD and run First Aid. Even if First Aid reports everything as Ok click on "Show Details" to see if there are any unfixed errors listed. If there are unfixed errors listed, then the file system is bad which will require erasing the whole physical drive and restoring from a backup or clone.

In some ways it almost seems like your SSD is taking too long to go ready. Is the SSD connected directly to the Mac? If you are using any adapters, dongles, or hubs it is possible they may be interfering. Disconnect all other external devices in case one of them is interfering. If the issue doesn't occur, then attach one device at a time to see which device (or possibly devices) is interfering.

Try using another USB cable. Try using a USB3 powered hub (a good respected brand).

When you restored from a backup did you try erasing the drive first?

To determine if you have a hardware or software issue will require performing a clean install of macOS on the external SSD (perhaps even the internal drive as well) by first erasing the whole physical drive:

https://support.apple.com/guide/disk-utility/erase-and-reformat-a-storage-device-dskutl14079/mac

Reply

Answer 2

Dec 20, 2020 11:32 PM in response to maythyme

There is a lot of discussion regarding issues with booting from an external SSD after this update:

https://discussions.apple.com/thread/252177156

I've encountered this problem as well after installing Security Update 2020-1 on my external USB SSD (Catalina macOS 10.15.7). I'm not sure if the problem originated with the 2020-1 SU, or was present in 10.15.7, but I discovered it when I tried to install the update and my iMac restarted ufrom the internal HD instead of the external SSD.

I was finally able to reinstall Catalina macOS 10.15.7 onto my SSD (w/o installing the 2020-1 SU) and boot from it.

Reply

Answer 3

maythyme Author

Level 1

8 points

Dec 21, 2020 10:55 AM in response to William Tomcanin

Thanks to all for the helpful suggestions. I think I have sorted it although i'm not absolutely sure how! I tried every kind of reinstall Mac OS, erasing disks, restoring from backups etc without success. As a test I tried creating a Catalina boot disk on a USB stick. I found that I was able to boot from this but only if the SSD was not plugged. If the SSD was plugged in then the boot defaulted to the Macintosh Hard Disk as before.

I also found that the SSD successfully worked as boot disk on my MacBook suggesting that there wasn't a fault with the SSD.

One of the suggestions was to disconnect all other devices and then try booting from the SSD. I tried this using a different USB slot – success! I then started reconnecting devices and found that the SSD boot up failed again when my backup hard disk was connected (to the slot that the SSD was originally in). I tried again, this time with the backup disk connected to a USB hub on one of the other ports – it worked.

It almost seems that a particular there is a problem with a particular USB port but why would the security update have caused such a problem?

Finally with everything seemingly back to normal again but having at some point reinstalled Catalina I was presented with a me message offering the security update again! Dare I risk the situation by installing this again? I decided to and this time it appears to have installed without any problem.

So I am hoping the problem is finally solved ( I've spent hours trying to sort it) but I'm just not really sure how I have done it or why the problem occurred in the first place!

Reply

Answer 4

HWTech

Level 9

56,372 points

Dec 21, 2020 5:20 PM in response to maythyme

maythyme wrote:

It almost seems that a particular there is a problem with a particular USB port but why would the security update have caused such a problem?

It was probably just a coincidence. It is unlikely a software update would break a single USB port.

So I am hoping the problem is finally solved ( I've spent hours trying to sort it) but I'm just not really sure how I have done it or why the problem occurred in the first place!

I'm glad you were able to figure out the source of the issue. It is odd things like that which I deal with all the time. Sometimes it does drive me crazy. At least now you have some new troubleshooting skills.

Enjoy the holidays.

Reply

Answer 5

maythyme Author

Level 1

8 points

Dec 20, 2020 2:29 AM in response to HWTech

Many thanks, will try that.

Reply

Answer 6

Dec 21, 2020 12:01 PM in response to maythyme

I'm glad that you were able to get things back to normal again. Were you able to boot from the external SSD after applying the 2020-1 Security Update?

Reply

Can't boot from SSD following security update

Similar questions